Correct Alternator/Fan V-Belt Sizes for 1986 911? 710 or 695mm?

[dictoresno]

the OEM Porsche belt that's on the car, which was new 10 years ago with few miles driven on it, is the 10x710mm part number 999.192.176.5A. this belt feels so loose and even after getting all shims on the outside of the pulley, its still horribly loose. I'm gonna order a new one but wanted to verify since the owners manual and Bentley say that 10x710 is correct, however it seems like both parts and different dimensions fit. is one correct over the other? I don't want to max out the shims again if the 10x710mm belt is too big.

I plan on cleaning up the pulley halves of any corrosion and reinstalling. could it also be bad shims?

[Flat6pac]

9.5x710
Times have it most supply houses ship 10x710
You can work with either.
Bruce

[dictoresno]

Originally Posted by Flat6pac

9.5x710
Times have it most supply houses ship 10x710
You can work with either.
Bruce

I see according to the old spec book that 9.5x710 is the correct size, it just seems so loose as I have all 6 shims outside.

maybe its just because the belt is so old its stretched? the car sat for 10 years without driving after a full maintenance. so again, its a new belt, low miles, but sat on the car for years. why do they offer the 695mm belt saying it fits also? I would hate to grab some more 710's and have them also be very loose.

[dictoresno]

when a new 710mm belt is installed, how many shims are you guys ending up with usually for a new belt proper tension?

[917_Langheck]

9.5x710 is original, but 10x710 works too, as Bruce noted.

If 9.5 is not working for you, get a 10. Easy enough.

[Jeff Alton]

The true 9.5X710 is a rare bird now. We buy Porsche branded belts from Porsche and they are 10x710. Do not fit quite as well.....

[dictoresno]

Originally Posted by Jeff Alton

The true 9.5X710 is a rare bird now. We buy Porsche branded belts from Porsche and they are 10x710. Do not fit quite as well.....

Well that’s why I’m unsure about the 710’s. Like I said I have all shims outside, proper torque on the pulley and it’s still extremely loose. So I was considering grabbing a 695 belt to see if that helps along with new shims. I grabbed two 710’s and one 695 to see which one ends up fitting best.


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[917_Langheck]

Well, if the 710s don't work, and the 695 does, you may have a Porsche. Hans and Fritz didn't always return from lunch sober.

[dictoresno]

Originally Posted by 917_Langheck

Well, if the 710s don't work, and the 695 does, you may have a Porsche. Hans and Fritz didn't always return from lunch sober.

sounds about right. Thanks!


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[wazzz]

Following this, as I too have my six shims on the outer side since I preventively replaced my belt with an original Porsche branded in 2018.

Since then belt has always been very loose, even with all six shims out. No squeaking but I wonder if this is right.

[dictoresno]

Originally Posted by wazzz

Following this, as I too have my six shims on the outer side since I preventively replaced my belt with an original Porsche branded in 2018.

Since then belt has always been very loose, even with all six shims out. No squeaking but I wonder if this is right.

When my dad had the belts replaced years ago, it was squealing immediately. I tightened it by putting five shims outside and one shim inside, and it was tight and stopped, but recently when I finally acquired the car, I ended up having to put the final shim on the outside, which did tighten it up a little bit, but once I took it for a 30 minute drive it became extremely loose again, which is, why I made this post.


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[smadsen]

I've used 710 belts on my '82 for 25 years. Three shims in, three shims out is where I end up. My philosophy is to loosen the belt till it squeaks, then tighten it up one shim at a time until it's quiet. It takes a little trial & error, but I run the belts about five years or so. Trying to keep as little stress on the alternator bearing as possible.

[PeteKz]

710x10 will be tighter than 710x9.5, so don't use 710x9.5, even if you find them. If that's still too loose, then go to a shorter belt. Something else to check: At the age and higher mileage many of these cars have, the pulley faces themselves may be worn enough to use up 1 or 2 shims. In that case, I would just use a smaller belt.

[dictoresno]

I pulled my pulley off and cleaned the one half, which has pitting and grooving. I assume there's no saving this. I need to try to clean the fan side a little with a wheel and see if I can remove the rust. guess this isn't helping my belt issue.

[porschyard]

Magnesium fan housings distort and collapse over time is the biggest problem reducing the distance from the center line of the alternator shaft to the crank pulley resulting in a looser belt. Over the years anytime I replaced a fan housing it made a big difference in shim position usually requiring more shims between the pulley than the previous housing. Also that pulley halve is not helping you situation and I would definitely replace it.

Richard

[dictoresno]

I was able to clean the fan side a little today with a fine grit sanding block while rotating the fan. its smooth now.

[dictoresno]

got the new belts on with new shims and pulley. looks like the old belt was definitely worn thin, which was the cause of my issue not being able to tighten it further. hopefully cleaning the fan corrosion will prevent future belt issues.

[911obgyn]

That rough surface will wear the belt over time!

[dictoresno]

Originally Posted by 911obgyn

That rough surface will wear the belt over time!

It’s no longer rough. It was sanded down with a 400 grit sanding sponge until it was perfectly smooth. Doesn’t look perfect, but it is indeed smooth.




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[PeteKz]

That should work. Now, don't let that engine sit for years collecting rust again! Drive the snot out of it regularly.