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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ET77 Main bearing distance piece
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<blockquote data-quote="timetraveller" data-source="post: 36775" data-attributes="member: 456"><p>OK Craig. I will try to describe the items. If you can handle either .dxf or .dwg files I could send you such a file but for reasons explained below it might not be very useful. The reason for the caveat is that not all mainshafts are the same diameter and hence any drawing of the items will not necessarily fit others. The standard mainshaft is 1" but people who raced sidecars, and some solo riders, started to use 1.125" diameter shafts for extra stiffness many years ago. If light series bearings were used then the outside diameters were the same as standard but inners fitted the larger shafts. More recently some of the later bikes (Eglis) have been built using metric mainshafts, 30 mm diameter which is even larger than the 1.125" size. Because of this the bearings and the final dimensions of all the parts will depend upon what you are using.</p><p></p><p>The idea goes back to Dan Smith as far as I know, about 30 years ago. I will describe what is needed and it might be easier to understand with a copy of your drawing to hand. ET92, ET19, ET77, ET91 and both circlips are discarded. The mainshaft housing is machined out both on its internal bore and on the outer face. A hollow 'top hat' housing is made which has an inwards facing spacer in the middle of it, machined as part of this bush. The flange is made large enough to take six countersunk holes with a diameter to match that of the outer part of the original bearing housing. The thickness of this flange and the amount machined off the outer (chain) side of the housing have to be matched so that the total length of the housing is the same as the original hole. The holes in the outer flange are there to take six counter sunk screws which hold the whole thing in place and prevent any chance of it rotating. The outer diameter of this top hat bush is made to be an interference fit in the opened out and newly machined, trued up housing. The idea is that a taper roller bearing outer is fitted into both ends of the new steel top hat housing, both pushed in so that they are tight up against the inner boss. The both have their wider ends facing outwards from the centre of the new housing. The central part of the inner bearing buts up tight against the flywheel, possibly with a shim to centre the con rods in the crank case mouths. Another loose spacer is required to fit between the two taper roller inners. The thickness of this spacer has to be such that there is about a 4 thou nip on the bearings when everything is tightened up. The outer end of the new steel housing has a left hand thread machined inside it to take a screwed in anulus which carries an oil seal. This oil seal carrier has four 'pin holes' in it's outside face in order to allow it to be screwed in with a pin spanner(wrench). The outside of the sprocket has to be machined and polished to fit inside this oil seal. (As with other main shaft oil seal systems).</p><p></p><p>I hope that you can see now why I have not given dimensions. It will depend upon the exact sizes of the bearing as to the thickness of the machined in central spacer and the loose spacer which goes between the two taper roller bearings. If this is not clear enough I could do a sketch but I have already put one in the Forum a couple of years ago but am not sure what words to used to search the Forum to find it.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 36775, member: 456"] OK Craig. I will try to describe the items. If you can handle either .dxf or .dwg files I could send you such a file but for reasons explained below it might not be very useful. The reason for the caveat is that not all mainshafts are the same diameter and hence any drawing of the items will not necessarily fit others. The standard mainshaft is 1" but people who raced sidecars, and some solo riders, started to use 1.125" diameter shafts for extra stiffness many years ago. If light series bearings were used then the outside diameters were the same as standard but inners fitted the larger shafts. More recently some of the later bikes (Eglis) have been built using metric mainshafts, 30 mm diameter which is even larger than the 1.125" size. Because of this the bearings and the final dimensions of all the parts will depend upon what you are using. The idea goes back to Dan Smith as far as I know, about 30 years ago. I will describe what is needed and it might be easier to understand with a copy of your drawing to hand. ET92, ET19, ET77, ET91 and both circlips are discarded. The mainshaft housing is machined out both on its internal bore and on the outer face. A hollow 'top hat' housing is made which has an inwards facing spacer in the middle of it, machined as part of this bush. The flange is made large enough to take six countersunk holes with a diameter to match that of the outer part of the original bearing housing. The thickness of this flange and the amount machined off the outer (chain) side of the housing have to be matched so that the total length of the housing is the same as the original hole. The holes in the outer flange are there to take six counter sunk screws which hold the whole thing in place and prevent any chance of it rotating. The outer diameter of this top hat bush is made to be an interference fit in the opened out and newly machined, trued up housing. The idea is that a taper roller bearing outer is fitted into both ends of the new steel top hat housing, both pushed in so that they are tight up against the inner boss. The both have their wider ends facing outwards from the centre of the new housing. The central part of the inner bearing buts up tight against the flywheel, possibly with a shim to centre the con rods in the crank case mouths. Another loose spacer is required to fit between the two taper roller inners. The thickness of this spacer has to be such that there is about a 4 thou nip on the bearings when everything is tightened up. The outer end of the new steel housing has a left hand thread machined inside it to take a screwed in anulus which carries an oil seal. This oil seal carrier has four 'pin holes' in it's outside face in order to allow it to be screwed in with a pin spanner(wrench). The outside of the sprocket has to be machined and polished to fit inside this oil seal. (As with other main shaft oil seal systems). I hope that you can see now why I have not given dimensions. It will depend upon the exact sizes of the bearing as to the thickness of the machined in central spacer and the loose spacer which goes between the two taper roller bearings. If this is not clear enough I could do a sketch but I have already put one in the Forum a couple of years ago but am not sure what words to used to search the Forum to find it. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ET77 Main bearing distance piece
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