What torque settings should I use on the 6 bolts holding the crown wheel to diff cage? The first time I rebuilt a diff, I used the workshop setting of 60 lbs/ft and tore the heads off 2 of them. The bolts have no high-tensile markings and 60 was obviously too much. I THINK I used around 35-40 lbs/ft. Any suggestions?
Thanks - Bill

I just did some up the other day and checked the workshop manual before hand. It said 60 lb/ft and I didn't have any issues with the bolts breaking. I'd be checking the accuracy of your torque wrench and the condition of the bolts.

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Curly
'64 Cooper 'S' (Group Nb spec)
'67 Mini Marcos GT www.mm7056.wordpress.com

I think the book says 55 but I do the stock bolts to 50ft/lb, no more. They stretch (and yes, my torque wrench has been checked).

Once I bought some 7/16" UNF grade 8s to replace them, they were plated. 40ft/lb stripped the threads and plating off.
If buying grade 8s at a bolt shop, go for the black ones.

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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.

Thanks for your replies.
"Curly": I can't guarantee my torque wrench, but the broken bolts were original and the car was bought new. These bolts are not high tensile - no markings other than manufacturers' GKN and NAP indicating "standard" tensile and most references quote about 35-40 lb/ft. for them.
Drmini: I think I ended up using a lower torque setting without loss. I have been told that grade 5 & 8 fasteners should not be plated as the process causes 'oxygen embrittlement' to the surface layer.
Bill

Also give threads a good clean with brake cleaner and loctite the bolts in

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The formula for the length of a piece of string is simple: Twice as long as from one end to the centre!

Can you get the correct bolts from Minispares or such - ATA7043? They are black high tensile bolts and, in the Minis I've worked on they were all torqued up to 60 ft lbs.

Cheers

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Your mother is a hamster and your father smells of elderberries.

https://www.boltdepot.com/fastener-info ... chart.aspx

Have to be careful these days. I bought a linisher kit for the bench grinder once. Stripped All the 8.8 grade bolts (unc threads) seems Chinese manufacturers will chop and chance standards to catch people out.

8.8 metric bolts are roughly equivalent to grade 5 imperial.

I'd bet they are no longer genuine GKN bolts and are sourced from the far east, like everything else these days.
There again, when flying I worry about who supplied the bolts holding the Boeing's engines on..

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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.

Id agree Kev they probably cheese and will get ugly if they break/strip.
Try to find a set of Genuine ones or a brand that offers tracebality like Unbrako? (they mark the heads)
We put cut down cap screws in mates LSD in his race car.
They were longer bolts, cut down, with the correct length of smooth shank to bear on the diff centre.
That way the crownwheel isn't 'driving' by the threaded section.

cheers Ben.

PS. I was told you used to be able to get the Ti, 'lifed and disposed of' bolts from Aircraft until one day they started to get re-used into aircraft.
Now they are apparently destroyed and melted down for conrods or front subframes?

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The formula for the length of a piece of string is simple: Twice as long as from one end to the centre!

That must be the same Ti used in some Group N minis ...?

AB

No mate you got it all wrong.
The Ti in the Gp N minis is recycled from Chinese Ti bolts that replaced the genuine Boeing ones!

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The formula for the length of a piece of string is simple: Twice as long as from one end to the centre!

You've got all the contacts when it comes to Ti & Duralium hey Ben...?

The issue I wanted an answer to referred to the torque settings for original bolts used in standard diffs. The bolts that I sheared were originals being reused in a mini K diff I owned from new (and still run). All the diff bolts I have seen since, including the mkI S I am rebuilding, are all "standard"/original bolts i.e. marked GKN- NAP or just NAP. Thanks to "keithj" for his comments, but the standard bolts were NOT high tensile and would never take 60 lb/ft.. There are no markings to indicate they are either grade 5 or 8 so should not be tightened over about 35 lb/ft for a 3/8th inch fastener. 3/8th inch head studs are tightened to 42 lb/ft but they are high tensile.
Thanks all for your input.
Bill

Bill, they are not 3/8, they are 7/16" UNF. So will stand a bit more. I find they can stretch at 55+ but 50 works OK.

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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.

drmini, they are 3/8" UNF threads but the head takes a 5/8" A/F spanner; rather than 9/16" A/F which is the standard head size.