GB gearbox assembly

[Terry.C.]

Hi all,
I have a spare GB gearbox that I am trying to re-furbish. The gearbox was working ok but needed new gaskets and a general tidy up. I took it apart and took lots of photos and loads of notes. After all the tidying it was time to re-assemble. Now I have run into a srange problem. All the gears are in correctly and the gear selecters all run up and down ok selecting different gears on the main shaft output. This is where the problem starts. When I try to put on the centre section cover the gearbox siezes up and the lay shaft selector rod will not move but the mainshaft selector does. I have tried all sorts of things to correct this but with no success. Does anyone out there have any ideas please
Many thanks
T

[Roger Gwynn]

The best way to find out where the problem lies is to assemble the box with some part(s) left out and then add or remove some part(s) until the problem has gone, then returns, then goes. This way it is possible to narrow down the area of the problem.

[Mick D]

Hi

Are you fitting a gasket when you trial assemble the centre cover?

Regards Mick

[will_curry]

Are you using the selector drum to move the selector forks or just pulling them by hand?

If you're doing it by hand you may well not have a problem at all.

Assemble everything, dry, and try the gears using the pedal.

[Terry.C.]

Hi Guy,s
Thanks for the replies. Update on gearbox problem.
I totally sripped the box again and assembled the mainshaft side wth its gears and selector rod. Placed outer cover on and had no problems with the selector rod sliding in and out and gears turning. Repeated this on the layshaft side with the same result. Assembled both shafts together and the selector rods on both shafts worked ok sliding easily and I could find various gears with no jamming.
Then I put on the outer cover with the same result as before every thing jammed up. The layshaft selector rod moved ok but the mainshaft did not.
I could,nt get as far as the gasket or the selector drum as the main shaft wuold not slide and allow me to fit the pin in the selector shaft.
I am at this stage totally baffled as the box worked before I took it apart and on re-assembly I followed all my notes and photos very carefully.
Any other suggestions please because I am now becoming paranoid.
Regards
T

[Roger Gwynn]

Does it work with the k/start case screws slightly loose. If so does the case move when the shaft(s) are rotated indicating a misalignment or bent shaft(s). If I remember you havn't done anything other than strip and clean, is that correct because one of the wisest things I was told a long time a go was that when something goes wrong check the last job you did and it is usually the fault of the biggest nut on the bike - you!

[Terry.C.]

Hi Roger,
Yes you are correct. All I have done is strip and cleaned everything.
There are no screws in the case at all and I cannot rotate the shafts.
Before putting the cover on everything works fine. The selector rods move freely and when moving them into various positions I can find gears with the clutch gear and output shafts.
But as soon as I put on the cover everything siezes up apart from the layshaft selector rod. The clutch gear shaft and the main output shaft will not turn at all.
Nothing has been forced to bend anything.
I have tried moving the layshaft selector rod into variou positions but nothing happens to the mainshaft selector or the output and clutch gears with the cover on.
A big mystery
Regards
T

[Chris Sealy]

You could try posting a picture or two. The reason for the problem may be obvious to someone on here.
Cheers, Chris.

[dennis.t]

I found out by chance that the selector drum needs to be positioned with the slight recess or dimple in the side facing towards the layshaft or the outer cover will not seat properly. It also helps if the gears are in neutral and the gear lever is on to stop the selector backing off into the case on assembly. I did a dry run assembling my GB box yesterday.
I had the final gear on the mainshaft the wrong way round so tightening the inner cover screws locked up the box. When that gear is the correct way round both sets of top gears are level and flush with each other.
Dennis