Jake, this isn't a Randy trashing. I never saw the instructions, and they'd been pitched by the time I picked up my engine. For me, it was a toss up as to who to trust. A guy I don't know who couldn't even provide me with the grade of material he uses,
Dr. D - same thing goes for other Aerospace quality hardware. Usually they use a military grade, or just give direct quote and description of the specification (IE: tensile strength, "suitable for application x", etc.) Would you want the Society of Automotive engineers, who specialize in cost-effective mass-production of automobiles, having a part in specifying what parts to put on an aeroplane? On a multi-million $ F1 racing vehicle consisting of very expensive, lightweight but highly stressed components? It's not the appropriate specification to ask for, IMO. If aerospace grading (NAS, MIL-spec, etc) is good enough for the space shuttle and Formula 1, etc, it's good enough for me! Just my opinon anyway. SAE grading are not reliable and cannot be relied on anyway, I believe they are manufacturing guidelines, not guaranteed tensile strengths. Aerospace grades are always more reliable than SAE grades from what I hear. I am not an authority on the subject, but if you wanted to learn more there are a couple books on the subject oriented at serious racecar engineering... and there is primarily a focus on fasteners, fittings, high strength to weight ratio materials, etc. "Engineer to Win" by caroll Smith (
http://www.amazon.com/exec/obidos/tg/detail/-/0879381868/102-1357718-6528149?v=glance) comes to mind. I don't have this book myself but I would say that is authoritative, and from what I hear, IIRC, Caroll Smith is quite the basher of using SAE-graded fasteners on racecars.
or my engine builder who has been involved in almost every facet of combustion engine technology from design to build, rebuild and modify in his time. If he'd simply said "I don't know" then I'd have gone with what Randy said. My engine builder insisted (and confirmed with ARP 'cuz Raceware had already closed for the day) that a 190,000 psi stud of that diameter is at least a grade 9, more likely a grade 12. (Randy said guaranteed minimum 190,000, but on average closer to 220,000) In that case, the torque spec should be as mentioned earlier.
As I said before, thread pitch must be considered. You can't assume they're the same, because the raceware head studs might have finer thread pitch than ARP, therefore require less torque to make the same clamp load. The thread pitch of the upper part of the raceware studs, which the nuts fasten on to, is certainly finer than the threads at the bottom which screw into the block (equivalent to the stock head bolts.)
I didn't measure the thread pitch on these studs, but they looked like the same fine thread pitch of the gas engine ARP studs I've used in the past.
You said you used the same 50# torque spec on your studs, perhaps Randy's info is wrong (he actually said his studs were grade 8 because grades higher than that don't exist!)
I haven't heard of any SAE grading high than 8 being used either actually... usually like I said before, you go to NAS (Navy-Aerospace) specification bolt, or other specification more suitable for a highly-stressed component than SAE grading when talking aerospace quality hardware.
and we could actually be getting so much more clamping power out of these sets. Really, the factory fastener is tightened more than 50#. Why would a stronger fastener use less? It simply doesn't make sense.
I would say primarily it's due to the finer thread pitch of the raceware studs/nuts vs the course threads of the stock head bolts.
That's why I chose to go with the rebuilder's recommendation. I've installed the head twice at those torque specs with no issues. Thoughts?
Different metal has different yield characteristics. Some yield abruptly, IE: shatter when they exceed their yield strength. This will be quite obvious when it happens... Other metals (including I think the high strength chro-moly steel used in these kind of bolts) will deform gradually and plastically, so yielding may not be obvious. An other example of this is the stock strength head bolts - they yield gradually (can we tell one that has already stretched vs a new one? I don't know - would be interesting to see how significantly the lengths actually differ, of used vs new factory stretch head bolts.) There could be some stretching along the length of the threaded part for example, caused by a 40% (considerable) overtorque. Assuming those specs Randy gives are close to the yield point, as I would expect they are, and as they should be. But I don't know. 50ft-lbs as recommended by Raceware, with non-synthetic oil, and with a beam-style torque wrench not a less-accurate "clicker", has worked well for me and everyone else I know of who has run them in VW Diesels.
Raceware makes it pretty obvious in their instructions/literature they send out with their vw diesel head studs by the way, not to use factory torque specifications but to use theirs for their bolts. Along with the added requirements of not using synthetic oil to lubricate the threads (but rather non-synthetic) and also not using a clicker torque wrench but an accurately calibrated beam-style. They are really quite fussy about proper torquing! It's too bad you didn't get that information when you got your fasteners and/or engine. Sorry to hear about this and good luck... you might ask Randy what he would advise, besides buying new ones.
Topic: RACEWARE HEAD STUDS (Read 12783 times)
