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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
TDC Timing Valve
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<blockquote data-quote="Tom Gaynor" data-source="post: 9505" data-attributes="member: 4034"><p><strong>Valve timing</strong></p><p></p><p>My current Manx Norton, my previous Honda K4 racer, my Rudge Ulster, my Vincent, all have equal lift between 5 (the median value) and 0 btdc. Only one of these was set that way by me. The Honda (works camshaft) came that way. </p><p>I asked the guy who takes care of my 86 bore Manx Norton (145 mph at Chimay last year), and who also builds all of Andy Molnar's 92 bore Manx engines (£27,000 a pop), if this was just coincidence. Nope. Any engine timed for equal lift within a few degrees of TDC will fly. Ignition timing is far more critical, and has to be right. (The Manx is 13.8:1...)</p><p>When I timed the Rudge, with a presumed hot cam for which I had no timing figures, I didn't bother with opening and closing figures, but set it for equal lift at TDC. I got about 3 degrees btdc. Before being detuned (down from maybe 7.3 to 7) it would touch 100 mph, now barely does 90. But cruises easily at 80. One swallow does not a summer make, but I think it indicative.</p><p>(As a sidenote, my experience is that the combination of a "race" cam with a low compression piston results in a motor that will go up the side of a house at zero rpm, not at all "buzzy".) </p><p>Even if you choose not to time your motor that way 1) it's a useful check to make sure you aren't a mile out and 2) if you should ever (heaven forfend) have to time a bike by the roadside, you now have an easy way to do it.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 9505, member: 4034"] [b]Valve timing[/b] My current Manx Norton, my previous Honda K4 racer, my Rudge Ulster, my Vincent, all have equal lift between 5 (the median value) and 0 btdc. Only one of these was set that way by me. The Honda (works camshaft) came that way. I asked the guy who takes care of my 86 bore Manx Norton (145 mph at Chimay last year), and who also builds all of Andy Molnar's 92 bore Manx engines (£27,000 a pop), if this was just coincidence. Nope. Any engine timed for equal lift within a few degrees of TDC will fly. Ignition timing is far more critical, and has to be right. (The Manx is 13.8:1...) When I timed the Rudge, with a presumed hot cam for which I had no timing figures, I didn't bother with opening and closing figures, but set it for equal lift at TDC. I got about 3 degrees btdc. Before being detuned (down from maybe 7.3 to 7) it would touch 100 mph, now barely does 90. But cruises easily at 80. One swallow does not a summer make, but I think it indicative. (As a sidenote, my experience is that the combination of a "race" cam with a low compression piston results in a motor that will go up the side of a house at zero rpm, not at all "buzzy".) Even if you choose not to time your motor that way 1) it's a useful check to make sure you aren't a mile out and 2) if you should ever (heaven forfend) have to time a bike by the roadside, you now have an easy way to do it. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
TDC Timing Valve
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