Can you weld the cog on the output shaft?

[Pete.]

What I am suggesting is that you have a custom sprocket made that has a 'dish' in it to move the sprocket closer to the engine. You could indeed bore out the working sprocket and weld it to another one which locates on the shaft but you're limiting yourself to a fixed off-set and apart from that it's a proper bodge.

 

[Flathead_Dave]

As stated,+1 on the custom sprocket.
My bodge idea is a way of obtaining a working prototype.
The alternative is bits of string and a tape measure,an engineer wouldn't be too happy if presented with that.

 

[Pete.]

I'd make a dummy sprocket from thin MDF layers glued together. You could easily drill a ring of hoes to make the teeth to test-fit the chain but all you'd really need is to turn a disc and make a ridge in the edge.

 

[busastars]

Off set sprockets are used all the time esp for all the RD350 with various rear ends. I am running a 5mm off set on my RD350.

Think if you post up a few photos it will give a clearer idea and may even be an easyer solution to the problem.

 

[breezer]

apart from that it's a proper bodge.

It's a motorbike engine in a scooter...

I'd be quite happy with that

Scooterboys seem to like a bit of a bodge - crisp packet used to hold a broken gear selector in place being the best I've read about recently...

 

[MrFluffy]

Before buying a sprocket normally Id suggest people have a browse at the jt sprocket catalogue, as often you can swap sprockets between different models within a manufacturers range to help get the gearing and offset right and you can end up paying a tenner instead of £50+ to get a special one off made up, however it looks a lot like the cd250 used a sprocket spline all to itself...

This has the specs if its any help, you can at least glean the stock gearing and from that and a approx rolling radius of the original wheel give you a idea of what sprocket ratios to shoot for with your smaller wheels and things :-
http://www.jtsprockets.com/52.0.html?&L=0&sel_uid=224&p=