AARRG! Did I strip my crank?

[davepl]

So I was torquing my flywheel yesterday in three increments, 15, 30, and 45. That's from the book. But I was using my 3/8th Torque Wrench, and it maxes at 75. Still, it's within its range.

Just as I was torquing the last bolt I was thinking "This seems like a lot of torque, why hasn't the wrench clicked?", it got easier to turn. Fearing I stripped something, I stopped.

When I backed the bolt out, it looked fine. But I set it aside and got a completely new set.

I took the flywheel off, ran a bolt through that hole in the crank with my electric impact lightly. It took a little force compared to a new hole, but it went in and out without incident.

So I put the flywheel back on, used new bolts. I wasn't sure if that one hole was going to hold 75 ft/lbs so I used red loctite and stopped at 45.

I probably need to go out and redo it to 75 and take my lumps, but I'm scared.

Will 45 ftlbs and red loctite hold it forever, or should I take it to 75 and get the crank repaired if needed?

[muley]

Sounds like you may have stretched the threads on that bolt. The crank should be harder than that.

[davepl]

Originally Posted by muley

Sounds like you may have stretched the threads on that bolt. The crank should be harder than that.

That's my hope!

[VetteVet]

Well you've got five other bolts with good torque, to me it would be a no brainer. If you're not going to race it I'd take the chance and check it in a few days.

[davepl]

I ordered new ARP bolts, I think I'm going to replace the GM bolts and see what happens.

Does anyone know if I can heli-coil a crank flange without (a) throwing it out of balance, and (b) taking the crank out of the engine?

The difference in weight would be small between a helicoil and the metal removed to install it, and it's close to the center of rotation, so I don't -think- it'd throw it out of balance, but I'm no machinist...

[jocko]

I would not helicoil the rear crank mounting snout personally. Balance might be an issue, but I wouldn't do it anyway. How certain are you that it's the crank threads and not just the bolt?

[kwmech]

The flange threads are pretty tough, then again anything is possible. So if the threads are stripped, I personally wouldn't hesitate to put a heli-coil in for the repair. Affecting balance, really? with the threads you're removing and the weight of the heli-coil, any weight or balance issue I think would not even be measureable.

[Valarius_Starchaser]

I have heli-coiled a front balance bolt hole before but never a flywheel it would likely throw it off balance but so slight you would never notice I imagine you could do it without taking the crank out as well

I always change flywheel bolts never have gone with ARP I likely will with my current BBC build though just for assurance

[trac209]

Personally I wouldn't worry about the one bolt at 45 with loctite. It should be fine

[DBK81]

Originally Posted by trac209

Personally I wouldn't worry about the one bolt at 45 with loctite. It should be fine

I agree, 45 ft/lbs with locktight, that thing isn't going anywhere, leave it and don't create a headache that isn't there. Just my $.02. If you'd like drive it for a few hundred miles and then give it a check to see if still at 45 ft/lbs.

[hugger6933]

The problem with driving it a few hundred miles the rechecking is the transmission is like in the way. I'd put it together and never think about it again. Heck you could probably throw that one bolt away and still not have any problems. Jim

[adricar1]

dave
helicoiling would not be a problem, and also i do not feel it will be a balance issue either, BTW the nearer the weight is to the centre of the crank , it make less differance,, What i mean if you balanced a flywheel , it would have weight removed or added at the outside edge and not near the centre, so dont worry about a weight issue.
Its good practice to run a tap down the threads to clean them up. But as has alraedy been said red locktite and 45 ft lbs , forget about it and run the motor.

[Jason Banks]

I attempted a helicoil on a front balancer bolt. It was a nightmare....the balancer had come off driving on the highway and messed up all kinds of pulleys and brackets. Even though I got the helicoil in it never seemed right and always scared me. I think it would be better on the flywheel side. Smaller threads and more of them.

[davepl]

Well, reality forced my hand. I need to get it on a proper engine stand to replace the oil pan and various other tasks, none of which I can do with the flywheel on (doesn't clear my stand nor the alternate I had access to).

If I were smarter, I -never- would have torqued it down until I was finally ready to button it up. Since I had a wheel fall off once I'm gunshy about leaving things not torqued down...

So, I had to pull the flywheel again, negating my "hope it'll hold" wishes. So I'll start with a fresh set of ARP bolts and try it ONE last time when it's ready to get buttoned up, and I guess I'll find out at that point.

The great mystery is whether the bolt stretched or something went bad with the hole. My machinist friend had this to say, which convinced me:

"If something -does- go wrong, it's your toes, because that's where it'll come apart. So if it were me, I'd like to know for sure".

That was enough logic for me! Thanks for all of the input, it helped the panic...