Hard tapping sound on startup?

[embe560sl]

Hi guys,
1989 560 SL 104,000 miles
Only sometimes and I mean just that, when I start up from cold, there is a hard tapping sound form the engine...it goes away after about 4 taps? Other times it just starts up normally.....now for my questions.....
1. Could this be the timing chain indicating it needs to be replaced?
2. Could it also be the chain guides and or rails that need replacing?

The motor runs superb and this is the only issue I have..(thank gawd)
Your comments will be greatly appreciated.

[RadioTek]

If it's "Timing Chain Slap", you might want to replace the tensioner if the guides look OK. It sounds like it's leaking down.

[embe560sl]

Thank you for responding, but what do you mean by leaking down?

[RadioTek]

Originally Posted by embe560sl

Thank you for responding, but what do you mean by leaking down?

The tensioner is hydraulic, working off the oil pressure. It's supposed to hold the pressure / position after the engine is turned off, by means of a check valve. If it loses pressure too soon after shutdown, that is what I refer to as 'leaking down'.

The check valve is internal to the tensioner, so the whole thing has to be changed out. http://www.**********.com/search/product.aspx?sid=c3rzbgj2ivovdkvho0rltabf&makeid=800016@Mercedes&modelid=1195332@560SL&year=1989&cid=20@Engine%20Parts,%20Seals%20%26%20Gaskets&gid=5736@Timing%20Chain%20Tensioner

If that is your problem. Remember, I'm just tossing a Wild Guess from someone elses' description.

Good luck

[Graham]

Originally Posted by embe560sl

Hi guys,
1989 560 SL 104,000 miles
Only sometimes and I mean just that, when I start up from cold, there is a hard tapping sound form the engine...it goes away after about 4 taps? Other times it just starts up normally.....now for my questions.....
1. Could this be the timing chain indicating it needs to be replaced?
2. Could it also be the chain guides and or rails that need replacing?

The motor runs superb and this is the only issue I have..(thank gawd)
Your comments will be greatly appreciated.

Either go to mechanic, or take off passenger side valve cover yourself and have a look at the castings near the chain - if it is hitting, there could be signs of it. At same time inspect the guides that you can see.

While open, might as well check chain stretch too. Set marks on camshaft supports in line, then read off how close you are to TDC on the balancer. Rotate the engine clockwise by hand to get those first marks to line up.

These cars all need the chain, tensioner and guides replaced sooner than later. Failure can cause terminal damage.

[79Mercy]

What kind of oil are you using, I recommend using Castrol GTX 20W-50 in this engine.

[embe560sl]

Thank you all, for giving your input as to what you think is probably the course and shall now have it checked out. This is one of the best forum group ever, thanks again for taking the time.

[jplinville]

I'd check the oil level first...sounds like it could also be lifters. Lower oil level can cause that to happen.

If your indie says it's the lifters and they need adjusted, it's a fairly easy job, if you have the right tool!

[embe560sl]

Thanks for you input.....the oil level is spot on. I think? if it were a lifter would it not do it every time I start up? as it is very intermittent when it happens.

[390pi]

Originally Posted by embe560sl

I think? if it were a lifter would it not do it every time I start up? as it is very intermittent when it happens.

These cars have hydraulic lifters.

It could be that one lifter is bleeding off oil pressure when it sits for an extended period of time, since you say it happens when it is cold.

You could change the oil (maybe to thicker 15w40) and see if that solves it or at least narrows it down.

[embe560sl]

Thanks, will check that out also and let you know.