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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ATD Springs
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<blockquote data-quote="Martyn Goodwin" data-source="post: 139267" data-attributes="member: 2433"><p>It has been a while since I visited this topic and despite much work on ignition timing, magneto setup and ATD tweaking I remain bugged by the phenomenon of having a motor that once hot will not return to a steady idle speed .</p><p></p><p>To recap I run an original magneto and an original ATD .</p><p></p><p>With the ATD off the bike - and cold - it returns smartly from the full advance position to the full retard position. And I assume it also does so when fitted to the bike, for , from cold, over the first 20 to 30 minutes of operation the motor will return to a steady idle. However once well and truly warmed up the idle speed increases significantly. Stationary, if I engage first gear and slip the clutch I can 'pull' the revs down to a sensible idle but as soon as I pull the clutch in the revs rise!</p><p></p><p>I gave this some thought and figured it must be temperature related - that the engine heat was somehow reducing the ATD spring force but allowing it to return when the springs cooled down.</p><p></p><p>Today I discovered the attached article which confirms that this is expected spring behaviour! </p><p></p><p>I have spoken with a local spring manufacturer about the issue and that have said they can custom make some ATD springs in a grade of material that will NOT exhibit this problem provided the springs get no hotter than FIVE HUNDRED degrees Celsius. I figure that's well within the temperature rise in the timing chest!</p><p></p><p>I am waiting on a quotation from them though they did warn me that the wire to be used was around US$3,000 per Kg. I have asked for a quote for 2 sets and also for 20 sets as I suspect anyone who actually rides their magneto equipped Vincent must experience this issue.</p><p></p><p>So if that's you, would you be interested in a set of heat resistant ATD springs?</p><p></p><p>Martyn</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 139267, member: 2433"] It has been a while since I visited this topic and despite much work on ignition timing, magneto setup and ATD tweaking I remain bugged by the phenomenon of having a motor that once hot will not return to a steady idle speed . To recap I run an original magneto and an original ATD . With the ATD off the bike - and cold - it returns smartly from the full advance position to the full retard position. And I assume it also does so when fitted to the bike, for , from cold, over the first 20 to 30 minutes of operation the motor will return to a steady idle. However once well and truly warmed up the idle speed increases significantly. Stationary, if I engage first gear and slip the clutch I can 'pull' the revs down to a sensible idle but as soon as I pull the clutch in the revs rise! I gave this some thought and figured it must be temperature related - that the engine heat was somehow reducing the ATD spring force but allowing it to return when the springs cooled down. Today I discovered the attached article which confirms that this is expected spring behaviour! I have spoken with a local spring manufacturer about the issue and that have said they can custom make some ATD springs in a grade of material that will NOT exhibit this problem provided the springs get no hotter than FIVE HUNDRED degrees Celsius. I figure that's well within the temperature rise in the timing chest! I am waiting on a quotation from them though they did warn me that the wire to be used was around US$3,000 per Kg. I have asked for a quote for 2 sets and also for 20 sets as I suspect anyone who actually rides their magneto equipped Vincent must experience this issue. So if that's you, would you be interested in a set of heat resistant ATD springs? Martyn [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ATD Springs
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