February 21, 20215 yr On 2/17/2021 at 11:14 AM, IDC said: Back on its wheels at last. Only taken 25+ years! Is the engine a 37a Villiers?
February 21, 20215 yr Author As far as I can tell it is a 37a but with a few variations on what I would expect. It has slimline crankcases and a slimline gearbox & chaincase with the 37a type outer cover but the flywheel cover is fully cast and has a large circular points cover instead of the classic villiers cut down casting and semi oval points cover. I am just rebuilding the gearbox as on checking the ratios it was not standard 37a in fact it was mainly 31a/35a as far as 2nd and 3rd was concerned but with a 15t mainshaft and a 26t ratchet wheel! I have a spare 32a gearbox so am planning to rebuild the gearbox with standard 37a ratios. By the way there are signs that the gearbox output bearing has turned slightly in the casing, a problem which I believe from your post in 2015 that you have come across before? loctite bearing fit on reassembly should sort it out as the bearing is still a slight interference fit. The other thing I was not expecting is that it has an oval con-rod fitted to standard crank webs, I thought these were only fitted to full circle crank webs ie the Alpha type.
February 21, 20215 yr Yes, I fixed the bearing issue with Loctite. mine also had the large round points cover! Good luck, it's a nice looking chassis
February 22, 20215 yr The points side 36A magneto outer case with the round cover is perfectly okay for a trials engine. Is the flywheel fitted the all brass one or has it got the additional weight ring fitted to the outer face? Your bike appears to be a late model similar to the one shown here Sprite Motorcycles (historywebsite.co.uk) these had a longer exhaust on the right hand side, this was a big improvement over the earlier short type fitted on the left hand side making the engine run much better. Edited February 22, 20215 yr by trialsrfun
February 22, 20215 yr Wow must be something in the air just started sorting my MK1 sprite out this weekend only when to have a look and bike ended up in bits. I had to sort the ratios out on mine it had 16 tooth crank sprocket 25 pinion gear 14 tooth front sprocket and 67 rear sprocket ? all over the shop. Rebuilt with more usable ratios. Now running but the exhaust is so loud it's untrue
February 22, 20215 yr Author Hi Trialsrfun, thanks for the link to the Sprite history website, mine was registered in 1967 and as you say looks very much like the one in the picture. Unfortunately I only have a short exhaust pipe for the nearside so it will be interesting to see how it runs with that. The flywheel does have the extra weight on it and the engine seems to be a mix of 36 & 37a unless it was supplied like that which I doubt, shame the picture on the history website does not show the offside so I could see which flywheel cover it had.
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