TTY bolts and why??

[mrvette]

I don't understand the switch to TTY in modern engines, except to sell bolts...

if a bolt is a certain size, and that pitch/diameter into X material torqued to Y ft lbs is going to make it clamp with Z force on the Head gasket....

WTF is the diff how much the bolt stretches?? why the TTY business??

engines been running with normal stock or ARP bolts for decades and even with aluminum heads on iron blocks....AFAIK also aluminum blocks like that Olds 215 from decades ago....

and, as long as the TTY was not over torqued, why can't they be reused??

:skeptic::clobbered:

 

[Ralphy]

Why intentionally stretch the head bolts? Engineers discovered they can get much more even clamping on the head gasket if all the bolts are evenly loaded. Since variations in friction between bolts always causes some uneven loading, stretching the bolts guarantees all the bolts will exert the same clamping force regardless of the torque reading on the wrench. The result is improved cylinder sealing, longer head gasket durability and less cylinder bore distortion (for reduced blowby and more power).

TTY head bolts are typically used on engines with aluminum cylinder heads (where there is a lot of thermal expansion) and with multi-layer steel (MLS) head gaskets. MLS head gaskets are very stiff gaskets with much less compressibility than standard soft-faced composition head gaskets. On the other hand, MLS head gaskets are almost bullet-proof and produce much less bore distortion than other types of head gaskets because they require less clamping force. But to seal properly, MLS head gaskets require very smooth (almost polished), flat surfaces on the head and block. This, in turn, requires very precise and even clamping loads by the head bolts. That's why TTY head bolts are used in these engines.

http://www.enginebuildermag.com/Art...sealing_starts_with_proper_head_bolt_use.aspx