mk1-forum.net

Ok guys I need some info here.

I've always used the standard main bolts with great success.
On the recent build, I'm using a mix between Swiftune bolts and MED-bolts for the fould bolt main cap.

The Swiftune guys say that their bolts should be torqued to 55lbs/ft with a dab of oil-
Med-guys claim 75lbs/ft including the outer two on the 4bolt main cap.

I have really no reason to distrust these guys, but I just found them to be rather inconsistant. after all, it's ust a 7/16 bolt in both circumstances.

Any input?

Rich: What does AEG323 torque to?

I would say they are both correct if we assume the MED figures are for dry assembly.

Typically when designing a bolted joint the following numbers are used:
50% of the applied torque is 'used' in bolt head friction, 40% in bolt thread friction and only 10% in stretching (tightening) the bolt.

Normally for highly stressed/safety critical joints these figures are revised by the use of strain gauges to measure the losses in each part of the joint. For most other joints the manufacturer has tables of proven torque/load capability which are used.

The addition of oil to the threads will reduce the friction and this will go into the bolt stretching.
Tightening a bolt using lubrication (loctite, oil etc.) to the dry joint specification will apply more load to the bolt and in some cases stretch it beyond its elastic limit leading to bolt (joint) failure.

This site gives a useful starter:

http://www.boltscience.com/pages/quality.htm

What grade of bolts are they, what's the length of the thread engagement, wet or dry?

All very critical and all make a big difference.

Spider wrote:What grade of bolts are they, what's the length of the thread engagement, wet or dry?
All very critical and all make a big difference.

... ARP even quote different figures between
"Oil" and THEIR "Oil".

Assuming the "odd" bolts are pairs, ie two inners and two outers,
on the four-bolt centre-main, why not just do each pair up as per
the individual manufacturers instructions?

You would need to make a note of which bolts are which for
when you dismantle and re-build next time...

Ian