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Why one-time use bolts on clutch? Fri Aug 16, 2013 5:02 pm
jjefferies
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I've been searching for the logic behind the one time use only policy on the clutch bolts. Best answer for one time use only any bolt that I've found is from a (Gasp) Harley forum
But are my K75 clutch bolts "torque to yield" as described above or is there some other mysterious BMW rationale? Curious minds and all. I'm off to buy more bolts.. The correct term for so-called stretch bolts is "torque-to-yield" bolts. The rotor bolts on my bike have six radial lines indicating that the bolt is a grade 8. A grade 8 bolt that has been properly torqued (never over-torqued) may be used over and over provided it hasn't encountered any fatigue damage, or otherwise obvious visual damage.
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Any bolt that has a direct torque specification of so many inch pounds or foot pounds is not a torque-to-yield bolt. Torque-to-yield bolts will always have a torque specification of a relatively low torque value followed by some number of degrees of additional rotation. Once a torque-to-yield bolt has been tightened past its elastic deformation state (usually at or near the initial torque value) it should not be reused. This is because the bolt has been permanently deformed once it is torqued beyond its elastic limits.
A standard grade 8 bolt is never torqued beyond its elastic limits in normal use.