pitching pulleys at revs

[ONQRACIng]

Has anyone ever found a fix for high rev 911's pitching the pulley? We are throwing our pulley after dyno runs at 9K, lock tite and torqued.. I know there is a 993 fix, but is there a 911 fix out there??

[cmonref]

"pitching the pulley?" Whazat?

[TimT]

We had the same problem.. the v-belt would turn over at high rpms.. sometimes it would jump off the pulley, others the belt would disintegrate..

The solution was to over tighten the belt, and assure both pulleys are operating in the same plane.

I have Racecar Engineering issue, which mentions the Nascar boys had the same problem with belts turning over or running off the pulleys. There solution ribbed serpentine belts..

[304065]

High Rpm Pulley Upgrade

[TimT]

guess I read the op incorrectly...

Also had an instance on an over rev where the pulley moved on the pin...Bill fixed the crank and pulley by machining the crank and pulley for a larger dia. pin

We have had problems with both flipping or throwing the belt at high rpm... and losing the pulley index..

[ONQRACIng]

Should have been clearer, we are shearing dowels and the pulley bolt is then backing out.. I like the three hole mod, but that will wait until next rebuild, 40 or so hours..

Thanks all.......

[TimT]

Are you using a steel pulley or an aluminum pulley? We use aluminum pulleys mostly because we have the steel toothed wheel mounted to it to trigger the ecu...

On over rev etc.. the movement of the pin would hog out the the aluminum, the pulley would shift, then the timing would be off by enough that the engine was barely running...

Our mod for the aluminum pulley was to cut a steel center from a stock pulley, and mount it in an aluminum pulley.... I just looked through a bunch of pics, and cant find one that shows the pulley.....

Never sheared the pin though

[Henry Schmidt]

Supertec Power pulleys. They are lighter and smaller than stock pulleys so that you can reduce fan drag and improve cooling.
You get a 60/61 hard anodized pulley, new crank pin and factory superseded bolt.
The pulley also has timing marks for better cam and ignition timing.
Add to that the Supertec Fan pulleys and the package is complete. Also made af 60/61 hard anodized aluminum to the early diameter to aid in fan speed reduction as well as the crank pulley.
Both reduce rotating mass substantially.

[ONQRACIng]

We are running alum. pulleys, and the dowels are seeing so much shear load, that the crank nose is taking the hit as far as damage. Dowel holes are elongating to the point that new holes are being drilled for a new pin.


Henry, I like the pulley you offer, what is the total thickness?

We are getting ready to start a billet crank, and need to sort this issue before it gets real expensive...

I think a new pulley design, coupled with the multi pin config. will do the trick..
TIA
Andrew

[Henry Schmidt]

Slow the fan down and reduce the rotating mass (pulley and fan center) then the high shear forces are greatly reduced.
To answer your question about fan thickness look to the early pulley for dimensions.