First gear jumps at high RPM

pierodn · Nov 11, 2019

Old story.
Bearings new.
To check the theet of first gears and the bushes of first gear mainshaft?.
What else?.
Ciao.
Piero

kommando · Nov 11, 2019

End float of Kickstarter shaft especially if a mainshaft roller bearing is fitted so the mainshaft is free to move.

maylar · Nov 11, 2019

First gear bushing.

pierodn · Nov 11, 2019

maylar said:
First gear bushing.

Both?

pierodn · Nov 11, 2019

B

kommando said:
End float of Kickstarter shaft especially if a mainshaft roller bearing is fitted so the mainshaft is free to move.

Ball bearing

kommando · Nov 11, 2019

pierodn said:
B
Ball bearing

Well unless that has a resin cage and not brass it needs to be changed to roller or ball with resin cage.

maylar · Nov 11, 2019

pierodn said:
Both?

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.

comnoz · Nov 11, 2019

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.

pierodn · Nov 11, 2019

comnoz said:
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

pierodn · Nov 11, 2019

comnoz said:
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

kommando · Nov 11, 2019

With more endfloat the dogs engage less so less force is needed to spread the gears apart and lose drive.

RoadScholar · Nov 11, 2019

Old Britts has a good description of G/B assembly and managing the layshaft end play:

http://www.oldbritts.com/gearbox_a.html

Best.

comnoz · Nov 11, 2019

pierodn said:
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.

Torontonian · Nov 11, 2019

Always replace the first gear bushing on any gearbox work. It's fragile .

concours · Nov 11, 2019

pierodn said:
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.

MichaelB · Nov 11, 2019

You can also eliminate the gasket and use sealer.

Torontonian · Nov 11, 2019

MichaelB said:
You can also eliminate the gasket and use sealer.

Yes this is easy fix.

Torontonian · Nov 11, 2019

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.

maylar · Nov 12, 2019

Torontonian said:
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.

baz · Nov 12, 2019

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

I changed a first gear bush a few days ago and yes I had to ream it

First gear jumps at high RPM

pierodn

kommando

maylar

pierodn

pierodn

kommando

maylar

comnoz

pierodn

pierodn

kommando

RoadScholar

comnoz

Torontonian

concours

MichaelB

"Sons of Arthritus"

Torontonian

Torontonian

maylar

baz

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