Bent mainshafts

[Phil]

Hi all, out of three gearboxes I have had My mitts on every one of the mainshafts are bent, what causes this and is there any one out there that straightens them ?

[chaterlea25]

HI Phil,
I have found several bent mainshafts on A's and other brit bikes as well
What bends them?? That probsbly depends where they are bent
If at  the clutch end I blame heavy hands on long spanners tightrning the clutch nut, or hammering the spanner/ nut
If in the middle it could be from a gear breaking up and forcing the shafts apart, I found that on a 5 speed triumph

Its an easy enough problem to spot on unknown bikes, remove the primary case plug and operate the kickstart with the clutch pulled in
If bent you can see the primary chain tension changing

I have straightened several different geabox shafts over the years, but prefer to replace them if possible
A lot depends on where the damage is

HTH
John

[Phil]

Thanks John, all three seem to be bent at the clutch end starting at the last bush . The one off my bike is 0.9mm at said bush going to 1.1mm at the clutch end threads.

I have just ordered a new one from Autocycle engineering who seem to be the only people in the whole wide world to still make them, anyone had experience of these shaft ?

[chaterlea25]

HI Phil,
Yes, I have bought new shafts from Autocycle Eng, They are absolutely fine
You will probably find that the sleeve gear bushes and maybe the sprocket bearing need replacing too
You can imagine the bend accelerating wear
You may find that the clutch adaptor winds up in a slightly different position on the new shaft????
So check primary chain sprockets alignment

HTH
John

[Phil]

Thanks again John, good to hear the shafts are usable and yes the sleeve gear bush has elongated, the main bearing seems ok but I have decided to change it any way.
Good call on alignment I would probably have over looked it.