Torque

gman

gman

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Graham
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I don't think this is something which can be calculated but I thought I'd throw it out there just in case! This is for a 14 litre V8 Scania tractor unit.

If you've got a brand new bolt going into a brand new cylinder head and the bolt is to be torqued to 220 Nm then the bolt turned clockwise further for exactly 90 degrees, what would be the final torque required?

This would be so that the remaining brand new bolts going into brand new heads could simply be tightened to the calculated torque without having to go through the whole process each time.
 
I thought that the point of stretch bolts is that they are set to a torque, & the further turn pulls them into a predetermined 'elastic' state. So, it's not the torque that's important, but the expansion available. This means that you have to follow the stetching pattern.
 
Comfortably Numb said:
the further turn pulls them into a predetermined 'elastic' state.
Click to expand...
Ah yes the technical term is apparently, as my brother would say, ( a diesel fitter) its the difference between TT & FT ...

That is Tight, tight, & f*****g tight.
 
Speaking as a girlie ....

.....I thought you had to tighten the bolts in a specific sequence to avoid warping the head? :thinking:
 
it would depend on the pitch of the thread, a fine threaded bolt wouldnt stretch as much as a coarse threaded bolt
 
Thanks for the replies. I did read up that the point of the 220 Nm then 90 degrees is to allow for elements which may cause additional resistance such as rust etc so the torque part is for seating the bolt and the extra turn is to ensure a tight fit or something.

Re. The sequence, yes he did it in the correct way. Very experienced mechanic.
 
reheat module said:
Tighten it.
Shear it.
Back off 1/2 a turn.
Click to expand...

I hate that feeling where you think you've managed to loosen the bolt but a little voice is telling you that this now feels a little too easy to turn and *snap*
 
Tigger.ufo said:
Speaking as a girlie ....

.....I thought you had to tighten the bolts in a specific sequence to avoid warping the head? :thinking:
Click to expand...
Mainly to ensure it's evenly torqued down to help prevent gasket failure, which could lead to the head warping due to the excess heat failures can cause. Actually warping the head by doing up a bolt would be a considerable achievement!

I always clean the threads both in the block and on the bolts before reassembly, and ensure I can finger tighten the bolts all he way down without hitting any resistance due to gunge / rust that might affect the torque wrench reading. In an alloy engine it's far too easy to strip the thread in the block, which means a load more work to helicoil it.
 
IIRC a big element of the torque comes from friction so the extra quarter-turn is probably guaranteeing a known amount of bolt elongation after the slack+friction has been taken up. If that’s the case you are probably right, it can’t be reliably calculated
 
Speaking of torque (off topic but this is the right forum for that:) ) I know a young man who bought himself an impact driver from Snap On and decided to test it's capability on one of our tractor wheel nuts, by seeing how tight it could get it, and it worked extremely well...
He says that the tractor wheel doesn't need 12 nuts:)
 
Use a torque wrench with a dial gauge instead of a ratchet, where ever the needle points after 90 degs past the point at which 220Nm is reached will be the total load.
 
Comfortably Numb said:
I thought that the point of stretch bolts is that they are set to a torque, & the further turn pulls them into a predetermined 'elastic' state. So, it's not the torque that's important, but the expansion available. This means that you have to follow the stetching pattern.
Click to expand...
This^
 
Thanks all. Engine rebuilt and running nicely.
 
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