Crankshaft / Bearing / Cylinder — Most Asked Questions
85 questions asked about crankshaft / bearing / cylinder across the General and Fn 6 and Fn 4b and Fn 3 papers, heaviest first. 4 of them are must-master.
Learn the system first
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1 Bottom end bearing clearance?
Answer
Bottom-end clearance is taken with the crank at BDC: feeler gauge for a quick check, lead wire or plastigauge for an accurate one, against the maker’s limit.
- Feeler method: turn crank to BDC, insert the feeler between the lower half and the crankpin.
- Lead-wire method: lay wires circumferentially in the bottom half at three places, torque the cap to full tightening torque, open up and measure the flattened wires.
- Main bearings are done the same way after removing the upper half, using a bridge gauge with feelers; micrometer beats feeler for accuracy.
- Excessive clearance means low lube-oil pressure, lost load-carrying capacity, pounding and hammering of the crankshaft — renew shells or reset shims.
Surveyor follow-up: lube-oil pressure has fallen on one unit with no leak — which clearance do you suspect and how do you prove it?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
2 How will you take tappet clearance?
Also asked: “what is tappet clearance? What happens when more or less? What happens if no tappet clearance provided?”, “What do u mean by tappet clearance”, “what you understand tappet clearance,how will you check & how will you adjust”
Answer
Bar the engine until the roller sits on the cam base circle, feeler-gauge the gap, and reset it with the tappet screw.
- Rotate the engine until the respective roller is on the base circle of the cam, then measure with a feeler between valve stem and tappet — or between roller and cam after pushing the pushrod up by hand.
- Exhaust clearance is set slightly larger than inlet because the exhaust valve runs hotter and expands more.
- Adjust with the threaded tappet on the rocker arm, turning the screw until the specified clearance is obtained.
- Cross-check: at firing TDC both pushrods are loose (both valves shut); fuel-pump marks coinciding also marks injection beginning.
Surveyor follow-up: you set the clearance with the roller on the cam flank instead of the base circle — what happens when she runs?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
3 piston ring clearance?
Also asked: “Piston ring clearances , what if clearance is less or more”
Answer
Three clearances define ring performance: butt (end) gap in the unworn liner, vertical (axial) groove clearance, and radial back clearance behind the ring.
- Butt (end) gap: Measured using a feeler gauge with the ring placed square in the unworn bottom portion of the cylinder liner; prevents ring ends butting solid under thermal expansion, which causes ring breakage and bore seizure.
- Vertical (axial) groove clearance: Measured between ring upper face and groove ceiling with ring pressed down; too small causes carbon baking and ring sticking; too large batters groove lands and breaks rings.
- Radial back clearance: Checked to ensure the ring does not bottom out in the groove, allowing high-pressure combustion gas to act behind the ring and force it outward against the liner wall.
- Condemning limits: Clearances must adhere strictly to maker tolerances stamped on the piston data plate; sudden increases in groove wear indicate failed cylinder lubrication, cat fines, or scavenge-air water carryover.
Surveyor follow-up: One cylinder shows high exhaust temperature and low compression — which clearance fault is the primary suspect and what damage does a stuck ring cause?
Full theory: Piston Crowns, Piston Rings & Thermal Mechanics -
4 Why we take crankshaft deflection
Also asked: “What is crankshaft deflection?”, “Why we need to do crankshaft deflection”, “Why we take crankweb deflection”
Answer
Deflections are the cheapest early warning of main-bearing misalignment: a change from the shaft’s natural deflection means bearings have moved.
- Every crank has a natural deflection from running-gear load and shaft weight; uneven main-bearing wear changes the web gaps, and that change is proportional to the height difference of the bearings.
- Readings therefore expose misalignment long before wiping, pounding or a cracked web does.
- Taken with a dial gauge between crankwebs at regular intervals, always at the same crank positions and same engine condition.
- Invisible movement — up or down by an amount the eye cannot see — is enough to set up dangerous web fatigue, so trending against maker limits is the whole point.
Surveyor follow-up: deflections shifted right after dry dock with no bearing work done — hull or engine, and what do you check first?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
5 Thick and thin shell bearing?
Answer
Thick shells are shim-adjusted white-metal mains; thin shells are replaceable tri-metal inserts with crush — different generations, different fitting.
- Thick shell: 30–60 mm white metal of tin, antimony and copper, clearances set with shims, used in main bearings.
- Thin shell: tri-metal insert — steel back, lead-bronze lining, nickel dam, white-metal overlay about 20 microns — wall near 2–2.5% of journal diameter.
- Thin shells fit by crush or nip with no shims; tin-aluminium variants exist only as thin shells.
- Both use the same white metal for embedability; renew thin shells, do not scrape them.
Surveyor follow-up: bottom-end knocking with clearance over limit on a thin shell — shim it or renew it?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
6 Cylinder head pressure testing
Also asked: “Cylinder pressure head test”, “Piston pressure test”, “AE cyl. head pressure testing”
Answer
Pressure-test the head to prove the water jacket: clean it, close it up, hold hydraulic pressure and read for weeps and cracks.
- Strip carbon, descale the water jacket and check for scaling and corrosion before any test.
- Blank openings and apply hydraulic pressure — about 7 bar on the jacket — holding and watching for weeps, seeps and pressure fall.
- Dye-penetrant backs the test on suspect faces; valve seats get checked for acid corrosion, bending and blow-by at the same opening.
- Springs, valves and seats renewed on condition — a head that will not hold pressure never goes back on.
Surveyor follow-up: pressure holds but one valve seat weeps water — head, seat or valve, and what proves it?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
7 Thrust bearing clearance
Also asked: “Big end bearing clearance”
Answer
Thrust clearance is the shaft’s ahead-to-astern freedom: new 0.5–1.0 mm, never past 2 mm in service, read with feelers at BDC.
- Bar the aftermost throw to BDC so the collar bears on the foremost segments, then feeler between the after lower main shell side and the crank throw side.
- New engines read 0.5–1.0 mm; anything approaching 2 mm in service means overhaul.
- Worn thrust shows as creeping shaft, wiped pads and jumping clearances on the neighbouring mains.
- Prove with the maker’s special gauge where supplied; log ahead and astern readings separately.
Surveyor follow-up: clearance 1.8 mm and growing each survey — run to next dry dock or open up now?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
8 Cross head bearing
Answer
The crosshead bearing joins rod to guide: pin, shoes and wedges checked at three places with the piston parked off bottom dead centre.
- Park the piston 90 degrees before bottom dead centre, then feeler the three gaps: shoe-to-plate across, rail-to-shoe axially, shoe-to-pin.
- Oil wedges machined in the guide shoes must be clean and sharp to float the load.
- Guide plates stop the shoes walking out; the attached pin carries rod load into the guides.
- Big-end practice beside it: 0.4–0.6 mm on a 550 mm shaft with bolts, grooves and movement marks all read.
Surveyor follow-up: one shoe gap double the book figure with the rest normal — wear, wedge or alignment, and what proves it?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
9 Tappet clearance why
Also asked: “Tappet clearance bc”
Answer
Tappet clearance guarantees the valve truly shuts when hot: set cold so expansion never holds it open.
- Without clearance the hot expanded stem keeps the valve off its seat — compression and power leak away.
- Too much clearance opens late and closes early with hammering gear; too little opens early, closes late and burns seats.
- Exhaust needs more gap than inlet because it runs hotter and grows longer.
- Set cold off the cam peak, recheck on schedule as seats bed in and gear wears.
Surveyor follow-up: exhaust seat burnt with clearances correct — cooling, fuel or timing, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
10 Connecting rod checks
Also asked: “aux eng connecting rod checks”, “Check connecting rod for bend and cracks”
Answer
Con rods are checked for truth, cracks and bolts: straightness, bearing halves, oilways and stretch marks.
- Sight for bend and twist with the rod stripped; cracked feet and beams condemn it.
- Bearing halves read for wear over 30% of contact area, cracks, overlay loss, oil-hole and groove condition.
- Bolts read for thread cracks, extension and twisting with joint fretting marks at the split faces.
- Clearance proved on assembly with holding-down faces clean — log every reading against maker limits.
Surveyor follow-up: fretting at the rod-foot joint with bolts correct — run, re-torque or renew, and why?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
11 Crosshead Bearing clearance
Answer
Crosshead clearances read three gaps with the piston parked off bottom dead centre: shoe-to-plate, rail-to-shoe and shoe-to-pin.
- Park the piston 90 degrees before bottom dead centre so the rod presses the rail on one side.
- Feeler shoe-to-plate across, rail-to-shoe axially and shoe-to-pin radially at three places each.
- One side should read near zero — a gap both sides means misalignment or liner wear.
- Oil wedges in the shoes must be clean and sharp; big-end practice beside it reads 0.4–0.6 mm on a 550 mm shaft.
Surveyor follow-up: clearance both sides with one side double the book — wear, wedge or alignment, and what proves it?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
12 How to take tappet
Also asked: “How tappet is taken?”
Answer
Take tappets stopped and shut: roller on the cam base circle, feeler in the gap, exhaust wider than inlet.
- Stop the engine with the exhaust valve shut — prove by open camcase door with the roller on the base circle.
- Feeler between stem and tappet, or roller and cam with the pushrod lifted by hand.
- Exhaust gap wider than inlet for hotter expansion; firing-TDC check shows both pushrods loose.
- Set with the tappet screw to maker figures cold, then bar round and re-prove every unit.
Surveyor follow-up: clearance set on the cam flank instead of base circle — what happens when she runs?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
13 type of crankshaft
Also asked: “Types of crank shaft”
Answer
Crankshafts run forged, fully built, semi-built or welded: one piece, shrunk pieces, half pieces or fused pieces.
- Forged solid shafts for smaller engines — one piece carrying torsional and fatigue load in low-alloy steel.
- Fully built-up shafts with shrunk journals, pins and webs for big two-strokes needing piece renewal.
- Semi-built with combined throws cutting joints and weight while keeping repairability.
- Welded throws for special builds — survey by crack detection at every weld with material certificates in hand.
Surveyor follow-up: web slip suspected on a built shaft — deflection, fretting or hardness, and what proves it?
Full theory: Marine Crankshafts — Builds, Bedplate, Chocks & Alignment -
14 safety on cylinder head
Also asked: “Saftey in cylinder head lifting”, “Safety on cylinder head of main engine”
Answer
Lift heads like glass: clear path, sound slings, level lift to wooden blocks — never drag steel on steel.
- Bar the engine clear, rig the crane vertical over the lifting eyes with certified slings.
- Lift dead slow with hands clear, guiding without touching adjacent studs, pipes and covers.
- Land on wooden blocks with the gasket face up, protected from knocks and weather.
- Piston work follows the same discipline with lifting tools fully bolted before the pull.
Surveyor follow-up: head swings and kisses a stud on the way up — land, inspect or carry on?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
15 Crank shaft deflection
Answer
Deflections read at five crank angles with the gauge opposite the pin: bottom twice, port, top, starboard — trended, never single-read.
- Fit the dial between webs opposite the pin in the same spot every time or readings lie.
- Bottom-centre webs close on the gauge for negative, top-centre opens for positive deflection.
- Table port, top, starboard with both bottoms; judge against maker limits with running gear noted.
- Gear removal, drafts and temperatures shift readings — record conditions beside numbers.
Surveyor follow-up: readings shifted after dry dock with no bearing work — hull, load or gauge position?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
16 Cylinder head overhaul complete?
Answer
A complete head overhaul strips, measures, renews and tests: valves, seats, springs, guides and jacket proved.
- Strip valves, springs and guides; descale the jacket and read scaling and corrosion faces.
- Lap seats, renew bent valves and tired springs, prove guides and spindle timing on reassembly.
- Pressure-test the jacket near 7 bar with dye backup on suspect faces before boxing up.
- Run with exhaust and cooling watched — blow-by, acid corrosion and hot seats show first.
Surveyor follow-up: jacket holds but one seat weeps water — head, seat or valve, and what proves it?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
17 High speed engines: Above 1000 rpm Based on Piston connection
Also asked: “• High speed engines: Above 1000 rpm Based on Piston connection”
Answer
High-speed engines run trunk pistons past 1000 rpm: compact, fast and geared — gensets, ferries and diesel-electric fleets.
- Above 1000 rpm with some families at 1500–2100 rpm on 10–11 m/s piston speed and 25 bar mean pressure.
- Trunk pistons carry gudgeon drive in one piece — short, light and mass-producible.
- Twelve-cylinder gensets prove the breed with twin electric starters on the flywheel.
- Fit where headroom is short and alignment must roam — ferries, offshore and electric propulsion.
Surveyor follow-up: high-speed trunk against medium-speed trunk — piston, speed or use, and what decides?
Full theory: Diesel Engine Basics — Terms, Strokes & Timing -
18 It is the ratio of brake power(delivered power) to the indicated power (power provided to the piston
Answer
That ratio is mechanical efficiency: shaft power over cylinder power with friction taking the difference.
- Indicated power from diagram area; brake power from shaft torque and speed.
- Efficiency equals brake over indicated — friction, pumps and blowers eat the gap.
- Specific consumption on brake always exceeds indicated, widening as load falls toward idle.
- Prove by back-to-back cards and torsionmeter readings at the same steady load.
Surveyor follow-up: efficiency falling with diagrams steady — friction, auxiliaries or measurement, and what proves it?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
19 Tappet Clearance full
Answer
Full tappet drill is stopped, warm, shut and proved: base circle, firing TDC cross-check, injection marks and feeler gaps.
- Warm stopped engine with roller on the cam base circle proved through the open camcase door.
- Firing-TDC cross-check shows both pushrods loose; fuel-pump sleeve marks meet at injection start.
- Feeler stem-to-rocker with exhaust wider than inlet for hotter expansion.
- Rocker screw set to maker figures, barred round and re-proved every unit before boxing up.
Surveyor follow-up: clearance closes to zero hot with figures correct cold — seats, stems or oil, and what next?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
20 Tappet clearance of ae?
Answer
Auxiliary tappets follow the same hot-cold logic at speed: early-late errors cost volumetric efficiency first.
- Too little opens early and closes late; too much opens late and closes early — both cost air.
- Early inlet pumps exhaust back to the manifold; late inlet wire-draws suction and wastes inertia fill.
- Early-closing inlet chokes the end of suction; late-closing pumps charge back out.
- Set cold off the peak, prove timing on marks and recheck as gear wears between overhauls.
Surveyor follow-up: one AE unit smokes with tappets correct — valve, timing or fuel, and what proves it?
Full theory: The Diesel Generator Set — Bedding Down, Coupling and Driving the Alternator -
21 What are the different methods of taking clearance in main bearing?where exactly we take clearance in telescopic feeler gauge?
Also asked: “Main bearing clearance .Methods & name of feeler gauge used to measure main bearing clearance”
Answer
Main clearances read bridge, direct-feeler or micrometer: upper half off for the bridge, lube insert out for the direct read.
- Bridge method: upper half off, bridge fitted, feeler between bridge and journal — the wear-down standard.
- Direct method: lube pipe and insert out, long telescopic feeler to the journal crown in situ.
- Micrometer beats feeler where access and practice allow for tenth-level truth.
- Excess means low oil pressure, lost carrying capacity, pounding and crank hammering — renew or re-shim.
Surveyor follow-up: bridge reads high with direct reading normal — bridge seating, gauge or journal, and what first?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
22 What is thrust bearing?
Also asked: “What is thrust bearing? How does it look like?”
Answer
The thrust bearing takes propeller push: tilting Michell pads build an oil wedge against the collar ahead and astern.
- Pads face the collar both sides with white-metal faces on tilting backs that self-shape to the wedge.
- Rotation with oil supply builds pressure only with a good leading-edge radius — a scraper edge kills the film.
- Radial ridges fulcrum each pad for tilt; separate housings carry cooling and foundations where fitted.
- Clearance 0.5–1.0 mm new with 2 mm service limit proved ahead and astern separately.
Surveyor follow-up: pads wiped one side with clearance correct — oil, alignment or manoeuvring, and what proves it?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
23 Write briefly on materials used with its key properties for a. piping b. valves c. diesel engine parts such as liners, piston rings and exhaust valves
Answer
Materials follow duty: pipes for pressure and corrosion, valves for seating and heat, hot-end parts for wear and acids.
- Piping in steel with corrosion allowance, galvanizing and compatible joints against seawater waste.
- Valves with bronze seats and spindles for seating under heat and pressure cycling.
- Liners in alloyed iron for honed wear against acid attack with controlled cooling.
- Rings in graded iron with chrome faces — compression sealing above, oil control and spreading below.
Surveyor follow-up: ring face scuffed with liner honing gone — material, oil or cooling, and what proves it?
Full theory: Marine Materials, Metallurgy & Mechanical Testing -
24 liner crack indications
Also asked: “Sign of liner crack”
Answer
Cracked liners leak water into gas and gas into water: rising jacket temperature, vent gulps, milky oil and wet scavenge air.
- Hot gas to coolant lifts jacket temperature with pressure flicker on the affected unit.
- Air vents spit intermittent gas instead of steady water — the crack breathing with the cycle.
- Stopped engine lets water into combustion and scavenge spaces; running engine leaks gas the other way.
- Causes stack overload, high firing pressure, fuel striking walls, scale-starved cooling and thin lubrication.
Surveyor follow-up: vent gulping with oil pressure steady — liner, head or cooler, and what do you open first?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
25 Take bearing clearance by inserting feeler gauge between bearing upper half and journal
Also asked: “Measure bearing clearance by inserting feeler gauge between bearing lower half and crankpin”
Answer
Bridge-gauge the bearing with the cap lifted: strip the top half, seat the gauge, and feeler the gap to the journal.
- Isolate lube oil supply to the bearing and lift the upper half with caps and shims kept in order.
- Seat the bridge gauge across the housing and slip feelers between gauge and journal at both sides.
- Micrometer checks beat feelers for accuracy — record against maker limits with bedplate condition noted.
- Excess clearance drops oil pressure, starves sister bearings and pounds the white metal to failure.
Surveyor follow-up: clearance high with oil pressure low and knocking present — renew, shim or run to next port?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
26 Why thrust bearing in Ae
Answer
The auxiliary thrust holds the crankshaft where timing lives: axial location with oil-fed pads against push and pull.
- Takes residual axial thrust from gears, couplings and thermal growth so the shaft cannot walk.
- Keeps crank webs, cams and alternator air gaps centred — wandering shafts wipe seals and mistime valves.
- Needs just enough clearance for oil flow: too tight overheats, too wide drops supply pressure and starves neighbours.
- Prove by axial float measurement against maker figures with oil flow and temperature steady.
Surveyor follow-up: axial float high with lube pressure sagging — thrust pads, alignment or oil supply first?
Full theory: The Thrust Block and Thrust Shaft — Clearance, Pads and Support -
27 how to remove broken tie rod
Answer
A broken tie rod comes out in pieces: withdraw the top, cut and lift the long lower stump without scoring the bore.
- Withdraw the upper broken part from the top of the frame after releasing its nuts.
- Cut a long trapped lower portion and remove it in sections with threads protected.
- Prove frame bore, threads and seating faces clean before the new rod drops in.
- Tension the new rod to maker stretch or load figures with nuts proved even all round.
Surveyor follow-up: lower stump seized with the frame bore scored — cut higher, pull harder or ream and bush?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
28 Putting hanging bar in position, connect chain blocks to crankcase door frame and eye bolts which is screwed into each side of the a top half. Then turn the crankshaft to the position where the top half can be taken out
Answer
Lift the bearing top half on chain blocks: hang the bar, screw in eye bolts, turn the crank to the freeing position.
- Seat the hanging bar across the crankcase door frame with chain blocks shackled to both sides.
- Screw an eye bolt into each side of the top half after its nuts come off, taking the weight on the blocks.
- Turn the crankshaft slowly to the position where the top half clears webs and frames for withdrawal.
- Lift the top half with its bolts outside the crankcase, marking every shim set to its own side.
Surveyor follow-up: top half cocked with one chain slack and the crank mid-throw — heave on, lower back or turn first?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
29 Remove locking arrangement and slackened the nuts. The bottom half lower a few and took out bearing clearance adjusting shim, each set being tied separately and note taken of the side to which each set belongs
Answer
Shim the bottom half by book: unlock, slacken evenly, lower a touch, and lift each side’s shim set tagged to its side.
- Remove locking wire and plates, then slacken nuts evenly so the half drops level without cocking.
- Lower the bottom half a few millimetres only — enough to free the clearance shims, never to hang on threads.
- Tie each side’s shim set separately with its side and position noted; mixed shims condemn the next clearance.
- Prove new clearance by lead wire or telescopic gauge at BDC, adding or removing shims to maker limits.
Surveyor follow-up: shim sets swapped port-starboard with clearance now uneven — regauge, reshuffle or renew first?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
30 Types of piston rings in ae
Also asked: “types of piston rings and their functions”
Answer
Auxiliary rings seal, scrape and spread: compression rings hold gas, oil-control rings meter oil, spreaders even it out.
- Compression or pressure rings seal firing gas above the piston — chrome-faced rams-bottom iron in square section.
- Oil-control or scraper rings pass oil up and down in metered film, never flooding nor starving the liner.
- Oil-spreader rings lay the film evenly round four-stroke liners and stuffing-box faces.
- Check butt gaps, groove wear and hammered inner faces on overhaul — gummed rings pump oil and pass blow-by.
Surveyor follow-up: compression good but oil consumption climbing with blued liner — rings, oil grade or scavenge first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
31 checks on crankshaft and connecting rod of AE
Also asked: “Inspectiion on Connecting rod of AE”
Answer
Prove the AE shaft and rod round, straight and crack-free: ovality, trueness, bolts and dye test.
- Ovality-check con-rod bores with bearings torqued home — beyond 0.05 mm condemns serrations and shells.
- Trueness-check by rod through the oil hole; full passage proves no bend from overload or hydraulic lock.
- Dye-test serrations, cap faces and oil-hole mouths where cracks start at the stress raiser.
- Gauge con-rod bolts for elongation — stretched bolts yield next, so renew past maker stretch limits.
Surveyor follow-up: ovality high with serrations fretted and bolts stretched — renew bolts, shells or the rod first?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
32 A connecting rod does the function of transforming the reciprocating motion of a piston into rotary motion of crankshaft. It also do the work of transferring power produced by the piston to the crankshaft
Answer
The connecting rod is the gas-load link: crosshead or gudgeon pin to crankpin, carrying firing force with cooling oil inside.
- Transmits peak gas plus inertia load at TDC in heavy axial compression through top and bottom ends.
- Conveys lubricating and piston-cooling oil through its bored centre — down in crossheads, up in trunk engines.
- Forged with top-end and crankpin bearings machined to carry load over many small contact areas.
- Four-stroke rods also pull tensile past firing TDC by piston inertia — size covers both senses of load.
Surveyor follow-up: rod bolts stretched with bearings wiped and oil flow proved — overload, lubrication or bolt torque first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
33 A crankshaft is a key component of an engine transmitting cylinder power to the propeller shaft. Basically what it does is to convert the oscillating motion of connecting rod / reciprocating motion of the piston to rotat
Also asked: “A crankshaft is a key component of an engine transmitting cylinder power to the propeller shaft. Basically what it does is to convert the oscillating motion of connecting rod / reciprocating motion of the piston to rotatory motion of the shaft”
Answer
The crankshaft turns push into spin: journals, webs and crankpins converting rod swing into shaft torque for the propeller.
- Throws phased for firing order turn each unit’s gas load into continuous torque at the flange.
- Built, semi-built or fully built with shrunk journals and pins — weight and size follow power and speed.
- Rides main bearings with thrust located, passing power aft through intermediate shafting to the propeller.
- Fails by fatigue from misalignment, overload and loose holding-down long before honest steel tires.
Surveyor follow-up: throws fair with one web cracked and holding-down slack — material, alignment or foundation first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
34 AE Main Bearing Overhaul
Answer
Overhaul AE bearings on hours or symptoms: open on high temperature or wear-down, measure, renew, prove oil flow.
- Open at maker running hours, on rising temperature, low pressure or visible white-metal distress.
- Measure wear-down by bridge gauge and ball micrometer against limits with caps and shims kept ordered.
- Renew shells past limits with oil holes aligned, clearances proved and locking devices made up.
- Run in on load with temperatures and pressures logged — a boxed-up bearing unproved is a failure waiting.
Surveyor follow-up: bearing boxed up with clearances unlogged and oil flow unproved — complete overhaul or open again?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
35 AE main bearing removal procedure
Also asked: “Ae main bearing bottem part removal”
Answer
Lift AE bearings in order: isolate oil, lift the cap, bridge-gauge the wear, jack the shaft, land the shell.
- Remove the oil feed to the top shell with keep nuts off and the cap lifted by its eye bolts.
- Seat the bridge gauge and feeler the journal gap both sides before the shaft moves.
- Jack the shaft true on webs with lift inside limits, then roll the shell clear without scoring.
- Lower the bottom half out with bolts outside the crankcase, tagging every shim set to its side.
Surveyor follow-up: cap cocked with one side lifting and the gauge unread — heave on, lower back or reseat first?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
36 Ans. The cylinder head assembly comprises of the following components
Answer
A four-stroke head is valves, springs, rocker and injector over cooling passages: name each with its duty.
- Rocker arms drive exhaust and inlet valves against springs with tappets set hot to figures.
- Valves with seats and guides seal firing gas; springs snap them shut against spring air or cam load.
- Fuel injector centred for spray pattern with cooling passages carrying jacket water round seats and guides.
- Head, piston, gudgeon pin, rod, cam and crankpin complete the assembly the surveyor expects drawn.
Surveyor follow-up: head overhauled with suction and exhaust valves swapped — start, timing or damage first to show it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
37 Back clearance is the clearance from inner diameter of the piston ring to inside diameter of the groove
Also asked: “• Back clearance is the clearance from inner diameter of the piston ring to inside diameter of the groove”
Answer
Back clearance breathes behind the ring: bore-to-groove depth letting gas load the ring without binding.
- Gas behind the ring drives it outward onto the liner — too little back clearance throttles the seal.
- Measure hard directly, so compare ring width now against last overhaul width for the working figure.
- Hold axial groove clearance near 0.40 mm new, renewing near 0.70 mm before flutter and blow-by.
- Butt gap sized for heat — shut gaps scuff liners, open gaps pass fire to the next ring.
Surveyor follow-up: axial clearance 0.70 mm with back clearance closing and blow-by rising — rings, piston or liner first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
38 CPP...how pitch rotates Crankshaft to camshaft relation...how many gears
Answer
CPP pitch turns on servo oil, not on gears: hub yoke driven through shaft-bore pipes while crankshaft-to-camshaft stays geared 2:1 four-stroke.
- Servo pump feeds the hub through hoses, sleeve grooves and shaft bores into the yoke motor.
- Yoke travel swings blade carriers through crank pins — ahead, neutral and astern without reversing the engine.
- Camshaft drive stays gear or chain from the crankshaft with moment compensators on long-stroke gears.
- Count gears by train layout with sizes setting speed and direction — chains stretch, gears chip, both mistime if neglected.
Surveyor follow-up: pitch slow with servo pressure steady and gears quiet — hub, control unit or oil first?
Full theory: The Propeller — Fixed Pitch, Controllable Pitch and Cavitation -
39 Cam and crankshaft relative motion?
Answer
Camshafts turn with the firing order: half crankshaft speed on four-strokes through gears or chains sized for direction.
- Four-stroke cams run one revolution per two crank turns, opening each valve once per cycle.
- Gear trains set speed and hand by wheel count and size; chains do it by sprockets with tensioners.
- Elongated chains retard cams and pumps together — re-time past 2%, renew past makers’ stretch limits.
- Moment compensators spin at engine or twice-engine speed on long-stroke gears to kill vibration.
Surveyor follow-up: exhaust timing retarded with the chain at 3% stretch — adjust tension, re-time or renew now?
Full theory: Camshaft Chain Drive, Hydraulic Tensioners & Timing Synchronisation -
40 Check by turning the engine and watch movement of piston in the liner, check for any . occurrence of binding at part of stroke (Binding indicates misalignment of piston) © ‘
Answer
Prove piston alignment by barring over: watch the piston run true in the liner with no binding anywhere in stroke.
- Bar slowly after a bad fire or overhaul, watching piston travel full stroke against liner marks.
- Binding at one part means bent rod, distorted liner or misaligned crosshead — stop before seizure.
- Back with scavenge relief springs, liner calibration and crown-template wear proved in limits.
- Log the turn with positions and findings; a free turn unwitnessed is a turn unproved.
Surveyor follow-up: binding mid-stroke with the rod proved straight and liner gauged round — crosshead, guides or foundation next?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
41 Check piston rings and liner for any distortion or reddish burning mark &
Answer
Read rings and liner by eye and hand: bright sealing faces, free grooves, oily mirror bore — black, red and dull condemn.
- Rings free in grooves with bright working faces; black patches and blurred mirrors mean leaking gas past.
- Liner mirror-bright and oily with dry black tops marking blow-by and striped dull bands marking film breakdown.
- Reddish burning and heavy crown carbon mark wrong fuel, timing or cooling — clean and correct the cause, not just the shine.
- Raise the piston in steps through scavenge ports with a lamp, checking ports clear of carbon narrowing.
Surveyor follow-up: bright rings with black dry liner tops and carbon-narrowed ports — rings, fuel or air first?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
42 Descnbe using sketches a top end bearing urrangemen! designed to minimise or prevent the msk of oil film overload. (10) (b) Explain why successful Iubrication of top end bearings is difficult to achieve im prachce (6
Answer
Crosshead bearings starve by geometry: pins that swing instead of spin wipe oil instead of wedging it.
- Hydrodynamic film needs relative rotation; crosshead pins only swing a few degrees while rods oscillate.
- Fork-end and wide-shoe designs spread load over area with high-pressure oil fed to the loaded arc.
- Main and bottom-end bearings spin full circles and pump their own wedge — crossheads only wipe.
- Sketch oil feed to the crown with guide shoes lined in bearing metal and telescopic supply proved flowing.
Surveyor follow-up: crosshead wiped with oil pressure proved normal and guides fair — design, feed timing or load first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
43 Diesel Engine Parts (Liners, piston rings and Exhaust Valves
Answer
Liners guide, rings seal, exhaust valves breathe: three parts deciding power, oil control and gas flow together.
- Liners carry the piston true with cooling and lubrication films deciding wear and scuffing.
- Compression rings seal gas and pass heat to the liner; scraper slots return surplus oil to the sump.
- Exhaust valves open by hydraulic cam force against spring air, sealing on seats that must stay clean and cool.
- Quote functions with failure signs — blow-by, oil pumping and leaking seats — or the list stays academic.
Surveyor follow-up: blow-by with oil pumping and a leaking exhaust seat together — rings, liner or valve first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
44 For cooling of the piston, the rods consist of two through and through concentric holes. These holes are for supply and return line of cooling oil
Also asked: “• For cooling of the piston, the rods consist of two through and through concentric holes. These holes are for supply and return line of cooling oil”
Answer
Piston cooling rides inside the rod: concentric bores carry oil up and back with telescopic joints at the crosshead.
- Upper manifold oil feeds each crosshead through telescopic pipes that flex with the running gear.
- Rod bores split at the crosshead to top-end bearings, guides and bottom-end halves in metered branches.
- Return oil falls back through the second bore to temperature-and-flow sight boxes before the sump.
- Prove by flow and outlet temperature per unit — a hot return with pressure steady marks the blocked leg.
Surveyor follow-up: one piston hot with manifold pressure steady and telescopics proved free — supply bore, return bore or crown first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
45 How camshaft is driven? Relative speed between camshaft and crankshaft for 2s and 4s engine?
Answer
Cams follow the crank by gears or chains: same speed on two-strokes, half speed on four-strokes, direction by train layout.
- Gear trains of sized intermediates set speed and hand without losing tension; chains use sprockets with tensioners.
- Four-stroke camshafts turn once per two crank turns, firing each cylinder once per cycle.
- Two-stroke cams turn with the crank, timing exhaust and fuel once per revolution.
- Long-stroke gears carry moment compensators at engine or twice-engine speed against vibration.
Surveyor follow-up: four-stroke exhaust timing late with the chain at 3% stretch — tension, re-time or renew first?
Full theory: Camshaft Chain Drive, Hydraulic Tensioners & Timing Synchronisation -
46 How to detect if piston gland( stuffing box) of ME is faulty while running?
Answer
A faulty ME stuffing box talks running: oil mist rising, scavenge fouled, drains weeping, temperatures splitting.
- Watch scavenge air-box temperatures and exhaust splits climb as blow-by and oil pass the rings.
- Sniff scavenge drains for lube oil with crankcase mist readings rising and oil consumption climbing.
- Listen and smell for hot oil with telltale drains weeping and under-piston spaces fouling.
- Confirm by temperature probes at oil returns and mist-detector trends — open only stopped and cooled.
Surveyor follow-up: scavenge hot with drains oily and mist steady — rings, box or purifier first to blame?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
47 How to take tappet of running AE?
Answer
Tappets are set stopped, proved running: feeler to figures cold with visual lift check as the surest proof.
- Set exhaust near 0.4 mm and suction near 0.3 mm with the engine barred to the firing mark per maker.
- Prove running only by watching valve lift rise and fall — feeler strips have no place in moving gear.
- Bumping clearances by lead wire through valve openings with rods jacked true cover the same discipline.
- Log hot versus cold figures with gaskets and shims to size — a tappet guessed is a valve burnt.
Surveyor follow-up: tappet noisy running with cold figures perfect and lift proved even — oil, wear or heat first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
48 How will you know crosshead is being lubricated
Also asked: “how lubrication done on croshead”
Answer
Crossheads prove oil by sight and heat: telescopic flow steady, guides wet, telltales dripping, temperatures even.
- Watch telescopic-pipe flow with guide-shoe faces wetted and oil reaching the pin and shoes together.
- Prove per-cylinder temperature and return flow at the sight boxes before passing load upward.
- Side thrust absorbed into the frame leaves shoes lined in bearing metal — dry shoes score in one watch.
- Inspect pipes for cracks, flow for steadiness and shoes for wiping with findings logged per unit.
Surveyor follow-up: one crosshead hot with manifold pressure steady and pipes intact — feed branch, shoe or load first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
49 If V type of Engine, you have one connecting rod or two. How con- rod is driving both units
Answer
V-engines use either a master and slave rod on one crankpin or a forked rod carrying both bottom ends at once.
- Articulated V designs pin a master rod through the normal bottom-end bearing with the slave rod on a boss above it.
- Forked designs give one rod a fork end gripping the bearing bush while the second rod rides between the fork and the bush.
- Either way the crankpin turns one bush and both cylinders push in the same transverse plane to shorten the engine.
- Inspect the fork blades, slave-rod boss and bush clearances — side thrust lands on the thin fork when play grows.
Surveyor follow-up: V engine running with the fork blade bright and the slave-rod boss unbroken — clearance, lubrication or load first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
50 If there is no back clearance, the rings take the side thrust. This results in high friction and possible piston seizure
Also asked: “• If there is no back clearance, the rings take the side thrust. This results in high friction and possible piston seizure”
Answer
Rings need room behind them: without back clearance they jam on side thrust, scuff, break and seize the piston.
- Gas pressure must load the ring against the liner — no back clearance means the groove walls carry thrust instead.
- Groove depth sets the working clearance; too little and the ring binds on wear, heats and rubs one flank.
- High friction then breaks rings and grabs the liner, turning a clearance fault into a seizure and a unit off.
- Measure groove depth, renew grooves or rings to maker figures and prove free movement all round the circumference.
Surveyor follow-up: rings jammed with grooves shallow and crowns cool — deepen, renew or re-bore first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
51 If you overhauled cylinder head and brought it to workshop , how will you identify which is suction and exhaust valve
Answer
Tell the pair by size, stem, guide and marks: exhaust is the bigger valve with the cooler, sodiated stem and bigger spring.
- Exhaust valves run larger in head diameter with sodium-filled hollow stems for internal cooling.
- Inlet valves are smaller, often lighter alloy, and sit in the same guide bores with matching spring seats.
- Match stems and springs to their original positions in the head layout rather than by size alone.
- Tag each valve and seat with its port and cylinder number before the head leaves the workshop bench.
Surveyor follow-up: swapped pair with equal springs and no tags — refit by port, by size, or reassemble and test first?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
52 Important Function of Piston rod
Answer
The piston rod carries the gas load: piston to crosshead to the rod, taking thrust and keeping the piston on its axis.
- Transmits firing pressure from the piston through the rod to the crosshead and then the connecting rod.
- Absorbs the lateral crank-rod forces that the piston rod alone cannot carry.
- Passes through the stuffing box, so it needs a smooth low-friction surface and concentric cooling-oil bores.
- Length follows stroke and design, flanged under the piston at the top and pinned to the crosshead at the bottom.
Surveyor follow-up: rod scored at the stuffing box with oil flow proved normal — packing, alignment or cooling first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
53 It is the distance between connecting faces of piston ring. ( or clearance between the end butt of the ring inside the liner
Also asked: “• It is the distance between connecting faces of piston ring. ( or clearance between the end butt of the ring inside the liner”
Answer
Butt clearance is the ring’s end gap: it must swallow thermal expansion without passing fire.
- Take the reading in the liner at the ring’s slowest speed and highest temperature, ring square to the bore.
- Too small and expansion closes the gap, loading the ring radially and burning liner and ring alike.
- Too large and gas blows past to the ring below, scorching the liner and loading the lower ring with pressure.
- New rings get maker’s butt gap; a worn ring renews rather than resets while scuff marks stay on the faces.
Surveyor follow-up: gap opened beyond limit with the liner scored at that ring — renew rings, hone liner or both?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
54 Liner material and reasons for cracking
Also asked: “Liner crack how to know”
Answer
Liners are alloy cast iron or steel; they crack from thermal shock, caustic attack, or overload beyond the thick-walled strength.
- Centrifugally cast alloy iron with hard chromed or honed bores gives wear resistance with a tough core.
- Thick walls resist hoop stress; boring oversize or thin liner sections set the cracking risk before anything else.
- Cold coolant on a hot liner, acid condensate or caustic carry-over attack the grain boundaries and open cracks.
- Confirm by dye-penetrant or magnetic inspection, then find the cause — a fresh crack in a young liner is usually handling or temperature.
Surveyor follow-up: liner cracked after 300 hours with feed and cooling proved in limits — handling, assembly or material first?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
55 Lower section prevents oil carry over by piston rod from crank case to scavenge space
Also asked: “• Lower section prevents oil carry over by piston rod from crank case to scavenge space”
Answer
The lower stuffing-box section holds the crankcase back: scraper rings wipe rod oil so none climbs into the scavenge.
- Upper scraper rings catch contaminated oil on the down stroke and drop it into the scavenge for drainage.
- Lower rings block crankcase oil following the rod upward across the pressure difference into the trunk.
- Packing and scrapers adjusted so ring segments never butt — butted rings let oil straight through.
- Watch the open tell-tales: heavy oil means the lower set is faulty, blowing air means the upper set is worn.
Surveyor follow-up: oil in the recycling tank with the tell-tale dripping — lower rings, upper rings or cylinder oil first?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
56 Main bearing clearance. Precautions for feeler. What to do if feeler breaks inside
Answer
Bridge-gauge clearances read with clean, straight, unstacked feelers — and a snapped blade comes out whole, never left in the housing.
- Strip the oil feed, lift the top half, seat the bridge gauge and keep the shaft dead so feelers do not pinch.
- Use single blades, clean and unbent, kept parallel; stacked strips read falsely against rough journals.
- If a blade snaps, stop and lift the bearing — retrieve the fragment before it works into the white metal or the sump.
- Check the crankpin for the gouge a lost blade cuts, and record the clearance with the broken-blade incident in the log.
Surveyor follow-up: clearance reading suspect with a blade snapped in the housing — reopen and re-measure before running?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
57 Material of crosshead, bottom end and main bearing
Answer
White metal on steel backs: tin-based alloy with antimony and copper gives tolerance, wear resistance and a run-in layer.
- Crosshead and bottom ends take thin-shell bearings with a soft matrix that swallows small misalignment.
- Main bearings use white-metal lines in thin steel-backed shells with nip that holds the shell in its housing.
- Tin aluminium suits only thin shells where hard running against toughness is needed at lower loads.
- Thick shells adjustable by shims appear in mains only; thin shells lock by crush and cannot be shimmed.
Surveyor follow-up: shell creeping in its housing with nip lost and bolts tight — housing, shell material or alignment first?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
58 Mean piston speed
Answer
Mean piston speed is the average travel per second: twice stroke times rpm over 60, and it sets power and wear together.
- C_m = 2SN/60, with 2S the distance covered each crank revolution and N in rpm — stroke in metres gives m/s.
- Power scales with mean piston speed, so it fixes the power an engine can make inside its limits.
- Wear, ring life and gas-flow losses cap the speed, and wear peaks at top centre where speed is lowest.
- Quote the formula, your units and the maker’s limit for the engine — a bare number fails the drawing test.
Surveyor follow-up: piston speed on figures with liner wear climbing at top centre — speed, film or both first?
Full theory: Diesel Engine Types — 2-Stroke Crosshead vs 4-Stroke Trunk -
59 Piston checks during decarb
Answer
Decarbing is a rebuild: rings out, grooves cleaned and gauged, crown templated, skirt and rod tested — all logged.
- Lift rings with the expander, clean grooves of carbon and measure their depth against the recoil recess.
- Templated the crown for burning-away against the maker gauge and re-dress only within allowable loss.
- Inspect skirts and rings for scuffing, distortion and lacquer, testing the cooling circuit by hand and gauge.
- Turn the piston and rod over, check rings free in grooves, renew soft or thinned rings and refit expander-wise to maker order.
Surveyor follow-up: crown templated within limit with rings jammed and grooves lacquered — clean, renew or decarb again?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
60 Piston rod packing spring also should be checked, which may have become weakened by 4 overheating
Answer
Packing springs weakened by heat let the rod leak: test spring action and renew before the box eats oil into the trunk.
- Check every packing spring for set and heat-weakness — a sprung spring cannot follow the rod as it reverses.
- Weak springs leave gaps that pass oil down into the crankcase and, worse, draw fire gas into the scavenge.
- Renew softened springs with the packing set and reset spring compression to maker figures.
- Log the finding: heat-weakened springs point back to persistent blow-by or cooling faults needing their own fix.
Surveyor follow-up: oil at the tell-tale with springs renewed and rod crowned — packing type, alignment or speed first?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
61 Piston rods are generally found in large two stroke engines. Piston rods help in transmitting the power produced in the combustion space to the cross head and the running gear of the engine
Also asked: “• Piston rods are generally found in large two stroke engines. Piston rods help in transmitting the power produced in the combustion space to the cross head and the running gear of the engine”
Answer
In big two-strokes the piston rod is the power link: piston to crosshead to con rod, staying straight under the heaviest gas loads.
- Piston, piston rod, crosshead, connecting rod, crankpin, web and crankshaft form the driving chain named in maker diagrams.
- Gas forces pass piston rod to crosshead to connecting rod to crankpin — the rod also takes the piston’s inertia.
- Length follows stroke and design, flanged under the piston and pinned through the crosshead at the bottom.
- It must run dead straight through the stuffing box, so alignment and packing control are life-and-death work.
Surveyor follow-up: rod running off centre in the stuffing box with thrust bearings new — alignment, packing or frame first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
62 Relation between ME crankshaft and camshaft rotation?
Answer
On a two-stroke the cam turns with the crank at 1:1, geared or chained, so pumps and exhaust valves fire once per revolution.
- Fuel pumps and exhaust valves both act once per cycle, so cam speed equals crank speed on two-strokes.
- Gear drives hold tension permanently; chain drives are light and narrow but elongate, with a life around fifteen years.
- Elongation retards both pump and valve timing together, re-timing by expanding the coupling with high-pressure oil.
- Firing order comes from throw phasing, not the cam drive — state the ratio, the drive type and the consequence of stretch.
Surveyor follow-up: exhaust and fuel both late with the chain at 3% stretch — tension, re-time or renew now?
Full theory: Camshaft Chain Drive, Hydraulic Tensioners & Timing Synchronisation -
63 Stuffing box is bolted to diaphragm through which piston rod passes
Also asked: “• Stuffing box is bolted to diaphragm through which piston rod passes”
Answer
The stuffing box bolts to the diaphragm to seal the crankcase: packing and scraper rings let the rod swing through without oil escaping.
- Bolted to the diaphragm, the box divides crankcase from scavenge with the piston rod passing through its seals.
- Upper packing sets the gas seal; scraper rings stop oil climbing into the trunk on the down stroke.
- Lower section blocks crankcase oil following the rod up across the scavenge pressure difference.
- Telltales read ring condition running: dripping oil means lower sets faulty, blowing air means upper sets worn.
Surveyor follow-up: box breathing past its seal with the diaphragm proved tight — packing, alignment or cracked gland first?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
64 Tappet clearance how to check piston at TDC
Also asked: “Tappet clearance and how to make sure piston is at TDC methods”
Answer
Set tappets at true TDC: bar the piston to top, confirm the roller on cam base circle, then feeler to figures.
- Bring the piston to TDC by barring and confirm it twice — rocking either way until the turning moment balances.
- On four-strokes remember the piston passes TDC twice: take the firing stroke, not compression.
- With the exhaust valve closed and the roller on the cam base circle, feeler the tappet cold to maker figures.
- Confirm by barring slowly through the position and watching when the thinnest blade first stops entering — that marks opening.
Surveyor follow-up: figures set cold but the engine touches the camshaft hot — re-set, shim or relieve rocker first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
65 The diagram is taken periodically from the indicator valve equipped on he cylinder head and combustion condition is to be confirmed
Answer
The indicator diagram is the combustion health chart: pressures against piston position, read at every watch for drift.
- Gives indicated output plus maximum and compression pressures to judge firing, timing and fuel delivery.
- Evaluate the combustion process itself — pressure rise angle, peak height and where the peak sits from TDC.
- Clearance volume and blow-by show as card shape losses; scavenging and exhaust quality read from the tail.
- Take it on the same load each watch — diagrams mean nothing unless load, grade and engine state are logged with them.
Surveyor follow-up: peak pressure drifting down on the same load with no fuel change — fuel, timing or compression first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
66 The lengths of these rods depend on the length of the engine stroke and the manufacturers design. The top end of the rod is flanged or attached to the underside of the piston and the bottom end is connected to the cross
Also asked: “• The lengths of these rods depend on the length of the engine stroke and the manufacturers design. The top end of the rod is flanged or attached to the underside of the piston and the bottom end is connected to the cross head”
Answer
Piston rods are sized by stroke: flanged to the piston crown above, pinned to the crosshead below, carrying the whole gas load.
- Length follows stroke and maker layout — too short and the piston crowds the head, too long adds whipping mass.
- Top end flanged or bolted to the piston underside; bottom end pinned through the crosshead to take the thrust.
- It passes the stuffing box, so concentricity with the cylinder and crosshead slide line is set by this length.
- Because it also carries piston cooling oil, its bores are part of the cooling circuit and get pressure-tested.
Surveyor follow-up: rod short enough to crowd the head with the engine at TDC — fit, re-machine or lower the piston?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
67 The piston rod passes through the piston gland or stuffing box so the rod should have smooth running surface and low coefficient of friction
Also asked: “• The piston rod passes through the piston gland or stuffing box so the rod should have smooth running surface and low coefficient of friction”
Answer
The rod surface lives in the gland: smooth, hard and low-friction so packing follows it without heat or wear.
- Running surface must stay mirror-smooth — any score becomes a groove the packing cannot follow.
- Hardened by nitriding, induction or flame hardening in the packing area so the seal rides on chrome, not soft steel.
- Low friction keeps heat down; friction heat at packing wear climbs fast once roughness breaks the film.
- Check rod straightness and diameter at the gland while stopped — a bent rod wears both rod and packings inside a voyage.
Surveyor follow-up: oil at the tell-tale with rod surface scored and packings renewed — rod, alignment or lubrication first?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
68 The ring expands against the liner. This increases the friction resulting in breakage of ring and Seizure of piston
Also asked: “• The ring expands against the liner. This increases the friction resulting in breakage of ring and Seizure of piston”
Answer
Heat-expanded rings jam the liner: friction climbs, rings break and the piston seizes inside its own bore.
- A ring heated and expanded beyond its groove clearance grips the liner, dragging against it every stroke.
- That friction becomes heat, heat becomes expansion and the ring either cracks, spreads or strips its chrome.
- Once rings break, gas passes to the next ring, oil follows the blow-by and the piston finally seizes.
- Prevent with correct butt and axial clearances, alkaline oil at load feed, and rings free in clean grooves.
Surveyor follow-up: one unit hot with rings intact and oil fed — fuel, cooling, clearance or scoring first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
69 The total distance travelled by the piston as it moves from bottom dead centre to top dead centre.It is determines by the diameter of the circle travelled by the connecting rod journals of the crankshaft as the crank is
Also asked: “The total distance travelled by the piston as it moves from bottom dead centre to top dead centre.It is determines by the diameter of the circle travelled by the connecting rod journals of the crankshaft as the crank is rotated”
Answer
Stroke is twice crank radius: the piston sweeps BDC to TDC over 2L, where L is half the crank throw.
- Crank throw is the radius of the circle the crankpin sweeps, so stroke equals twice that radius.
- The piston travels 2L each revolution — that figure feeds mean piston speed and the engine’s length of stroke class.
- Draw throw, rod and piston on the same diagram so the surveyor sees the 2L relation, not a remembered number.
- State it with your engine: bore, stroke, and L/L2 ratio deciding displacement and hull form.
Surveyor follow-up: stroke quoted as crank radius with the rod length ignored — geometry, notation or both wrong?
Full theory: Diesel Engine Types — 2-Stroke Crosshead vs 4-Stroke Trunk -
70 Tie rod function
Answer
Tie rods hold the engine together: bedplate, A-frames and entablature pre-stressed in compression against gas blows.
- Long steel rods through hollow columns bind bedplate, A-frames and cylinder entablature into one compression member.
- Gas force tries to lift and split the structure; tie rods replace that with preload so the structure only ever compresses.
- Squared nuts seat in cast bedplate pockets so tightening stays square, with load shared between at least two rods.
- They also resist thrust and vibratory movement — loose rods mean the frame works and breathes every firing stroke.
Surveyor follow-up: rod nuts slack with the frame cracked at a pocket — re-tension, investigate cracking or renew rod first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
71 Tie rod function. A/E present or not?
Answer
Tie rods belong to the big two-stroke: they bind bedplate, A-frames and entablature, and auxiliaries carry none.
- Main engines pre-stress the whole column in compression because gas loads on a large cylinder are huge.
- Auxiliary engines are small enough for bedplate and frame stiffness to hold the entablature without rods.
- The A-frame carries crosshead guides and the entablature on main engines, and on auxiliaries the block itself does it.
- Say the engine type with the answer — claiming auxiliaries carry tie rods fails the very first question.
Surveyor follow-up: auxiliary with two long rods through the casing — designer’s choice or error, and who signs it?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
72 To measure back clearance, measure the depth of the piston ring groove by means of the depth gauge
Also asked: “• To measure back clearance, measure the depth of the piston ring groove by means of the depth gauge”
Answer
Back clearance comes off a depth reading: groove depth minus ring height is the working gap behind the ring.
- Depth-gauge the groove floor and measure the ring height, then subtract for the working back clearance.
- Where the gauge is awkward, compare ring width with the reading taken at the last overhaul and take the difference.
- Keep axial groove clearance near 0.40 mm new and renew the piston or rings near 0.70 mm before flutter.
- Record both numbers — groove and ring — because back clearance fails when either moves, not only the ring.
Surveyor follow-up: back clearance 0.80 mm with the ring free in its groove — renew ring, groove or piston?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
73 To measure butt clearance, insert the rings in the bottom of the liner and ensure that they are in line with the liner axis
Also asked: “• To measure butt clearance, insert the rings in the bottom of the liner and ensure that they are in line with the liner axis”
Answer
Butt clearance is read low in the bore: stand the rings square to the liner axis at the bottom and measure the gap.
- Set rings upright in the liner bottom, square to the axis, and measure between the ends with a feeler or gauge.
- Read at the hottest part of the ring travel so the gap you see is the gap it will run with.
- Compare against maker’s new-ring figure; renew the ring rather than squeezing ends to fit.
- Worn ends pick up scuffing and blackening — those marks tell you the gap was shut and the ring has been rubbing.
Surveyor follow-up: gap measured wide at the top but shut at the ring land — measure cold, hot or renounce the ring?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
74 Types of crankshafts of 2S engine. And the problems that arises with them
Answer
Two-stroke cranks are monolithic castings or welded assemblies: each choice brings its own failure and repair story.
- Monolithic cast or forged shafts carry journals, crankpins and webs in one piece — no weld risk, heavy and costly to cast.
- Welded assemblies build crank throws from journal and web sections for larger outputs, needing stress relief and proof testing.
- Welded shafts go to the furnace at high temperature for stress relief, then ultrasonic and magnetic-particle proof of the welds.
- Semi-built shafts use shrunk journals on a smaller core — cheaper, but shrink-fit slip and web fatigue need watching.
Surveyor follow-up: welded shaft flagged at one web after 8000 hours with no alarm — fatigue, weld defect or alignment first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
75 WHAT CHECKS ON PISTON AND LINER
Answer
Piston and liner checks are a matched set: template the crown, gauge the liner, ring free, bore mirror-bright and oily.
- Crown burn-away checked by template against maker limits, with grooves gauged and recoils found.
- Rings free in clean grooves with bright working faces, renewing any stuck, thinned or black-blurred ring.
- Liner gauged at fixed levels and directions, mirror-bright and oily; black tops and striped dull bands are defects.
- Cooling circuit and piston tested during decarb with findings logged per cylinder before refit.
Surveyor follow-up: crown and rings within limits but liner black at the top — rings, fuel or air first?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
76 Why connecting rod not coupled with piston in ME
Answer
On main engines the rod is pinned to the crosshead, not the piston: the piston rod bridges the gap and keeps the piston on its axis.
- Crosshead engines place the connecting rod on the crosshead pin, with the piston rod between crosshead and piston.
- Direct coupling would let the rod’s swing twist the piston, breaking the bore seal and the rod’s own bearing.
- The piston rod takes the gas and inertia thrust while absorbing the lateral crank forces the rod cannot carry.
- Trunk-piston auxiliaries do couple rod to gudgeon pin directly — name the engine type when you claim the difference.
Surveyor follow-up: rod bolts loosened to reach a liner and refitted to the piston — refit to crosshead or renew first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
77 Why relief valve on cylinder head if not there what will happer
Answer
Cylinder-head reliefs are the last defence: they vent pressure spikes the indicator never saw, before the cover lifts.
- Blow-by or mist ignition can spike head pressure between strokes faster than the safety valves elsewhere can answer.
- Blocked ports, water hammer or a late-closing exhaust valve all deliver the spike the head relief catches.
- Without a relief that pressure lifts the cylinder cover, cracks the joint or blows a man overboard across the casing.
- Prove free lift on schedule with the relief port proved clear — a relief tested only at overhaul is a relief untested.
Surveyor follow-up: head relief lifted twice this voyage with normal readings — clean port, set pressure or test rig first?
Full theory: Safety — Crankcase Explosion, Scavenge Fire and Starting Air Line Explosion -
78 Why use Tie rods
Answer
Tie rods turn a stack of castings into one pre-stressed column so gas loads compress structure instead of splitting it.
- They bind bedplate, A-frames and entablature through hollow columns, sharing every firing load evenly.
- Preload keeps cast iron permanently in compression — the frame never sees the tensile stress it is weakest against.
- They also stop the frame breathing, which is what makes the vibration that cracks housings and distorts bore alignment.
- Tension is set and re-checked at inspection; slack rods quietly hand the job back to the structure they were built to spare.
Surveyor follow-up: crack at a tie-rod pocket with nuts tight and preload unmeasured — preload, alignment or casting flaw first?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
79 approx length of tie rods. what arrangements are provided to prevent vibrations in tie rod?
Also asked: “• approx length of tie rods. what arrangements are provided to prevent vibrations in tie rod?”
Answer
Tie rods run the full height of the engine, in two parts where stroke is long, with pinch bolts killing lateral vibration.
- Length follows engine height — on very tall engines they split into two sections for removal through the casing.
- Pinch bolts hold adjacent rod sections in line so one cannot bow and start a whipping mode.
- Squared nuts in bedplate pockets stop rotation so preload stays square through every check.
- A gauge or check at inspection proves rods still carrying their share, not just present and nutted.
Surveyor follow-up: rod bowed between sections with pinch bolts loose — re-tension, re-align or renew the rod?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
80 checks on piston crown
Also asked: “Piston crown inspection”
Answer
Crown checks are a template job: measure burn-away against the maker gauge, then find why the crown lost metal.
- Template the crown at several radii with allowable burn-away from the maker gauge — past it the piston goes.
- Inspect grooves for carbon, recoil and wear depth, and check the skirt for scuffing and distortion.
- Pressure- or leak-test the cooling space so a burnt crown is not cooling failure repeated next overhaul.
- Record crown, grooves, rings and skirt per cylinder in the decarb log with the cause, not just the number.
Surveyor follow-up: crown burnt within limits with the cooling circuit proved tight — timing, oil or fuel first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
81 how to know piston at tdc
Answer
TDC is found by feel and by mark: bar slowly, confirm by touch, and check the flywheel timing reference.
- Bar the engine slowly and watch the piston through a valve opening until it just stops and reverses.
- Confirm by feeler at the tappet — the thinnest blade first fails to enter when the valve begins to lift.
- Flywheel or crank-timing marks give the exact reference for opening and closing angles to log.
- On four-strokes remember two TDCs per revolution: take the firing one for valve work and the other for compression checks.
Surveyor follow-up: tappet gap measured at compression TDC instead of firing — how much error, and which way?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
82 tappet clearance adjustment
Answer
Tappets are adjusted cold at true TDC: shim or swap the cup so the gap reads maker figures, then re-verify hot.
- Shims under the cup change clearance; never grind the cam or the tappet face to make a number.
- Set with the exhaust valve closed and the roller on the cam base circle, piston at firing TDC.
- Check visually on the running engine — lift must be free and even with no lash hammer in the gear.
- Recheck hot after a run, since clearance changes with expansion — record cold and hot figures together.
Surveyor follow-up: tappets touching hot with correct cold figures — lift height, shims or camshaft first?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
83 types of crankshaft duty of 4th engineer watch taking over purifier start but didn't pick speed same reason
Answer
A purifier that will not reach its marked speed is a drive problem before it is a bowl problem: clutch, alignment, bearings or supply.
- Single phasing or a motor running overloaded, and motor low voltage or current, are the electrical causes.
- A worn friction clutch or friction pad, and a brake that is not fully released, both stop the speed building.
- Vertical and horizontal shafts out of alignment, or bearings worn down, make the machine run rough and slow.
- Excessive sludge in the bowl, too high a sump level, and back pressure from a closed service tank valve are the process causes.
Surveyor follow-up: purifier slow to pick up with the clutch and brake proved — is it alignment, the bowl sludge or the supply?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
84 what is linear polishing? how to remove main bearing bottom end shell? i guess this was decider?
Answer
Linear polishing is the cross-hatch a hone leaves to hold oil; bottom shells come out by dropping the cap and rolling the shell clear.
- Honing cuts scratches at roughly 50–60 degrees so they cross-hatch and hold oil for rings and piston.
- A straight-line polish instead of cross-hatching gives rings a single wear line and lets the oil film go.
- To remove a bottom shell, slacken the cap, drop the cap onto the web supports and roll the shell out square.
- Never lever the shell against the bore — the white metal wipes and the shell is scrapped, not the rod saved.
Surveyor follow-up: shell cocked in the housing with a wiped patch — dress the housing, renew the shell or both?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
85 which has more tappet
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.