Hot Rods Crank threads help

Have a 79 sbc 350 where one of the threads on crank flange is stripped, motor is in car so before I bolt flex plate on will 5 out of 6 bolts with thread locker hold flex plate enough or do I heli-coil / time sert and if I do that will it throw off balance of crank? Thanks

 

Find someone who has a drill jig and install a helicoil or timesert. Don't take a chance on this. The jig will hold the bit where it needs to be. The inserts are a standard repair.

 

Have you tried a thread chaser through the stripped boss, may clean up well enough to loc***e

 

I did thread chase it, only have a few threads at rear of crank flange towards motor ,

 

Helliciol should work best

 

The amount of metal removed to rethread and replace it with an insert is about the same, so the "balance" should equal out the same, too.

 

Ok thanks ! Yeah I’ve just never been in this spot before so I didn’t want to just send it with an insert then when the flex plate gets spinning at high rpm have another problem haha

 

Don't use a Heli-coil - they generally can't take the required torque / clamp load a flywheel bolt requires. I say this as an employee of a shop that grinds dozens of cranks each day. We do not allow the use of Heli-Coils, only Time-serts or other similar heavy wall thread inserts. In rare cases, we will TIG weld the hole shut and re-drill and tap.

 

Thank you ! I’ve only used time serts on other things I’ve never trust a coil because I’ve had them break, would you suggest a regular time sert or the big sert? Thanks again

 

I thought the purpose of the big sert was to repair a threaded hole that had already been drilled out and repaired with a heli-coil.

 

Even if there was a slight imbalance I don't think you'd notice it so much with it so close to the crank centerline. If it was closer to the O.D. of the flexplate it might be more of an issue.

 

Any way to get a longer bolt and nut on the back?

 

Another way to do it is to just tap it to a larger size bolt. You can use a Std Thread size or even a Metric thats slightly larger. There won't be a balance issue because you are removing metal when you drill and tap and just replacing that metal with the bolts metal. The bolt head will be slightly heavier but its close to the center of the crank and doesn't have much effect. If all your bolts are a little knarly you can replace all of them. They sell some nice Grade 8 bolts with flanges and serrations on E Bay.

I know a lot of people don't consider this as a kosher solution, but it may be an option considering what a timesert installation kit costs. Drilling oversize and tapping to the next larger size is a time honored solution...........

 

Tighten the bolt as tight as you can get it and put a couple tack welds on it.

 

Here's one that hasn't been suggested, from the house of sketchy, and I can't afford that fancy stuff, clean the surface area in and around the hole, follow up with waxing or wd 40 a coating to a bolt to act as a release agent, pick up some fine metallic chop saw metal tailings with a magnet and mix them in to some premixed JB weld. Then lather the inner hole and screw in the bolt so it goes into the good threads then stop, don't tighten, finger it in and just let it set up. Once it does, finger nail scratch resistant firm hard, gently work the bolt free and carefully back it out then let it completely harden for 24 hours. After that badda bing budda boom. Bob's your uncle. Not knowing how much good thread you had left in the hole, don't go all impact gorilla retightening and you should be good. Think of it like adding gl*** strands to polyester body filler. No, I never used this approach on a crank, but I have used it to great success.

I'm surprised no one suggested you get a nut, round it on a lather or a drill press and grinder, drill the hole to fit and weld it in.

 

Just use a quality insert. The "homegrown" workarounds won't give you confidence for good reason.

 

That will depend on what you have room for. If you have enough room, use the big sert, but sometimes there isn't enough material between the flange edge and the hole to drill it out that far.