Quote:
Originally Posted by t walgamuth
The torque stretching bolts are made that way because it is a more reliable and accurate way to get the clamping force needed for good service. The book specifies dimensions to be checked for stretch. Have your machinist do that and you should be fine if they meet the spec.
Of course if you want new bolts you cannot go wrong that way.
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I fully understand the theory behind the TTY bolts. But I also know that in practice engines with TTY head bolts tend to lose head gaskets, some more than others. The OM617s seem to hold up really well while the Ford 3.8s lost head gaskets right and left (literally - they're a V engine).
My explanation is that TTY bolts experience cycling thru thermal excursions and those cycles eventually elongate the bolts slightly which relaxes the clamping force. I'll admit up front that I haven't done any research on this but this is where my Einstein-like thought experiments take me. Because the ARPs solved the gasket failures on my Ford 3.8 I can add some experimental data though admittedly with a sample size of 1.
All in all, I'd say either TTY or tough conventional bolts can work and if I was replacing the head bolts on Mutt I'd go with ARP studs because it's a race engine now and I can reuse the ARPs indefinitely. If Mercedes wants stupid money for a set of head bolts ARPs are at least worth considering.
Dan