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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Primary Belt drive by Bob Newby
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<blockquote data-quote="Monkeypants" data-source="post: 42009" data-attributes="member: 2708"><p>David,I wonder if all of the belts Bob uses have the same pitch? The setup I have here is 40mm with a 71 tooth clutch drum and 43 tooth engine pulley. This gives a ratio of about 1.65 to one. Bob was aiming for 1.6 to one and had a setup nearly finished in that ratio when he realized it wouldn't fit. I've forgotten what part wouldn't fit, but it was likely the engine pulley which would have been larger than the one I currently have.</p><p>Looking at the diameter of the clutch drum gave me concern that it would not fit, so I tried it and the pulley on an engine Robert Watson was building for his son. The engine pulley fit with good clearance, however the clutch drum did not. Some material will need to be removed from the crankcase for it to fit on. </p><p>As far as the primary cover goes, Bob and I discussed that a bit but decided that it was not important for this engine as I can always build a primary cover to suit.</p><p>I may have put the fear of God in him re clutch requirements, but neither one of us wanted to end up with a clutch that was not up to the job. That is why he used seven thinner plates rater than five standard plates and I suspect it is also why the diameter of the clutch is so large, which goes against his other goal to get the primary ratio close to stock.</p><p></p><p>He had some concern about the large engine putting too much torque thru the trans and one way to reduce this is to bring that primary reduction down. I believevwe talked about Roy Robertsons 1272 egli which has been raced so much and apparently has eaten several transmissions (early Triumph 5 speeds?). Roy has one of Bobs primary drives, must be in the old higher ratio he wanted to avoid.</p><p>So he managed to get the ratio quite close to stock Vincent , has made a clutch that is probably good for about 200 hp and it looks as though it will all fit in there with a bit of case trimming.</p><p>I may or may not use the stock type primary cover, but if I do, it won't be a bolt on fit, there will be some renovating required.</p><p></p><p>Glen</p></blockquote><p></p>
[QUOTE="Monkeypants, post: 42009, member: 2708"] David,I wonder if all of the belts Bob uses have the same pitch? The setup I have here is 40mm with a 71 tooth clutch drum and 43 tooth engine pulley. This gives a ratio of about 1.65 to one. Bob was aiming for 1.6 to one and had a setup nearly finished in that ratio when he realized it wouldn't fit. I've forgotten what part wouldn't fit, but it was likely the engine pulley which would have been larger than the one I currently have. Looking at the diameter of the clutch drum gave me concern that it would not fit, so I tried it and the pulley on an engine Robert Watson was building for his son. The engine pulley fit with good clearance, however the clutch drum did not. Some material will need to be removed from the crankcase for it to fit on. As far as the primary cover goes, Bob and I discussed that a bit but decided that it was not important for this engine as I can always build a primary cover to suit. I may have put the fear of God in him re clutch requirements, but neither one of us wanted to end up with a clutch that was not up to the job. That is why he used seven thinner plates rater than five standard plates and I suspect it is also why the diameter of the clutch is so large, which goes against his other goal to get the primary ratio close to stock. He had some concern about the large engine putting too much torque thru the trans and one way to reduce this is to bring that primary reduction down. I believevwe talked about Roy Robertsons 1272 egli which has been raced so much and apparently has eaten several transmissions (early Triumph 5 speeds?). Roy has one of Bobs primary drives, must be in the old higher ratio he wanted to avoid. So he managed to get the ratio quite close to stock Vincent , has made a clutch that is probably good for about 200 hp and it looks as though it will all fit in there with a bit of case trimming. I may or may not use the stock type primary cover, but if I do, it won't be a bolt on fit, there will be some renovating required. Glen [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Primary Belt drive by Bob Newby
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