AMC Gearbox

[Bird dog]

AMC Gearbox resumed.
I love it when a plan comes together and swirls around the body in the form of those welcome endorphins signalling all is well until the guano hits the twiddly bits again, as it sometimes does.
You may have guessed by now that I have "solved" the non-changing gear change problem as outlined at the beginning of this topic, having stripped the front cover off four times!
In essence. I set the end cover up bolted to a steel plate with the plate clamped in the vice inside facing forward with the mechanism visible.
To stop the gear ratchet (040111) flopping about whilst operating the gear lever, I then cut and drilled two holes in a piece of ply wood 3/4" x 3/4", long enough to straddle two bolt holes in the cover that would line up with the gear ratchet pivot (5/8" O/D).
Using two Allen cap heads long enough to clamp the ply down on the pivot, I tightened them up sufficiently to hold the ratchet in position once the gear lever has moved to its allowed travel within the gearchange stop plate (gsp) (040052).

With this set up one can observe what is actually happening between all of the relevant components as the gear lever is operated.
What was observed was the pawl was not moving the ratchet far enough to line up for the next change in the sequence consistently.
After quite a time jiggling the lever about and confirming in my mind what needed to be done to alleviate the inconsistency, I came to the conclusion that to gain a wee bit more of travel on the pawl the gsp needed .25mm grinding from the internal surface at the top only.
This small amount of metal removal was more than enough to compensate for lack of travel by the pawl.
An aside here. I found that once or twice after refitting the gsp the pawl arm mechanism would foul the internal surface of the gsp by a fraction and prevent it returning to its reset position.
This can be remedied in two ways.
One is to push the gsp towards the Kickstarter bush whilst tightening it up, or second, use the Dremel with a drum sander to remove a small amount of the offending metal.
Once I was satisfied that all was working as it should whilst still clamped in the vice, the components were reassembled and the bike road tested.
As soon as I selected 1st gear it was soon clear that something had improved and continued to do so throughout the gear changing sequence as I put 5miles on the odometer.
What convinces me that this box has never been set up properly from the factory is the lack of notchiness and not having to flap about searching for gears whilst changing gear in a hurry, all of that previous palaver is now absent along with the Juke Box Jury action (hit and miss). One, for those of us who remember David Jacobs their folks!
I hope that this article will help other AMC gearbox owners with similar issues to flush out the gremlins and make a change for the better!
Kind regards.
Cessna 01, 19, Bird dog.

[Dixter]

Hi Paul, sorry to hear about your plight. This article at Old Britts has helped me in the past.

http://www.oldbritts.com/gearbox_a.html

Best Wishes,
DC

[Bird dog]

Hi DC. Many thanks for your link. I recognise most if not all of the images in the article!!! I even dreamt of some of them waiting for the light to dawn on me as to how my problem could be resolved.
As described previously vast improvements have been made with the careful removal of metal .025mm (.010") at most that's all it took for reliability to be restored.
Currently waiting for a bespoke racing tank to be delivered from Cumbria this week and hopefully my Siamese exhaust and reverse cone mega too from the chrome platers.
I have had to purchase a new pair of fork stations from the Club spares scheme along with seals and other items.What a bargain they were!
This set of procedures will be the last in my lifetime of owning the G9 from 1967 and could possibly be the fifth major upgrade in that time.
I've enjoyed every minute of owning the bike along with Freda my lady wife who has encouraged me throughout.
Keep the wheels turning RideNut.
Regards.
Paul.

[mikeydpippin]

I have had to renew the plunger and spring, also the pawl. This has sorted my issues out, once I put the hair pin spring back in correctly. My pawl didn't have any obvious wear, but did make a difference.

I can go up through the amc gearbox but having problems with changing down to 2nd from 3rd, have to stop bike to get 1st, spring correct way up and 1mm either side of pawl.
I will replace spring, and pawl, but what is the plunger as quoted above please?
TIA.

[SPRIDDLER]

I suspect it's the cam plate (detent) plunger and spring. 040034 and 040045. Page 21 here:

http://archives.jampot.dk/book/Spares_l ... ingles.pdf

Illustration on page 18.

[bob121]

I suspect it's the cam plate (detent) plunger and spring. 040034 and 040045. Page 21 here:

http://archives.jampot.dk/book/Spares_l ... ingles.pdf

Illustration on page 18.

Correct. I've had no problems since.

[mikeydpippin]

Thanks again Nev, Jason👍👍