Author Topic: noisey cam chain, opinions wanted (Read 2698 times)

Ramblin MAn · « **on:** November 01, 2009, 12:50:39 PM »

I can't go into a lot of detail without turning this into a story so I'll keep just to the facts.

M42 with recent head replacement(not by me, but supposedly by a authorized BMW mechanic on his own time). Cams, top side of head, cam gears and chain all look brand new. I replaced the the cam chain tensioner only to find that it already had the new tensioner.

Problem:
When the engine is running at idle, you can hear the cam chain. It sounds like it's slapping the top of the valve cover. Raise the rpm just a little and it quites down. Let it idle and the noise comes back. This motor is in my e21 autocross car. The motor in my 91 e30 does not make this noise. It is very quiet. Both are 91 m42s

Diagnosis:
Pulled the valve cover to inspect cam gears and chain expecting to find worn teeth. Instead, found that the source of the noise appears to be the plastic guide between the cam gears. I can grab the chain and wiggle it up and down and when it hits that guide it makes the noise I was hearing. FYI, oil pressure is excellent.

Questions:
Is there a superceeded or older part that is quieter? Does the valve cover have any kind of sound insulation that is supposed to be there? How tight should the cam chain be between the gears with the motor at rest? I assume it's supposed to be a little loose because there is no oil pressure to the tensioner. Is that the correct assumption or am I way off base?

quinn11m20 · « **Reply #1 on:** November 01, 2009, 02:45:25 PM »

No you are correct. I have the same noise but I also have 250k. I plan to change soon. I have read in other threads that its a common sound with this engine. I would check everything to be sure. It will be a tedious process. Oh and by the way what oil are you using? I use 20W50 and its kinda quiet.

KenC · « **Reply #2 on:** November 01, 2009, 03:14:59 PM »

That guide is probably just worn beyond spec. Just replace it. The guides should fit snug around the chain.

Ramblin MAn · « **Reply #3 on:** November 01, 2009, 05:58:01 PM »

Since I don't drive it much, The last time I changed the oil I went with Castrol Syntec 5-50. It's noisier than with 20-50 for sure. But most rails I have see have some kind of hard rubber coating and this doesn't. It can't see any wear marks on it at all. It looks brand new.

quinn11m20 · « **Reply #4 on:** November 01, 2009, 06:05:51 PM »

I would suggest going to Castrol High Mileage 20W50. I wouldn't put synthetic in mine. I have been running 20W50 since 97 when I bought her. Good luck with your quest. I can't really offer any more help on this subject.

Ramblin MAn · « **Reply #5 on:** November 02, 2009, 09:16:33 AM »

I plan on putting 20-50 back in after I do something about the guide rail. I have put maybe 2 hours on this car since I bought it 3-4 years ago. I wanted the oil to stay in good shape during long periods of down time.

Maybe someone who has looked at their's can tell me what it looked like. The one on this motor is a dark green/olive drab color and is a hard plastic, like bakelite All of the tensioner pictures I see on the part sites are black and look like hard rubber. I'm going to go ahead and take a chance and get a new one, I just don't want to end up recieving the same thing that's alreay in there. If anyone has replaced theirs recently, what did it look like and what was it made of?