Nail Those Noises
Worried About That Strange Sound Under The bonnet? Here’s How To Name That Tune In One! Published: 14th Sep 2012 - 0 Comments - Be the first, contribute now!
A good decoke and valve grind can work wonders… 
Many ills due to lack of maintenance, like tappets 
Some noises may be cheap and simple fi xes: fan belt, etc 
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A noise annoys as they say, but it can also cost you dearly if you let it fester and become louder. Engines usually make the biggest racket when they are wearing… the trick is to know what dins demand fixing – and fast. And by knowing your noises you can also pick up a classic bargain!
DON’T WORRY
Hum a tune WATER PUMP
Annoying… but a noisy water pump rarely gives
trouble. It is usually caused by the gland rubbing
the casing and as the only lubrication a pump
receives is the cooling water, there’s not much you
can do although there are aftermarket additives.
In days of yore a little squirt of washing up liquid
did the trick but we wouldn’t advise it anymore.
Rat-a-tap-tap TAPPETS
Or to be more accurate it’s the rocker assembly as the ‘tappets’ are the cam followers. The continuous bashing rockers receive causes them to wear but it doesn’t unduly affect the performance. A new assembly is the cure although some mechanics set the tappets with the engine running to counteract some of the wear.
Slap happy PISTON SLAP
This is found even on only moderately worn engines and is the sound of the piston slightly rocking in the cylinder bores due to slight piston ring and bore wear. The noise usually disappears once warmed up, rarely hurts performance and only makes itself heard at idling speed.
Feeling tapped up? SMALL ENDS
Not dissimilar to piston slap, this noise is more a light metallic sound that’s constant with the revs and is caused by the piston’s locating pin (gudgeon pin) wearing away. Will always get worse but you can live with it until engine rebuild time.
DON’T LET IT LINGER…
Screech away FAN BELT
Very common, this is invariably the fan belt being too slack and slipping under load meaning loss of cooling performance or the generator unable to work properly. Usually just tightening the belt up cures the noise but sometimes the belt can wear smooth and become glazed and thus won’t grip no matter how much you tighten the adjuster, meaning a new belt. Don’t over tension as it places excess loading on the water pump and generator bearings. The same rules apply to power steering and air conditioning belts.
Wolf whistle INLET MANIFOLD/CARB FLANGE
A whistle, not unlike a boiling kettle, is due to a leak on the induction side, usually a blown inlet manifold gasket or perhaps a poor joint (checkbolt tightness all round) or warped urfaces allowing air to escape. This problem needs to be sorted as soon as possible as it effects engine performance, possibly to the point that it could weaken the fuel mixture seriously and even lead to piston burn out at high speeds.
In the pink and fancy a tinkle? PRE-DETONATION
Better known as ‘pinking’ this is a light metallic sound pronounced under large throttle loads; sounds a bit like a nut pinging around the engine and if excessive will also burn out a piston. The problem is generally down to mal-adjusted ignition timing but it can also be down to a worn distributor, unduly weak mixture or a heavily coked up cylinder head – although the latter is usually in conjunction with ‘running on’ when switched off. Some engines that are tuned for emissions, like later MGBs, are known to pink no mater what you do so speak to a specialist fi rst before fi xing.
Rattling on and on… TIMING CHAIN
If the front of your engine sounds like a cement mixer, then it’s a good chance that the timing chain has stretched or become excessively worn. Unlike cambelts, they rarely snap and it would have to be very slack indeed to jump a tooth – but don’t risk it! Some chains have provision for a certain amount of manual adjustment.
Clunk click every trip CAM FOLLOWERS
Cam followers wear once their case hardening fails and gives a sound no amount of tappet adjustment will fi x. Will usually survive until an engine rebuild unless it’s an overhead cam engine where renewal is a much simpler task.
FIX NOW!
Chuffing heck! EXHAUST
A blathering chuffi ng or rasping noise signifi es an exhaust leak, either the pipe or joint but it can also be a fractured manifold (especially tubular GT types). Attend to immediately as exhaust gases (carbon monoxide) can kill.
Knock-knock BIG ENDS
A hollow knocking sound under load signifies major wear to the shell bearings located at the crank end of the con rod – big ends to you. It is possible to locate the offending cylinder by cutting out the spark plug; the noise will disappear. If the sump can be dropped in situ these are cheap and easy to replace and may save the crankshaft from a pricey regrind (and so a full engine strip).
Ready to rumble? MAIN BEARINGS
A growling rumbling noise under load from the bowels of the engine can only be failing main bearings (these are the ones that the crankshaft runs in). If these are worn then usually the oil pressure is much lower than normal, too. Like big ends, renewal – if you can wrestle the sump off – is quite straightforward and again may mean the crank won’t become scored although if it is already worn, shell renewal won‘t cure a thing.
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