Balance Shaft Belt Tension

Lawrence Coppari · 02-25-2001, 02:54 AM

Just got through replacing idler wheels and belts on my '86 951. I noticed that if I set the balance shaft belt to recommended 28 pound tension following Krikit recommendations, I get a whirring noise from the toothed tensioner pulley. Letting the tension be a little less quiets it. Running the motor with the belt cover off reveals that at the lower tension, the belt vibrates at low RPM but runs true at anything other than idle. Wonder if I should offset the smooth idler wheel a little more. That is where the belt lateral movement is. I am sure the noise is from toothed tensioner, brand new, because I used a stethoscope on it. Old one would do that too which is why I replaced all idlers/tensions along with the belts.

Any comments. Thanks.

lm6y · 02-25-2001, 10:08 AM

I would stick to the recomended setting. The "whirring" noise is typical of a gilmer type belt. that's why the 6-71 blowers on street cars make noise, it's the belt.

nigel · 02-25-2001, 03:03 PM

I took some advice from a local independant dealer. He told me, when I replaced all the tensioners and pulleys, that if when adjusted the belt is noisey, slacken it slightly until it isn't. He also said that the smooth idler for the balance shaft belt should lie about 1mm below the belt, so in effect the belt doesn't actually touch it, unless it whips. You may also find that the belt gets noisey as the engine gets hot, in this case slacken the belt slightly until the noise stops. Remember that belt is going twice engine speed!!

Lawrence Coppari · 02-27-2001, 02:51 PM

I've been talking with some friends who race the 944turbos plus one of the PCA technical gurus. They all say loosening the balance shaft belt to quiet the tensioner is ok. Don't worry about the spec on this one.

scottewid · 02-28-2001, 12:24 PM

My 951 just had all belts rollers and tensioners replaced 3k miles ago by PO. I've only had it a little over a week, but noticed it makes a whirring noise when cold. After it warms up 5 minutes, it's gone. Do you think the belts are too tight and if so, will there be premature failure?

Lawrence Coppari · 02-28-2001, 02:14 PM

If it is the balance shaft belt I would not worry. If it is the cam belt, I would worry. The first time I had my belts done at the shop here (the shop is good but expensive), there was a whining noise that went away after a while. I figure the belt streached and losened up. The noise comes from my balance shaft tensioner. The belt will elongate and the noise should go away. The tensioner is new and makes the same noise the old one did.

I'll find out. I am going to a BMW drivers school for 3 days at Road Atlanta next weekend. If it blows up I am sure you all will hear about it!