1986 CG125 Brazil Gearbox

[ColinH]

I have just rebuilt the engine and gearbox and done some test runs. Occasionally it is reluctant to go from 1st gear to 2nd it feels jammed.
If you keep trying maybe with a few more revs it changes nicely. 2nd to 1st is fine as are all the other gear changes and it finds neutral beautifully! Any help, as ever, gratefully received.
Cheers!

[Nobby the Bastard]

Stationary or whilst moving?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[ColinH]

Whilst moving

[Robby]

If the chain is too tight it could be the reason. If the chain tension is fine, you probably cocked something up while you had it apart.

[ColinH]

Yes, chain tension was too tight before but I set it correctly. I’ll recheck as when it was looser, it rattled against the chain cover, so I tweeted a bit tighter. I’ll loosen off again and try it.
Thanks for the clue..

[ColinH]

I adjusted the chain so it was not too tight and it still occasionally jams. If it jams, I just go back into first gear and then it changes up okay. It jams maybe one in ten times. Revs dont seem to make any difference.
When it jams and doesn’t go into second, it has effectively changed from first into neutral.
With bike on the centre stand and the back wheel off the ground, it changes through all the gears perfectly.
Any ideas as to where it may be having an issue?
I’m thinking maybe the selector mechanism......

[Robby]

It's selecting gears, mostly behaving, and always behaving when there's no load. You've also had it apart. I don't know if this includes taking the gears off of their shafts, or keeping the clusters complete and together.

My greatest fear when I have a gearbox apart is missing one of the shims or washers in the stack. That would lead to a slightly misaligned gear, which could cause this problem.

Also possible is a bent selector fork.

Gearboxes are evil things. I would be stripping it down very carefully and comparing everything to the workshop manual as I pull it apart. The exploded diagrams on CMSNL.com are also useful.

[virus]

if it changes gear perfectly fine under no load testing 'i.e' engine off, rotating the crank and hand changing, and also shifts fine engine running on Centre stand with the back wheel in the air then I'd be leaning towards Robbys suggestion of a missing/added/misplaced shim or bent selector tbh. Also if the chain is correctly tensioned and the clutch isnt dragging then that rules out everything else really on a CG.

Double check your clutch is in good working order and then think about splitting the cases again im afraid.
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[ColinH]

So near and yet so far......
Thanks for the suggestions.
I had the clusters stripped down to clean out debris from catastrophic top end failure! Bits everywhere.
Clutch is good I think, it releases early in the bar lever travel.
Back to the workshop I think......
Thanks again.