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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Burman Gearbox failure
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<blockquote data-quote="Howard" data-source="post: 11961" data-attributes="member: 271"><p>Hi Vic</p><p> </p><p>Hope I'm not teaching my Granny to suck eggs, but it's not the gear teeth that are the problem. They are straight cut, and won't cause the axial loading that has caused the damage, even when worn.</p><p> </p><p>The axial (side) load as I see it can only come from "foot on the gear pedal" or "worn dogs" as mentioned by others. Your photos don't show the dogs, but you'll probably find that the original sharp corners are rounded off with wear and tear and the mating faces of the dogs have worn so that they are no longer parallel to the shaft. This causes a wedge action pushing the dogs out of mesh, if not restrained by the selector fork, which isn't designed for this type of loading.</p><p> </p><p>I'd be surprised if it's only the top gear dogs that are worn, unless the gearbox has been partially rebuilt, so check all the dogs before rebuilding.</p><p> </p><p>I've never had a grease filled Burman gearbox, but while it's apart I'd try to get the seals right, and fill it with a good gear oil instead. I'm sure someone will tell me why grease was used, and oil can't be substituted, but I've run a lot of oil filled Burmans with no problems that I remember.</p><p> </p><p>H</p></blockquote><p></p>
[QUOTE="Howard, post: 11961, member: 271"] Hi Vic Hope I'm not teaching my Granny to suck eggs, but it's not the gear teeth that are the problem. They are straight cut, and won't cause the axial loading that has caused the damage, even when worn. The axial (side) load as I see it can only come from "foot on the gear pedal" or "worn dogs" as mentioned by others. Your photos don't show the dogs, but you'll probably find that the original sharp corners are rounded off with wear and tear and the mating faces of the dogs have worn so that they are no longer parallel to the shaft. This causes a wedge action pushing the dogs out of mesh, if not restrained by the selector fork, which isn't designed for this type of loading. I'd be surprised if it's only the top gear dogs that are worn, unless the gearbox has been partially rebuilt, so check all the dogs before rebuilding. I've never had a grease filled Burman gearbox, but while it's apart I'd try to get the seals right, and fill it with a good gear oil instead. I'm sure someone will tell me why grease was used, and oil can't be substituted, but I've run a lot of oil filled Burmans with no problems that I remember. H [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Burman Gearbox failure
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