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PostPosted: Fri Aug 11, 2017 8:37 pm 
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1098cc
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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


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PostPosted: Fri Aug 11, 2017 9:09 pm 
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Helicoil will be fine.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Fri Aug 11, 2017 9:18 pm 
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Thanks Kev. Now to find one thats not $100.


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PostPosted: Sat Aug 12, 2017 6:36 am 
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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.


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PostPosted: Sat Aug 12, 2017 8:28 am 
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If you get stuck, I have a bunch here I can send you one. With the grooves for the tab thrust washers.;)

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Sat Aug 12, 2017 5:32 pm 
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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


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PostPosted: Sat Aug 12, 2017 7:24 pm 
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Can I ask what torque setting you were using when the thread stripped?


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PostPosted: Sat Aug 12, 2017 9:43 pm 
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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.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Sat Aug 12, 2017 10:07 pm 
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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.


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PostPosted: Sat Aug 12, 2017 10:51 pm 
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I agree. I have seen many of these with stripped holes.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Sun Aug 13, 2017 11:06 am 
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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


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PostPosted: Sun Aug 13, 2017 7:54 pm 
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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.


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PostPosted: Sun Aug 13, 2017 8:31 pm 
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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


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PostPosted: Tue Aug 15, 2017 10:06 am 
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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"...

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PostPosted: Tue Aug 15, 2017 4:53 pm 
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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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