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914World.com _ 914World Garage _ Flywheel minimum thickness?

Posted by: Cazz Dec 6 2017, 03:03 PM

My flywheel is grooved and needs to be machined.
-Does anyone know the minimum thickness of the flywheel surface where the clutch disc mates?
-the thickness I get using my cheap calipers is 4mm thickness on the face.
-what is the minimum thickness after a machine shop cuts the face?

Posted by: Jeff Bowlsby Dec 6 2017, 03:17 PM

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Posted by: Mark Henry Dec 6 2017, 08:59 PM

I used to post that pic, then found out that brand new German flywheels were out of spec (dimension C) according to it. wink.gif


If I had 4mm, about .160" I'd tell the shop to remove just enough for clean up, Then you may likely have to grind the raised part of flywheel bolt heads off flat.
Depending how much you had to take off the flywheel face you may have to put a shim under the release bearing arm pivot bolt on the trans.

(note the 4mm you measured is likely dimension C but I'm guessing you are measuring in the wrong place compared to the chart.)

Posted by: Dave_Darling Dec 7 2017, 03:06 PM

The image is actually specifically for the 914-6. There are no official specs for the 914-4 flywheels that I know of.

The specs should be OK as a general guide, but they are not actually for the four-cylinder flywheels...

--DD

Posted by: Mark Henry Dec 7 2017, 03:23 PM

QUOTE(Dave_Darling @ Dec 7 2017, 04:06 PM) *

The image is actually specifically for the 914-6. There are no official specs for the 914-4 flywheels that I know of.

The specs should be OK as a general guide, but they are not actually for the four-cylinder flywheels...

--DD

agree.gif

and that's not actually a Porsche drawing, it's out of an aftermarket workshop manual, the Drake book IIRC, I have it here somewhere.

Posted by: porschetub Dec 7 2017, 04:19 PM

QUOTE(Dave_Darling @ Dec 8 2017, 10:06 AM) *

The image is actually specifically for the 914-6. There are no official specs for the 914-4 flywheels that I know of.

The specs should be OK as a general guide, but they are not actually for the four-cylinder flywheels...

--DD


agree.gif good spotting Dave,thats the drawing I used to check my flywheel,confirmed it was in spec but had been cut maybe once,pulled my gearbox and added a 1mm + spacer under the pivot ball,much improved and the release arm now has clearance on the gearbox housing.
The flywheel bolts on the "6" motors aren't an issue...tends to limit resurfacing on a T4 however.

Posted by: Dave_Darling Dec 7 2017, 06:45 PM

The pic looks like the one from the Little Spec Book. I looked through that thing six different ways to try to find definite 914-4 flywheel specs! Then through the factory manuals. No joy--that's how I knew that wasn't a -4 flywheel diagram explicitly.

Had a debate with Jerry Woods about it once, too. When I picked up my work from him, he conceded that I was right.

--DD

Posted by: Mark Henry Dec 7 2017, 08:21 PM

Just speculation, but I think the reason there was no spec with the original /4 is because it had the 4 spring clutch disc, likely the dealer would say it's a one use only and replace the flywheel. With the original 4 spring disc you were lucky if you could cut it once, even grinding down the bolts, as it would hit the big ass disc springs.
If I'm correct on this it would explain why we can't find a spec anywhere for the /4 flywheel.

I know the fitment issue is fact as I had an NOS 4 spring back in the day, IIRC I had to use an uncut fly to use the thing. Also my 914 was a low mile dealer maintained car and had the bill for a clutch job at 56K, it said the flywheel was replaced. Late 80's bill, tune-up, oil, RMS and clutch was something like $1300.

The /6 six (small) spring disc has way more clearance and with grinding the bolts has 3-4 surface grinds before it becomes an issue.

Posted by: rjames Dec 8 2017, 05:31 PM

QUOTE(Dave_Darling @ Dec 7 2017, 01:06 PM) *

The image is actually specifically for the 914-6. There are no official specs for the 914-4 flywheels that I know of.

The specs should be OK as a general guide, but they are not actually for the four-cylinder flywheels...

--DD



agree.gif

I did a ton of research trying to track down the specks to see if I needed a new flywheel when I changed out the clutch, and couldn't find anything but the pic you posted, but am confident that it's wrong. I finally just bought a new flywheel (from Pelican, IIRC), and although I can't remember what the specks of the new one were, I know they didn't match what's shown in the diagram.

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