Re: Header bolts
One thing that could be happening is this; If the fastener is not designed for the use, it could stretch while hot and stay where it is. This is in fact annealing it (softening it). Another issue to keep in mind is trying to use an old, used fastener. Bolts that have been stretched from prior use. This is why in many cases head bolts/studs are not re-usable. Once they have been stretched, they have lost, or used up their "memory".
The tensile strength varies depending on the steel. 8740, 4140, 4340 alloys, 9CRMO Chrome Molly, 625 & 718 Inconel Nickel-Based Alloys and 304, 316, 17-4PH & 15-5PH Stainless's are all chosen based on their use and requirements. "Tensile" is pull strength, or stretch and "memory" (will it return (or not) to it's original state after heat has dissipated). The more torque applied to the fastener, the more it will "stretch" to a lesser torque when heat is applied. It is at this time that the fastener can move radially and loosen. This is why rotor bolts get "Wired", so they don't rotate loose.
Bolts that are designed for heat cycling contain the specs that should withstand the application. But here's the thing; If the wrong fastener material is used for the application, even if you have it locked so it will not rotate loose, it could still stretch and stay, basically loosening even though it did not rotate loose.
IMO, three things need to be followed;
Make sure the correct material fastener is chosen for the application
Do not over-tighten
Lock it in place so it cannot rotate loose (I would not use Locktite).
And........On my car, I will look to ARP first. I do like the Stage 8 system as well. I was unaware of the Taylor Vibe-Lock so it's good to get positive feedback on them.
1969 SS 396 X66 - RS Conversion - TKO600 - 3.73 Posi - Paint Code 71-LeMans Blue
Last edited by Brettallen59; Apr 14th, 19 at 05:42 AM.