911 alternator belt tension???

[ArnieB]

Ever have problems changing the fan/alternator belt on the 911?

I have a '88 3.2 Carerra. My old belt finally announced (loudly) that its time to retire. It needed it.

When I put the first replacement on (Conti), it was way to loose for my satisfaction even with one shim. I cranked the engine to insure it was not pinched and it was not.

So bought a Dayco belt, much better fit, or so I thought. Went out for a run yesterday, and the belt broke after about 75 miles on it. Forturnately, I was about 12 miles from home and could keep the car moving/cool. It got warmer than usual but no where near the red zone. Since the belt broke, I guess the belt must have been too tight, although I had ½” of deflection, with the one shim.

Anyway, put the second belt on (Conti). Put the shims in (4 at first), way too loose. The belt squealed when I ran the engine. So I took one shim out and left three in. It tightened up a bit (with about 1" deflection) but it did not squeal with the engine running. Then after about 10 miles, the belt squeals (indicating to me that it is still too loose. On the way home the belt broke with about 15 miles on it, which seems to indicate it was too tight. Now I am really confused.

Any advice/experience?

[ivangene]

you broke 2 belts in 30 miles?

I would love to help but I need more data and pics of the car, what year, motor, pics and specs, year, mods, miles and maybe a few pics

where do you live, maybe someone close can offer a hand...when you say it squeeled maybe it was too tight already? maybe it was loose, maybe the pulley has damage or something else that needs to be looked at...maybe post a pic of the car too.

1/2" of play is subjective to the amount of force applied -

[na2ub]

1/2" deflection is correct. Make sure you use all the shims (6) either on the inside or outside of the pully half. Also, make sure you are routing the belt on the correct drive pully. It should be the very inner pully next to the engine.

[ArnieB]

It is a 1988 911 Carerra with the 3.2 engine. I do not have any pic with me know but will take some tonight. The car is an annivesary edition (Jubilee). As such, I have kept the car as stock, no mods other than a K&N filter.

The car came equiped with an A/C, but I have not connect the belt to the A/C. Don't use it and try to save the HP for something more useful.

The car has 62K miles (original) and is very clean.

Other than that I do not know what to tell you other than I am in NE Pennsylvania. Quite a ways from Washington state!

Thanks for your help.

[ivangene]

as stated, use ALL the shims. and IMO, try the loosest first....(all shims between pulleys)

I think you might have to take a loot for a smoking gun somewhere else though. bent pulley? maybe the alternator housing cracked or got moved out of alignment..the can come out a bit causing mis-alignment of the two pulleys, that would wear a belt out quickly...or if the alt bearing are worn badly?

it's not too far, I'll swing over at lunch

[CCM911]

Where are you at in NE PA? I grew up there and still maintain contact with a bunch of 911 guys. You definitely have something going on that is not normal. Are you sure you are hitting the inside pulley, and not the outside? Have you checked your pulley halves for burrs or scoring?

[ArnieB]

I am going to disassemble the pulley tonight, inspect and wire brush it. Maybe that it is it. Since I did not have problems with the old belt, other than it being old, it is hard to imagine problems the alternator or its bushing. But will check just to be sure.

I am about 30 mins east of Scranton.

Thanks for your interest and help.

[Driver_X]

+1 for ivangene's suggestion. Make sure that you are putting the belt on the correct part of the pulley. It's pretty easy to have the belt on the A/C portion of the pulley and not realize it. That could explain your broken belts.

Here is an excellent write up by Grady: Pulley Shims, Wrong Config?

[ArnieB]

The belt was on the inside (closest to the block), the A/C belt did not have any issues. Thanks.

[BKC]

I recently changed my first belt. I find it strange that you were able to install a new belt with only one shim on the belt side. I tried and tried to use three (the same amount that was on that side) but couldn't get the pulley halves to mate up. I had to settle for five. I have since gotten it down to two on the inside and the rest on the outside after a couple thousand miles. I guess what I'm asking is, are you sure you're getting the pulley halves fully mated together?

[86 911 Targa]

Here is the configuration for our '86.


I suspect that you may have a re-assembly issue with your outside pulley half.

Good luck,

Gerry

[Tippy]

Sounds like the belt is riding up the pulley half until it snaps.

Gotta find out why.