Snapping the flywheel bolts upon tightening? - Saab 900 Bulletin Board - Saabnet.com
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Snapping the flywheel bolts upon tightening?
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Posted by StoicBlue87 [Email] (#1829) [Profile/Gallery] (more from StoicBlue87) on Sun, 6 Sep 2020 11:25:03 Share Post by Email
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Hello all,

A surprising thing just happened to me.

On my 92 900S, I've been pondering a persistent and plentiful oil leak coming from somewhere near the flywheel and realized last week that I committed a mistake last year when reattaching the rebuilt transmission to the crankcase: I forgot to apply thread-lock/sealant to the flywheel bolts.

It looks like I'm losing a couple tablespoons of oil every night.

I disassembled everything this morning and verified that the threads were pristine and free from any lock/sealant. So I cleaned the holes and bolts, put the flywheel in place and began applying a new threads product from Permatex called "Seal + Lock" (#57535). It's a combo thread-seal and thread-lock. Goes on thick white almost like toothpaste and I'm using it as directed on the package.

I get all the bolts hand-tight, then crank lightly with 3/4 ratchet to just snug things up. Then I apply a torque wrench set to 63 ft-lbs, based on the manual reference for these 19 mm bolt heads.

I'm slowly applying pressure on the torque wrench but things are feeling "soft." It seems like I'm cranking and torquing but there's no accompanying click response from the torque wrench. The bolts are still feeling soft; I'm getting nervous that I'm about to snap something. I remove the wrench and set it down to something softer like 40 ft-lbs and verify on one of the bolt heads and the wrench DOES click.

So I set the wrench back to 63 ft-lbs and resume trying to get a click from any of the bolts. Finally one responds with the proper torque click.

Move to the next bolt...this one snaps. I've snapped one of the flywheel bolts in half.

Is this common?

I think I've only had this flywheel removed once before so there's not a lot of "traffic" on tightening and loosening these bolts. They look original and they're the low-rise bolt heads with "NEDUR" and "10.9" stamped on the bolt head.

I backed out all the remaining bolts, removed the flywheel and fortunately had enough of the broken bolt sticking out from the crank mount that I could spin it off pretty easily with some vise grips.

So now to head off and find a replacement bolt. Or should I replace ALL of these bolts? I've got a decent hardware store in mind that has a pretty strong specialty fastener section. I doubt there's 10.9-rated hardened 10 x 1.5 x 30 metric bolts at this shop but...I'm short on options. They may have something close.

I'm a little bothered that I could twist one of the originals in half. I'm looking at my remaining originals with some skepticism and thinking some new bolts may be viable even if they're not quite an exact match.

As long as they're decent grade, would an approximate match of these bolts be wise? I think I should replace them all but curious if anyone has a different idea. I'm also not sure...is the low-profile bolt head a requirement? I checked the clutch disk and it seems like I've got some margin for a possible taller bolt head between the flywheel mounting and the clutch disk.

And when I attempt this again, I think I'll use a progression of torquing (35 then 45 then 63 ft-lbs) instead of slightly tightened to fully torqued.

Thanks, I hope nobody else is working on their flywheel sections in 100+ heat and sunshine like me.

-StoicBlue87


->Posting last edited on Sun, 6 Sep 2020 12:43:14.


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