G15 chain gearbox sprocket.

pierodn

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Nov 10, 2012
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Hi All.
I must remove the 20 theet chain sprocket!
The chain touchs against the collar of the external side of the primary inner cover chaincase and doesnt permit to the gearbox to rotate ahead.
So that i cannot join the 68 links of the primary chain tat bocomes short.
Or replace the original 19 theet sprocket or remove the protection collar.
Piero
 
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Please explain what you mean by "protective collar". Can you post a picture?
Any engine sprocket between 17T and 23T was an option from the factory and should be free of interference problems. Do you have the correct spacer between inner chaincase and crankcase #030243 ?

-Knut
 
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Hi Knut
The external side of the inner chaicase has up the rounded plate where fit the gearbox mainsshsft a semiirular protection fo thechsin.
20 tht chain touch iy and garbo ont rotat shad
Piero
 
Do you mean the disc surrounding the mainshaft in this pic?

G15 chain gearbox sprocket.
IMG_20190923_100145376 by Mick Doul, on Flickr

Or one of the projections off the rear of the inner primary cover?

Either way, is it possible the gearbox is adjusted too far to the front? It's not possible the primary chain is a link short, is it?
 
AgentX said:
Do you mean the disc surrounding the mainshaft in this pic?

G15 chain gearbox sprocket.
IMG_20190923_100145376 by Mick Doul, on Flickr

Or one of the projections off the rear of the inner primary cover?

Either way, is it possible the gearbox is adjusted too far to the front? It's not possible the primary chain is a link short, is it?
Click to expand...
Off the rear where is the sprocket
 
AgentX said:
Do you mean the disc surrounding the mainshaft in this pic?

chain is 68 lonk correct and the gearbox doesnt rotate full ahea because the secondary chain stops against protection
G15 chain gearbox sprocket.
IMG_20190923_100145376 by Mick Doul, on Flickr

Or one of the projections off the rear of the inner primary cover?

Either way, is it possible the gearbox is adjusted too far to the front? It's not possible the primary chain is a link short, is it?
Click to expand...
 
Chain is 68 link correct but is the gearbox that doesnt rotate full ahead
 
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Hi Piero,
Your post #3 is a bit hard to comprehend. I guess you mean the final drive sprocket is touching the sliding disc on the "external" of the inner cover. I must ask again: Did you fit the correct spacer between inner chaincase and crankcase, #030243 ? If you didn't, there will likely be an interference problem ....
On the other hand, if the spacer is in place, then there must be something wrong with your gearbox transverse location .....

If it's the angular rotation of the g/b which doesn't fit the aperture in the chaincase, (a) do you have the correct inner chaincase, and (b) is your final drive chain slack, allowing the gearbox to rotate forward? Maybe there is paint residue in the engine plate slots, preventing the upper bolt to slide? Take a closer look.

-Knut
 
Piero seems to be talking about the large cast projection on the inboard side of the inner chaincase which essentially shrouds the mainshaft and drive sprocket.

I cannot figure out how the sprocket would contact this; IIRC I have a 21-tooth on there now and there are no clearance issues.

Seems like the transmission shaft is too close to the fore of the bike, based on what I can envision, but I don't see how that could be if the primary chain is of the proper length.

Edit: Piero, is this the problem, crudely outlined in red?

G15 chain gearbox sprocket.
s-l1600 by Mick Doul, on Flickr
 
AgentX said:
Piero seems to be talking about the large cast projection on the inboard side of the inner chaincase which essentially shrouds the mainshaft and drive sprocket.

I cannot figure out how the sprocket would contact this; IIRC I have a 21-tooth on there now and there are no clearance issues.

Seems like the transmission shaft is too close to the fore of the bike, based on what I can envision, but I don't see how that could be if the primary chain is of the proper length.

Edit: Piero, is this the problem, crudely outlined in red?

G15 chain gearbox sprocket.
s-l1600 by Mick Doul, on Flickr
Click to expand...
Yessssss!!!!!
It is!!!!!!?
Chain case is stock.
With 20 theet sproket and 3/8 /5/8 secondary chain the gearbox doesnt rotate ahead because the secondary chain link touchs against the top of “the large cast projection on the inboard side of the inner chaincase”.
If the gearbox doesnt rotate full ahead i cannot join the primary 68 links chain.
I have replaced the 19 theet sprocket and the secondary chain doesnt touch anymore the “the large cast projection on the inboard side of the inner chaincase”.
Spacers and so and so were all in place and secondary chain were not tight.
May be the 1964 inner chaincase cover had such “large cast projection on the inboard side of the inner chaincase” that is for 19 sproket only.
Piero
 
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The older bikes with simplex primary chains generally didn't change the gearbox sprocket to alter the gearing, they changed the engine sprocket instead. Most Nortons used a 19 tooth gearbox sprocket and it appears that your G15 was probably the same. If you want to change the overall gearing change the engine sprocket size and use a different length primary chain.

Ian
 
pierodn said:
With 20 theet sproket and 3/8 /5/8 secondary chain the gearbox doesnt rotate ahead because the secondary chain link touchs against the top of “the large cast projection on the inboard side of the inner chaincase”.
Click to expand...

A 20T g/b sprocket is really quite big, considering standard fitment was 17T for all G15 models (Dommies even used 16T). What's the gain using such a big sprocket? I take it you have now fitted a 19T sprocket which clears the cast shroud.

Going by your post #1, the 20T sprocket and chain interferes with the shroud even if the g/b is rotated backwards as far as possible. If you aim at reducing the engine revs at a given speed, you need to increase your engine sprocket (22T -> 23T) and possibly fit a primary chain longer than 68 links. Hopefully your 19T g/b sprocket still clears the shroud if the g/b is rotated forward.

-Knut
 
According to the Roy Bacon Norton Twin Restoration book the 1964 G15 had a 23 tooth engine / 42 clutch sprocket where as the same year Atlas / 650SS had 21 tooth engine 42 tooth clutch, so it would appear that the G15 was higher geared than similar Nortons of the time, is there a need to raise the gearbox sorocket to 20? when 19 is standard.
Al
 
21 tooth engine sprocket with 42 clutch tooth need 68 link primary chain.
How much primary links need with 23 tooth engine sprocket?
With 23 instead of 21 how much RPM is lower?.
Thank you to All.
Ciao
Piero
 
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The engine rpm or road speed will change in direct proportion to the ratio change of the sprockets.

42/21 = 2.0
42/22 = 1.91

% change = 100*(2.0 - 1.91)/2.0 = 4.5%

The rpm will be 4.5% lower at a given speed, or the speed will be 4.5% higher at a given rpm. The opposite will be true if a smaller engine sprocket (example 20T) is fitted.

My Atlas gearing (42/21 primary) produces 17 mph per 1000 rpm, or 68 mph at 4000 rpm. If I were to change to a 22 T engine sprocket, I would get 17 * 1.045 = 17.77 mph per 1000 rpm, or 71 mph at 4000 rpm.

With a 23 T engine sprocket, my Atlas would get nearly 74 mph at 4000 rpm.

Slick
 
texasSlick said:
The engine rpm or road speed will change in direct proportion to the ratio change of the sprockets.

42/21 = 2.0
42/22 = 1.91

% change = 100*(2.0 - 1.91)/2.0 = 4.5%

The rpm will be 4.5% lower at a given speed, or the speed will be 4.5% higher at a given rpm. The opposite will be true if a smaller engine sprocket (example 20T) is fitted.

My Atlas gearing (42/21 primary) produces 17 mph per 1000 rpm, or 68 mph at 4000 rpm. If I were to change to a 22 T engine sprocket, I would get 17 * 1.045 = 17.77 mph per 1000 rpm, or 71 mph at 4000 rpm.

With a 23 T engine sprocket, my Atlas would get nearly 74 mph at 4000 rpm.

Slick
Click to expand...
Hi Slick.
One theet more how many chain links are?.
Piero
 
pierodn said:
One theet more how many chain links are?
Click to expand...

What I can deduce from the Matchless workshop manual is this:

Engine sprocket size 19T & 20T Chain length 67 links
Engine sprocket size 21T & 22T Chain length 68 links
Engine sprocket size 23T & 24T Chain length 69 links

Primary chain size for all Matchless G3/G80/G9/G12/G15 models is 1/2 x .305".

The N-V workshop manual contains a printing error, stating the G15/N15 has 76 links.

-Knut
 
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