First gear jumps at high RPM

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Old story.
Bearings new.
To check the theet of first gears and the bushes of first gear mainshaft?.
What else?.
Ciao.
Piero
 
End float of Kickstarter shaft especially if a mainshaft roller bearing is fitted so the mainshaft is free to move.
 

The bushing is press fitted into the gear. Replacing it requires an arbor press, and the bushing will need to be reamed to size. It's a machinist's job. You can also buy the gear with bushing already reamed to size but they are expensive.
 
Kicker shaft end play. It doesn't matter if it's a ball or a roller layshaft bearing. Too much end play will cause it to jump out of first when you rev it.
 
Kicker shaft end play. It doesn't matter if it's a ball or a roller layshaft bearing. Too much end play will cause it to jump out of first when you rev it.

Hi.
To reduce the kicker shaft end play i can use the isolastic shim?
Thank you.
Piero
 
Kicker shaft end play. It doesn't matter if it's a ball or a roller layshaft bearing. Too much end play will cause it to jump out of first when you rev it.
Please,
could you explain me why the more end play does the first jump?.
Thank you.
Piero
 
With more endfloat the dogs engage less so less force is needed to spread the gears apart and lose drive.
 
Please,
could you explain me why the more end play does the first jump?.
Thank you.
Piero

The kicker shaft is what locates first gear on the layshaft.

Shimming the kicker shaft moves first gear over so it has more engagement with it's mating gear's cogs. The mating gear is located by the shift fork so it does not move with the layshaft.

The actual end float of the layshaft has nothing to do with gear engagement -but shimming the kicker to move 1st gear over does reduce the amount of endplay in the layshaft.

 
Hi.
To reduce the kicker shaft end play i can use the isolastic shim?
Thank you.
Piero
Yes, but you must increase the inside diameter of the shim, to clear the radius on the kicker shaft.
First gear jumps at high RPM
 
You can also eliminate the gasket and use sealer.
 
My new first gear from Andover came with a new first gear bushing pressed into place and was a perfect sliding fit on the shaft.
 
My new first gear from Andover came with a new first gear bushing pressed into place and was a perfect sliding fit on the shaft.

Yes, but if you buy the bushing separately and press it in it'll be undersized and need reaming.
 
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