Twin gearbox problems

Simon Dinsdale

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
Jock,

While you are setting up the end float clearance, check that G6 engages deep enough with G11 when 4th gear is engaged as Bill Thomas mentions. I check this by placing a piece of bluetack on the appropriate part of G11 (the large double gear) where 4th gear G6 engages. Put the box together and select 4th gear. Then dismantle and check the two gears are engaging deep enough by looking at the impression in the bluetack. If 4th gear doen't engage deep enough, it can jump out and round off the teeth. This can then over time put side load onto the selector arm that engages G11 and eventually wear the selector. Then a new selector, G11 and G6 are required (don't ask how I found out!!!).

When I put my gearbox together correctly checking everything, I put two shims in totaling 41 thou thick and this still gave just over 5 thou clearance on the mainshaft. The total thickness of the shim is not important. Good engagement of 4th gear is, along with 5 to 10 thou mainshaft end clearance as Trev states.

Cheers,
Simon.
 
D

Don Morris

Active Forum User
VOC Member
Totally agree with vin998, I did the same with my post-war twin to fully engage top gear. Having seen other bikes where the selector was very badly worn and dogs worn rounded.

To enable the input shaft to go further in, thus ensuring full engagement in top, I ground off part of the chamfer that is on the output shaft (by hand is OK). The end float, without any washers, is measured. This can be done either with a D.T.I. or feeler gauges between the end of the input shaft and a fixed point. The appropriate shim/s are then fitted just giving slight clearance. As clevtrev says as the engine heats up the clearance increases.


You should ensure that G11 is free when in neutral just in case you overdo the shims, it's an easy job but you must keep thinking about what you are doing. I am remember reading, in MPH, about someone, in neutral, who engaged a gear when he leant the bike over to pick something up and the bike shot round in a circle. This was probably due to wear on the selector forks or loose cam plate pivot or general wear and tear. In case this causes any concern this is not a common fault and has never been reported again.
 
J

Jock English

Forum User
Non-VOC Member
stumpy lord said:
hi,
dont forget that the shim E76 comes in varius thickneses, o.oo5 and 0.o10. It could be that on your engine a 0.031 shim is to thick.
perhaps worth trying with a thiner shim.
regards stumpy lord.
Click to expand...

Took your advice and got a selection from Kettering, and assembled with .010" in the end.
Got it back together at 12.05am last night but have not had a chance to road test it yet.
Family committments mean it will be Sunday at least now befor I try it.
Will let you know how it goes.
Jock
 
J

Jock English

Forum User
Non-VOC Member
Thanks for your message, unfortunatley I got it after I had got the whole plot back together!
I found that I had to go down to a .010" shim to allow me to engage neutral, any thicker and the whole cluth shaft/final drive shaft were turning together. I tried to pull the clutch shaft towards the nearside while testing this to replicate the effect of tightening the clutch nut.
I will try it and watch out for jumping out of gear.
Previously it would very occasionaly jump out of 3rd, but 4th was always OK.

You may be able to help with a related issue, when tightening the ESA nut I found that I had to temporarily rebuild the clutch and chock the back wheel in 4th gear to stop the ESA rotating. Is there an easier way. please?
Thanks again, regards
Jock
 
Paul Ennis

Paul Ennis

Well Known and Active Forum User
VOC Member
Jock,
I use a sprag between the engine sprocket teeth and the clutch sprocket teeth when tightening my ESA nut.
A quick visit to my workshop to measure it ....... 3/8" x 1/4" x 4.7" long mild steel.
Cheers,
Paul.
 
O

ogrilp400

Well Known and Active Forum User
Non-VOC Member
G'day Paul and Jock,
Make that a piece of 1" x 1/4" x 4.7" and along each end, staggered off the centre line, bronze a piece of 1/4" round bar. This fits snugly into the root of the teeth instead bearing on the tip of the tooth.

Phelps.
 
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