Hello I have a problem with my car. It’s a 1991 940 turbo now im pretty sure it’s the crankshaft pulley but it’s the one on bottom in the middle. It makes a knocking noise which is very annoying and I looked in and here its rubbing the timing belt housing. And might be un balanced but when engine is runnung it seems to be balanced but make a horrible knocking noise any ideas please help me solve and fix the issue thanks here are some pics so you can see the rubbing.

 

the crankshaft has a freaking rubber in the middle that gets all cracked and causes problems like out of timing and possibly yours. Does it have the bold loose?

 

what is bold loose?

 

or did you mean bolt loose i have to check but im pretty sure its not.

 

I just came up with the same problem....the timing belt cover is rubbing on the alternator belt, just a tad but noticeable. These belts are old and will change and adjust the tension on the alt. This could be your case

 

As Redbottle mentioned, the crankshaft pulley has a rubber center that eventually dries out and starts coming apart. When it does, it can move in or out on the shaft and can rotate independently of the shaft. One symptom is a sound like slipping belts when you first start up in the morning, which goes away after awhile. I ignored mine for a long time and it finally moved forward enough that it threw off all three belts, which caused all the instrument warning lights to come on - this happens when the alternator belt breaks as well - and spoiled my day. A new one is about 80-90 bucks. Replacement is pretty straightforward. Might as well do the timing belt too, while you're at it. Worst part of the job will be breaking loose the big nut that holds on the pulley, and if you have access to an air compressor and an impact wrench even that isn't a problem.