Caleb Matthew

At about 103,000 miles my 2000 E55 engine developed a klacking noise at start up from a cold engine. The klack goes away after about 1 to 2 minutes of idling. The dealership said it was lifters, but first try to clean out the injectors. That was done without any result. At a cost of over $1,200, the lifters were replaced. The klack was still there. Then a cleaning of the engine with some type of fluid was done. Still klacking. Next the timing chain tensioner was replaced. No change. Next the solution was to change the timing chain. However, with only an 80% chance that would solve the klacking, I put further repairs on hold.

I had my retired airline avionics tech brother-in-law listen to the klacking last week and he said it sounds like piston slap. I never heard of piston slap, so I researched it on the internet/youtube. The sound I hear from my E55 engine sounds just like some of the engines with piston slap on youtube videos.

I read that the cause of piston slap is due to a piston being smaller than the cylinder and thus the piston hits the sides of the cylinder causing the klack until the engine heats up and the piston/cylinder expand.

I can live with this klacking, unless there is a chance that piston slap will result in complete engine failure. Any thoughts from the MB Techs out there?

Ausmbtech

It sounds like carbon build up on the piston crowns. Very commonly misdiagnosed.

Basicly the clearence between the piston crown and the bottom of the cylinder head is very small on the N/A 55 engines, particualrly the later 11:1 compression engines, and they can get a buildup of carbon which will make contact with the cylinder head each time the piston gets to top dead center.
The carbon is hard when cold at to makes the conrod bearing "bottom out" making a noise both near the sump and at the heads at the same time. When the engine warms up the noise will deminish and most likely won't be heard when hot. The noise will reoccur when the engine cools again.

Various upper engine cleaners can help but they are mainly designed for cleaning intake valves, not piston crowns. The best way to clean the crown is some hard running.

Warm the engine up gently, get it to full operating temp for at least 5-10 mins and then give it maximum engine load in the upper rev ranges (4k rpm+) for an extended period.

Obviously local conditions will dictate how you achieve this, it's a little harder to do in a E55 then a C200. My suggestion would be to do it on a quiet highway at night, using full throttle runs from 15kph/10mph in 1st gear to redline in 2nd gear then slow and repeat at least 10 times. Dont hold it back using the brakes.

Continue driving for another 10mins an then see how it sounds the following day.

mrbobby

I don't know if you'd want to try this with a Mercedes AMG engine but "way back when" we used to put small amounts of water down the intake to clean out carbon build up.

samdunlap

I've had a similar problem with my 2002 ML320 engine, and it wouldn't go away, so we pulled the engine and found evidence of scaring on the cylinder walls. Rislone and running it hard didn't help.
I'm about to buy a used replacement engine and hope for the best but I'm interested in what solution you found or if there was any resolution at all?
Sam

exhaustgases

The piston has to be smaller than the cylinder else it would not fit or slide up and down in it.
So the correct thing to say is the piston to cylinder clearance is excessive, and that is the cause of piston slap. And in my opinion a high end engine, in a luxury car should not have this problem. The engines are a trade off, they are manufactured with too many cost cutting short cuts, all aluminum cylinders are one of them, essentially the purchaser is not getting what they are paying for. In years past a low end engine was built with better engineering design than these newer engines these days.
Depending on the amount of clearance the slapping that quiets down at operating temperature should not hurt a thing. If it continues at temperature then its something that needs attention. Put it this way an old 1996 Geo metro does not have piston slap, neither should a many more thousand dollar Mercedes.

samdunlap

We've pulled it out of the vehicle for a look inside and see scoring in the cylinder walls.
it's looking like a rebuild or replacement is inevitable.
​​​​​​​Sam