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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Big End Replacement
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<blockquote data-quote="timetraveller" data-source="post: 87513" data-attributes="member: 456"><p>The way that I true flywheel assemblies as follows. It presupposes that the ends of the main shafts are in good order. If you do not have them then you should be able to use your lather to make a couple of centres. One centre in the chuck and the other in the tail stock. I fit the crankpin into the drive side flywheel, which already has the main shaft fitted. I then fully tighten the crank pin nut. I then assemble the big end, con rods etc. and then press on the timing side flywheel and loosely fit the nut to the timing side of the crank pin. Put it in the centres, making sure that they are tight, but not too tight, and then measure the out of round near to the flywheels on the main shafts as the whole assembly is rotated on the centres. You will now need a block of hard wood, oak is good but other woods might do, and an immovable object. I normally use the concrete foundation of any local structure but others might have access to a large anvil etc. This is when you do your body building exercises. Having worked out in what direction the timing side flywheel needs to move, pick up the whole assembly by the drive side main shaft, taking care to hold the small ends loosely, and hit the block of wood with the timing side flywheel. Go back to the centres and measure again. This will tell you whether you need to hit harder or more often. Start to tighten the timing side crank pin nut, but not fully, and then go back and do the body building again. If the neighbours see you doing this then explain to them that you had wood worm in the piece of wood and were trying to give the insects a headache. It might take a few goes but it is better to sneak up on the correct settings slowly rather than go too far and have to come back on it. Once you have it correct then fully tighten the timing side crank pin nut and go back and check again that nothing has moved. If this does not work then either the flywheels have different distances between the crank pin holes and the mains shaft holes or the faces for the crank pin to sit against are faulty. I have seen the former but never the latter.</p><p>To show how things have moved on; I have somewhere a 1940s or 50s motorcycle hand book which advises using a set square against one face of a flywheel and across the two circumferences of the flywheels. This was clearly considered good enough for bike used during the second World War or in the forties and fifties. In the hands of a skilled mechanic this might have been good enough. I'm pretty sure if I tried it then the bike would vibrate the flywheels to pieces very soon.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 87513, member: 456"] The way that I true flywheel assemblies as follows. It presupposes that the ends of the main shafts are in good order. If you do not have them then you should be able to use your lather to make a couple of centres. One centre in the chuck and the other in the tail stock. I fit the crankpin into the drive side flywheel, which already has the main shaft fitted. I then fully tighten the crank pin nut. I then assemble the big end, con rods etc. and then press on the timing side flywheel and loosely fit the nut to the timing side of the crank pin. Put it in the centres, making sure that they are tight, but not too tight, and then measure the out of round near to the flywheels on the main shafts as the whole assembly is rotated on the centres. You will now need a block of hard wood, oak is good but other woods might do, and an immovable object. I normally use the concrete foundation of any local structure but others might have access to a large anvil etc. This is when you do your body building exercises. Having worked out in what direction the timing side flywheel needs to move, pick up the whole assembly by the drive side main shaft, taking care to hold the small ends loosely, and hit the block of wood with the timing side flywheel. Go back to the centres and measure again. This will tell you whether you need to hit harder or more often. Start to tighten the timing side crank pin nut, but not fully, and then go back and do the body building again. If the neighbours see you doing this then explain to them that you had wood worm in the piece of wood and were trying to give the insects a headache. It might take a few goes but it is better to sneak up on the correct settings slowly rather than go too far and have to come back on it. Once you have it correct then fully tighten the timing side crank pin nut and go back and check again that nothing has moved. If this does not work then either the flywheels have different distances between the crank pin holes and the mains shaft holes or the faces for the crank pin to sit against are faulty. I have seen the former but never the latter. To show how things have moved on; I have somewhere a 1940s or 50s motorcycle hand book which advises using a set square against one face of a flywheel and across the two circumferences of the flywheels. This was clearly considered good enough for bike used during the second World War or in the forties and fifties. In the hands of a skilled mechanic this might have been good enough. I'm pretty sure if I tried it then the bike would vibrate the flywheels to pieces very soon. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Big End Replacement
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