Just curious. General question about ALL helicoil applications. The one I am doing is on a thermostat housing on an aluminum intake (which doesn't matter THAT much), but, is the torque spec the same as factory spec on most everything, even though it has been helicoiled? I would never do integral suspension/steering or head threads, etc... with one....but? I don't know, the amount of cash spent on a heli-coil set that I paid for, you would think they would put it in the instructions as a sidenote. Thanks, ***o
It should be the same. My brother told me that when ever he needs things to be strong in aluminun he helicoils it because it will effectivly give you a larger thread, with deeper thread. Then the helicoils steps it down to the size thread you actually want, but in a stronger material. I hope that made sense. I'm tired.
Helicoils are stronger than the original threads, especially so in aluminum. Torque is all about the bolt and stretching it to - but not beyond - what's called it's modulus of elasticity. The proper torque gives the most clamping pressure. Excess torque, the bolt exceeds its modulus of elasticity and clamping pressure is less. Go to the ARP bolt's site and read their stuff on torque et al.
Helicoils are for the most part **** and I won't use them in a serious situation. I much prefer Time Serts http://www.timesert.com/ As a matter of fact building race engines (motorcycle road racing) I pre-emptively used them in a lot of palces I knew the aluminum sould take a beating...
man, i can't believe i'm disagreeing with C9! okay not disagreeing exactly, but in this application i don't think the given torque values have anything to do with the modulus of elasticity of the bolt, it has to do with not warping the **** outta the thermostat housing and making it leak. but yeah, the helicoil should handle the torque required.
Torque in many situations has nothing to do with bolt stretch or elasticity, more so clamping force to hold two pieces together. The force required or recommended will not change weather the bolt goes into raw metal or a helicoil.
From the ARP site: "Appropriate preloads are specified for each ARP bolt. These preloads can be attained in a connecting rod by applying proper torque using a torque wrench or by measuring the amount of stretch in the bolt using a stretch gauge (it is known that a bolt stretches in proportion to the tension in it). The torque method is sometimes inaccurate because of the uncertainty in the coefficient of friction at the interface between the bolt and the rod. This inaccuracy can be minimized by using the lubricant supplied by ARP. Other factors, equally as important as design, include material selection, verification testing, processing, and quality control. These aspects of bolt manufacturing are discussed elsewhere in this do***ent. The foregoing discussion concentrated on the design of bolts. The same considerations apply in the design of studs." http://www.arp-bolts.com/Tech/Tech.html
Modulus of Elasticity (Young's modulus) is a measurement of the STIFFNESS of a material. It is used to predict Stretch/Compression while loaded in the ELASTIC range. I respectfully disagree. Example being "torque to yield" bolts. The factory uses these because they can get MORE CLAMPING FORCE out of a similar sized fastener (or the same Clamping Force out of a comparitively smaller fastener - smaller = cheaper) the downside is that since the bolt is torqued to yield you have compromised it's "life" making it a throwaway item. You can also look up "pull test" results to see this illustrated - the force required to "break" a part does not immediately REDUCE as the fastener starts to fail but instead goes up first even when there is the start of a reduction in diameter - this happens inpart due to work hardening. "Proper torque" is based (in part) by the working load of the fastener. The working load is defined by the designer who initially chose the size bolt appropriate to the task at hand. Actually bolts are really "metal rubberbands" used to hold our parts together. The stretch has as much to do with design loads as it does in keeping everything tight (preloaded). When working loads exceed preload - the result is usually bad.
I think somebody is about to Torgue C9! All of these are valid points. The application of a given fastener can be just as important as the material it is used in and what it is made of. Back to the original question.... A helicoil in aluminum is not the weak link. Torque to spec. A helicoil in a connecting rod? ummm....
I read up on these. I can see why you chose them. Part that impressed me is the synchronized inner and outer threads which keeps the hole size down. Similar thread products I've seen require a fairly large hole which can be problematic in some cases. That said, I've had no probs with Helicoils in aluminum and have been bailed out by them a few times . . . as I suspect most of us have. ~~~~~~~~~~~~~~~~~~~~~~~ Fwiw - I use studs on thermostat housings. Standard nut and lock washer works well. Use a little NeverSeize as well.
I've heli-coiled threads for in blocks for head bolts, some needing 150 + ft lbs of torque never a problem. Plus you can get heli-coils with Military specifications (MIL), or National areospace standards (NAS).
I also dislike heli-coils. All too often I have had them follow the bolt on removal. I prefer to use Keenserts: http://alcoafastener.thomasnet.com/ImgSmall/35KEENSE.jpg
Yep, helped a friend by helicoiling the flathead in his truck that was cracked in the center bolt hole, between the center cylinders, crack ran between cooling p***ages. Fixed it right up, then my buddy sells it because he thought it was just a band aid, saw that little '53 running around town for years!
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