
Main bearing knocking
Typical knocking or thumping noticeable at sudden throttle opening at idle which intensifies with higher crankshaft rate. Excessive endfloat
of crankshaft causes sharper irregular knocking, especially noticeable during smooth increase or decrease in crankshaft speed.
1. Early ignition
2. Insufficient pressure oil
3. Loose flywheel securing bolts
4. Excessive main bearing running clearance
5. Excessive thrust washers-to-crankshaft clearance
Big-end bearing knocking
Big-end bearing knocking is sharper than that of main bearings. It is noticeable during engine idle at sudden throttle opening. The origin of
knocking can be easily identified through switching off spark plugs one at a time.
1. Insufficient oil pressure
2. Excessive big-end bearing running clearance
Piston slap
Thumping noise caused by piston «runout» in cylinder. Most noticeable at low crankshaft speed and under load.
1. Excessive piston-to-cylinder bore clearance
2. Excessive gudgeon pin-to-piston groove clearance
Knocking of intake or exhaust valves
Excessive valve clearances cause typical regular noise; its frequency is lower than the frequency of any other engine noise, since the valves
are operated by camshaft rotating at half the crankshaft speed.
1. Excessive valve clearances
2. Broken valve spring
3. Excessive valve-to-guide clearance
4. Worn camshaft lobes
5. Loose locknut of adjuster bolt
Excessive noise of camshaft operation line
Noise from camshaft operation line is caused by clearances between engagement elements and becomes noticeable in general engine noise
at low crankshaft speed.
1. Loose chain caused by general wear
2. Broken chain tensioner shoe or damper
3. Seized chain tensioner plunger rod
Insufficient oil pressure at warm engine idle
1. Foreign particles entrapped under oil pump relief valve
2. Seized oil pressure relief valve
3. Worn oil pump gears
4. Excessive main bearing running clearance
5. Excessive camshaft bearing journal-to-bearing housing clearance
6. Incorrect oil grade or inappropriate oil quality
Excessive oil pressure on warm engine
1. Seized oil pressure relief valve
2. Excessively tough spring of oil pressure relief valve
10
1. Adjust ignition timing
2. Refer to subsection «Insufficient oil pressure at idle»
3. Tighten bolts to torque specified
4. Grind journals and renew bearing shells
5. Fit new thrust washers, check clearance
1. Renew valve
2. Renew spring
1. Refer to «Insufficient oil pressure at idle»
2. Fit new bearing shells and regrind journals
1. Adjust clearances
2. Renew spring
3. Replace worn parts
4. Renew camshaft and levers
5. Adjust clearance between lever and cam, tighten locknut
1. Renew pistons, rebore and hone cylinders
2. Fit new rings or new pistons with rings
1. Tighten chain
2. Renew tensioner shoe or damper
3. Eliminate seizure
1. Clean valve from foreign particles and flash, clean oil pump
2. Renew valve
3. Repair oil pump
4. Turn journals and renew bearing shells
5. Renew camshaft or bearing housing
6. Change oil as recommended in Attachment 4
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