Loud clatter from engine

[Socrates]

Perhaps I'm just whittling unnecessarily - I was always told that loud clatters from the engine when cold are not a worry providing that they disappear quickly.
Well I have a loud clatter that lasts for about 2 seconds (three would be stretching it). It sounds like a single element - I can hear individual revolutions of the engine - and the noise is a loud metalic clatter.

I have a 1990 300SL with the 103 engine. Does it have hydraulic valve stem adjusters, is one of them loosing pressure overnight? Is it anything to worry about? Should I get it fixed? What would a fix involve?

Has anyone any ideas? Many thanks all, in anticipation.

 

[television]

Its either valves or timing chain,you can tell by opening the bonnet before you start up, timing chain noise will be low down at the front,and vlve noise on top. Thain is more or a ratle and the valves make a tapping noise.

Do you know what oil is in the engine.

Malcolm

 

[kth286]

Socrates

It is likely the timing chain tensioner is losing it's tension whilst the engine is dormant, and therefore initially is not exerting much tension on the chain until the oils pressure builds up again.

A new tensioner which screws into the side of the engine is probably the answer.

This job should only be entrusted to an experienced (Merc only) tec as there is a special proceedure if not followed can cause the expensive hollow camshaft to break almost instantly.

You must ask the tec if he/she has successfully done the job on a petrol Merc previously (diesels are easy and different so exclude those).

See other posts re chain tensioners.

 

[eric242340]

Take Malcolms advice and try to descern if its coming from the top of the engine or low down at the front. Open the bonnet get your head close to the engine and ask someone to start the engine for you as you only have a few seconds to listen to it. And does this only happen on the first morning start?

 

[Socrates]

Thanks all,

I assume the oil is merc spec - just had full service at a highly recommended specialist.

Yes it only really happens in the morning and more so when it has been cold. It sounds more like a clatter (valves) than a rattle, but I'll have a closer listen. If it is valves, then what?

Oh, one more thing, if the timing chain is going slack overnight, does that mean that the timing is out before it tightens and that the engine is in danger?

 

[eric242340]

Thanks all,

I assume the oil is merc spec - just had full service at a highly recommended specialist.

Yes it only really happens in the morning and more so when it has been cold. It sounds more like a clatter (valves) than a rattle, but I'll have a closer listen. If it is valves, then what?

Oh, one more thing, if the timing chain is going slack overnight, does that mean that the timing is out before it tightens and that the engine is in danger?

To the timing thing the answer is no, no problem there. As soon as you start the engine the oil pressure operates the tensioner and they very rarely go wrong. However if its a cam follower, and this is more likely, then its better to change all the cam followers. This could prove to be quite expensive, but once one goes, others will follow. Sorry but this is the reality with this type of problem its never a cheap fix.

 

[Socrates]

Thanks Eric

 

[Chazchuzzlewitt]

I had the same noise with my 103-powered 300E. I suspect your engine has quite a few miles on it?
As long as it dissapears within a few seconds once the oil pressure has built-up I wouldn't worry about it too much.

 

[television]

I had the same noise with my 103-powered 300E. I suspect your engine has quite a few miles on it?
As long as it dissapears within a few seconds once the oil pressure has built-up I wouldn't worry about it too much.

Nice sensible answer from Chaz

Malcolm

 

[Socrates]

Thanks everybody you've all been most helpful.
Best wishes to you all
Don