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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
John Emmanuel Fork Shock Absorber Length
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<blockquote data-quote="timetraveller" data-source="post: 113719" data-attributes="member: 456"><p>Hi Vincent, I've just been out to the shed and measured a new AVO damper, top hole centre to bottom hole centre and I make that 252.3 mm, fully extended. There are two continuing mysteries with this conversion. The first is that on some bikes the front wheel can move far enough rearwards to hit the front exhaust pipe. This only happens if the handlebars are moved to the left and a very large bump is hit. On other bikes this does not happen. The second mystery is that on some bikes the AVO damper fouls the inside rear of the top link and the link has to be relived. On my own bike the maximum depth removed was 5 to 6 mm. On other bikes this does not happen. I cannot believe that either top or bottom links can differ in their for and aft centre distance to cause this and so far no one has found an explanation. Neither stops everything working well once the system is installed.</p><p>From your photograph and the text it seems that you have put a 1.5 mm spacer in under the bottom bearing. but you also show a Works damper. I don't know their centre to centre distance but unless it is about the same as the AVO, 252 mm, there might be some problems. Although John Emmanuel designed the new system I spent a lot of time with a Vincent front end off a bike and held on a work bench to work out the wheel spindle movement and over what range of total movement the system would work properly. With the original length over the steering head lug it is important that the lower link is about horizontal when the bike is fully loaded with the rider etc. If the front of the lower link is up to about 3 -4 mm lower then that will not be a problem. If it is, say, 8 - 10 mm lower, or more, than the rear then the wheel will move forwards at the start of its upwards movement, rather than upwards and rearwards, and so defeat what John was trying to achieve. If you start off with the front of the lower spindle too high then there will be no problem with the geometry but it will cut down the total movement available.</p><p></p><p>The extent of the downwards movement and position of the lower link front is controlled by the combination of damper length of eyebolt length. You can check this before the springs are fitted.</p><p></p><p>I designed the combination of spring strengths, damper lengths etc to try to give maximum movement and thus maximum comfort at the front end. You will have to experiment with the system to discover whether a 1.5 mm spacer makes any difference.</p><p>Also, just to clarify, the system is designed to work with the long lower eyebolts, as used with the Armstrong dampers, not the earlier short ones which work with the original Vincent dampers.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 113719, member: 456"] Hi Vincent, I've just been out to the shed and measured a new AVO damper, top hole centre to bottom hole centre and I make that 252.3 mm, fully extended. There are two continuing mysteries with this conversion. The first is that on some bikes the front wheel can move far enough rearwards to hit the front exhaust pipe. This only happens if the handlebars are moved to the left and a very large bump is hit. On other bikes this does not happen. The second mystery is that on some bikes the AVO damper fouls the inside rear of the top link and the link has to be relived. On my own bike the maximum depth removed was 5 to 6 mm. On other bikes this does not happen. I cannot believe that either top or bottom links can differ in their for and aft centre distance to cause this and so far no one has found an explanation. Neither stops everything working well once the system is installed. From your photograph and the text it seems that you have put a 1.5 mm spacer in under the bottom bearing. but you also show a Works damper. I don't know their centre to centre distance but unless it is about the same as the AVO, 252 mm, there might be some problems. Although John Emmanuel designed the new system I spent a lot of time with a Vincent front end off a bike and held on a work bench to work out the wheel spindle movement and over what range of total movement the system would work properly. With the original length over the steering head lug it is important that the lower link is about horizontal when the bike is fully loaded with the rider etc. If the front of the lower link is up to about 3 -4 mm lower then that will not be a problem. If it is, say, 8 - 10 mm lower, or more, than the rear then the wheel will move forwards at the start of its upwards movement, rather than upwards and rearwards, and so defeat what John was trying to achieve. If you start off with the front of the lower spindle too high then there will be no problem with the geometry but it will cut down the total movement available. The extent of the downwards movement and position of the lower link front is controlled by the combination of damper length of eyebolt length. You can check this before the springs are fitted. I designed the combination of spring strengths, damper lengths etc to try to give maximum movement and thus maximum comfort at the front end. You will have to experiment with the system to discover whether a 1.5 mm spacer makes any difference. Also, just to clarify, the system is designed to work with the long lower eyebolts, as used with the Armstrong dampers, not the earlier short ones which work with the original Vincent dampers. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
John Emmanuel Fork Shock Absorber Length
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