How strong are retapped threads?

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I was putting the motor back in when I found the dealership had stripped 2 bolts from years ago when they did a rear main under warranty.

Got the tap I needed and fixed the threads but I'm unsure about torquing them. I can't find specs anywhere in my service manual or online (it's just a bracket that braces the engine and trans together) but if I go by size which is M10 - 1.5 I'm getting a max of 34 lb ft.

The holes stripped out of an aluminum transmission case.
 
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It depends on the % of remaining material.

Sometimes, it's best to epoxy in a stud (and use a nut on it) - if there is room for it.
 
Forgot to add it was only the first 2-3 threads that were messed up. The bolt itself is about 1 1/2" long and turns out the spec is 24 lb ft. I'll ease it in with a torque wrench and blue loctite and go from there.

The deeper you go into the hole the better the threads are.
 
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Originally Posted by Linctex
It depends on the % of remaining material.

Sometimes, it's best to epoxy in a stud (and use a nut on it) - if there is room for it.


Just curious, what epoxy would be used and would the stud hold up if it hardly had any thread to hold onto from the beginning?

__________________________________________________________________________

In this situation, if it's the first few threads out of 1.5", I think you'd be fine either way.
 
We are drill and helicoil fans here. Just used a GIANT one to rethread the crank bolt on a 13 6.0 Chevy. Then torqued to 100+ foot pounds plus like 45 degrees rotation! The helicoil folks have a lot of data for you if you are interested.
 
Originally Posted by SteveSRT8
We are drill and helicoil fans here. Just used a GIANT one to rethread the crank bolt on a 13 6.0 Chevy. Then torqued to 100+ foot pounds plus like 45 degrees rotation! The helicoil folks have a lot of data for you if you are interested.


I've used them too with great success.
 
I wouldn't trust buggered up threads in a critical area like that. It's hard to get to, once you've put it together, and if those threads fail, then you're going to break something. Engine - Transmission bolts are holding critical parts and face potentially high loads. So, if you break something, it's a big deal. This isn't like an accessory on the front of the engine, that's easy to get to, and can be checked for security later.

If it were mine, I would use a Time-sert. I've used helicoils, too, and keep a few in common sizes (like M4/6/8) on hand, but the Time-sert is more secure and higher strength.

The heli coil is simple: drill out to the specified size, run the provided tap, thread the helicoil in place, and when it's in, break off the tab. It really is a coil, threads on the inside, threads on the outside, but ti looks like a spring with a trapezoidal cross-section.

The Time-sert is more complex: drill out, then use the countersink tool, run the provided tap, and then use the installing tool the thread the insert in place. Here's where the Time-Sert is better - when you use the installing tool, which requires a bit of oil, it actually expands the deepest threads of the Time-sert, and locks it into place. The Time-sert is a complete insert, and the depth is set when the rim of the insert fits snugly into the recessed countersink. Time-serts are recommended for things like head bolt repair - where strength and durability are critical.

You may find a heli-coil easier to source locally.

Here it is on Amazon:

https://www.amazon.com/Helicoil-5546-10-Metric-Coarse-Thread/dp/B0002SRF80

Here is the Time-sert. Note the differences in the insert itself, and the extra tool for the countersink. It's also quite a bit more $$.

https://www.amazon.com/TIME-SERT-Me...mp;sr=1-2&keywords=time-sert+m10x1.5
 
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I also like timeserts and keyserts in addition to helicoils. Seems there is a rash of garbage helicoil kits especially the taps on the market these days, the taps just won't cut. In search of a decent kit I came across a supplier who uses US Made taps, inserts and drills, beautiful products in all sorts of sizes. I can't recommend them highly enough. The business is Thread Tool Supply out of Wisconsin. Link ---->>>> Click Here

To the OP, if it's only the first thread or two that is mangled I wouldn't be concerned. I'd me more concerned if the damage was 50% or more of the thread engagement.
 
Originally Posted by Hemispheres
Forgot to add it was only the first 2-3 threads that were messed up. The bolt itself is about 1 1/2" long and turns out the spec is 24 lb ft. I'll ease it in with a torque wrench and blue loctite and go from there.

The deeper you go into the hole the better the threads are.

At my previous job, our 'rule' was the tap depth needed to be 1-1/2 times the fastener diameter. In your case, 15mm would satisfy our design requirements. We designed and produced pumps used in the chemical industry. For your situation, it will be fine.
 
Originally Posted by SteveSRT8
We are drill and helicoil fans here. Just used a GIANT one to rethread the crank bolt on a 13 6.0 Chevy. Then torqued to 100+ foot pounds plus like 45 degrees rotation! The helicoil folks have a lot of data for you if you are interested.

What do you think about time serts?
 
Of all the blocks we have had to re-tap over the years while doing heads / head gaskets and various other places where bolts are required none of them came back. This includes just tapping where possible and using Heli-coils where they were required. The Heli-coils require a bit of skill to get them to stay put when taking the bolt out used to install the coil. If there is meat for just a re-tap that is the best.

Working the tap in/out slowly and cleaning well between removing it is the best. Even if it feels loose going in/out after tapping run it a couple of times and then super clean the threads before putting the bolt in and tighten down slowly to Torque Spec.
 
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Originally Posted by FlyNavyP3
I also like timeserts and keyserts in addition to helicoils. Seems there is a rash of garbage helicoil kits especially the taps on the market these days, the taps just won't cut. In search of a decent kit I came across a supplier who uses US Made taps, inserts and drills, beautiful products in all sorts of sizes. I can't recommend them highly enough. The business is Thread Tool Supply out of Wisconsin. Link ---->>>> Click Here

To the OP, if it's only the first thread or two that is mangled I wouldn't be concerned. I'd me more concerned if the damage was 50% or more of the thread engagement.


Thread Tool Supply looks like a great resource!

Even places like Fastenal don't have a good selection of thread inserts. Thread Tool supply has a great selection.
 
Originally Posted by Hemispheres
Forgot to add it was only the first 2-3 threads that were messed up. The bolt itself is about 1 1/2" long and turns out the spec is 24 lb ft. I'll ease it in with a torque wrench and blue loctite and go from there.

The deeper you go into the hole the better the threads are.


If you have 1.5x the bolt diameter of good thread in the hole regardless if the first 2 or 3 are damaged you may just need to adjust your bolt length a little longer (not too long that it bottoms out) to insure full thread engagement, on an M10 you need 15mm of good thread available. If not use a Time Sert, they are far better than a heli coil.
Back in the day when I did a lot of VW air motors VW had spark plug inserts at the parts counter for $1 ea.
 
If the first few threads are messed up those are the ones that carry most of the load, though as long as you have the diameter of the thread past that it should be ok. 24ft/lbs isnt very high (8.8 bolt torque dry 37.2ft/lb)

[Linked Image]
 
Originally Posted by dlundblad
Originally Posted by Linctex
It depends on the % of remaining material. Sometimes, it's best to epoxy in a stud (and use a nut on it) - if there is room for it.
Just curious, what epoxy would be used and would the stud hold up if it hardly had any thread to hold onto from the beginning?


3M 2216 A/B

I have had holes so stripped (or drilled out) where you could barely see where any threads had ever been in a the past (just a very thin spiral line).

If you have depth remaining at least 3X diameter, that usually works fine.
 
Originally Posted by Trav
If the first three are buggered they are no longer the first three. The first good thread after that would be the first thread.


"Like"
 
Originally Posted by thescreensavers
If the first few threads are messed up those are the ones that carry most of the load, though as long as you have the diameter of the thread past that it should be ok. 24ft/lbs isnt very high (8.8 bolt torque dry 37.2ft/lb)

[Linked Image]


This is interesting... Thanks
thumbsup2.gif
 
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