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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Crankshaft Balance Method
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<blockquote data-quote="LoneStar" data-source="post: 115521" data-attributes="member: 585"><p>Thanks, everyone, for the informed discussion!</p><p></p><p>Re. my basic approach of trying to muddle through myself, rather than delegate to Qualified Professionals - </p><p></p><p> - I enjoy messing with old bikes, so the time spent isn't a loss</p><p> - Not sure why drilling and weighing should require professional skills or equipment</p><p></p><p>Re. buying a new crankshaft, which would be of better quality - </p><p></p><p> - I'm cheap, and my current crank (being free) is 2500 USD less expensive than a new one</p><p> - The original cranks, despite their low-grade steel construction, have provided millions of riding miles since 1947 without a lot of failure. A new crank would no doubt be safer in a modified engine on a race track - but what benefit would a rider notice on the road? My current flywheels are now assembled with new rods, and true to .001 on the drive side, .0015 timing side.</p><p></p><p>Balance factor - I settled on 50% after reading a variety of opinions (including OVR - thanks Martyn). While experienced people can be found endorsing values from 35% to 66%, the original value of 46% can't be too bad, and most people think a bit higher is smoother. As my "frame" is original Vincent, no need to deal with variations due to Egli frame structure or similar. And since by most accounts, anything from 45 - 60% is acceptable, there's no need for great precision when balancing.</p><p></p><p>I'm still looking over all the posts on the balancing process. I see the benefit of removing weight from the crankpin side rather than adding to the opposite, but it will require removing quite a lot of material. Assuming equivalence of removing weight to adding it 180 degrees away, I'd need to remove 17.3cc of steel near the flywheel rim at the crankpin. </p><p></p><p>This would be a new axial hole through both wheels of c. 2cm diameter (no room), or equivalent enlargement of the existing ones. But I'm a bit scared of drilling or expanding axial holes there, due to the risk of damaging the rod big ends or getting swarf into the bearings. </p><p></p><p>Alternatively, it would require radial holes of 1/2" diameter with total depth of 14cm, or 3/4" holes with total depth of 6cm. </p><p></p><p>Given these factors, I'm still looking at adding tungsten plugs. True, the flywheel assembly doesn't need to be any heavier - but given it's current weight, I doubt an extra 135g will be noticeable.</p><p></p><p>Dave</p></blockquote><p></p>
[QUOTE="LoneStar, post: 115521, member: 585"] Thanks, everyone, for the informed discussion! Re. my basic approach of trying to muddle through myself, rather than delegate to Qualified Professionals - - I enjoy messing with old bikes, so the time spent isn't a loss - Not sure why drilling and weighing should require professional skills or equipment Re. buying a new crankshaft, which would be of better quality - - I'm cheap, and my current crank (being free) is 2500 USD less expensive than a new one - The original cranks, despite their low-grade steel construction, have provided millions of riding miles since 1947 without a lot of failure. A new crank would no doubt be safer in a modified engine on a race track - but what benefit would a rider notice on the road? My current flywheels are now assembled with new rods, and true to .001 on the drive side, .0015 timing side. Balance factor - I settled on 50% after reading a variety of opinions (including OVR - thanks Martyn). While experienced people can be found endorsing values from 35% to 66%, the original value of 46% can't be too bad, and most people think a bit higher is smoother. As my "frame" is original Vincent, no need to deal with variations due to Egli frame structure or similar. And since by most accounts, anything from 45 - 60% is acceptable, there's no need for great precision when balancing. I'm still looking over all the posts on the balancing process. I see the benefit of removing weight from the crankpin side rather than adding to the opposite, but it will require removing quite a lot of material. Assuming equivalence of removing weight to adding it 180 degrees away, I'd need to remove 17.3cc of steel near the flywheel rim at the crankpin. This would be a new axial hole through both wheels of c. 2cm diameter (no room), or equivalent enlargement of the existing ones. But I'm a bit scared of drilling or expanding axial holes there, due to the risk of damaging the rod big ends or getting swarf into the bearings. Alternatively, it would require radial holes of 1/2" diameter with total depth of 14cm, or 3/4" holes with total depth of 6cm. Given these factors, I'm still looking at adding tungsten plugs. True, the flywheel assembly doesn't need to be any heavier - but given it's current weight, I doubt an extra 135g will be noticeable. Dave [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Crankshaft Balance Method
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