GB7 Mainshaft bent.

[allan.walker]

I am going to rebuild a GB7 gearbox which has a bent mainshaft. The drive end oscillates around the axis very noticeably - probably 2mm total deflection. I've searched on here and it seems that this is quite common, but I was wondering if this is fixable at home.

I have access to a press, v-blocks etc and have dial gauges, but does the shaft need to be heated locally at the main point(s) of deflection, or can it be straightened cold?

Can anyone offer any advice, please?

[Mick D]

Hi

I'd locate the distortion using vee blocks and a dial gauge, support it in vee blocks accordingly and gently press out the bend cold.

Regards Mick

[allan.walker]

Thanks, Mick.
I was unsure about the need for heat. Looking online, there are videos of people using oxy-acetylene on the bent areas, but the shafts in question are much larger than a GB7 mainshaft.
According to what I've read on this forum, a bent mainshaft is often caused by tightening the mainshaft nut by wedging something between the primary chain and clutch sprocket. If that's the case, cold straightening sounds feasible.

[nevhunter]

No harm in taking it to the tempering figure. Dark straw. Bend a bit past straight and then come back a bit. Of Course a new one is best. Check for cracks.. Nev

[allan.walker]

Good point about the cracks, Nev. Maybe a new one would be safer.

[nevhunter]

IF the gearbox locks up, no point in Pulling the clutch in. Nev

[allan.walker]

IF the gearbox locks up, no point in Pulling the clutch in. Nev