Alternator & what is correct number of shims?

jet528e · 11:46 AM

Pulled the alternator last night out of my '86 Carrera for a required rebuild and discovered there were a total of 7 shims, two on the inside and 5 on the outside. According to 101 Projects, as well as Wil Ferch's tech article, there should be 6. My guess, according to service records, is that the PO had the voltage regulator replaced and during that process, an extra shim was added. The wierd thing is that the work was done by the Porsche dealer. Is it OK to include the 7th shim on the outside or not. I'm getting different opinions. Help.... as I plan on re-installing the alternator tomorrow and want to get it right. Could it be that the extra shim was part of the reason the bearings went bad? Any and all input is appreciated.

Thanks in advance!

TerryBPP · 10-27-2003, 10:40 AM

The more shims the looser the belt will be. If your belt is fairly new I would stay with 7 shims. If it has some miles on it go to 6 shims to tighten it up a bit. The reason for 7 shims might be that the belt was a tad irregular. No big deal.

jet528e · 10-27-2003, 10:42 AM

Thanks Terry, Am looking at replacing belt with new one.

Rot 911 · 10-27-2003, 10:42 AM

Jet you are really nervous about this. I saw your post over on Rennlist. For an '86 Carrera you should have 6 shims. As for the 7th shim it is not needed. The more important shims are the inner ones as they determine how tight the belt is. On the other hand, too many shims on the outside and you won't be able to thread the pulley nut down.

Superman · 10-27-2003, 10:53 AM

You're correct, Jim, to be focused on this question. I ran with one less shim than I should have had, and as a consequence the nut was not able to put enough pressure on the stack of stuff behind it, and the pulley rattled. IT chewed up the dished washer, which I had to replace. Perhaps having one too many is better than having one too few.

jet528e · 10-27-2003, 11:03 AM

Kurt,
I wouldn't call it "really nervous," just concerned and I want to get it right! I've gotten a couple different responses, some say no big deal, some say only six. I really don't want to screw-up the new bearings on the rebuilt alternator as I understand it, if the belt is too tight, it will effect the bearings shortening their life. Simply put, I don't want to re-do this again in a couple of months because I did it wrong. I think I will go with the 6 and keep the extra in the old tool box for future use if needed. Thanks!

Wil Ferch · 10-27-2003, 12:32 PM

The proper drill is to have 6 "total" shims...in whatever combination under or over the pulley to get the tension you need. If Superman went too few, the nut won't tighten properly and will "hog out" the rectangular hole. If too many, well...it depends on what side the pulley the "too many" shims are. If the additional shim is between the pulley halves, it might be OK for a belt mismatch ...but if it's on the outside, then maybe you can't get the nut on with enough "bite". Proper belt is the hard-to-find 9.5mm width variety. Too many are labelled 9.5/10 , and those typically can get you into trouble. I think the proper belt for an 86 is 9.5 x 710 mm.

Stay with 6 like the factory manual says .....

BTW...thanks for the plug...

---Wil Ferch

jet528e · 10-28-2003, 06:02 AM

Wil,

Thanks! I followed your article step by step. It made it very easy!

I did install the alternator last night and ended up using six as you stated. It took three times adjusting the shims from the inside to the outside as the new belt was very tight. (Got the belt from the local Porsche dealer). I ended up with three on the inside and three on the outside. I saved the "extra" shim that was there as a spare for the future if needed.

Once again thanks for your article it was a great help!