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Old 08-18-2008, 03:37 PM
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SBC crank threads partially stripped

The threads in my 350 SBC crank snout are partially stripped. I can JUST about get the original balancer bolt with thick washer to bite down on some good threads, but I haven't tried torquing it down more than about 20lbft, as I don't want to swing on it and strip anymore threads in the crank snout.

Are longer bolts available? I believe the threads extend quite a bit beyond the reach of the stock bolt? I suppose using a thinner washer is also an option (in conjunction with a longer bolt). I'm aware I could tap the threads, but I'd rather work around this with a longer bolt if I can. I'll use permanent-strength red threadlocker, too.

Thanks.

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Old 08-18-2008, 04:05 PM
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V8hed in your other post enginejr mentioned a moroso bolt being longer. Look at Post #8. You can get a longer bolt just make sure it's Grade 8 or better. Not sure how there graded across the pond.

SBC harmonic balancer install
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Old 08-18-2008, 04:07 PM
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Also keep & use the large thick washer.
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Old 08-18-2008, 04:08 PM
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Quote:
Originally Posted by SSedan64
V8hed in your other post enginejr mentioned a moroso bolt being longer. Look at Post #8. You can get a longer bolt just make sure it's Grade 8 or better. Not sure how there graded across the pond.

SBC harmonic balancer install
Magic, well-spotted, thanks. Funny, I saw a pic of a Moroso bolt and thought it looked a tad longer than the stocker.

Thanks!
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Old 08-18-2008, 04:34 PM
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Having done this for the number of years I have, there is one thing I have learned. If it's questionable, It's going to mess up on you. It has to be bulletproof. The threads in the crank were probably only tapped with a starting tap. Bulletproof means using a bottoming tap to finish out the threads and then using the appropriate length bolt that will torque down to spec within just 1/16th of an inch short of the end of the hole. Been there, done that too many times.
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Old 08-18-2008, 07:25 PM
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I was going to suggest trying a helicoil, but I don't know if they make them in fine thread.

I lost a balancer on my 406 two years ago. Not a lot of fun and plenty of damage.
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Old 08-18-2008, 07:41 PM
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Sounds like you are trying to use the bolt as an installation tool.I think you might cause more damage no matter what length bolt you use.Also I think you will regret using "loctite" on the bolt threads.Torque to correct specs. and use assembly oil.Just a little friendly advice, good luck ..Ron
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Old 08-19-2008, 01:46 AM
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Quote:
Originally Posted by cbreezer
Sounds like you are trying to use the bolt as an installation tool.I think you might cause more damage no matter what length bolt you use.Also I think you will regret using "loctite" on the bolt threads.Torque to correct specs. and use assembly oil.Just a little friendly advice, good luck ..Ron
Nope, I was using a Moroso installation tool. The last little bit of getting the balancer 'home' caused the install tool to try to tighten itself further into the crank snout when it was already screwed-in as far as it would go, hence partially-stripped threads. Longer bolt should work, as there are good threads beyond the damaged ones at the front.
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Old 08-19-2008, 09:35 PM
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If worse comes to worst, you could tap the hole 1/2"x20 and use a big-block bolt & washer.
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Old 08-20-2008, 12:52 AM
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even though i always try to check, there have been a few times i've spent good money on a crank only to find the first few threads are damaged. i have had good luck using a stud to save the crank in those cases. if the threads are too bad, drill & tap for a bigger bolt is the way to go.
when using a stud i use a drop of blue loctite to insure it doesn't loosen up, the red is too extreme IMO.
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Old 08-20-2008, 01:49 AM
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Thanks guys. Will try a new (and 0.22" longer) bolt first. If that doesn't work, I'll tap to 1/2". If I tap to 1/2", I'm assuming I can use the existing 7/16" hole as a pilot hole for the tap?
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Old 08-20-2008, 02:35 AM
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Quote:
Originally Posted by v8hed
Thanks guys. Will try a new (and 0.22" longer) bolt first. If that doesn't work, I'll tap to 1/2". If I tap to 1/2", I'm assuming I can use the existing 7/16" hole as a pilot hole for the tap?
Wrong post. sorry

Last edited by SSedan64; 08-20-2008 at 02:43 AM.
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Old 08-20-2008, 07:27 AM
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Quote:
Originally Posted by v8hed
Thanks guys. Will try a new (and 0.22" longer) bolt first. If that doesn't work, I'll tap to 1/2". If I tap to 1/2", I'm assuming I can use the existing 7/16" hole as a pilot hole for the tap?
1/2"-20 Tap needs a pilot hole 29/64" or .453". The hole for a 7/16"-20 tap would be 25/64" or .390", The hole may be too small & break the tap. You don't want to break the tap off in the crank snout.
But you probably don't have room to redrill with the engine in the car.

Have you thought about using a 7/16" Stud with a nut & the thick washer?
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Old 08-20-2008, 05:09 PM
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Quote:
Originally Posted by SSedan64
1/2"-20 Tap needs a pilot hole 29/64" or .453". The hole for a 7/16"-20 tap would be 25/64" or .390", The hole may be too small & break the tap. You don't want to break the tap off in the crank snout.
But you probably don't have room to redrill with the engine in the car.

Have you thought about using a 7/16" Stud with a nut & the thick washer?
I've placed an order for a +0.22" ARP bolt/washer. Hopefully (with some luck), that will save me from tapping the crank to 1/2". Will keep this thread updated
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