NH chain alignment

[Pete.Silson]

I have just acquired a 1949 rigid NH (with a 500 top-end fitted). One issue (among many) is that the rear chain appears to be cutting its way through the back of the primary chaincase. I have tried padding the bottom case/frame bolt but this simply causes the back of clutch basket to rub.

Does anybody know how far the gearbox sprocket should be from the engine plate and what thickness the spacer behind the spocket (3112-33) should be? I have to disassemble the gearbox to fit a new sprocket and am tempted to reduce the thickness of the spacer to increase the clearance on the back of the chaincase.

Any ideas/suggestions welcome.

Pete

[Paul Slootheer]

Assuming your rear wheel is spot on and in the right position, you can lay a ruler against the rear sprocket. The ruler will show you if your gearbox sprocket is out of line. I've got the feeling the gap between the gearbox and the sprocket is quite wide, also because of the grinding... This is how it looks on my 1952 Anstey link Ariel.

[Simon.Gardiner]

Pete - has it got the right gearbox? (I think there's a gearbox letter/number reference doc on Drags site)

SG

[Pete.Silson]

Simon - The gearbox number is G92 D 49 which I believe is correct for 1949.

Paul - The sprocket position in your picture looks radically different from mine - is your gearbox a CP or a GB?

[Paul Slootheer]

Pete, my gearbox is fitted to a 1952 KH.
Despatched on oktober 1951.

[Bob.Murphy]

A bit of an 'aside' . .

Whilst browsing through bike bits on e-Bay I came across this laser wheel alignment tool:

https://www.ebay.co.uk/itm/Laser-Monkey ... SwzsNckmJ5

I don't have one but if you have a number of bikes it might be an effective means of checking wheel / chain alignment (I have shaft-drive BMWs of course ).

Has anyone got one ?? What's the verdict ??

Bob.

[Pete.Silson]

Or you can try this cunning eyeball assisted thingy that doesn't need batteries and doesn't mind getting dropped into the oil tray too much:

http://www.ebay.co.uk/itm/163497562729

Pete

[Bob.Murphy]

True . . But with the laser you only need to see the destination end. No lying on your stomach sighting along the rod (in the cold, and the wet, and the oil) .

Bob.

[alan.moore]

Pete
If you gearbox is a CP type the part number for the spacer is as you quoted (3112-33) listed as 1933-52. My '42 WNG has a CP box so the spacer should be the same. The details of the spacer (sourced from AOMCC gearbox spares) is shown below:

3112-33 spacer

showing distance from back of sprocket to casing face

I have had the gearbox shell mounted in the frame and the sprocket aligns correctly with the rear wheel sprocket ) so for my CP this spacer is correct

Hope this helps

Cheers
Alan

[Pete.Silson]

Thank you for the pictures Alan - this is just the information I needed to eliminate the issue being with the gearbox. Unfortunately the bad news is that I am now fairly sure I have identified the real problem. When I checked the rear sprocket alignment relative to the chainline it was significantly offset to the left. Taking a centreline along the top tube the rear wheel lugs are offset to the left by about 7/8".

Advice please anybody - how can I fix this?

Pete