Hey all,

I am in the process of buying a '91 E31 from a family member. The car is in great condition but does not run. It will start but there is a loud knocking sound coming from the engine while it idles. The car will drive, but we have not since the noise began. Any thoughts on what this could be? I have read some internet forums on knocking sounds. From what I have seen it could be an easy fix. The car is perfect aside from this. Never wrecked, 82k miles and always garaged.

Any help from you would be very appreciated. I am currently a member of the Mazda Rotary club in Dallas, Texas. I've been in that group for years. This will be my first Bimmer. I'm very excited!!

Thanks in advance for any help!!
Irish8

Knocking sound, that sounds pretty bad! I would have the car towed to either your local BMW dealer or a reputable independant garge that is familiar with these cars and have the engine completely checked out! It could be a number of things but I wouldn't start the car until I knew for sure what was causing the knocking sound, it could be worse than you think! and the m70 isn't a cheap car to fix! I hope this doesn't scare you off but better safe than sorry. Good luck with it!

Thanks for the response. I have talked to a couple of BMW specialists in my area. They all sound very optimistic about the problem. I will take your advice.

Thanks!!
Irish

If you do not work on your cars, and connot do a compresion test and other engien dianostics. Take it to a mechanic that knows this engines. Parts are expensive and/or hard to get. Good luck

Is the sound only present at idle or does the frequency of the knocking increase with engine RPM's? If so it sounds like a spun bearing which will require an engine rebuild $$$$$$ However if it is only heard at idle it may be something less expensive like the timing chain tensioner.

Is the sound only present at idle or does the frequency of the knocking increase with engine RPM's? If so it sounds like a spun bearing which will require an engine rebuild $$$$$$ However if it is only heard at idle it may be something less expensive like the timing chain tensioner.

That's a great question and point. I will check tomorrow. I will be transporting the car to Dallas tomorrow (on a flatbed).

Wish me luck!!

good luck man

No mechanical update yet. The car is at my home in Dallas. Will try and get it into a Bimmer place soon. After further review the noise is more of a ticking sound. My research leads me to hope it is only a bely tensioner issue. Hopefully my gut won't let me down.

I gotta say....the car look amazing sitting in my garage. What a work of art.

Stay tuned.

- Irish