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Crankshaft Centering

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One of my older tuner friend "Tune by Fune", Tommy Griffin & Ron Turner/John McCorquodale helped me a lot w/ older 2-smoke crankshafts. I assume this would hold true for 4-strokes, as it is a check I verify before building top end.

If I remember it involves literally making sure crank outer clearance in cases is equal. He use to bump only bottom end cases w/ crank/trans assy. on wood to shift crankcase centered upon assembling bottom end. Then he woud verify it turns smooth and not binding. 

Other than actually truing on a crankshaft jig for equal amount of radial/lateral movement, that is my experience w/ the terms from Techs and shops I worked at that actually built and trued crankshafts.

Edited by AMSinator
add. info

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Will not center itself and you'll ruin crank if tight to one side.  Crank is tight in bearings no way it will center itself

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I've split my YZ125 cases twice and each time the crank has needed centering upon re-assembly.

(it's also a verification step in the service manual during assembly)

 

Once it wouldn't spin at all, the other time it spun free but the crank was not exactly centered in the cases.

(feeler gauges to measure between case and counterweights)

 

Un-easy to tap on the end of the crank with a plastic mallet, I use a crank puller and case splitter in conjunction to carefully nudge to crank over.

Edited by mlatour

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Thanks guys. I am speaking with the mech tomorrow and telling him he either needs to go back in and do it properly or refund me all my money. First crank repl ever in over forty years, very frustrating. I am not wanting to ruin something at this point and have ZERO confidence in even attempting to start the bike.

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13 minutes ago, Piney Woods said:

Thanks guys. I am speaking with the mech tomorrow and telling him he either needs to go back in and do it properly or refund me all my money. First crank repl ever in over forty years, very frustrating. I am not wanting to ruin something at this point and have ZERO confidence in even attempting to start the bike.

Ya definitely dont start it it tight to one side. Doesn't have to be perfectly centered i just ?? them . He should know this

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Only engines ive ever done that crank will slide in bearings is ktm 65s and just didn't seem right but they run lol

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Well maybe I'm ok! She started on the fourth kick! Carb was totally dry and it took a couple kicks to prime it I guess. Everything sounds great and no unusual noises like the possible "screeching" the mech mentioned. That had me concerned greatly. Just doing a couple starts in the shop and then will give it a real test this weekend. Thanks for all the help and info folks. 👍:applause:👍

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