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peter hooper
Experienced User
Username: grubber

Post Number: 14
Registered: 12-2016
Posted on Saturday, 20 April, 2019 - 18:52:   Edit PostDelete PostView Post/Check IP

What causes the flywheel friction plate to crack? I have three radical cracks in mine all the way through the plate and are they available?
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Bill Vatter
Frequent User
Username: bill_vatter

Post Number: 74
Registered: 9-2004
Posted on Tuesday, 23 April, 2019 - 13:25:   Edit PostDelete PostView Post/Check IP

Many severe heat cycles causes initiation of cracks on the surface, and then a crack will grow pretty quickly.

Awhile back you could get used ones at Introcar or Flying Spares. If it was my car, and in your position, I would get a new one made. That way you would be starting fresh with something you know is OK i.e. without any undetectable surface fatigue that will eventually lead to inception of cracks.

The flywheel plate is easy compared with the pressure plate, which is similarly subject to cracking and quite a bit more difficult to fabricate.

When you eventually get good parts, make sure that when the clutch releases and engages it moves with the pressure plate and the flywheel plate EXACTLY parallel to each other. That is important for operational smoothness, but also minimizes uneven heating and temperature, which is the fundamental cause of surface fatigue of the friction components. You achieve this using a Borg & Beck gauge to adjust the release levers and and matching the springs as closely as possible with equal strength springs positioned opposite each other in the pressure plate assembly.

A Borg & Beck gauge may be difficult to find, but you can improvise the function of the gauge with some precisely machined spacers and height measurement jigs.

I happen to have a couple of complete flywheel and clutch sets, one is original dimension (no machining since new) and without any cracking that could last virtually forever in enthusiast ownership where they would be very unlikely to receive harsh use. I will never use these parts myself, but the shipping cost from eastern US to Australia will be pretty expensive.
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Bill Vatter
Frequent User
Username: bill_vatter

Post Number: 75
Registered: 9-2004
Posted on Tuesday, 23 April, 2019 - 13:38:   Edit PostDelete PostView Post/Check IP

Oh yeah, make sure both flywheel plate and pressure plate are perfectly flat. I do it with my lathe and a tool post grinder, and I can achieve maximum surface variation of 0.001 inch (my lathe run-out less than 0.0005 inch), but a good surface grinder on a magnetic table will also work very well, maybe better. However, not every machine shop will have that kind of surface grinder

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