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Fan Belt & Crank Pully
I'm in the process of putting the fan belt on and noticed that when I do the belt is extremely loose. I had to replace the pulley (bolted to the crankshaft) when the bolt would not budge and I broke one side of it. I got a used one at a dismantler and I thought I looked at things pretty closely when replacing it, same diameter but the groove may be deeper???Causing looseness in the belt. I have a new belt as well as the one that came off and they both do the same thing. Did the folks at Porsche make different pulleys? If this is slightly different than the old one will it be able to provide proper cooling?? Or could there be some other problem I'm overlooking??? Thanks.
------------------ 78 3.0L/3.2L CIS 911SC |
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05-12-2001, 02:43 PM
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There are differnt diameter pullys. But I don't believe your problem is related to that issue.
The width/depth of the groove is dictated by shims, each car has some shims between the pulley halves and extra ones stored under the nut on the outside of the pulley. If the groove is too wide/deep take some shims from between the pulley halves and place under the nut on the outside. This will narrrow the groove restoring tension to the belt. [This message has been edited by Bill Verburg (edited 05-12-2001).] |
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05-12-2001, 02:50 PM
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Bill,
I had four shims under the pully and one under the nut before I took the engine apart and everything was good and snug. Using the same configuration with the new pully the belt is not even close to tight. I took out all the shims and the belt still has lots of play. I really can't think of anything other than the pulley being the problem at this point. The old pully had several more markings on it than the one I have now but I could have swore they were the same when I put them on top of one another. Same diameter, but could the groove be deeper on this new pulley causing much more play in the belt??? Again I have tried both the old and a new belt??? ------------------ 78 3.0L/3.2L CIS 911SC |
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05-12-2001, 07:45 PM
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David - what engine did your "new" problem pulley come from? As previously stated, all pulleys are not created equal. It is a common trick to use a '78 pulley on slower ratio motors to speed up the fan. Find another 78/79 SC pulley and go from there.
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05-13-2001, 08:10 AM
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You need to make sure that you match the pulley half to your fan. Different fans were used over the years, and sometimes they were swapped by previous owners. Also, I believe that you need a minimum of six shims (off the top of my head, I'm in the airport now, and don't usually carry my spec books with me).
Also, check out our tech article on fan belt tightening. Make sure that you turn the engine over a bit with the starter to tighten the belt when you are attaching it. -Wayne |
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05-13-2001, 09:25 AM
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Just wanted to post the conclusion to this thread. Went back to the dismantlers (PAP)with the pulley we thought was for my 78 and sure enough we discovered the OD was slightly smaller than the one I needed. I thougth I'd give them a plug since Jack was very helpful. They pulled another and sure enough it looked exactly like my old one with matching stampings etc.
Problem solved. Thanks to all of you as well. It's back to reassembly tonight... ------------------ 78 3.0L/3.2L CIS 911SC |
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05-17-2001, 10:07 AM
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