Pulley/Fan Ring interference - 964

Moriartyhlms · Moriartyhlms's Garage

Hello,
Just finished rebuilding my 964 engine, and the crankshaft pulley is too close to the cooling fan ring. I know that these two parts normally have a pretty close clearance, but on my engine the pulley actually rubs on the fan ring once the parts are warm and expand (and/or when vibration from driving moves the fan housing closer to the pulley?). I’m using an aftermarket crank and pulley, so it’s pretty clear that at least one of those parts is made wrong (my guess is the crank). Any ideas on the best way to fix this?

The pulley vendor, Rothsport, suggested lengthening the mounting slot on the bottom of the magnesium fan ring. Any opinions on whether or not it’s safe to just die grind or dremel that slot longer?

The other option I was thinking of is adding a shim between the crank snout and it’s mounting face on the pulley. The downside to this is eating up the pin engagement between those two parts.

Thanks,
Sam

BURN-BROS · 07-12-2019, 07:17 AM

I would machine the fan housing face to gain the clearance. Or machine the backside of the pulley.. I would leave the location alone if possible.

blue911rsr · 07-13-2019, 01:25 PM

How is you belt alignment if straight I would machine fan housing do no shim pulley bad idea

Moriartyhlms · Moriartyhlms's Garage

Thanks all for the advice. Machining the fan housing was a good idea. I had my local machine shop drop the interfering face by .100” and then I had the part re-cerakoted. I’ll reassemble everything this weekend and expect it will take of the problem.

88911coupe · 07-08-2023, 11:29 AM

This is the only thread I could find on this but I'm having same problem on my '88. I have dropped the engine to replace the pressure plate and some other things but I noticed the pulley has worn a small bit out of the lower edge of the fan housing. Maybe 1-2 mm's if I had to guess. I assume there is no washer that is supposed to be behind the pulley that I missed when I had then engine out 10 years ago? could the housing have shifted maybe? How big a problem is this? Thanks!

mikedsilva · 07-15-2023, 02:33 AM

Quote:

Originally Posted by 88911coupe

This is the only thread I could find on this but I'm having same problem on my '88. I have dropped the engine to replace the pressure plate and some other things but I noticed the pulley has worn a small bit out of the lower edge of the fan housing. Maybe 1-2 mm's if I had to guess. I assume there is no washer that is supposed to be behind the pulley that I missed when I had then engine out 10 years ago? could the housing have shifted maybe? How big a problem is this? Thanks!

There is no washer between the pulley and crank snout.

Often, the strap holding the fan is not sugged enough, and the fan/alt assembly moves rearward a little causing the rubbing...

88911coupe · 07-21-2023, 05:47 AM

Thanks Mike, I was able to move the fan housing forward a bit and then re snugged the strap down. Will see if is stays in place and doesn't move rearward and start rubbing again.

Jeff Alton · 07-24-2023, 08:21 PM

Back to OP. The Mag housing on these 964 cases have shown significant deflection over the years.

Not saying that is your issue. It usually results in the fan hitting the housing.

Measure the pulley groove centerline you have (Rothsport I think you said) to the mounting surface where it meets the crank on both the new on and stock pulley. Also measure from the back of the pulley at its largest diameter vs the mounting surface where it meets the crank on both pulleys.

Compare and report.

Does your factory pulley fit correctly and not interfere? If yes, and the aftermarket part does interfere, it is pretty easy to see where the problem is....

Cheers