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MG MGA - ARP head studs

Since one of my "new" (purchased 15 years ago) head studs stretched and broke while being torqued (with a torque wrench, of course), I have obtained a set of the ARP racing head studs. Is there any good reason why I should not use the (also new) original style nuts, for a more original look? The head stud kit came with aerospace style 12 point nuts which I think would look a bit out of place.

As for the one that broke, I don't remember for certain where I bought it so I will not mention any names. They were purchased as a full set from one of two well known MG suppliers, and have been brought up to torque twice but the engine hasn't run. I'm just glad that it didn't stretch later in service, possibly causing my head to be warped, which would be annoying considering my investment in valve upgrades. Per Barney, the ARP studs are way overkill, but at this point that is exactly what I want. I've left the box open on my workbench in hopes that they will install themselves, which they should do for as much as they cost!
Del Rawlins

No such thing as overkill when it come to head studs! I put the same studs in my '67 BGT and I'm putting another set in my '65.
Steve Simmons

Del,
I would not be afraid of using the origional nuts with the new studs provided they have a good fit. The problem is with the studs not the nuts. They are just made of inferior material. Be sure to use the hardened washers under the nuts. Have a good day!

John
John Progess

I installed the new head studs yesterday using the original style nuts (new from Moss last fall), and the washers that came with the stud kit. They are thick like the original type washers and coated in black oxide matching the studs. To my surprise, the kit also included the 4 smaller diameter studs for the rocker assembly, but they were all the same length, instead of 2 different lengths. I had to substitute the original (also new this fall) length studs in the inner positions, otherwise my cast aluminum valve cover wouldn't fit. They would have worked with the original style stamped cover if I were going to use one.

I found the torquing procedure specified by ARP to be interesting. Normally, fasteners are torqued assuming dry threads; lube is strictly verboten since it will change the torque wrench setting for a given amount of tension applied to the fastener. In this case, the stud set included a packet of assembly lube which was applied to the threads, and the nuts were then torqued to ARP's spec, which was actually less than the factory MG spec. So clearly, the lube makes a huge difference in the amount of tension present in the studs, since these studs are MUCH stronger than the originals.
Del Rawlins

Del-
"lube is strictly verboten since it will change the torque wrench setting for a given amount of tension applied to the fastener. " - Not necessarily, since surface finish and coatings on new parts are frequently lubes in and of themselves. In some cases, these will eliminate any changes due to use of supplementary lube. In many cases, OE studs are supplied with black oxide and oiled, but if you wash them, the oil goes away - do you put it back? But it's a good general thing to keep in mind.

"So clearly, the lube makes a huge difference in the amount of tension present in the studs," True in this case, but it also involves the surface finish as above.

"...since these studs are MUCH stronger than the originals." The strength of studs is not the only issue. It is also a matter of the loads desired in the joint, and you may want that to be up, down, or the same as original. The strength of studs is immaterial so long as it is more than required, and the torque necessary is a matter of the load desired and the conditions at hand.

I have in the past sent out an article on fasteners, surface finish, lubes and torque. If you want a copy, ask.

And, I prefer OE studs, to the point that I am willing to pay (within reason!) for used but good OE studs marked "22" or center drilled as later MGA,B or A-series. So all you worry warts who can afford ARP, send me your junk! I have a desperate need of a single MGB short stud, could use a few sets for B-series, and wouldn't mind some spare A-series ones.
FRM
FR Millmore

It is true that oiled studs need less torque to achieve the desired tension. But oily studs and nuts are the norm when messing with engines. It would be absurd to clean and dry all the threads as we reassemble. So just allow for the difference. I have messed with a lot of old cars in my time and have never encountered a broken stud, except exhaust. I am a bit amazed by all the correspondence on the subject.
Art

Well, in my training as an A&P mechanic, I was taught that unless stated otherwise, that torque specifications assume clean, dry threads. Obviously, that is only going to be achieved in a perfect world, particularly where the inside of an engine is concerned. Still, unless lube is called for, the threads should be kept as clean as possible for consistency. The torque specification is really only an approximation of what we are really after, which is the tension applied to the fastener. We only use torque wrenches because it is a fairly reliable field approximation. In some critical aerospace applications, they actually measure the amount of tension in a stud by tightening until it has stretched a certain amount according to a micrometer or some other job specific gauge. In a case like that, oil on the threads would be irrelevant because you are taking a direct measurement of what you are really after.

What I hadn't realized is exactly how much difference lubing the threads would make in terms of the required torque wrench setting. I am pretty sure that the tension applied to the ARP studs is greater than that applied to the factory studs using the factory torque specs, yet they only called for 40 foot pounds when using the supplied moly thread lube. The same chart specified 50 foot pounds when using regular motor oil, although it recommended against that. I believe that is equal to the original factory setting, although my manual is out in the garage so I didn't double check. The "22" or "dot" studs can take a little more, as you mentioned.

For what its worth, I don't really have much of a problem with the original studs, other than liking to use new hardware in general, due to things like metal fatigue and other invisible flaws. My problem is mostly with reproduction parts that are supposedly equivalents of original, but turn out not to be. The ARP studs were simply a way of getting a known quantity, from a manufacturer with a good reputation, and the fact that the studs will be way overkill for my bone stock engine isn't a bad thing. I could probably go through my boxes of old parts and piece together a set of acceptable original studs, but sometimes I'd rather just spend the money and find something else to worry about instead.
Del Rawlins

This thread was discussed between 26/02/2007 and 01/03/2007

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