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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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<blockquote data-quote="Martyn Goodwin" data-source="post: 78615" data-attributes="member: 2433"><p>Having had time to consider and re-examine the installation of the modified head stem on my bike I have a few post installation recommendations.</p><p></p><p>The main effect of the mod is to change the path that the front axle moves through as the suspension compresses or extends, thus reducing the likely hood of a tank slapper. Unmodified, as the suspension moves upwards the wheel moves outwards - away from the motor, the modification reverses this in that as the wheel/axle move upwards it now also moves backwards, towards the motor. The modification also changes the relative position of the axle and the front links so in any given state (of loading) they are higher than with the standard setup.</p><p></p><p>With this in mind there appears to be some caveats that need to be carefully checked before you can call the modification complete - it’s a tad more involved than simply replacing the head stem.</p><p></p><p>With the spring boxes removed AND the front wheel off the ground you need to make sure that there is at least a 3/4 inch clearance between the rear of the mudguard/mudguard stay and the front of the motor. At this stage also move the forks from full left lock to full right lock checking to ensure that NO cables ir wires are catching anywhere or are being stretched or are at risk of being squashed.</p><p></p><p>Now slowly lower the bike onto its front wheel (again without the spring boxes in place) and check again for a minimum ¾ inch clearance between the front guard and the motor throughout the full travel of the suspension. Again, do the cable check. </p><p></p><p>If you have less than ¾” inch clearance <u>at any point of the front suspension travel</u> between the mudguard/mudguard stays and the motor, you will need to reduce the radius of your front mudguard, shorten the mudguard stays to suit and also make up replacement mudguard hangers (FF68) to match the reduced radius mudguard. </p><p></p><p>While the bike is sitting on its front wheel without the spring boxes and with the front shock absorber fully compressed, measure the distance between the spring box mounting points - that’s the bolt in the centre of the concentric bush in the lower link and the bolt hole at the foot of the fork blade. Now take a pair of the spring boxes without any springs in them and push them together and measure the distance between the mounting points on the spring boxes themselves. This second measurement needs to be at least a 1/2" shorter that the distance between the mounting points on the bike. If this is NOT the case then there is a risk that the spring boxes themselves may 'bottom out' when riding SO you will need to shorten both your inner and outer spring boxes, by as much as need to give the minimum 1/2" clearance.</p><p></p><p>If you attend to these matters, the implementation of the improved head stem should proceed without any suprises.</p><p></p><p>Martyn</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 78615, member: 2433"] Having had time to consider and re-examine the installation of the modified head stem on my bike I have a few post installation recommendations. The main effect of the mod is to change the path that the front axle moves through as the suspension compresses or extends, thus reducing the likely hood of a tank slapper. Unmodified, as the suspension moves upwards the wheel moves outwards - away from the motor, the modification reverses this in that as the wheel/axle move upwards it now also moves backwards, towards the motor. The modification also changes the relative position of the axle and the front links so in any given state (of loading) they are higher than with the standard setup. With this in mind there appears to be some caveats that need to be carefully checked before you can call the modification complete - it’s a tad more involved than simply replacing the head stem. With the spring boxes removed AND the front wheel off the ground you need to make sure that there is at least a 3/4 inch clearance between the rear of the mudguard/mudguard stay and the front of the motor. At this stage also move the forks from full left lock to full right lock checking to ensure that NO cables ir wires are catching anywhere or are being stretched or are at risk of being squashed. Now slowly lower the bike onto its front wheel (again without the spring boxes in place) and check again for a minimum ¾ inch clearance between the front guard and the motor throughout the full travel of the suspension. Again, do the cable check. If you have less than ¾” inch clearance [U]at any point of the front suspension travel[/U] between the mudguard/mudguard stays and the motor, you will need to reduce the radius of your front mudguard, shorten the mudguard stays to suit and also make up replacement mudguard hangers (FF68) to match the reduced radius mudguard. While the bike is sitting on its front wheel without the spring boxes and with the front shock absorber fully compressed, measure the distance between the spring box mounting points - that’s the bolt in the centre of the concentric bush in the lower link and the bolt hole at the foot of the fork blade. Now take a pair of the spring boxes without any springs in them and push them together and measure the distance between the mounting points on the spring boxes themselves. This second measurement needs to be at least a 1/2" shorter that the distance between the mounting points on the bike. If this is NOT the case then there is a risk that the spring boxes themselves may 'bottom out' when riding SO you will need to shorten both your inner and outer spring boxes, by as much as need to give the minimum 1/2" clearance. If you attend to these matters, the implementation of the improved head stem should proceed without any suprises. Martyn [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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