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MG MGA - Don't use anti-seeze on manifold studs
|Don't do what I just did. I used anti sieze compound on the manifold studs on my MGA 1600 cylinder head. I thought that this would make them easier to remove sometime in the future. I tried to torque them to 25 foot pounds and sheared one stud and stripped another. I summize that the anti sieze compund acts like a lubricant and so you can't get the correct torque. |
I tested a sample 5/16" nut and bolt and it torqued to 40 foot pounds before it sheared. I added anti sieze compound to my test nut and blot and the bolt stripped before getting to 20 foot pounds.
Andy MGA Coupe restoration 90%.
|Interesting. Yet the torque specs for most bolts specify that they be lubed, right?|
|Andy, My "stud work" if you pardon the joke is scheduled for this weekend and I am deeply indebted to you. I check Barney's site which to sum it up say, "LOTS OF Those studs and manifolfs are gonna shear and theri aint nutin you ca do about it. Please let me knowhow the babble firnalytrnas Please please plese se e fi|
|"Yet the torque specs for most bolts specify that they be lubed, right?"|
That is correct, but they don't specify the type of lube to use and that is a problem. If you get a set of ARP high tensile strength bolts and nuts, they give two different torque specs, one using engine oil as a lube and the other using ARPs lube (that looks very similar to moly-lube anti seize). The torque spec using the ARP lube is roughly half the spec when using engine oil.
Torque is an inexact method of pretensioning fasteners to 75% - 80% of yield strength. The most accurate method is measure the bolt stretch. When a bolt is torqued a given amount, the spec is saying that for X amount of torque will cause the bolt will stretch to the proper amount for the bolt to be pretensioned to 75% - 80% of yield strength. This is fine as long as the spec also specifies if the torque is done with no lube, or with a specified lube. In the world of submarine work, all critical assemblies (those that are intended to keep water out of the people tank) always specifies exactly which lube is to be used when torquing a given bolt - use the wrong lube and the assembly is disassembled, everything cleaned and new fasteners are used with the specified lube and the whole assembly is redone. In the general automotive world (not racing) torque is normally done using engine oil unless some other lube is specified (like ARPs lube).
To show how the torque required to produce a given amount of stretch on a bolt, Bob Grunau of the Ontario MG T Register torqued a high tensile strength bolt, fresh out of the box to a given torque, then measured how much it had stretched, while another bolt was passed around for people to look at. He then too the bolt that had been passed around and subjected to the oil on poeple's skin and torqued it to exactly the same amount as the first "clean" bolt. The result was that the "lubricated" bolt had stretched more than the first one had. Not only did this demonstration show how show how lubrication affects the pretensioning of a bolt when using torque as a method of measuring, it also demonstrates why torque is not the best method of pretensioning fasteners. Cheers - Dave
|That's all very true Dave, but most car mechanics don't have any equipment to measure stud extension, so we are left with torque + lube type. Also, most fasteners just don't need to be stretched that close to yielding. exhaust studs are in this class.|
|Dave, great information!|
|"...but most car mechanics don't have any equipment to measure stud extension, so we are left with torque + lube type."|
Yes, I am aware of this (particularly the home mechanic) and in fact, in spite of all I know about the theory of fastener torquing, I too use a torque wrench and engine oil for lube. I have experienced first hand what can happen with a fastener that is over torqued and breaks when the vehicle is at speed (new engine required) and as a result will only use a properly calibrated torque wrench and use only engine oil for lubrication unless something else is specified by the manufacture or supplier of the fasteners. The information that I used above is really only important when using high tensile strength fasteners, such as rod big end bolts, Head studs and such. Manifold studs are not what I would refer to as high tensile strength fasteners, being a grade 5 at most. My real point is to use only engine oil unless otherwise specified by the supplier or manufacture, otherwise over torqued and broke fasteners will likely result. Cheers - Dave
I don't know if it's been mentioned before but "Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook" is a must have. If you work on your own car which we all do, you owe it to yourself to read this book. Personally, unless the bolt is so special that I can't find it new, I don't reuse old bolts especially in critical high stress situations like suspension and engine. For these applications new grade 8 and for body work etc. stainless steel. For my current restoration, I went through the parts manual and made a list of all the fasteners needed (checked it against the list on the Dutch MGA website), and ordered all new fasteners for the car. Organised them in divided container boxes. When it's time to put something together I just look in the parts manual for what's requiered and go to my supply. I started doing this years ago on an E-Type and would ecourage everyone to do it. Yes it'll cost several bundred dollars for the entire car but it's so worth it. here's a link for the book http://www.amazon.com/gp/product/0879384069
|Garland - Good reminder, replace all critical fasteners when doing a rebuild. A couple of hundred bucks worth a fasteners is cheap when compared to a replacement engine. Thank you for the Amazon link - that has been given to my wife as a birthday item for me. Cheers - Dave|
|Be careful, some modern replacement engine fasteners do not seem to be made to the same standard of quality as the originals. I ended up buying a set of ARP head studs to replace the replacements I bought, when one snapped during torquing (dry).|
You're correct. Not all fasteners are made the same. Even some which are stated to be of a certain quality, aren't. Carroll Smith talks about this in the book and how to avoid this problem.
|Andy and David,|
Interesting discussion and something to remember for the future, thanks for imparting your experiences and advice.
I hope you do not mind but I would like to pass your experiences on Andy and your knowledge on David to people on the Triple-M register as this discussion has just coincidentally come up and will be of benefit to them.
|Peter, please pass on the experience. Sometimes we learn more by other peoples mistake than anything else. Today I replaced all of the studs with new ones and all of the nuts with new brass nuts and didn't use any lubrication and torqued everything to 20 foot pounds with no problem.|
This thread was discussed between 03/02/2009 and 06/02/2009
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