Odd Timing Chain Noises

[Patty rice]

Hello everyone!

Couple of questions, I recently started hearing some odd noises coming from inside the engine, mostly a constant meshing sound. After using a stethoscope and placing it on the timing chain harness on the inside of the oil cap on the valve covers. I realized that it was from the timing chain. The engine runs fine but I do not want to push it where I am not comfortable. There are a couple of misfires but they are not constant or have a specific pattern.

My initial concern is that the plastic on the timing chain tensioner has begun to dry due to its age and is starting to chip away. My secondary concern is that the timing chain may have stretched, which I do not know why, but it is possible.

My question would be, how can I diagnose whether this is a timing chain problem, and if so...is it possible to replace the tensioners without removing the entire engine?

Thank you!

[BMSman]

I would start by dropping the oil pan. If the timing tensioners are disintegrating (which is very rare on an M70) you will find debris in the pan and oil pickup.

Changing the tensioners is a big job but can be done without removing the engine. You'll need to remove everything off the front of the motor and the valve covers too. I'd verify the timing chain tensioner is OK, you can make a small adjustment to the spring preload. You can evaluate timing chain stretch by checking the engine timing which also requires removal of the valve covers.

[E31 850i]

I think my M70 have the same problem.
See this video: https://www.youtube.com/watch?v=FmP8BewRnTc

I have put my finger in the oil cap. Finger on the chain plastic. The noise comes from there.

I have put more preload on the spring -> no change in the noise.

See the attachment.
-> Maybe the red parts are broken?

[shogun]

There was a service info for the M70 timing chain tensioner

Group 11 Engine Bulletin Number 11 10 90 (3144) Woodcllff Lake, NJ October 1990 Service Engineering

SUBJECT: Modified Timing Chain Tensioning Rail

MODEL:E31, E32 (with M70 engine)

Situation:A modified timing chain tensioning rail has been phased into production as of mid-June 1990. The new style timing chain tensioning rail incorporates a roller (sprocket) in addition to the plastic-coated sliding surface. The new configuration reduces the relatively high friction loads in cold operating conditions and thus reduces wear.

Installation Note: The timing chain adjustment distance has been reduced by 1 mm to 5 +/- 0.5 mm due to the use of the new style timing chain tensioning rail. See repair manual for details on adjusting timing chain tension.

Parts Information:The new tensioning rail (P/N 11 31 1 725 682) can be installed retroactively whenever engine repairs are performed. Upon depletion of the current parts inventory the old part number will be superseded to the new part number, 11311725682.


I posted a link to many pics I collected in this thread, old and new version https://www.bimmerforums.com/forum/s...hain+tensioner