Engine Noise Descriptions

[Leo Bolter]

I thought his might be a handy reference:

ENGINE NOISES

What are the symptoms of big-end knock?
A fairly heavy, dull metallic knock evident when the engine is pulling under light load, and becoming more pronounced as the engine warms up and the oil thins out. Oil pressure gauge reading too low.

What are the symptoms of small-end knock?
A light, sharp metallic rattle, mainly audible if the engine is raced in neutral and the throttle quickly snapped shut. Some slight noise during tick-over.

What noise symptoms indicate a worn timing chain?
A 'thrashing' noise. Most obvious when standing in front of the radiator when the engine is ticking over fairly slowly. The noise tends to disappear as the engine r.p.m. rises.

If one cylinder is knocking, how can it be traced?
Short out each plug in turn, and note which one causes the knock to disappear.

What sort of noise is caused by worn main bearings?
A heavy, low-pitched rumble, generally most audible when the engine is pulling hard in top gear.

What sort of noise is piston slap?
A fairly sharp metallic sound, at its worst with a cold engine and gradually diminishing as the engine warms up.

What sort of noise would indicate excessive tappet clearances?
A sharp, light, consistent clicking sound, which alters in direct relation to the speed of the engine, Clearly audible at tick-over, especially with a cold engine.

[Forumadmin]

And one I had on the Subaru, which was a similar to a worn or maladjusted tappet in being a light tap. This turned out to be a worn big end that caused the piston to slap against the head. Whilst on the way to the garage down the M4 and driving at about 50mph the piston let go causing a dense cloud of oil smoke behind me that stopped three lanes of traffic. Luckily I coasted up the slip road to be towed away by the garage. Engine was a total write off! Piston on display in the JH&BS (Jowett Health and Beauty Salon) to be joined by the dropped valve heads, broken piston rings eating through the liners, welded up diff, broken gearbox bits and many other examples of 40 years of Jowett motoring!

[Keith Andrews]

Cracked or Collapsed piston skirt is near to impossible to find or diagose by sound.
tap/tick is not there cold, or under load and usually put down to something else like a tappet till that is eliminated.
Sure way is a $20 mechanics stethosope, a must in any tool box, and will find all of the above without having to diagaone sounds.

[Tony Fearn]

ENGINE NOISES

What are the symptoms of small-end knock?
A light, sharp metallic rattle, mainly audible if the engine is raced in neutral and the throttle quickly snapped shut. Some slight noise during tick-over.

What sort of noise would indicate excessive tappet clearances?
A sharp, light, consistent clicking sound, which alters in direct relation to the speed of the engine, Clearly audible at tick-over, especially with a cold engine.

...except in the case of one of the two cylinder liners moving up and down with the piston and rattling against the cylinder head on 'Mary Ellen'!


...except for a smaller diameter split pin than was necessary (put there by others I might add) through the front of the cam shaft allowing the cam shaft sprocket retaining nut to unwind a few thou. on 'Sarah Jane'!

Tony.

[george garside]

my favourite is the case of 'the loose cylinder base nut' To quote a 1947 factory service bulletin

"This trouble may show symptoms of a more deep seated fault, and has occasionally caused considerable wasteof time in unnecessarily checking cylinder bores, big end bearings, main bearings and flywheels
When servicing Bradford vehicles these nuts should always be checked and tightened if necessar"

I nearly got caught out with this one and phoned Roy Braddock from a roadside phone box to tell him of the stange and serious sounding noises eminating from within the bowels of the thing. Just tighten the cylinder base nuts said Roy- you will probably get a quarter turn on some of them.. This I did outside the phone box and immediately normal running was restored!

george

[k. rogers]

I've told the story many times about a situation regarding George's comments above. At the end of the Grange-over-Sands Rally in the early 80s, my Kestrel at the time (JF 6786) developed the very same knock before the journey home to Cornwall. Neither my dad or me belonged to either of the recovery associations in those days, so with a suspected 'big-end' problem we decided to do as it stated in the handbook, ie an extra pint of oil above the maximum level so that the bearing dips into the oil "....to get you home...."! I don't think Jowett's actually meant 400 miles home! Believe or not, we drove all the way to Cornwall with this problem until the engine lost neary all its power ten miles from home, where we had to be towed the rest of the way. Contemplating the work in renewing the big-end, I set about stripping the engine when I found the nuts holding the cylinder base down were all extremely loose. realising the actual problem I tightened them down and the car needed no work whatsover. I was informed we were extremely lucky not to break a con-rod or worse.