January 2, 20224 yr Hi folks, just a question for future sprocket alternatives. I have a motor which is B40 cases, with B44 crank and top end, 23 eng sprocket and 52 clutch....gearbox is 11 teeth with 55 on rear. I'm guessing standard side point motor gear box ratio's, but no clue realy. So bike handles sections in first gear reasonably well if not realy tight, and second good for hill climbs, so quite usable. Was just wondering if I went to a 18 tooth engine sprocket....I may be able to go up a tooth or two on the gear box and less teeth on the rear and shorter chain, and still lower the overall gearing slightly. Sounds feasable to me, but any input welcome. My biggest worry is the 18 tooth would put more strain on the gear box with the oompf from the B44 grunt. Cheers, Bashplate.
January 2, 20224 yr changing primary ratios from 2.2 to 1 up to almost 2.9 to 1 would make starting VERY hard for the average leg. I also think it would be the clutch that suffers more than the gearbox. what is the number of engine revolutions to one wheel revolution in first gear? on my pre-unit singles I get as close to 27/1 as possible. it is always a compromise, going too small on the gearbox sprocket can wear out the swinging arm as well as the chain.
January 5, 20224 yr Author Hi Stan, good point, hadn't thought about how it would alter the kick start revolutions. Will check out the revs per rear wheel ratio too. Motor is #1888. Cheers, Trev.
January 6, 20224 yr Author Having a problem getting the primary drive off, as I need to get to the gear box sprocket to replace the seal behind it. Got the clutch off the taper ok with a wee puller I made, but the engine sprocket is stuck on the crank with no room to get a 2 legged puller behind it and the chain....no threaded holes in the sprocket either. Any one had this and found a remedy?
January 11, 20224 yr Author Latest up date, got the crank pulley off with another home made puller, gear box sprocket also off now too. So gear box oil seal dropped out as it had been spinning in the housing, no i.d. numbers on it as they all rubbed off. Part # BSA....41-3054 in the B44 parts book, is it the same for the B40 ( which my cases are), or is there a seal I can get from the local bearing outfit, had a look on web, but nothing seams to fit the bill. Hoping Charlie Prescott would have drifted by with his wealth of knowledge by now, may need to try him on the Otter site.
January 11, 20224 yr Hi Guy's... Hi Trev... You probably have the later crank cases with a circlip to hold the seal in, this has a larger diameter than the original seal the original was 40x52x7 mm still available from most bearing shops. The later seals had an OD of 52-4 mm... Fit a bearing with oil seals I don't even remove the seal that faces inside the gearbox this looks after both jobs the out side seal just then stops the dirt and dust... Regards Charlie... I will update that page on the Otter Site...
January 12, 20224 yr Author Thank you Charlie, spun out housing measures about 53mm, so would make sense for out side diameter, no circlip groove or room for one.....but the part of the 11 tooth sprocket the i.d. rubs on is 37mm????. The 40mm i.d. you are saying was also my understanding, as it is the same as the engine sprocket on the crank seal, so not sure what's going on here....your thoughts are most welcome.
January 12, 20224 yr Hi Guy''s... Hi Trev... Sounds like someone has played with that engine..... Look you can get a 37x53x7 mm rotary shaft oil seal off the shelf from my bearing supply company... someone has turned down your sprocket to fit one of these, or it is the Pattern Part thing again... With a 11 tooth sprocket I fit a 2mm spacer before the sprocket to stop the chain chewing up the crankcase seal holder, Is that what it has done?... I will update the BSA Dizzy Upgrade page for you and put the information onto there... Take Care... Regards Charlie...
January 13, 20224 yr Author Mmmmm, interesting Charlie. no 2mm spacer behind the sprocket so may be why it snagged the seal.Just looking at the sprocket...if the shoulder the seal lip runs on was 40mm, would the 520 chain rub on it, looks very close even with the 37mm I have. Saying all that i am hopefully getting a new 11 tooth sprocket as this one is toast, but need a seal that will fit what ever size it turns out to be. Old bikes aye, so much has been done both good and bad over the years, they certainty tell a story!!!
February 4, 20224 yr Author Well thanks to Charlies advice fitted new sprocket with 53mm od seal and looks good. Made a special nut and locking screws as standard nut fouls the chain.
February 7, 20224 yr Hi Guy's... Hi Trev... Good job mate... Like the nut... I just knock the corners off of a standard nut. But I have also drilled holes in a couple to use a peg spanner like yours. Well done... Regards Charlie...
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