First gear jumps out to high RPM

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pierodn

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Hi.
Bike runs great but now the first gear, that engages well, jumps out at high rpm.
What i must check?
Thank you.
Piero
 
Excessive endfloat on the layshaft if a roller bearing is fitted, worn dogs and holes on the layshaft sliding gear and layshaft first gear.
 
Does it always jump out of gear?
If not it may not be engaging properly , maybe try replacing the hair pin spring
 
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.
 
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.
 
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.
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Hi.
Not roller bearing but FAG celeron ball bearing (those that M H suggests).
Piero
 
baz said:
Does it always jump out of gear?
If not it may not be engaging properly , maybe try replacing the hair pin spring
Click to expand...
Hi.
Airpin new and has the right clearance.
First gear jumps always to high rev (not 4/5000 of course)
Pieto
 
pierodn said:
Hi.
Not roller bearing but FAG celeron ball bearing (those that M H suggests).
Piero
Click to expand...

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.
 
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...........
 
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.
Click to expand...
Hi.
Dogs means bush or sprocket’s theets?
If bush, is new.
Piero
 
pierodn said:
Hi.
Dogs means bush or sprocket’s theets?
If bush, is new.
Piero
Click to expand...
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:
First gear jumps out to high RPM
 
A worn layshaft first gear bush can also contribute to it jumping out of gear.
 
Norton 1st and sliding gears, arrows pointing to dogs and holes.

First gear jumps out to high RPM


and the 2 gears in first gear engaged position.

First gear jumps out to high RPM
 
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
 
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
Click to expand...

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

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
 
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
 
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