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Yamahajoe292

08 head bolts

8 posts in this topic

Ok reading up on the head bolts and it says to torque them in degree, I work on cars for a living and when I'm told that's how head bolts are torqued they have to be replaced, is this the same with these bikes?

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No. YZF head bolts are reusable.

alright and via the manual it's 22ftlbs, back them off and reset to 14ftlbs, then 90 degrees and then a additional 90 degrees, correct?

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Some cars use head bolts torqued like that as well, and not all are one time use (my Subaru had similar instructions and they didn't say to replace them). 

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Some cars use head bolts torqued like that as well, and not all are one time use (my Subaru had similar instructions and they didn't say to replace them).

Well we replace them all because in cars they are torque to yield bolts and they stretch, ran into it a lot (even on subaru's) where the bolts will break after assembly while the engine is running.

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Not all angle torqued bolts, even in the automotive world, are torque to yield.  The primary purpose of angle torquing is to better assure that the desired clamping force has been achieved, and is uniform across the assembly.  Using an angle beginning from a low torque value eliminates errors caused by both the friction in the threads and the torsional resilience of long bolt shanks.  The bolts do not necessarily permanently stretch when this methodology is used.

 

One of the things a lot of fuel drag car engine builders used to do, and some still may, is to replace head bolts with studs, and then torque them based on the stretch readings of a dial indicator placed to read the top of the stud as torque is applied. 

 

Torque to yield is another matter, and is independent of the tightening method used.  Torque to yield involves actually stretching the bolt beyond its elastic limit, which is usually done by angle torquing, but does not have to be. 

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Well we replace them all because in cars they are torque to yield bolts and they stretch, ran into it a lot (even on subaru's) where the bolts will break after assembly while the engine is running.

I'm sure it happens sometimes, but the factory manual for mine (99 Outback, EJ25D) didn't say to replace head bolts (but did say to replace head gaskets, among other things). Forums (which are always 100% correct) said no need to on the engine I had.

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