This car (1982 300D) had this knock ever since I bought it. I replaced the injector nozzles, I loosened the fuel lines one by one, the knock persists.

The engine does not smoke at all, and at 1000rpm it is very smooth. It does have a vibration at 650 rpm, not loping, just kinda vibrating more than I'd like.

I did the following (engine related) work on it so far, in addition to the misc stuff like new drivers side seat

- air cleaner mounts
- blowby drain tube
- injector nozzles
- motor mounts and engine shocks
- timing chain stretch corrected
- valve adjustment
- new spring for the chain tensioner


I finally took it to a local foreign car mechanic for a look, just to keep the project moving, so to speak. I didn't expect a miracle (and didn't get one). Just wanted a second opinion.

After having the cover off, here is what he told me:

- the knock is definitely coming from cylinder #1
- the knock is definitely coming from "top", i.e. head, not crank
- everything under the cover looks good; camshaft looks great, nothing obviously worn or loose
- the cylinder pressure is 340 or something like that, so its good
- fuel pressure is good
- probably not a worn or loose valve guide because NO smoke
- probably not piston slap because NO smoke

He does not think it is broken rod or rod bearing because we both had the car on the highway and it still runs.

The knock sounds like its just about once per engine revolution.

Naturally, I wanted options. He said the next logical step here would be to pull the head and inspect the bottom of the head and the top of the piston.

His working theory now is something fell in the cylinder - a piece of a glow plug or broken precombustion chamber, or maybe even something through the air cleaner.

I don't mind pulling the head off and spending time on it. I have a beer fridge in the garage, so its all good times. Should I stick with it? How likely is pulling the head to uncover the cause? Any words of encouragement?


here's the link to the clip with the sound it makes:
http://www.youtube.com/watch?v=s2pEM3fAepw