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In Reply to: 1990 525i Sounds like diesel posted by Archer Parnell on July 01, 2000 at 23:05:23:
While it is most noticeable at idle, is the noise still there when the engine is revved up a bit? Is there a threshold RPM where the noise drops off as compared to the other sounds? The fan will tend to drown out a lot so see if you can compensate for that, mentally.
A diesel-type clatter could mean one of many things. The most obvious is valve lash but you've checked that. Did you examine the valve springs for broken ones?
A badly stretched timing belt can cause irregular valve timing. Do you know the condition of your belt? Last replaced at how many miles? Other than this factor, there really isn't anything unique about an OHC configuration; the same things can happen with a pushrod engine.
Does it sound like detonation? Try a higer octane gasoline or a decoking treatment to see if things quiet down. If you see some reduction even, then the culprit has been identified.
I don't know if a mild exhaust leak at the manifold would fit the description of clatter but try and probe around the exhaust side of the head while it's running to see if you hear or see something.
Since your engine has a lot of miles (do you know the maintenance history?), it is possible that there is a fair amount of wear. The next thing to consider would be piston slap, caused by worn rings/bores or wrist pins. That would mean serious $$ so I'd advise having a pro look at it.
Happy hunting,
Adnan
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