Woodpecker in my 500 SL engine ?

[Crouchy]

Some advice would be appreciated from those who know the R107 SL. I have a 1988 500 SL with 68k on the clock. Fantastic car in blue black with grey leather. Had it two years and use it fairly regularly all year rond when the weather allows. It runs like a dream, pulls strongly, doesn't burn oil but there is one thing that bothers me. There is a strange tapping sound from the engine when pulling away. I can only describe it as sounding like a woodpecker ! Several taps per second. The noise lasts a few seconds then dies away at around 2500 rpm. It doesn't appear until the engine has warmed up and only when accelerating, not when cruising. If I rev the engine in neutral cannot hear the sound then either. If I pull away very gently, don't notice it then either, seems to only appear when the engine is under load say pulling away from the lights or a little burst of acceleration. My mechanical knowledge is fairly limited but I'm guessing it might be something in the cylinder head area. First noticed it around a thousand miles ago last summer. It hasn't got any worse but would like to get it sorted. Any ideas ? Any other owners of this engine experienced the same. Should I be worried and get it inspected asap ?

Thanks

 

[grober]

Sounds like "pinking" or pre-ignition which is related to ignition timing or the octane rating of the fuel you are using. This can sometimes be exacerbated when the engine is warm as "hot spots" in the engine can promote this. Some of the V8'S had knock sensors on the block to counteract this but not at your age of car I don't think?? Other possibility is a problem with the actual transistorised ignition unit bolted to the wing. These can go faulty and overheat.

Other possibility is mechanical noise from the timing chain/tensioner. Its a known weak spot on the V8s This is serious since if the chain goes the engine can get wrecked.
Time to get it checked at a specialist who knows these cars ASAP.

 

[Crouchy]

Thanks Graeme. The noise does sound more mechanical than "pinking" which I've experienced on my wife's Polo. I've since read the timing chain on these V8's should be replaced at 70k which is right where mine is at so going to book it in to SS Motors in Weybridge for them to take a look.

 

[Uberwagon]

That to me sounds like an exhaust leak at the manifold.

Dave!

 

[V12]

Joe at SS knows these cars inside and out...you're in safe hands!

 

[wobbly]

Thanks Graeme. The noise does sound more mechanical than "pinking" which I've experienced on my wife's Polo. I've since read the timing chain on these V8's should be replaced at 70k which is right where mine is at so going to book it in to SS Motors in Weybridge for them to take a look.

The timing chain, may possibly make a small rattle when the engine is cold, until the pressure builds up in the chain tensioner.

I changed the chain and tensioner on my 500 last year, not a huge job, just had to take time to make sure the chain didnt jump a cog.

 

[jaymanek]

maybe a leaking exhaust? expands when hot so a crack in the manifold maybe?

 

[wobbly]

maybe a leaking exhaust? expands when hot so a crack in the manifold maybe?

And you would know about that.

 

[jaymanek]

exactly!!

 

[x332race]

Some advice would be appreciated from those who know the R107 SL. I have a 1988 500 SL with 68k on the clock. Fantastic car in blue black with grey leather. Had it two years and use it fairly regularly all year rond when the weather allows. It runs like a dream, pulls strongly, doesn't burn oil but there is one thing that bothers me. There is a strange tapping sound from the engine when pulling away. I can only describe it as sounding like a woodpecker ! Several taps per second. The noise lasts a few seconds then dies away at around 2500 rpm. It doesn't appear until the engine has warmed up and only when accelerating, not when cruising. If I rev the engine in neutral cannot hear the sound then either. If I pull away very gently, don't notice it then either, seems to only appear when the engine is under load say pulling away from the lights or a little burst of acceleration. My mechanical knowledge is fairly limited but I'm guessing it might be something in the cylinder head area. First noticed it around a thousand miles ago last summer. It hasn't got any worse but would like to get it sorted. Any ideas ? Any other owners of this engine experienced the same. Should I be worried and get it inspected asap ?

Thanks

Did you find an answer to this noise?....I have similar on my clk500 and would be interested to know your conclusion...

 

[Barbanasos]

Could it not be the injectors? Are they not suppose to make a slight ticking noise almost as they were the tappets? I have picked sth up and if I concentrate I can hear it when I accelerate. The faster the revs under acceleration the more synchronised it gets.

Obviously if I open a window or have the radio on, you can't hear it. But realised that we are talking about very different engines.

I have been interested in this myself. Lets see what the mechanics say.

 

[x332race]

I can only hear the sound if accelerating with the hood up and the radio off (and I have to listen carefully...my OH cannot hear it, but then she is not mechanically minded)....Does not burn any oil, drives beautifully and accelerates like mad (makes a beautiful noise on full throttle!!)

A Google search on injector noise indicates that this might be the source..

 

[twobarrows]

Sounds like "pinking" or pre-ignition which is related to ignition timing or the octane rating of the fuel you are using. This can sometimes be exacerbated when the engine is warm as "hot spots" in the engine can promote this. Some of the V8'S had knock sensors on the block to counteract this but not at your age of car I don't think?? Other possibility is a problem with the actual transistorised ignition unit bolted to the wing. These can go faulty and overheat.

Other possibility is mechanical noise from the timing chain/tensioner. Its a known weak spot on the V8s This is serious since if the chain goes the engine can get wrecked.
Time to get it checked at a specialist who knows these cars ASAP.

I thought these later 500SLs had twin Cam chains? It's the first I've heard of it being a weak spot!

 

[wobbly]

I thought these later 500SLs had twin Cam chains? It's the first I've heard of it being a weak spot!

Yes they do have the twin chain, the problem was with early 380 engines.

Timing Chain Inspection Mercedes Benz 107 SL SLC Resource Center

 

[Oily Rag]

Could it not be a small amount of little end knock from the crank-shaft, if it is, (and please don't quote me) it may require a crank regrind and bearings, may as well do the con-rod shells at the same time. Please take this with a pinch of salt, as i'm not au-fait with the nuances of the MB engine, as the last one I did was back in the 90's when I had the time.