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Diff cage is it ok to helicoil a stripped thread
https://www.ausmini.com/forums/viewtopic.php?f=2&t=95882		 Page 1 of 2
Author:  kiwiinwgtn [ Fri Aug 11, 2017 8:37 pm ]
Post subject:  Diff cage is it ok to helicoil a stripped thread
Hi guys
Thought I would do a simple six bolt job after tea and bolt my Diff back together with a new pin etc.

But no the last bolt stripped out as I was torqueing up the bolt.

Do you think its safe to helicoil it or is it bin fodder.

I just had the slots machined in it to take a plus thrust washers.

Not happy sam.

This gear box is fighting me to the end

Thanks kiwiinwgtn
Author:  drmini in aust [ Fri Aug 11, 2017 9:09 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Helicoil will be fine.
Author:  kiwiinwgtn [ Fri Aug 11, 2017 9:18 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Thanks Kev. Now to find one thats not $100.
Author:  minimans [ Sat Aug 12, 2017 6:36 am ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Just make sure you drill and tap the hole square to the flange! If you can set it up in a pillar drill to get the hole square it should be as strong as the original thread.
Author:  drmini in aust [ Sat Aug 12, 2017 8:28 am ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
If you get stuck, I have a bunch here I can send you one. With the grooves for the tab thrust washers.;)
Author:  kiwiinwgtn [ Sat Aug 12, 2017 5:32 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
drmini in aust wrote:
If you get stuck, I have a bunch here I can send you one. With the grooves for the tab thrust washers.;)



Thanks Kev

Got it helicoiled this morning and diff now fitted. One step closer.

Appreciate the offer. Thanks B
Author:  Bill B [ Sat Aug 12, 2017 7:24 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Can I ask what torque setting you were using when the thread stripped?
Author:  drmini in aust [ Sat Aug 12, 2017 9:43 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Bill B wrote:
Can I ask what torque setting you were using when the thread stripped?

Yes these do tend to strip at 55 ft lb and the 3/8 bolts can stretch too.
The diff cage is cast iron.
I only use 50 ft lb now.
Author:  Bill B [ Sat Aug 12, 2017 10:07 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
drmini in aust wrote:
Bill B wrote:
Can I ask what torque setting you were using when the thread stripped?

Yes these do tend to strip at 55 ft lb and the 3/8 bolts can stretch too.
The diff cage is cast iron.
I only use 50 ft lb now.


I know I am revisiting an old thread with my question. Sorry Drmini, I wasn't trying to sneak round the back on this (well....) but I still suspect the torque setting quoted in the books is way out and people ought to be advised.
Author:  drmini in aust [ Sat Aug 12, 2017 10:51 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
I agree. I have seen many of these with stripped holes.
Author:  kiwiinwgtn [ Sun Aug 13, 2017 11:06 am ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
HIi Bill
The setting was 60 ft lb when it stripped as per manual. Agree its way to high for a hardened bolt into cast iron. Torqued to 50 ft lb second tim2e round. I have checked a few of my manuals and they all so 60.

Sent from my GT-I9505 using Tapatalk
Author:  Bill B [ Sun Aug 13, 2017 7:54 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
kiwiinwgtn wrote:
HIi Bill
The setting was 60 ft lb when it stripped as per manual. Agree its way to high for a hardened bolt into cast iron. Torqued to 50 ft lb second tim2e round. I have checked a few of my manuals and they all so 60.

Sent from my GT-I9505 using Tapatalk


Thanks for that torque number. All the books quote that.
Many years ago on one of my first rebuilds, I did the same and stripped several bolts (luckily not the holes) and had to buy new bolts. The bolts don't have any tensile markings so are possibly only standard grade. Even high tensile would be on a limit at 60 lbs/ft - head bolts/studs are only 43 lbs/ft. For the diff cage I think I only go to about 45 now.
I just think people should be aware.
My understanding of 'helicoil' type thread repairs is that the repair is stronger than original plain threaded hole. The factory used them standard on the extra 5/16 inch bolt hole near the thermostat housing on Cooper S blocks.
Author:  kiwiinwgtn [ Sun Aug 13, 2017 8:31 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Hi Bill the bolts in my cooper s diff are definantly high tensile thats why the diff housing stripped. I will take a diff bolt to my friend who has some rockwell testing files and confirm next time i pop in. They are very hard. Hope this helps

Sent from my GT-I9505 using Tapatalk
Author:  Convertible Mini [ Tue Aug 15, 2017 10:06 am ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
Just put some silicone around the thread and don't do it up tight! I have seen it done on the 11th stud on a 1275 head. "Don't you dare"...
Author:  Bill B [ Tue Aug 15, 2017 4:53 pm ]
Post subject:  Re: Diff cage is it ok to helicoil a stripped thread
kiwiinwgtn wrote:
Hi Bill the bolts in my cooper s diff are definantly high tensile thats why the diff housing stripped. I will take a diff bolt to my friend who has some rockwell testing files and confirm next time i pop in. They are very hard. Hope this helps

Sent from my GT-I9505 using Tapatalk


I have wondered about using higher grade fasteners in rebuilds.
A higher tensile strength bolt/stud requires a higher torque force to stretch the fastener so that it can do its job effectively. But how much extra torque?
If it is torqued to the standard tension, it won't have stretched the fastener enough to clamp well. Too much torque and something else is overloaded.
I only have limited experience building standard road cars so I guess the rest comes with trial and error.
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