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G: Gearbox New Gearbox: Help Needed


ehb86

New Website User
VOC Member
I'd like to thank everyone again for their suggestions and offers of help. I'm happy to report I've solved the problem and I'm able to engage all gears with the gear indicator. I ran through the checks of gear fitment, etc. as suggested and all was well. So I took Ernie's suggestion to set the gearbox up in the vice in the cover plate. and check the shifting with the camplate. That is how I had initially put the gearbox together for insertion but I don't believe I tried shifting gears with the camplate. I had just slid things back and forth and they meshed so I thought all was ok. After Ernie's suggestion I set it up again and this time rotated the camplate by hand and it became obvious that the selector forks were hanging up on the selector bar. Not really hard, but enough to make shifting very difficult in first and second.

I removed the selector bar and chucked it in the lathe and it was straight so I took about a thousand plus off of it and polished it up. On reassembly I was able to shift first through fourth with the gear selector so I'm a happy fellow and I'm going to proceed with getting her back together and running. That will be a happy day.... it's been too long off the road. Thanks again for everyone's help, it's hard to overstate how great this club is.

Ernie, thanks again.

Best regards,
Mark
 

highbury731

Well Known and Active Website User
VOC Member
Is there a sample of the McDougall cam plate (and presumably a revised index plunger assembly) and would anyone make them?
Paul
 

Bill Thomas

Well Known and Active Website User
VOC Member
Having Raced Twin for 17 years, I have found the gearbox , Not too bad !, But the Clutch can make it seem
Bad. A Standard Clutch can be made to work well, But it's not easy, A Multi plate makes it feel like a different Bike. Cheers Bill.
 

highbury731

Well Known and Active Website User
VOC Member
Comparing the horizontal Norton box and AMC box is revealing. Apart from an improved positive stop mechanism, the main difference between them is the curved cam profile of the index plunger. It's a MUCH better box. So if someone can make a similar improvement to a Vincent box, I'm keen. And right now, my gearbox door is off....

Paul
 

oexing

Well Known and Active Website User
VOC Member
Paul,
I guess you are thinking of a shape like that below from a /5 series BMW box, with all these humps on the o.d. of the camplate :

Schaltscheibe.jpg

Actually that was meant to be an "improvement" to the older shape similar to the Vincent camplate. The older BMW plate was like this:
Schaltscheibe alt.jpg 2.jpg

You can see the indexing lever just above the camplate, that is where I got my idea from for my mod to the poor Vincent indexing plunger type which induces a lot of friction in its bore from side loads when shifting gear.
I said the new type of camplate on the 2 valve flat twin BMWs was a bad idea because all gears in a BMW gearbox do about crankshaft speeds , no reduction from a primary drive there. So gearchanges are widely known to be very clunky on these BMs when going down , say, from third to second gear as you are faced with big differential in gear speeds at a high reving gearbox.
With the older type of camplate, circular o.d. , you have the chance to find a "false" neutral between all gears so you can perform truck/ tractor changes like on unsynchronized boxes.
I got my 1965 R 69 S in 1972 so am used to its gearbox quite well. So it is second nature to do downshifts with false neutrals and extra clutch action so real SILENT gear changes on a BMW for sure. I had clutch Bowden wires snap once or twice far from home so this came very handy to do gear shifts without clutch at all BUT using false neutrals for silent changes nevertheless. No way to do that with the humped camplates !
Well, this is no argument with the Vincent gearbox, certainly. When looking at the Vincent camplate I do not see a lot of scope for extra humping: You´d have to shorten the bore of the plunger pin but same time it had to do a longer stroke into the deeper v-slots, making things even worse friction-wise with the pin-in-bore design. In that case the lever indexer would help a lot - I hope.

Vic
P1050791.JPG
 

highbury731

Well Known and Active Website User
VOC Member
I understand what you are getting at... the humped cam plate is most useful on bikes with lighter flywheels and closer ratio gearboxes. Perhaps the ideal arrangement for older bikes would be a low-friction index, a two-angle ramp to encourage the camplate into gear if it's anywhere near, and a region of flat top constant diameter in between allowing a 'shifting neutral' between ratios for synchronisation.
Paul
 

Glenliman

Well Known and Active Website User
VOC Member
Is there a sample of the McDougall cam plate (and presumably a revised index plunger assembly) and would anyone make them?
Paul
A few years ago John showed me the AMC style camplate he had made and fitted to the 4 spd in his Shadow. At that point in time he had removed the 4 speed and installed a Quaife 5 speed in the bike. According to John, the 4 speed with his revised plate shifted as well as the Quaife, which is a slick shifting setup.

I'm guessing that the 4 speed gear set and special camplate are put aside as part of the Black Shadow, which his family has kept.

Glen
 
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vibrac

Well Known and Active Website User
VOC Member
The guy who has done a lot in this area including an external to the gearbox mod all of which transform the gear changes is Tomo ( he of the 4 valve Vincent)
 

highbury731

Well Known and Active Website User
VOC Member
The guy who has done a lot in this area including an external to the gearbox mod all of which transform the gear changes is Tomo ( he of the 4 valve Vincent)
My guess is that he added an extra index system in the gearbox outer cover
 

oexing

Well Known and Active Website User
VOC Member
Hmm, I was thinking of just limiting travel of linkage in there by setting stops so as not to overselect gears beyond the proper index on the camplate. So another indexing would be a bit too much.

Vic
 

greg brillus

Well Known and Active Website User
VOC Member
I've seen pictures of it all.........Yes it has an external sprung index and roller on the outside of the kickstart cover that runs directly on the G 40 shaft, and replaces the camplate plunger for a sprung roller with much larger detents in the camplate. The second part looks quite easy to do.
 

highbury731

Well Known and Active Website User
VOC Member
G61/1 has tabs on it to prevent over-selection. I bought one, and had to bend both tabs back to get enough travel to engage gears. I have heard of people making their own version with adjustment screws to set the limit stops where they want them. I may have to do that myself.
Paul
 

vibrac

Well Known and Active Website User
VOC Member
Yes I have done this on the twin racer by brazing 1/4 bsf nuts on edge and using cap heads for adjustment the kick start spring prevents this on a standard bike but racers and people who have confidence in the electric start could use it
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
G61/1 has tabs on it to prevent over-selection. I bought one, and had to bend both tabs back to get enough travel to engage gears. I have heard of people making their own version with adjustment screws to set the limit stops where they want them. I may have to do that myself.
Paul
The G6/1 can improve the gear change but due to the mix/match of components, they need some tweaking to have an effect. The standard G6/1 is quite flimsy. I made my own with two nuts for adjustment and some bracing to stop the nuts being bent backwards. A problem with this mod is that there is not much space here and the nut closest to the timing cover is fouled by the kick start mechanism. I have space as I have an electric start and the kick start mechanism removed.
This mod is only a partial solution as the G61/1 only limits the movement of the G59/AS. The rest of the mechanism inboard can carry on turning due to the momentum of the camplate etc. This is probably not so much of a factor for normal gear changing but more of a problem when going for a fast change or people who are used to stamping through the gears on more modern gear boxes..
Phil Irving proposed a fix by welding and filing to make a revised G43 that acts like more of a gear to keep it locked to the corresponding part on the G59/AS and so preventing the G40 shaft continuing to turn due to momentum. This is easier to understand with an M003 parts drawing to hand.;) I think you may find it described fully in 40 Years On. I have not tried this yet, maybe sometime.
 

timetraveller

Well Known and Active Website User
VOC Member
I get the G43s made and supply them to the Spares Company. Years ago I saw a drawing by Phil Irving in which he drew up a modification which resulted in 'square' teeth rather than the triangular ones. That is probably the same one that BigEd refers to. I have never been able to find this drawing again. My memory is that the part of G59AS which meshes with G43 would also have to be modified. If there was sufficient interest, and someone can find the drawing, then I would be prepared to investigate getting a batch made. Over to you.
 

genedn

Well Known and Active Website User
VOC Member
A few years ago John showed me the AMC style camplate he had made and fitted to the 4 spd in his Shadow. At that point in time he had removed the 4 speed and installed a Quaife 5 speed in the bike. According to John, the 4 speed with his revised plate shifted as well as the Quaife, which is a slick shifting setup.

I'm guessing that the 4 speed gear set and special camplate are put aside as part of the Black Shadow, which his family has kept.

Glen
Glen,

The whole gearbox and cam plate are part of the engine I purchased from the estate. We had some issues trying to fit the gearbox into the cases yesterday. The alignment of the bearings on the main shaft is out.

It was a G2 issue that is now resolved.

So I have the cam plate and could post a photo.
 
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