240D Engine Noise: Piston Slap

The cause of a loud noise in a 1982 Mercedes Benz 240D (OM616 912) with 259,000 miles. Following complete strip down of the engine, one side of Piston No. 3 (below gudgeon pin) was missing (it was found in many pieces in the oil sump). Engine was still running well (but loudly) before it was dismantled. Hopefully this video will help others to recognise the sound of piston slap in these old MB diesel engines (video of engine running to be uploaded also). This problem gradually gets worse and will eventually result in a broken piston or worse (which of course will happen suddenly). Cylinder head/ camshaft / followers etc., precombustion chambers, main bearings, gudgeon pins, big end bearings, vacuum pump bearings, valves and valve caps all appeared to be in good condition. There was some slap also in the other pistons / cylinders, but No. 3 was by far the worst and the only one to be heard in this video as the engine was turned over by hand. All pistons (including the pieces from No. 3) showed some polishing on the same side. Engine was very clean internally and oil seemed to be getting everywhere it was needed. Compression was OK also (about 360 psi) but there was quite a bit of blow-by with the oil cap removed. It was burning oil too. This should be relevant to all OM615, OM616 and OM617 diesel engines (and maybe more).

Category:

Autos & Vehicles

Tags:

• 240D
• Piston
• Slap

[om616912]

dirtcurt1: The bores seemed fine to me. Polished, but no damage to report. (I don't have the tools to measure the bore precisely). I just had a 2nd hand replacement engine fitted (cheapest option) - that's running fine now. I didn't get all the bits back from the original engine, so I never got it going again.

Macmizan: Piston slap is an indicator of advanced bore / piston wear. So blow-by will result. It's not the only cause though. Worn valve guides is another possibility...

[om616912]

dirtcurt1: The bores seemed fine to me. Polished, but no damage to report. (I don't have the tools to measure the bore precisely). All the rings were fine too - nothing jammed. I just had a 2nd hand replacement engine fitted (cheapest option) - that's running fine now. I didn't get all the bits back from the original engine, so I never got it going again.

[watchitnz]

Thank you, this helped me quite a bit.

[om616912]

@watchitnz You're welcome! Glad to hear it was helpful. Regards.

[neil1li]

popmarter: You = Cunt.

[EvilTwinBrotherBob]

@om616912

That piston is so loose I can't believe it was still runing!!! I was just following along until the shot from the piston crown. That got my attention in a hurry.

The D15 in my Civic has the same condition I believe, though I imagine not anywhere near that bad.

[dirtcurt1]

Can you tell me how bad the bore was? Did you have to sleeve the block or did you go to oversize pistons?

[Macmizan]

so when Piston Slap occurs, that would also cause Blowby gases being form in the crankcase right.?!

[tonyboy4410]

what a onoying sound

[94diesel]

@popmarter You can take your Toyota supra and drive it up your ass.

[1100HondaCB]

@uknowwhatimsayin piston slap is the result of excessive piston to bore clearance as a result of wear. Usually, a rebore and new pistons solves this by bringing to bore clearance back to the manufacturer's standard figure, but the engine must be run in as if it were new.