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[JasonO]

I know It's not the wisest choise just to pop a new one on and observe, I did a small drive, checked, ran some errands checking each time, I just looked back and It was 4 years ago I changed It, and I should have paid more attention!.Other than that I cant see any way (yet) how this happend, I've ask'd a lot of people and all are perplexed so far as well.
The old belt was made by gates.
There Is a car show literately 2mins from my house today I'll ask around when I'm there.

On the "note" of frequency, pitch, and tension. The belt on my car is tuned to whats called A sharp, or written as A#
I noted that when cranking over by hand the tension and Pitch changes as the the engine cycles... but there Is "tightest point" which Is pretty easy to hear.
If I set It so I can "just" turn 90 degress It would be slightly Higher In pitch,

So far a A# pitch fork (tuning fork) was right on.

My ears worked pretty well.

A electric guitar tuner kinda worked but Most are poxy and Chinese.

I cant be stuffed to set up a fancy condenser mic/gear/software just yet but It's doable.

Ill look Into It tonight...my minds humming now and Id like to know what the pitch of other peoples belts are

[Mike9311]

Impressive your ear is

When I did it, many moons ago, it was with a laptop and a program called TrueRTA on my Ducati 748. I looked back just now because this topic was big on DucatiMS and I was sure expanded upon since I did it back then. Funny how easy it is now and the belt tension on a Ducati 748 is 110Hz

No need for TrueRTA or other fancy meters either. Use your phone and an App. Easy. There is talk in this thread of a lower frequency once broken in (85Hz).

http://www.ducati.ms/forums/56-superbikes/75942-guitar-tuner-timing-belt-tension-app-android.html

Pic of the way I did it back then...I wonder if my little clip on guitar tuner would pick it up? No need to try though since its so easy with just a mobile phone. I am going to try it on the '82 once I get to where it is and I will let you know.

Just so you know this bike saw regular track abuse, after setting belt tension this way, to 11.5K rpm. no issues


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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[RC]

Sounds like that belt is too tight, from the description not the frequency.
It should be fairly easy to twist the belt over 180* midway on the long span. With a deflection of ~15mm it should easily touch the flat backside of the water pump outlet with finger pressure.

While it may be possible to achieve correct tension at a particular resonant frequency, there is no data available, particularly none from Porsche. Please be the test mules guys & report back in a few years time with a reliable 100,000Ks on the belt(s) and the correct frequency.

Until then, the simplest, cheapest and most reliable tension method is with a Krikit tension gauge, made/ supplied by Gates and about $20. Set the tension at 30LBS cold and be done with it. No $$$ P9201 tool required but also no guesswork, = No repeat posts about shagged belts or bent valves.
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World`s quickest 924 2L slushbox

[Mike9311]