I've seen, on various forums, that it's not possible to get the same clamping force in the two head bolt lengths, 66mm v 96mm, and that's one reason studs are better.
I've been curious about this claim and why Land Rover would use them if that was the case, so decided to write to a place that might know the answer, BoltScience.
This is part of the reply I received from an engineering specialist at BoltScience asking about the clamping force of a shorter vs longer bolt.
Tightening into the plastic zone, the angle of rotation is not
usually that critical (past a certain point) and so what may have been done
here is that the angle of rotation is set to ensure that the longer bolt
will be yielded, the shorter bolt will essentially sustain a bit more
plastic deformation. The preload in both cases will be similar. Essentially
once past yield, the torque-preload verses angle of rotation of the fastener
is almost horizontal.
I then replied specifying that it was a Land Rover V8 and asking about studs vs single use bolts.
Companies are increasingly going for screws instead of a stud and nut. In
this application, since the fastener is going into the plastic zone there
are a limited number of re-uses of the fastener, probably about three hence
a stud may not be such a good idea. The plus point about studs is that they
don't wear out the internal thread.
PS I've done training for Jaguar/Landrover engineers on the analysis of
bolted joints which includes tightening methods - they also use Bolt
Science's BOLTCALC program for joint analysis. I've done training courses
around the world and in my opinion, in general, they are the most
knowledgeable engineers that I've come across.
His PS was certainly interesting.
I've been curious about this claim and why Land Rover would use them if that was the case, so decided to write to a place that might know the answer, BoltScience.
This is part of the reply I received from an engineering specialist at BoltScience asking about the clamping force of a shorter vs longer bolt.
Tightening into the plastic zone, the angle of rotation is not
usually that critical (past a certain point) and so what may have been done
here is that the angle of rotation is set to ensure that the longer bolt
will be yielded, the shorter bolt will essentially sustain a bit more
plastic deformation. The preload in both cases will be similar. Essentially
once past yield, the torque-preload verses angle of rotation of the fastener
is almost horizontal.
I then replied specifying that it was a Land Rover V8 and asking about studs vs single use bolts.
Companies are increasingly going for screws instead of a stud and nut. In
this application, since the fastener is going into the plastic zone there
are a limited number of re-uses of the fastener, probably about three hence
a stud may not be such a good idea. The plus point about studs is that they
don't wear out the internal thread.
PS I've done training for Jaguar/Landrover engineers on the analysis of
bolted joints which includes tightening methods - they also use Bolt
Science's BOLTCALC program for joint analysis. I've done training courses
around the world and in my opinion, in general, they are the most
knowledgeable engineers that I've come across.
His PS was certainly interesting.