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MG MGB Technical - head stud snapped

ok I got new studs and a new torque wrench, lubed the studs and nuts with anti-sieze, placed the head on the new head gasket, torqued the nuts to 25 foot pounds. So far so good. Then after setting the torque wrench to 50 foot pounds attempted to torque the first nut, it just kept turning and the head stud snapped. So I tried the second nut. It also snapped. Are these studs supposed to be torqued dry? Or with 30 weight oil? I still have the original studs and a complete set of washers and nuts.

George
G.E. Bulwinkle

"I got new studs and a new torque wrench"

First I would try to borrow another torque wench and compare the two wrenches. Use Wheel studs for testing the wrenches, wheel studs are less likely to break.
Normally I believe a lubricated fastener should use less torque than a dry fastener, off hand I don't know how much difference. ARP studs have instructions for that.

Clifton
Clifton Gordon

George. The currently supplied Rover brand cylinder head studs have had a problem with snapping for a number of years now. I buy mine from Chris Betson who has some better than factory quality studs available through his Octarine Services website.

Cylinder head studs were intended to be torqued to the required setting with the studs lightly oiled. ARP supplies a special lubricant which can be used with their various sets. If you torque them using oil, you torque to one specification and, when using the supplied lubricant, to a lower specification.

I, too, have had the Rover brand studs, supplied by Moss Motors, break when using an accurate torque wrench and know of several other people who have had similar problems. Not often, but enough that I now use either Chris's studs or the ARP studs when doing a rebuild.

Les
Les Bengtson

George, it could be that anti-seize was the problem and not the studs. You have to reduce torque significantly when using anti-seize. Better just to use oil on head studs.

Tom
Tom Custer

Thanks for your help. I installed the original studs, oiled the threads and torqued 10 of them to 45 foot pounds. The eleventh one couldn't make it to 45 foot pounds and eventually snapped. I ordered a set of ARP studs from Brit-tek. I'm sure I was wrong to use anti-seize.

George
G.E. Bulwinkle

How much should the torque be reduced if you have anti-seize on the studs? I used that when I put on a new cylinder head last year, and then tightened carefully to only 40 lb ft. No trouble so far.

Tore
Tore

Tore, the reference I have does not specifically list the torque reduction for anti-seize but I've seen values as high as 50% in non-technical publications. Not sure of the strength of a typical mgb head stud but the reference I have indicates, for example, that a 3/8 coarse-thread grade-8 bolt lubricated with SAE 20 oil should have torque reduced by 38%. Dry torque for this size is listed at 47 ft-lbs for coarse thread and 51 ft-lbs for fine thread. This of course brings up the question of whether the manufacturer's recommended torque values include the use of a lubricant such as oil. I assumed it was standard practice to put a few drops of oil on the studs and that the torque values in the manual accounted for this but I really don't know for sure!

Tom
Tom Custer

All factory torque figures are for oiled threads.

The use of anti seize or moly grease will cause the bolt or stud to stretch beyond its elastic limit before the torque required to turn the nut or bolt reaches the factory figure.

The only way to establish the correct torque using other lubricants is to accurately measure the bolt or stud stretch as ARP recommend.

Original factory studs were replaced early in production by stronger studs marked with a dimple or "22" - these will take 55 ft lb of torque, oiled. There is a greater margin of safety to cope with inaccurate torque wrenches.

I was dissatisfied with current offerings which, while the steel used was adequate, the machining of the threads left sharp edges especially at the bottom of the stud that resulted in stress fractures at the top of the thread sometimes long before the standard torque had been applied.

It is for this reason that I have had studs made by hot rolling the thread rather than machining it - this "forging" strengthens the steel in the vulnerable areas and doesn't leave sharp edges. Additionally the steel used is 170,000 lb steel which compares favourably with ARP's 190,000 lb steel - I don't know what the original spec steel was but I believe that other current studs are made of 90,000 lb steel.

However the hot rolling process leaves the studs with a black scale surface, which isn't as pretty as the ARP finish!
Chris at Octarine Services

This thread was discussed between 25/11/2008 and 01/12/2008

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