9.5 vs. 10 mm fan belt

[Tom F2]

Porsche spec says 9.5 x 710 for my fan belt. Pelican only sells 10 x 710. The belt that Porsche sells is marked 9.5 x 710 and, to my eyes, completely indistinguishable from a 10 x 710.

The 10 x 710 is TIGHT. In fact, I can't get my alternator pulley nut started, which is first for me in 16 years of 911 driving/tinkering.

Has anyone else noticed this, and what have they done?

[javadog]

There was a thread about this in the last couple of weeks. Get the correct 9.5x710 belt and you'll be fine.

JR

[Tom F2]

Got a link to the thread? I searched without finding an answer, though I found discussion about the issue. My guess is that no one is making a true 9.5 x 710 belt, these days.

[David E. Clark]

According to one of the posts in this thread you should be able to get the correct 9.5x710 belt from the dealer.

Originally posted by jet911
I went to the local Porsche dealer and got an OEM belt which is 9.5 X 710.

Good luck.

[Tom F2]

The one from the dealer is 10. This must not be a problem, must be me!

[javadog]

Tom,

You don't mention what year car for which you need a belt, so I am going to make an educated guess.

In 1980 Porsche changed the fan size used on the 911SC to the larger one used on the turbo. They produced part number 999.192.176.50, which was for a 9.5x710mm belt made by Goodyear. They also changed the method of adjustment, which is seldom discussed. I'll quote from the introductory Service Information book for the 1980 models:

"Only the approved belt from Goodyear, Part No. 999.192.176.50, may be used.
The new belt must be tightened more than previously.
Adjustment: Tighten belt as usual (10 to 15mm deflection). Then reduce the number of spacers between the pulley halves by one. (ca. 5mm belt deflection)."

I have found that Pelican can get (order) any part from Porsche, if they don't stock it. In this case, they may be using a belt, supplied by the aftermarket, that may be a slighty different size or have a different taper. Perhaps, if you call them and let them know the problem that you're having, they'll add another line item to the catalog (or change the part they supply) and people will quit having this problem.

Hope this helps,
JR

[javadog]

A picture of the elusive belt:

[Scott at Pelican Parts]

I will add the Genuine Porsche 9.5x710 belt to the online catalog. Note that this is not a "service free" belt (doesn't have the notches inside), meaning you may have to retension it.

We sell hundreds of the Contitech belts each year, with only a few people mentioning problems with it.

[Mysterytrain]

I found that the notched belt was the cause of some strange low frequency oscillations from the fan and housing. I replaced the belt with the OEM belt and the noise is gone.

[Tom F2]

Originally posted by javadog
Tom,

You don't mention what year car for which you need a belt, so I am going to make an educated guess.

In 1980 Porsche changed the fan size used on the 911SC to the larger one used on the turbo. They produced part number 999.192.176.50, which was for a 9.5x710mm belt made by Goodyear. They also changed the method of adjustment, which is seldom discussed. I'll quote from the introductory Service Information book for the 1980 models:

"Only the approved belt from Goodyear, Part No. 999.192.176.50, may be used.
The new belt must be tightened more than previously.
Adjustment: Tighten belt as usual (10 to 15mm deflection). Then reduce the number of spacers between the pulley halves by one. (ca. 5mm belt deflection)."

I have found that Pelican can get (order) any part from Porsche, if they don't stock it. In this case, they may be using a belt, supplied by the aftermarket, that may be a slighty different size or have a different taper. Perhaps, if you call them and let them know the problem that you're having, they'll add another line item to the catalog (or change the part they supply) and people will quit having this problem.

Hope this helps,
JR

Thank you, that helps a lot! That is the belt that I have, so I guess I have a lesson to learn about getting it mounted. It sure is tight!

[Wayne 962]

Either belt should work fine, as long as you adjust the number of shims around the pulley. Most people don't know how to properly tension the belt (it is *very* confusing for someone who hasn't done it before), and the opportunity for error is high. Turning the engine over slightly after initially placing it on there is key. 101 Projects, and this tech article explain the process:

http://www.pelicanparts.com/techarticles/911_fan_belt/911_fan_belt.htm

-Wayne

[Tom F2]

I found it easier just to loosen the alternator nut, slip the belt over the alternator pulley, partially start it over the crank pulley, and then turn the crank to pull it over the crank pulley. Then tighten up the alternator nut, and it's done. Yep, with 5 shims, I just get 5 mm deflection.

I'm just surprised at how tight this factory belt fits.

I guess that I haven't had this problem before, because I have always used the aftermarket belts, like Pelican sells.

Is there a lesson there?

[TSwede]

My problem similar and I'm stuck.. I ordered a Contitech 10x710 and it is too loose...!! How can this be when the goodyear I took off (999.192.176.50) is narrower (9.5) and wasn't loose - surely the 10 should be tighter - it must be something to do with profiles and people's fan/pulley combination. My feeling is that as pulleys and fans are changed over the years there might be slight profile differences/powder coating thicknesses/mismatches (double pulley took off - single put on - 5 blade fan took off - 11 blade put back on)...... So - even though I am in the UK I am gong to order the 999.192.176.50 off pelican in the US...

[joey d]

I could really use some help as to where i can order the correct 9.5 x 710 belt for my 1971 Porsche 911 T. My belt says - Contitech 9.5 x 710. Any help would be much appreciated. Thank you.

[sugarwood]

Dealer

[manbridge 74]

A good rule of thumb since there are so many pulley configurations is to make sure belt is flush with outer pulley edges.

[GH85Carrera]

Spend the time and money to get the Porsche spec 9.5 mm belt. The 10 mm belt will work if that is all you can get at the time, but it is almost impossible to get it the proper adjustment.

I carry a spare belt in my car, in the trunk, under the mat on top of the spare. It is a 10 mm belt. I run the 9.5 mm belt to get the proper adjustment with no too much pressure on the alternator bearing, and tight enough to not slip under full electrical load and I want all the cooling air the fan can produce.

[Vin-barrett]

I purchased a genuine Porsche belt , says Porsche with the green color and it was 10 x 710. If there are 9.5 belts available somewhere I'd like to know where.

[Starless]

I just replaced my belt. I got it from my FLAPS. The owner has had a few 911's and the one he sold me is a Dayco Top Cog 15280 11A0710. That number would leave me to believe it's 11mm but it fit perfectly with 3 shims in and 3 shims out.

[walt]

Just went thru this in the past few weeks. The 9.5 is difficult if not impossible to find, I found the 10mm installed just fine and adjusted with approximately an equal amount of shims on the inside and outside.