Our 81 220D, a car I have owned for a number of years, started tapping pretty loud when I fired it up this week. The car is only at about 170+, and has been excellent until now.

Because this is not a bearing type knock, but a sharp metallic rap seeming to time with one cylinder, I immediately checked and reset the valves, but nothing was loose. The chain is very nice and tight, the tensioner seems fine, the shoe is good, so I don't see anything in those categories, but am open to suggestion.

I then put a hose to it for a scope, and it's definitely coming from the front of the engine, internal, either hole one or two. I figure it has to be piston slap, though I have never seen that in owning half a dozen of these cars back to 1965 diesels, and her last 220D we sold running good at well over 400K after 11 years of service when I found this 125K clean coach with a bad clutch and replaced it.

So I'm about to pull the front pan, take number one rod loose, (as I suspect that is the right cylinder), and if that is the sloppy one, leave the piston in for obvious reasons, take the rod in for a new sleeve, put a new wrist pin in, and call it good, provided everything else checks to specs. Any opinions or advice?

I am really surprised to have this problem, as the thing is tight otherwise, has not been abused, doesn't use oil to speak of, only gets Delvac or Rotella every 3-4K, and wear is nil in the top end, as I suspect is also the case in the crank components, excepting this failure. Anybody ever seen one of these do this, or suspect something else?

Thanks a million for your input,

Alley Oop

 

I am waiting to hear how this works out. I know it's a long shot but have you looked at your air cleaner to see if it is intact and not rodent chewed and something metallic went through intake?[/align] S.[/align]

 

Since I made the original post, before I tore the pan off, I bled off the injectors one at a time manually, which should radically lessen compression by depriving of fuel/fire, and the noise did not lessen, which it should if a wrist pin was loose. Having already inspected the cam and valve components, I had to re-inspect chain components, and jerked the pan for good measure. Everything is tight in the lower end, with absolutely no slop in the con rods or wrist pins detectable, so I looked back up top.

When I checked the tensioner a second time, I decided it was weak, but no rail, shoe, or slide problems detectable, so I'm scratching my head how such loud slap could even be possible. I decided it was worth a try, and ordered up a tensioner. It came in yesterday, and I put it in today, noting that it is much stronger than the one which was in there - at least half again the tension, maybe times two.

It was still rapping when I fired it up, so I went through the injector bleed off again, slowing it to just above stall with the thumb lever, and no difference again. I got my hi-tech rubber hose scope out and stuck it to my ear again. Definitely coming from the front of the engine, loudest at the cam cover above the chain, as opposed to further back or anywhere on the block, including the front.

Then I listened to the fuel pump, then the power steering unit, then the vacuum pump - whack whack whack! I can't believe I missed that, but it just didn't occur to me it could make that sort of noise. I went all around the vac pump with my hose, including the block next to it on the side, the front, and no doubt, the bell shaped housing on the vacuum pump is where the noise is.

I don't have it off yet, but my Haynes is completely worthless on pump detail, and it appears those things are spendy - probably $350, with a rocker repair kit at $280. I suppose I will find out when I get it off, but is this thing repairable or adjustable without all that expense? I assume it is a rocker problem from the extreme whack, and would appreciate any experienced advice on where to go from here. Can a cave man do it?

Thanks,

Alley Oop