Here is the problem, my belt has jumped off my Pulley 4 times, see photo (the tension was set properly). My first question is about Pulley alignment. I have not touched or moved the AC compressor but I have done a TB/WP on my car. I put the AC pulley back on the Main crank with the Porsche part numbers facing out cause that was the way it came off...but would there be any concern if that Pulley was installed incorrectly? (flipped over) Does it matter? I have taken a straight edge to check the stagger between the two pulleys (ac compressor and ac crank pulley) and there is a slight stagger of maybe 1 cementer. Do these pulleys have to be in perfect alignment?? I also thought I had the wrong belt...but I ended up having the correct belt for the Pulley, so the belt is not an issue. It was suggested that maybe the compressor was seizing up. There are no leaks in the compressor so what else could cause the compressor to seize. Is there a way to check the compressor with the high and low AC pressure gauges to determine its health?
Or am I going to have to remove and rebuild the compressor....

 

Is the car converted to R134a? An R134 car can spike pressures to the point the compressor cannot be turned if there is a loss of even just 1 condenser (cooling) fan at high ambients. Usually this exhibits noticeable engine loading and obvious belt squeal - late GTS cars have a refrigerant overpressure switch - in this case it will eventually cycle off - older cars do not have this. This is much less an issues with R12.

Alan

 

Hi Alan, no the car is R12 and there was no belt squealing. last year I added R12A to the system (about 6oz) and it was running fine. I was concerned it was a belt alignment...but i don't think that is the issue either...

Frankly I'm not sure what to think.

 

Well one experiment would be to get it back on and run for a while without AC on (so just exercising the pulley as an idler).

If it stays put OK like that - then it may indeed be down to a belt loading/tension issue.

Did you check the cooling fans anyway? (do both run in AC mode)

Alan

 

Yes, both cooling fans are running well. At this point the car is on jack stands with the alternator and power steering pumps have been removed.
The AC belt has to be the closest one to the block
I have another belt coming tomorrow to put back on it....but i really don't what to have to pull this all apart again.

 

I'd check the alignment of the two pulleys to make sure that the belt runs straight between them. A straght-edge on the big pulley should just barely touch the edge of the smaller one. In industrial drives, the biggest cause of belt problems is misalignment, even small amounts. After that it's a belt tension issue. A belt that has slack-side whipping is a candidate for jumping. A belt that isn't new should allow no more than maybe half a belt thickness deflection with hard thumb pressure at mid-span. There are easy belt tension gauges available ("cricket") if you aren't comfortable using the 'rule-of-thumb' method. You might also consider swapping a straight-walled belt for the cogged one you have. It would be less prone to 'catching' on the sides of either pulley, and therefore less prone to being rolled.

Your picture isn't from a point where it's possible to accurately see the alignment of the pulleys. It may be a function of that angle that makes it look like the AC compressor is forward of the crank drive pulley. Plus the belt is obviously loose enough to allow it to ride up on the outside of the drive pulley.

Alan's pressure-spike description is a possibility. The AC wiring diagram of the pressure switch in the '89 car shows that it has a high-pressure cutoff. I didn't bother to rely on that, rather just found a dual-switch replacement when I did the R-134a conversion way back when. Unless you have a high-pressure cutoff, the compressor will continue to run even when high-side pressures get too high. The protection such as it is becomes a blowout disk in the drier that relieves/fails, usually around 450-500 PSIG. That pressure is available in a liquid-locked system, but is usually too high for a vapor head. Regardless, compressor damage is common before that disk ruptures.

 

My '88 would do this about once a year. The problem was the mounting bracket for the A/C compressor had been welded in the past and was off just enough to cause the belt to jump. Put a new bracket on and it's just fine now.

 

O.k, well im going to go back in tonight and look again at the alignment (I'll try to get some pics as well) that said, why on earth would they be out of alignment now...can the AC crank pulley be on backwards??

 

I took a photo last night with a straight edge to check the alignment between the two pulleys. as you can see there is a small gap between the two...not sure if its a big deal. Is there some way to eliminate this discrepancy?
Note: the compressor was replaced with a rebuilt as some point 928126101FX and the crank pulley is a 92810211803...where I think it should have been a 92810211804 for a GT. I guess if nothing else they are a matched set.

any suggestions?

 

That certainly isn't aligned. Assuming the compressor is where it is supposed to be, the other place to start looking is a "flange washer" that sits in front of the toothed gear of the crank and A/C pulley. There is also a "thrust washer" that is between crank bolt and front pulley. I don't know what is the story with your part numbers you cited, but those pulleys need to line up.

 

Hi Steve, are you referring to #6 & 12 on this diagram? if so yup they are on there and are brand new too! The 2 washers (#6) are on with the lips of the outer edges away from the crank gear...if you know what i mean.

 

The GT pulley, IIRC, was slightly smaller. Most US cars got the bigger one anyway, as part of the high-capacity AC package (M470?).

The replaced compressor would get my attention first, along with all the brackets that hold it up. Many compressors fail in service due to impact with road hazards. The brackets bend or break as part of that failure. Better I guess than fractuing the mounting bosses on the block, something that also happens with severe impacts. I can't think of a good way to shim the compressor forward either.

 

It looks like i'm going to have to pull the compressor and have a good look at the bracket to see if there are any issues (breaks). I cant seem to see anyway to shim either. The ears must fit inside the bracket

 

One of the more commonly overlooked/ignored items when the compressor is R&R'd is the need to put ALL the bracket bolts back in and torque them correctly. That heat shield mysteriously disappears too since it can be more than a chore getting all that stuff back in correctly with the engine already in the car.

With the car raised up to work underneath, arrange a support for the compressor so it won't be dangling by the hoses when you unbolt it. Disconnect the clutch wire and make sure the short section of wire to the compressor is free. Then unbolt it and move it to the nearby support you've arranged. You can then let your fingers do the walking through the bracket slime to verify that all the bolts and the heat shield are in place correctly and tight. Clean it up and inspect the whole mess to see if there are any broken or even just bent arms on the cast support bracket. Verify correct bolt torques on those bracket bolts before loading the compressor back in. Something has moved in there, just need to find out what it is.

 

Thank you, i will be doing exactly as you have indicated after work tonight...and strangely i'm mildly looking forward to it...i think its a sickness..