5 replies to this topic

[Trog]

Quick one...

Re-building my diff with a Minispares cross pin diff. Torqued the crown wheel bolts up to 48 lb/ft, following the torque shown in my Metro Haynes manual. Then looked in my Mini Haynes Manual which shows 60lb/ft...

Which is it?

[MRA]

It's to do with the method used to create the bolts and the materials used........ ie a rolled thread needs less torque to gain the same clamping loads.

Are you using new bolts ? if so are they the same grade as original bolts ?

It is highly unlikely that the Mini Spares cross pin diff wil have rolled formed threads I am 99% sure that they will be a cut thread so use the higher torque figure

If on the other hand you are using rolled bolts then use the lower setting, if you over stress a thread it cna fail at a later date, due to crack probagation.

If you are using new bolts of a lower spec use the lower setting

Use stud lock instead of lock tabs and it will be fine....

[Ethel]

Won't a higher tensile bolt stretch less requiring less torque to generate the same clamping force?

I realise it's more complex as the torque is in a large part generated by the bolt stretching.

It will still be the same threads in the cage so the risk is overloading them.

[Trog]

When all else fails read the instructions! Minspares instructions tell you the torque, it's 60 lb/ft... Their threads would, as MRA said, be machined requiring the higher torque. Thanks for response, it made me think and go back and look...

Who looks the fool now

[MRA]

Won't a higher tensile bolt stretch less requiring less torque to generate the same clamping force?

I realise it's more complex as the torque is in a large part generated by the bolt stretching.

It will still be the same threads in the cage so the risk is overloading them.

Just because a bolt doesn't stretch doen't mean it imparts a lower clamping load.... two elastic bands, one small and one large, wrap the small one around two objects and stretch as much as you can..... now do the same with the bigger (tougher) band but don't stretch it quite as far or as many turns, tight but not too tight, you will see that with a little imagination the two could have a similar clamping force but have different "torque" levels.

Also a higher tensile bolt tends to rolled after heat treatment which gives the surface a much harder smoother finish than a cheaper lower quality bolt

Torque figures are calculated from several different bits of information..... for instance a burnished thread (as you would get with rolling) creates a micro thickness of work hardened material and also a highly polished finish which gives it a lower frictional coefficient.... in other words more slippery you would get a similar effect if you oiled the fastenings first, try undoing a loose bolt by hand, it can be a little difficult if its rusty (rough surface) spray some oil in and hey presto it's now loose.... well sometimes anyway, but hopefully this explains what I was trying to say before


Because the threads in the Mini Spares diff are cut they have a higher friction, you as a spanner operator have to turn against this frictional force hence why 60ft lbs of torque is required to get the same clamping force.......

[MRA]

When all else fails read the instructions! Minspares instructions tell you the torque, it's 60 lb/ft... Their threads would, as MRA said, be machined requiring the higher torque. Thanks for response, it made me think and go back and look...

Who looks the fool now

You shouldn't feel like that..... you have found the information and no damage has been done... so all is well