G: Gearbox (Twin) Twin Gear Change Adjustment

John Cone

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Advice needed please. On my Prince i can select 1st Gear ok. When you go for second with the pedal at full travel it doesn't quite go in all the way but if you let the pedal return then put gentle pressure on it you can feel the indent plunger locate. This is the same for 3rd and 4th but top will drop out if you put the power on to much, come out of gear every couple of miles or so. Which adjustment is required please. Not much good at following Richardson's instructions in the book.
 

vibrac

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I confess I have been playing with these things for to long to contemplate. But I still find Richardson's instructions hard to follow,I honestly could not tell you after adjustment if that lever will work in all gears or not. Sometimes it does and I have even been able to smack smack smack as per the book up and down, and some times nothing is right, and worst of all is a perceived perfect action on the bench and then one gear is not always trustworthy on the road. Its not that I dont understand the mechanism and I know if a part is worn, Its just I find the difference between a good gearchange and a poor one can be an almost imperceptible adjustment. Having also worked on the Albion box I think I can see where the ideas came from.
If anyone has an understandable foolproof method with or without Gismos now is you chance to tell us.
Alternatively I rather fancy trying the modifications developed by Thomo (He of the Four valve Vincent).
 

Ducdude

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Hi John, My 52 twin did this same thing a few years ago. If you go to page 40 in the handbook you will see the sequence for adjusting gear-change mechanism.

This is all done with 2nd gear selected and the shifter cover removed. First you are adjusting G61/1 So that the shifter ratchet is centered in the shifter pawl ( there is a good picture ) to show what they are talking about .

Once that is done you are adjusting the lever stop-G49's position by turning eccentric adjuster G57 just so again in 2nd gear, up gives you a solid interface with 1st and down gives you 3rd..

What they do not tell you is this is an iterative process that can yield 1st, 2nd working but 3 and 4th popping out as well as the inverse. I found it helpful to just leave the pipes and cover off and have a short spin down the drive way to see if I can pick up all 4 gears. (warning parts can ejected if the cover is not on) If not re adjust the eccentric again.

In my case it only took small adjustments with new parts to get the bike shifting just so. The original bits G49 and G57 had to much ware to properly adjust for any reasonable duration.

Once the new parts were on I tried adjustments with G57 full on in one direction then the other losing 1st and 2nd but having 3rd and 4th then losing 3rd and 4th but 1st and 2nd were good. Then with it set just about in the middle with a small bias to the direction that picked up 1st and 2nd better (I had been losing 1st at this exercise's start) I locked it in and all has been well since.

If this does not fix your the shifting then I would give very close attention to the cam plate spindle under the generator and make sure it does not spin or pivot or is lose in any way while the gear selector is moved. All ways good to check this every so often. I can just get my finger on it with the miller installed) Mine is safety wired and lock tightened to make sure it stays in place. (I would weld it in place if I thought it would help) I have been told that Phil Irving did NOT feel that the cam plate spindle support was his best work as it is a weakness in an otherwise sturdy design.

Wishing you the best of luck!

Eric
 

greg brillus

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Remove the inspection cap off the kick start cover, using a 6" extension with a 1/4 drive ratchet and either an 11 mm or 7/16" socket reach in and back off the 1/4 BSF screw clamping the G 61 plate and rotate it slightly clockwise then clamp the bolt up tight and try that. You will only need to move it about a mm or so to make a difference. The adjustment on the G 49 adjusts the movement of the G 66 shift lever assembly overall, that is the travel is fixed but it will move it in one direction for the extent of its travel. I might ask as to what has caused this to happen, or has it been like it for some time........Cheers.......... Greg.
 

vibrac

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Way back in 2016 I published a picture of this little tool.
camplate_spindle_tool.jpg
It is secured in the top of the camplate pivot screw by an Allen screw and the pivot is tightened by the hex.
That emphasises how long I have been sorting this problem I have to say one great step forward was the 5-speed box unfortunately in this reiteration I am using a standard box.
Riding a short distance with the cover off is not something I have resorted to yet but it helps to show what a pain in the bum the mechanism is.
 
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stu spalding

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When adjusting the gear selectors it helps if the shaft G40 is held back in the opposite direction to the gear lever travel with a spanner on the nut G44, that way, any further movement of the shaft necessary for full engagement can be felt and the relevant adjustments made. Cheers, Stu.
 

erik

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When I tried to adjust the gearbox I saw that the pawl carrier cetralizer was restricting the way of movement .If you look on this piece of metal you see two ears facing towards you. I bent the right one to make the space between the two ears wider.This made things better but not good. in the end I cut off the right ear completely so that the stop is now the kickstart quadrant G83AS. Now all the gears work as they should.Erik
 

greg brillus

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Some of the earlier engines seem to need more travel to select gears, the use of the later type G 61 is too limiting and they just wont pick up the gears properly. But most poor shifting especially on high mileage machines is just wear in the ratchet parts.... the G 43 and the G 59 AS replacement of these usually restores the shifting nicely.
 

vibrac

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On the Egli racer (which is as near to a good gearchange as I ever got) it was not just the 5 speed. but because I had no kick start I opened out the ears of G61 (later pattern)flat and brazed two 1/4 bsf nuts on edge and added some adjusting screws this allows independent fixed stops for the mechanism. Another good idea from 40 years on.
Eriks removal of the ear on G61 suggests that by putting the ears on G61 in an upgrade by the factory they were struggling to get the system working properly as well, I am obviously not alone....
 
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