Quote:
Originally Posted by MSS
Kaiser and Lovel,
This is a genuine question. Are you saying that these are not in fact stretch-to-yield (more correctly stretch-to-beyond-yield-point) bolts used on the K-series?
I have seen some previous threads on this topic and note that they were not conclusive.
Personally, I would have thought that to use bolts which stretch into the plastic region would render the whole assembly unstable following temperate cycling that occurs in an engine and therefore the application must be within the elastic region. But this thinking may be somewhat overly simple.
I wonder if the bolts operate close to the yield point but within the elastic region during normal tightening and temperature cycling but may go into the plastic region due to overheating and then become incapable of being reused due to permanent (i.e. plastic) stretch.
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Stretch to yield is the wrong term for these bolts, it should be torque to yield.
TTY bolts are designed and used correctly by taking the bolt from its elastic state to its plastic state by taking it past the yield point between the two states, to attain the required clamping force, expansion and contraction due to temperature changes of all the components within the clamping area, metals with different thermal characteristics including the bolts, is taken into account at the design stage to ensure that when the assembly is subject to max and minimum working temperatures, the clamping force is within spec.
Another more descriptive term for these bolts is TTT, Torque Turn to Tighten, torque initially, then turn ( x degres )to tighten.
Even after being fastened to the correct setting taking it into the plastic region, the bolt will still have elastic properties.
If the temp rise goes over the design max, which has a safety factor built in, a hose bursts and goes unnoticed, then look out for HG problems.