First gear jumps out to high RPM

pierodn · Jun 7, 2018

Hi.
Bike runs great but now the first gear, that engages well, jumps out at high rpm.
What i must check?
Thank you.
Piero

kommando · Jun 7, 2018

Excessive endfloat on the layshaft if a roller bearing is fitted, worn dogs and holes on the layshaft sliding gear and layshaft first gear.

baz · Jun 7, 2018

Does it always jump out of gear?
If not it may not be engaging properly , maybe try replacing the hair pin spring

oldmikew · Jun 7, 2018

When you come to a halt ,at say traffic lights leave bike in bottom gear , and pull in clutch .it should then be ok when you move off. Go into neutral and then bottom it will jump out.

dave M · Jun 7, 2018

I had this happen to while I sold the buyer came back after a couple of weeks complaining that it was jumping out of gear at 6,000 rpm in first, I had never thrashed it this hard in first so hadn’t noticed but sure enough it did jump out at high revs, I took it apart and found some wear on the gear dogs and the slots so replaced both gears and it was fine thereafter.

pierodn · Jun 7, 2018

kommando said:
Excessive endfloat on the layshaft if a roller bearing is fitted, worn dogs and holes on the layshaft sliding gear and layshaft first gear.

Hi.
Not roller bearing but FAG celeron ball bearing (those that M H suggests).
Piero

pierodn · Jun 7, 2018

baz said:
Does it always jump out of gear?
If not it may not be engaging properly , maybe try replacing the hair pin spring

Hi.
Airpin new and has the right clearance.
First gear jumps always to high rev (not 4/5000 of course)
Pieto

kommando · Jun 7, 2018

pierodn said:
Hi.
Not roller bearing but FAG celeron ball bearing (those that M H suggests).
Piero

So you are left with worn dogs on sliding gear and the holes in gear the dogs mate with. The hairpin spring is worth checking fix but as its only first that is less likely.

marinatlas · Jun 7, 2018

I think than Jim comstock had said that even with ball bearing the end float must be checked on the layshaft.........could help !! otherwise as the other told you : worn dogs...........

pierodn · Jun 7, 2018

kommando said:
So you are left with worn dogs on sliding gear and the holes in gear the dogs mate with. The hairpin spring is worth checking fix but as its only first that is less likely.

Hi.
Dogs means bush or sprocket’s theets?
If bush, is new.
Piero

Bob Z. · Jun 7, 2018

pierodn said:
Hi.
Dogs means bush or sprocket’s theets?
If bush, is new.
Piero

I hope this helps to understand.
Quick search for gear dogs brought this up, not Norton gears of course but shows the difference between teeth and dogs:

baz · Jun 7, 2018

pierodn said:
Hi.
Dogs means bush or sprocket’s theets?
If bush, is new.
Piero

No "dogs " are the pegs on the side of the gear wheel

L.A.B. · Jun 7, 2018

A worn layshaft first gear bush can also contribute to it jumping out of gear.

kommando · Jun 7, 2018

Norton 1st and sliding gears, arrows pointing to dogs and holes.

and the 2 gears in first gear engaged position.

comnoz · Jun 7, 2018

Shim your layshaft.
Roller or ball bearing makes little difference.
Excessive layshaft endplay will cause it to jump out of low gear when you rev it hard. Jim

pierodn · Jun 7, 2018

comnoz said:
Shim your layshaft.
Roller or ball bearing makes little difference.
Excessive layshaft endplay will cause it to jump out of low gear when you rev it hard. Jim

Hi.
Shim in the rear of kick start shaft?
Thin Isolastik sheem are good?
Thanks
Piero

comnoz · Jun 7, 2018

pierodn said:
Hi.
Shim in the rear of kick start shaft?
Thin Isolastik sheem are good?
Thanks
Piero

Yes, that works good. You may need to open up the center of the shim a little to clear the radius on the kicker shaft

ashman · Jun 7, 2018

Easy to fix, don't rev it out so high in first, no need to rev it so high in first anyway, let the other gears do the reving out lol.
I replaced my layshaft bearing with a quick change bearing in 79 when the old bearing blew up and its still in there after 39 years and with over 150k on it, no shims, no jumping out and smooth gear change, only other work since replace kick start pawl a few times and the kick gear where the pawl sits in.

Ashley

First gear jumps out to high RPM

pierodn

kommando

baz

oldmikew

dave M

pierodn

pierodn

kommando

marinatlas

pierodn

Bob Z.

baz

L.A.B.

Moderator

kommando

comnoz

pierodn

comnoz

ashman

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