Engine Tapping

[rees_A]

My engine has developed a wierd tapping noise, I'll explain further -

When cold, it sounds fine, drive until the car gets to 80 degrees, sit in traffic, at idle there is a tapping noise like a tappet or something.

Drive away tapping noise disappears until at idle again when it resumes.

I thought the standard thing would be noisy at start then stop when hot not the other way around. Anyone got any ideas on what this could be?

 

[grober]

low oil pressure

When your engine is warm and at idle, oil pressure tends to fall. The sound could indicate that some part of the engine is not getting sufficient oil and you hear this as a tapping sound. Not sure of the origin without hearing it tho, sorry. For a start I would be checking my engine oil level is correct, not to low or full, oil is the correct viscosity/grade and not contaminated with water, and oil filter and oil change has been performed as recommended.

 

[rees_A]

Thanks Grober, I've checked oil and it was serviced/changed 4000 miles ago. Could it be a failing oil pump or would a warning light come on if that was the case?

 

[Vips]

It could be the small shock absorber on the belt tensioner that is worn. To check, when engine is on idle, place your finger with a little pressurer at the top of the shock absorber. If the noise is reduced than you would need to replace this as it worn.

 

[grober]

Thanks Grober, I've checked oil and it was serviced/changed 4000 miles ago. Could it be a failing oil pump or would a warning light come on if that was the case?

Certainly worth checking out what Vips said. Without an oil pressure gauge its difficult to tell about the pump. The oil pressure warning light should guard against low oil pressure/pump failure. Doesnt sound like a failed oil pump from what you have said. see this post.http://mbclub.co.uk/forums/showthread.php?t=26882&highlight=oil+pump

 

[paulmb]

i had a similar tapping sound and it did turn out to be the shock absorber on the belt tensioner.......they can be quite noisy when they are worn.........noise sounds serious, but nothing to worry about.

 

[rees_A]

Thanks for all the info, I guess I'll have to find this belt tensioner thingy and give it a shove. Anyone know where I would find such a thing? And what it looks like?

 

[Vips]

here you go: http://www.detali.ru/cat/oem_mb2.as...GM=717.441&CT=M&cat=520&SID=20&SGR=045&SGN=03

Its No. 17 where one end sits behind the belt

 

[rees_A]

Just had another look listen to the noise, it sounds like its coming from where the injection system is rather than the top of the engine. Would this make sense or is that wehre you would expect to hear the noise most

 

[Vips]

That is where you would expect the noise to come from, but it actually comes from the shock absorber as its worn.

I had the same problem and I thought it was a noisy tappet but it wasn't. It can be quite misleading!!

Did you apply the finger pressure?

 

[grober]

little end??

If its coming from the piston area it could be a dodgy little end on one of the piston gudeon pins?? If it is, best to get it repaired before you throw a rod thro the block. Have you been using a lot of high revs recently?? Could be something to do with the camshaft advance mechanism which is oil driven/electrically controlled but the sound would be located at the front of the engine for this. It could be several other things ,difficult to diagnose from a distance. Maybe best getting it checked by a good specialist

 

[rees_A]

Couldn't see the damper thing. Is it at the front left right back etc of engine?

 

[Dieselman]

The problem with noises on these engines is that due to the light castings the noise transmits through the whole engine away from the source.
Buy an engine stethascope and listen to the engine. Any untoward knocks will be immediately obvious.
You mention the noise coming from the injection system, this is normal, injectors do tick when operated and this is especially noticable at idle. Grip one of the injectors to see if you can feel the solenoid clicking in time with the noise.

 

[Bazzle]

Also 1st thing to do IMO is to have the oil AND filter changed .

Bazzle

 

[kth286]

rees_A

You do not have the shock absorber on your engine poly belt adjuster.

You have a later automatically adjusting belt tensioner, which just needs a spanner on a nut to relieve the tension to change the belt.

Your c36 engine is basically the standard (104) 3.2 litre engine bored out with longer throw crankshaft etc. and so was the latest configeration for the inline 6 engine, before Merc changed to V6 engines.

Regards

 

[rees_A]

thats probably why I couldn't find it then... Cheers, kth 286

 

[Dave Bailey]

Just a thought....

I had the same sort of problem on my car. It turned out to be normal, the noise is caused by a small solenoid valve that happens to make a sound that sounds very much like a loose tappet. I'm not sure if your car has one (mine is a V6), but on my car the valve is located on the passenger side chassis member, near to the washer bottle. The valve cuts in and out at idle when the engine is hot.

 

[Dieselman]

I had the same sort of problem on my car. It turned out to be normal, the noise is caused by a small solenoid valve that happens to make a sound that sounds very much like a loose tappet. I'm not sure if your car has one (mine is a V6), but on my car the valve is located on the passenger side chassis member, near to the washer bottle. The valve cuts in and out at idle when the engine is hot.

That'll be the emission valve releasing benzine from the charcoal filter.