TTY Head Bolts?
02-14-2008 | 04:06 PM
#1
TTY Head Bolts?
Do we use "Torque-To-Yield" style head bolts? I just ordered some head bolts since I'm taking the heads off this weekend (cause if they are tty bolts, I'm better off replacing them). My Cometic head gaskets come in on Monday. Just curious if the 2nd Gen CL's use these style head bolts...
02-15-2008 | 05:34 PM
#4
This is the info I found on TTY bolts:
"Many engines today use "torque-to-yield" (TTY) head bolts that stretch slightly when installed. This provides more even head loading and allows the bolts to hold torque better for improved head gasket sealing.
When the bolts are installed, they're first tightened to a specific torque - then tightened an additional amount that's measured in degrees of rotation. This final twist stretches the bolts to their yield point and creates the elastic clamping force that provides more even loading across the head and gasket.
Because TTY head bolts stretch slightly (only a few thousandths of an inch), some auto makers say they should not be reused when the cylinder head is removed. Reusing TTY bolts will cause them to stretch further, which increases the risk of breakage. A stretched bolt also will not hold the same torque load as before, which may cause a loss of clamping force resulting in head gasket leakage. The best insurance may be to replace all TTY bolts when rebuilding and reinstalling a cylinder head with new head bolts. "
After reading the manual, it doesn't seem to be TTY bolts either. But I'm just paranoid I stretched the bolts when lifting the head on nitrous which showed on the dyno (coolant was spraying out). So I'm not 100% sure whether I needed new bolts or not, but I rather pay and do this my way for my peace in mind. Did I make the right choice? Or did I just waste $150...?
"Many engines today use "torque-to-yield" (TTY) head bolts that stretch slightly when installed. This provides more even head loading and allows the bolts to hold torque better for improved head gasket sealing.
When the bolts are installed, they're first tightened to a specific torque - then tightened an additional amount that's measured in degrees of rotation. This final twist stretches the bolts to their yield point and creates the elastic clamping force that provides more even loading across the head and gasket.
Because TTY head bolts stretch slightly (only a few thousandths of an inch), some auto makers say they should not be reused when the cylinder head is removed. Reusing TTY bolts will cause them to stretch further, which increases the risk of breakage. A stretched bolt also will not hold the same torque load as before, which may cause a loss of clamping force resulting in head gasket leakage. The best insurance may be to replace all TTY bolts when rebuilding and reinstalling a cylinder head with new head bolts. "
After reading the manual, it doesn't seem to be TTY bolts either. But I'm just paranoid I stretched the bolts when lifting the head on nitrous which showed on the dyno (coolant was spraying out). So I'm not 100% sure whether I needed new bolts or not, but I rather pay and do this my way for my peace in mind. Did I make the right choice? Or did I just waste $150...?
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