Flywheel Specifications

[304065]

On Monday I am taking my flywheel to the local machine shop to be resurfaced. I plan to furnish the shop owner with a scan of the factory's technical specifications to guide him.

Can someone help me interpret the factory specs?

Dimension

a- this is the "register" or the distance between the mating surface of the pressure plate and the friction surface of the flywheel (thanks OTTO for the clarity!). This seems like it's the first step: grind some material off the friction surface, then grind some material off the step to maintain the distance at 22.5mm. Otherwise the pressure plate will be too far from the friction surface and it won't squeeze the clutch tight enough when engaged.

b- this is the distance between the rim of the clutch that holds the ring gear and the outside the flywheel. Not sure why you would have to cut this down.

c- depth of the friction surface. When this is less than 11mm thick, the flywheel is junk.

Now, there are a couple of chamfers on the outside edge, it appears. One is a 45 degree chamfer, 1.5mm long. The other is a 45 degree chamfer, 0.3mm long, on the outside, on the gear teeth.

The gear tooth modulus is 2.11. The "Modulus" of a gear is the ratio of the diameter to the number of teeth. This isn't going to change, but it's always good to check it against the starter to make sure you don't have the wrong flywheel or starter.

Now, what are the dimensions circled below? What are those triangles all about? Is that surface irregularity?

Thanks! There are only about three useful threads here on PP, you would think flywheels would be more discussed!

[304065]

Well THIS should be pretty unambiguous, right?

[jasam]

Hi john, don't you like al flywheels?, they work great on my car

[euro911sc]

Good thread, John! How did you know your flywheel needed to be resurfaced? If it were never resurfaced What is the spec that determines it needs to be? Mine is different than yours, but there is still no spec on making this decision... just a wear limit... from my 3.0 spec book:

The flywheel bearing surface on the drive plate can be machined on a lathe, if there is serious scoring or considerable burnt spots.

Keep lathe cut as small as possible.

Wear limit of flywheel thickness:

911 SC 8.5 mm
911 Turbo 9.9 mm

Mike (TerribleHondo) was helping me put the crank together on Sat. and he asked me if I was going to resurface the flywheel... I said, 'No, I never have either.' His experience lies with domestics and apparently he resurfaced every time the tranny was separated from engine... I have done that 4-5 times and never thought about it...

He pointed to the micro cracks:



Cracks are evenly spread around the flywheel and radiate radially. None are very deep that I can determine, but I'm now questioning the re-use of this piece. There are also slight grooves radially that I could feel with my finger, but not really measure...

Comments?

Best regards,

Michael

PS I'm pretty sure the little triangles specify the surface smoothness in terms of grinding/cutting it.