S90 Flywheel Selection

[Dennis Vogel]

We're trying to settle on a flywheel for our S90 engine rebuild. We've decided to go with a used 912 crank. Going through the Maestro book and forum posts, there are lots of possible permutations. Some require more work or fiddling than others. Related questions:

1. Am I correct in understanding that a Super 90 flywheel (200 mm) can be used with a 912 crank? The only implication being the number of shims needed to adjust endplay?
2. Do all S90 flywheels have ring gears to match 6v generator?
3. Are all Porsche genuine factory parts not equal? Sunset appears to have a new S90 Porsche flywheel for $282. If I look up the same 616.102.201.02 part at Stoddard it's almost 3x the price.
4. Is there any benefit in looking at used flywheels? I assume by the time you surface / balance them you wouldn't save much money?

Thank you.

[Al Zim]

Zim's can restore your 356/912 or 911 push clutch type flywheel. To install a new ring gear, speedy sleeve and resurface the flywheel usually runs in the low $300.00 range. This precludes purchasing a flywheel and having it refurbished. BE AWARE that sometimes the flywheel is balanced with the pressure plate which means balancing again to make sure you have no vibrations. Many times the flywheel cannot be rebuilt. You can check this on the bench by placing the gland nut in the flywheel and putting some clay on the area surrounding the gland nut and the head of the gland nut. Press your clutch disc into the flywheel and then wee how thick the clay is. I would say you are pressing your luck when you have less than 3MM clearance. S-90 flywheels will fit a non S-90 crank you will obviously need a new shim measure carefully. We have just completed an engine with this configuration and can report that there is plenty of clearance between the dowels and the end of the S-90 flywheel. It is nearly impossible to know how or what your vendor is marketing. Most of them do not install the parts they sell! If the part needs a modification to fit correctly they do not have an in house machine shop to do that modification. al zim 800.356.2964 2019/02/17

[Martin Benade]

How does the S90 flywheel differ at the crank mounting area? Just that it needs a thicker shim?

[Dennis Vogel]

Zim's can restore your 356/912 or 911 push clutch type flywheel.

Thanks for your reply Al. Unfortunately, our original flywheel was lost during shipping. I'm starting from scratch on that component. Likewise, the crank found in the engine was an SPG roller crank that we've decided not to use. So we've gone with a 912 crank.

[Dennis Vogel]

How does the S90 flywheel differ at the crank mounting area? Just that it needs a thicker shim?

If I understand the Harry Pellow books correctly, the Super-90 flywheel hub protrudes less towards the crankshaft than the other types of flywheels. The understood benefit of the S90 flywheel is that it's roughly 4 lbs lighter.

[Dick Weiss]

Any flywheel can be machined to S90's backside shape to 14-lbs. (or more) and the disc depth and face is checked for any re-machining them to the 180 or 200mm
relationship and re-balanced w/the crankshaft mounted.
As Al Z. mentioned, the clutch disc's hub clearance to the gland nut (I still call it a bolt) must be checked if the disc and P/plate faces were machined; The proper disc
thickness should be around 10mm vs. some aftermarket VW discs are only 8 or 9mm thick. Proper disc should have the spring hub and recently, the local resto shop
had a 4-spring hub which couldn't be fitted! The hub springs were larger!!!