G: Gearbox (Twin) What More Do I Need To Know About The G49 and Its Adjustment

[CarlHungness]

I'd estimate I have adjusted the G49 on my Twin at least twice if not three times in past years and was pretty fortunate the first couple of times. Now, getting the bike into first gear is not always an assured circumstance. Sometimes it snicks in per normal but once in a while she's recalcitrant, so I gently boot the G81 lever backwards.

I've followed all of the instructions on how to adjust the (fiddly) G49 and am not on a first-name basis with the eccentric and its attendant adjusters. I recall trying, guessing, attempting to see, just how much I was moving the plot so that I get clearance 'here' and every gear pops into place. Seems like the eccentric and its 327 bolt heads are just so close together that one's comfort zone for adjustment isn't what you'd really like.

My G61 'stop' had ears on each side (my bike is a '54 Shadow) and I'd previously seen a mod whereby the owner brazed tabs with adjuster bolts on either side to limit travel. Ultimately I cut the ears off. Now I can get nearly a false third gear, she goes in, seemingly, and then I feel ham-fisted as the engine revs and the gearbox lets me know she wasn't fully home in third.

Is a new G61 and eccentric recommended after years and miles of wear. I have a bit over 100,000 miles on the machine.

Thus seeking advice from the group as I want to take the plot apart this winter and see if I can get it all working as smoothly as possible.

 

[vibrac]

Actually after years of frustration (and it was me probably extolling the virtue of 1/4 BSF nuts and alan screws on the G61) It was my Son who finally showed me how to get a good twin gearchange and it is indeed getting the G49 to properly limit its range of movement of the G66 at that end and not trying restricting it at the other where the G61 is.
I suppose coming it to a hairpin with a brace of Manx Nortons on your heels and just a couple 7" saucepans to help, means you learn a lot about getting a Vincent gearbox to be reliable

 

[MarBl]

It was my Son who finally showed me how to get a good twin gearchange and it is indeed getting the G49 to properly limit its range of movement of the G66 at that end and not trying restricting it at the other where the G61 is.

I struggled for quite some time with missed gears and finally got it sorted out via G61, which in my case needed a wider gap between the "ears".

But I would be very interested to learn, how you can get there using G49. Is there a "how to" somewhere in the literature or the forum?

 

[Vincent Brake]

Milled it out and put in an adjustable stop with M5 grub screw.
Easy pizy

 

[oexing]

Regulars here will not be surprised that my view is different to common Vincent religion:

I believe it is bad practise to set gear change linkage at the G 49 stop as a small amount of adjustment means big position change at the G 66 actuating arm end engaging in the G 59 AS change speed pawl - which drives the G 43 ratchet and its gear change shaft and bevel gear inside the box. Instead I made an alu stop next to the change speed pawl, see my photos below, the alu block with allen bolt and two dowels. The position shown is like shifting up to first gear and the pawl touching the stop.

When shifting down to second gear it will stop at the opposite alu face next to the other dowel. So stops are one face next to one dowel, the other stop near the other dowel. Good thing is I don´t mess with the stops for the actuating arm, not used here and not great as the stops there are effectively the ends of the centralising leaf spring getting squeezed onto the curved alu faces of the G 49 lever stop - not perfect in this job.

You could do my idea of alu stops on the bike with a hand drill and dremel the faces for fine adjustment, for reaching positions of camplate just near enough for slipping into camplate notches. Be sure to have allen bolt and dowels way out close to the cover as not a lot of space there for filing the stop faces to achieve the perfect stops.

For keeping the lever stop in position I made massive plates under the torx bolts and a simple eccentric bush, no hex on it. I set the linkage stop by looks as required , bolt up one torx and place the plain eccentric plus a split washer for a bit of preload over the second M 6 thread hole and tighten the other torx bolt and its massive plate onto the lever stop. Should do I believe…

Certainly very first thing is the camplate settings in the gearbox have to be exactly as required. I did corrections on notches and curved slots in camplate for maximum engagement in all gears. So when setting the linkages you take care by feeling the clicks in the gearbox to set linkage stops like with my doweled alu blocks. After this job I cannot imagine how gearchanges can be faulty.

Vic

 

[CarlHungness]

Regulars here will not be surprised that my view is different to common Vincent religion:
I believe it is bad practise to set gear change linkage at the G 49 stop as a small amount of adjustment means big position change at the G 66 actuating arm end engaging in the G 59 AS change speed pawl - which drives the G 43 ratchet and its gear change shaft and bevel gear inside the box. Instead I made an alu stop next to the change speed pawl, see my photos below, the alu block with allen bolt and two dowels. The position shown is like shifting up to first gear and the pawl touching the stop.
When shifting down to second gear it will stop at the opposite alu face next to the other dowel. So stops are one face next to one dowel, the other stop near the other dowel. Good thing is I don´t mess with the stops for the actuating arm, not used here and not great as the stops there are effectively the ends of the centralising leaf spring getting squeezed onto the curved alu faces of the G 49 lever stop - not perfect in this job.
You could do my idea of alu stops on the bike with a hand drill and dremel the faces for fine adjustment, for reaching positions of camplate just near enough for slipping into camplate notches. Be sure to have allen bolt and dowels way out close to the cover as not a lot of space there for filing the stop faces to achieve the perfect stops.
For keeping the lever stop in position I made massive plates under the torx bolts and a simple eccentric bush, no hex on it. I set the linkage stop by looks as required , bolt up one torx and place the plain eccentric plus a split washer for a bit of preload over the second M 6 thread hole and tighten the other torx bolt and its massive plate onto the lever stop. Should do I believe . . .
Certainly very first thing is the camplate settings in the gearbox have to be exactly as required. I did corrections on notches and curved slots in camplate for maximum engagement in all gears. So when setting the linkages you take care by feeling the clicks in the gearbox to set linkage stops like with my doweled alu blocks. After this job I cannot imagine how gearchanges can be faulty.

Vic

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Just fabulous work. Thanks for posting.

 

[greg brillus]

The 2 adjustments need to be made together.......It is pointless having the G 61 set up if the travel available at the G49 is not letting it go that far in either direction. It is quite true that some gearboxes do not like the G61 with the tabs either side, sometimes a little extra travel is needed. On bikes that have done lots of mileage the parts of the shift mechanism do wear quite a bit, so replacement with good new parts will definitly go a long way to fixing it. This is especially true of the G 40 shaft and its slot that fits in the bevel gear in the roof of the box......once this gets sloppy, the shift can suffer as some of the selector travel is lost........the G49 and the G 57 eccentric aduster work ok , but can give trouble as the hex edges of the G57 tend to sink into the soft alloy of the G 49.......this makes fine tuning adjustment difficult, so replacements are the best way........the G59 AS pawl is very hard, and these dont wear too much , but the ratchet G43 can suffer, and a new one can make quite a difference to the shift behaviour.......Another common issue is the detent plunger springs being a bit too strong, this makes the shifts a bit hard, and overselecting and/or finding nuetral can be difficult........ I simply compress a new spring in the jaws of a vice till it coil binds, this shortens the spring by about 2 mm.......this makes the shift much smoother and far easier to find nuetral........All good fun really........especially if you have a good head of hair.......Cheers.

 

[CarlHungness]

The 2 adjustments need to be made together.......It is pointless having the G 61 set up if the travel available at the G49 is not letting it go that far in either direction. It is quite true that some gearboxes do not like the G61 with the tabs either side, sometimes a little extra travel is needed. On bikes that have done lots of mileage the parts of the shift mechanism do wear quite a bit, so replacement with good new parts will definitly go a long way to fixing it. This is especially true of the G 40 shaft and its slot that fits in the bevel gear in the roof of the box......once this gets sloppy, the shift can suffer as some of the selector travel is lost........the G49 and the G 57 eccentric aduster work ok , but can give trouble as the hex edges of the G57 tend to sink into the soft alloy of the G 49.......this makes fine tuning adjustment difficult, so replacements are the best way........the G59 AS pawl is very hard, and these dont wear too much , but the ratchet G43 can suffer, and a new one can make quite a difference to the shift behaviour.......Another common issue is the detent plunger springs being a bit too strong, this makes the shifts a bit hard, and overselecting and/or finding nuetral can be difficult........ I simply compress a new spring in the jaws of a vice till it coil binds, this shortens the spring by about 2 mm.......this makes the shift much smoother and far easier to find nuetral........All good fun really........especially if you have a good head of hair.......Cheers.

Good advice Greg, thanks.

 

[vibrac]

Yes its a design that requires thought and good engineering modifications hardly ideal for the new owner, no wonder the Irving Vincent uses a gear change from a jap two stroke.

 

[CarlHungness]

Yes its a design that requires thought and good engineering modifications hardly ideal for the new owner, no wonder the Irving Vincent uses a gear change from a jap two stroke.

I didn't know that fact. Then too I understand the Godet engine is cast so it
will accept a Harley starter. But I'm awfully glad the machinists are out there
doing these modifications to keep the marque growing.