Quote:
Originally Posted by mgarblik
I think I can answer this one. As you know Bill Miller comes from the top fuel world. His primary focus is nitro engines and other "real" race engines as he calls them. He specifies motor oil only on his connecting rod fasteners. No special sauce from anyone. Rod stretch tools and even torque to yield is impractical when the rods are going on and off hot in an oily environment in a 75 minute time interval with multiple people handling the parts. His bolts and the threaded area in the aluminum rods are way over-designed for a given application. His "torque value" puts the fastener in a very wide elastic range of the bolt. So even if the torque value ends up +- say 15-20%, it is still in the elastic range and the clamp load is sufficient to keep the joint closed.
As far as Molnar rods having some kind of interference fit between bolt and threaded hole? It's possible Molnar has some sort of special machining process that produces a slightly higher engagement % than the standard 75%-up to 85% on a precision fastener set. Or he has ARP spec. a slightly larger fastener blank to produce the same higher %. Actual interference would create friction which is the enemy of the joint and a wild card when tightening. Next time i talk to him at PRI, I will ask. When I run the bolts into his rods, I don't feel any resistance until they seat.
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Interference fit was not the right word for their threads. Its been awhile since my talk with Tom.
What they are, asymmetrical threads. Or threads like a big C clamp would have. Flat on the top. If you put a Molnar 7/16" rod bolt in a Scat/Eagle rod there would be interference. They won't fit.
Standard "V" shaped threads have more load on the bottom/base of the thread and less on the tops.
The uneven loading is where problems/cranks start.
The Molnar thread results in a even load across the threads when tight.