Just curious how KZ racers are determining when it’s time to rebuild the crank. I typically do a swing check on the rod (how far it will tilt to the side) and replace it once it is approaching 50% over new.
How do you decide?
12 - 14 hours from last rebuild.
Blanket rule i apply.
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Mine had 11 hours when the swing check measurement got to 50% over new. Maybe I can push it a little farther next time.
Depends on how hard you’re running it, particularly with downshifts. 10-12 hours is what I generally do, depending on timing relative to a big race. The engines I’ve seen recently with that time show radial play of about 1.45mm.
As with any engines parts, I wouldn’t try to stretch it too far, as it’s always easier to change parts than repair heavy damage from a failure.
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That’s exactly the value I was at, 1.45mm
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What is the process of measuring the swing?
Dial indicator on the side of the rod at the wrist pin journal (or piston just above the wrist pin bore). Slide the rod all the way to one side of the crank. Then you rock the rod on the big end pin, measuring how much the rod can “swing” on the pin. This directly correlates to the radial clearance of the big end.
It takes a little finesse but you can do it pretty easily once you get the feeling.
For other forum member’s benefit, This video shows it as you’ve written it.
What is the swing with a new rod, pin and bearing installed?
Is there a specification manual for the R2 or any of the TM engines?
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No manual. New ones I’ve seen lately are ~1.05-1.10mm
My new one was right at 1.0 mm