stevegbr
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BIRMINGHAM
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Post by stevegbr on Jul 18, 2023 13:16:41 GMT
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Post by buster on Jul 21, 2023 10:41:06 GMT
I did a rough measurement on this myself (I got around 17mm offset, as I said rough measurement) so I wouldnt argue with his 20 point whatever milli meters. I'll wait and see if he can manage this, bet its expensive if he does pull it off
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willy3pigs
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Post by willy3pigs on Jul 21, 2023 11:06:29 GMT
I did a rough measurement on this myself (I got around 17mm offset, as I said rough measurement) so I wouldnt argue with his 20 point whatever milli meters. I'll wait and see if he can manage this, bet its expensive if he does pull it off I would look into machining 17mm or whatever it is of the four lugs that carry the sprocket. With the tyre removed you would probably have enough Y axis table travel on a little Bridgeport type mill that you find in every small machine shop to fit it on the table, or I would imagine it wouldn't be too hard to grip inside the brake drum with reverse jaws on a lathe with sufficient swing, and do it that way. Altering the cush drive sprocket mounting part of the job shouldn't be that hard, you could even fit solid bushes if necessary if finding or making rubber ones is a problem. |
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Post by buster on Jul 21, 2023 13:38:10 GMT
I did a rough measurement on this myself (I got around 17mm offset, as I said rough measurement) so I wouldnt argue with his 20 point whatever milli meters. I'll wait and see if he can manage this, bet its expensive if he does pull it off I would look into machining 17mm or whatever it is of the four lugs that carry the sprocket. With the tyre removed you would probably have enough Y axis table travel on a little Bridgeport type mill that you find in every small machine shop to fit it on the table, or I would imagine it wouldn't be too hard to grip inside the brake drum with reverse jaws on a lathe with sufficient swing, and do it that way. Altering the cush drive sprocket mounting part of the job shouldn't be that hard, you could even fit solid bushes if necessary if finding or making rubber ones is a problem. if only it was that easy  the early 250rs wheels present very little problem, modify the wheel spacers slightly and your there sprockets align, wheels align, no problem. the later 250rsa is a completely redesigned bike, its really got nothing to do with the original 250rs and (I think) has more in common with the later GB250. aligning the sprockets on the rsa wheel could be done but you still need to offset the rim by a hell of a lot to get it centralised in the swinging arm and aligned with the front wheel. sadly theres no shortcut, like I said he's setting himself a hell of a task, I'll be amazed if he pulls it off |
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Post by buster on Jul 22, 2023 7:55:58 GMT
the problem he's up against (assuming I'm right and its an RSA wheel that he's got hold of)  a rough measurement says the sprocket needs to move about 1/8" towards the back brake, easy enough. the problem is that puts the rim miles out of alignment. superdream boomerang wheel (with nighthawk sprocket carrier) for rough comparison  and the 250 RSA wheel with sprocket in roughly the right place  as I said before I measured this at roughly 17mm offset required, at that point I gave it up as I already have an earlier 250rs wheel that fits perfectly with modified spacers |
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