Hairline crack in starter ring gear-- run it?

[johnm01]

Hello All,


I purchased a used single mass flywheel for m20. Discovered a hairline crack on face of starter ring gear. See photos below. Very small hairline crack. Barely any depth. One part of me says this is no bueno and crack could spread. The other side of me is rationalizing because I do not have the money for a new flywheel. My rationale is that these teeth aren't under heavy load. Only some load when first cranking over the car.


Anyways. Wanted to get the $.02 from the community. Opinions are appreciated. Would you guys install this flywheel on your car?



This is a shame too because I wanted to send this flywheel out for lightening. I think that this is now off the table. I do not want a lighter flywheel that is going to be more prone to twisting and spreading this crack.

[nrubenstein]

Is thatr a crack, or a machining mark?

[johnm01]

It really does look like a small crack to me. Actually what I notice are two very very small cracks. My two photos are enormous (sorry) and yet still don't capture it very well. The second photo is even out of focus.

Really what I am hoping for is some reassurance here. I know a bunch of you have done flywheel jobs and I am wondering if these types of cracks have been seen by any of you guys.

Thanks,
John

[nrubenstein]

If it’s cracked (and I don’t see any cracks visible in the pictures), I would not install it.

[e30austin]

Doesn't look cracked to me, but those teeth do look chewed up.

[johnm01]

Well I'd be damned. What i perceived as two small cracks are the edges of a small region that appears to be machined. It's as if there used to be a pad of material on the ring that was removed and nearly taken flush to the rest of the ring face but not quite because it is raised slightly. I don't really know what to make of this but I am a heck of a lot less concerned.

Thanks for the feedback guys.

[e30davie]

Yer i cant see any cracks.

If it is cracked a decent machine shop can probably weld it up to stop it going further.

[TobyB]

That's where it's welded...
looks like that one started life as bar stock, got wrapped,
welded, ground, and then teeth were hobbed into it.

t

[roguetoaster]

That's where it's welded...
looks like that one started life as bar stock, got wrapped,
welded, ground, and then teeth were hobbed into it.

t

Looks like a cast part to me, and this may be a mold blemish or intentional component that was ground down.

[TobyB]

Hmmm, I don't think cast gears would work in that application
(it's shrunk onto the flywheel)
and it'd be too brittle to take all the abuse it's obviously gotten!

The few ring gears I've gotten up- close and personal with have
been some version of hobbed bar stock, but then, there's always something different.

t
ringy ding- ding!

[Andre3127]

If it was cracked, it would be obvious because the ring would've fallen off or spun. They are held on in tension by press fit. If cracked, it would disconnect from the flywheel.

[earthwormjim]

Looks like the location where the gear is welded together from the factory. It's not cast as a solid ring.

[digger]

Yeah it's just the butt weld