Head Studs the real problem?

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dynodave said:
Have you ever tried an extended preloaded stud. I'll have to sketch one. The sample I have in mind is like on a lotus twincam head and has a extended 135 degree tip smaller than the diameter of the threads. It bottoms out in the drilling and preloads the threads engaging in the threaded part of the aluminum.

I know what you are referring to but I have not tried one.

Any preload applied to that type of stud would be subtracted from the total holding power of the threads so I don't think that would be the answer. Jim

PS, I suppose it might help reduce the cyclic loading and unloading of the thread due to heat expansion. That was what they were designed for.
 
if Norton parts and customs were as conistent as major modern water cool engines then one size fits all bottoming torque spreader might apply but other wise nope. Non ferric cryo treatment [so tempering term don' apply] like women nylons, guitar strings, copper electrical components etc is very contraversial except to those repeat customers with real life results. For those capable why not get some alloy similar to our heads and test threads before and after cryo treatment which takes a couple-3 days to do right. Alu is claimed to resist deminisonal changes, cracking and wear better - more than increase failure strength but that seems enough to make some hot head racers and NASA repeat customers.

Frederick (Materials) 3 Oct 14 11:00
First a word of disclosure. I own a cryogenic processing firm. I am co-chair of the ASM Cryogenic Committee. I have hosted ASM webinars in concert with a NASA engineer and a metallurgical engineer from Air Liquide. I think I can speak with authority on the subject.

The paper that tbuelna cites is named Effects of Cryogenic Treatment on the Residual Stress and Mechanical Properties of an Aerospace Aluminum Alloy, by PO Chen et al. The conclusions the researchers came to were:
1. Residual stress was reduced by up to 12 ksi in the HAZ of weld specimens and by up to 9ksi in the parent metal.
2. Significant improvements in SCC (Stress Corrosion Cracking) performance were seen for weld specimens.
3. Minor increases in tensile strength and hardness were noted for parent metal.
4. No significant changes were found in the tensile properties for weld specimens or in fatigue properties for parent metals.

Nowhere does this paper state that DCT is not very effective with most aluminum alloys. The research only covered one alloy and the results were listed for "this particular alloy."

Effect of Cryogenic Treatments on Mechanical Properties of 2A11 Aluminum Alloy, Wag et al, Advanced Materials Research Vols 146-147,(2011) pages 1646-1650 states: "The influences of different process parameters on mechanical properties of 2A11 aluminum alloy were compared, and the results showed that cryogenic treatment could improve mechanical properties of 2A11 aluminum alloy. The dimensional stability increases after cryogenic treatment once, and increases further after cryogenic treatment again."

More are available on Google. The point is that the DCT has been tested and found effective on aluminum alloys. The practical tests in use on engines is also significant. Our customers have reported 5 times the life on racing engines. One was a national champion go kart racer racing a Briggs & Stratton engine.

Too much more here if interested
http://www.eng-tips.com/viewthread.cfm?qid=372224
 
ludwig said:
Maybe a more realistic test would be to torque the stud to specs cold .
Then see if/how much tension it lost after a few heat cycles .
Retorque and repeat till it evt stabilises or pulls out ? .

Like a suction cup on a window : amazingly tight when first applied , but lying on the floor the next morning ..

Normal use on the engine does a pretty good job of that.

Just the factory hole and stud does hold the required torque just fine when everything is new.
The threads normally pull after the head looses a little of it's hardness.
When I was trying to make the video the first stock head with no inserts pulled the threads before I even got to 300 inch lbs.

That happens normally with high mileage and hard use. It can happen sooner if the bike is run with incorrect timing or mixture. Welding on the head -more than just fin repairs or welds on thin sections -softens them right away.

Fin repairs or careful welding around the outside of the exhaust port does not do much damage because the heavy sections of the head do not get hot enough for serious damage.
Welds to the heavy sections of the head or thread inserts welded around the bottom of threads do serious damage to the hardness. Jim
 
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