sprockets

[Dick Vandevelde]

hi, I am looking for about a 60 tooth real wheel sprocket for a 1969 TR25w or B25. Where can I find one of these? New or used. Thanks, Dick V. 

[chaz]

the parts book shows 49t sprocket, if you want to go bigger its a big jump.
If you cant find one you could try getting one made by Talon or an engineer with the know how. When I wanted a hard to find one, I found a "blank" on ebay.
The blank had the required teeth but a smaller home in the centre. this then went up on a vertical machine centre and bored out  to required size and bolt hole pattern machined in.

[Spaceman]

It would be interesting to know why you need a 60T rear sprocket? If you were to replace the standard 16T front sprocket with a 13T sprocket, this would be the equivalent of using a 60T rear sprocket with the standard engine sprocket!

[Dick Vandevelde]

Hi spaceman, the reason is that I would like two sprockets side by side on the back wheel so I can use it for on road or off road.  I have bored out the cylinder to put an 850 norton sleeve in it.  I installed a 750 piston in it from the early kits. (650 Triumph kits)  It is harder to kick over so i installed 441 engine spocket and clutch does not slip now. Gear box has 15 teeth and rear wheel  has 52 teeth. Dick V.

[Spaceman]

I'm intrigued - is it practical to have two sprockets mounted side-by-side on the back wheel - at the minimum, I would have thought it would lead to clearance problems with any chain guard fitted and could the same rear chain length be used for both sprockets? For one of my non-BSA bikes, I use separate back wheels for on-road and off-road which, of course, can use different tyres suitable for each type of use!

[Beesy]

Yeah, that is intresting. What happens to the chain when you switch from one sprocket to the other?


Does it involve rear wheel and back brake adjustment? Is there enough fore and aft movement to take up the slack.

Sounds a great idea if it works.

[Mike Farmer]

 

I guess you are going to need a serious chain tensioner.  I would imagine that a further problem is that on one (or both) of your sprockets the chain will not run true. I havent worked it out but what will the difference in chain length be.

Mike

[Dick Vandevelde]

i may have clearance  problems with 2 sprockets. I will try to offset the main sprocket and then the larger one inboard. If that doesn't work then I will have to put an overlay over the original sprocket like the racers used to do and carry a few extra links in my pocket for switching. It may be a wild idea but I like to try. Dick V.

[Derek996]

How to propose to keep the chain aligned for both sprockets?

[chaz]

I think sitting down with a pencil and paper and a derailleur from a cycle would be the only rear answer , this would still use a single chain with different gears on the back.
fag packet engineering .

the only other way to take up slack would be a rubber chain roller as used on motocross bikes but the twin sprocket means needing a spring loaded roller which may not be strong enough

[cdsdorset]

This has been done before successfully.  I think it was suzuki in USA did it. It came with an extra length of chain in the toolkit.

[Dick Vandevelde]

i first need to find  big sprocket

[Mike Farmer]

 

Hi

I should have thought of this before, probably an age thing.

When I built my A50 Trike, I had to have a differential custom made for it. It had to be bolted in solid to maintain the integrity of drive shaft postioning. Consequentially there is no chain adjustment. I have overcome this by fitting a third spocket. The is adjustable but it is not flexible, and is easily adjusted by a simple brake rod type adjuster. It sits in the return side of the chain. Mine is permanently in place but could be adapted relatively simply to be quickly removed/replaced.   

By the way thanks to all the members here for input when I was trying to sort it.

Mike