Engine Knocking/Valve Tapping on 1996 M3

Just bought a 1996 BMW M3 w/ 135,000K miles & a manual trans. No mods have been made to the engine. I have noticed a sound at idle that sounds like the pistons knocking or the valves tapping. It is not
extremely loud, but it is noticeable. The frequency of the tapping increases with engine speed. I have heard about issues with the chain tensioner, and also about how some BMWs simply have a 'diesel knocking' sound to them naturally. What do you think this knocking could be?
Thanks, Niles
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Possibly VANOS problems? Where exactly is the sound coming from? If it's the front/top of the engine, it may well be VANOS related. This would not explain the 'knocking' though. Get onto one of the M3 boards or forums. I seem to recall there being some 'issues' with the bottom-end of some M3 engines.
JB
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JB wrote:

The vanos including tensioner is discussed at length if you do a google search. I had a kncok (mor of a whack) from my cams for a while on an old 325 but it went away.
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snipped-for-privacy@gmail.com wrote:

It might be the VANOS unit (That's the variable valve timing actuator). What oil is in the engine right now? They (VANOS) are known to make noise if the oil you are using is too low a viscosity. It is actuated by oil pressure.
My '95 325i made a racket when using Mobil 1 5W30. I now use Mobil 1 20W50 and it's much quieter. 20W50 is within the range of oils for use in my engine. Check what is recommended for yours and try one at the heavy end of the spectrum.
--
-Fred W

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snipped-for-privacy@gmail.com wrote:

It would be worth your while to pick up a mechanic's stethoscope. This is like the one the MD uses but instead of the flat COLD disk - it has a long metal probe on it.
Using this - you should be able to determine exactly where the sound is coming from. It might be as simple as you are hearing the injectors.. good injectors DO make some clicking/tap sort of noise. Dirty plugged up ones are quiet.
Without localizing the noise a bit - it's just guesswork on anyone's part (which you've gotten already..)
It would also be useful to know what engine you have in the M3.. In the US this was an S52US - which is basically an M52 in 3.2L size. In Yurop you got the regular S52 - which is a real M engine with solid lifters. If this is the engine you have - you may be overdue for a valve adjustment. The US engine doesn't need this since it uses hydraulic lifters.
Given the name Niles (not a very common US name) - I'd guess the UK, but that's just guesswork.
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admin wrote:

I'm in the UK but the only Niles I can think of is Niles Crane - Frasier's brother. Just a not very common name at all I think.
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Thanks, I will try the mechanic's stethoscope, check my oil type via maintanence records, and search on the M3 forum. At least I will have some weight on my side when I take it in to get serviced. Feel free to keep posting if ideas come to mind. Thx - Niles - S.F. California
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