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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Setting valve timing
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<blockquote data-quote="Tom Gaynor" data-source="post: 18713" data-attributes="member: 4034"><p>Manx Nortons are (or can be) timed on "valve drop", making sure that there is 0.04" clearance between valve and piston. This is the way the instruction sheets (think Vin instruction sheets, typed on foolscap.) Even if one did NOT time them that way, it would be imprudent not to check. One tooth out on the bevels and the inlet valve will, just, touch. Amazingly, it didn't bend. Don't ask how I know this. </p><p>But if the timing IS done by valve drop, then the point of equal lift is - you've guessed - 4 to 6 degrees BTDC. I take that to mean that Norton wanted the maximum possible lift consistent with safety, and the maximum practicable compression ratio, and designed the motor that way. A Norton head has a cr of around 11.5:1. (A Summerfield "bathtub" head has 13.8:1 using the same fuel (and ignition advance) but does have different cams, said to be higher lift.) A standard Vin has a cr of about 7:1...</p><p>If at maximum valve drop you had a couple of feet of clearance, Vincents (and Rudges), having combustion chambers like the dome of St Pauls, then obviously there would be far more latitude for altering the overall valve timing. And some good might come of this, in some circumstances.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 18713, member: 4034"] Manx Nortons are (or can be) timed on "valve drop", making sure that there is 0.04" clearance between valve and piston. This is the way the instruction sheets (think Vin instruction sheets, typed on foolscap.) Even if one did NOT time them that way, it would be imprudent not to check. One tooth out on the bevels and the inlet valve will, just, touch. Amazingly, it didn't bend. Don't ask how I know this. But if the timing IS done by valve drop, then the point of equal lift is - you've guessed - 4 to 6 degrees BTDC. I take that to mean that Norton wanted the maximum possible lift consistent with safety, and the maximum practicable compression ratio, and designed the motor that way. A Norton head has a cr of around 11.5:1. (A Summerfield "bathtub" head has 13.8:1 using the same fuel (and ignition advance) but does have different cams, said to be higher lift.) A standard Vin has a cr of about 7:1... If at maximum valve drop you had a couple of feet of clearance, Vincents (and Rudges), having combustion chambers like the dome of St Pauls, then obviously there would be far more latitude for altering the overall valve timing. And some good might come of this, in some circumstances. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Setting valve timing
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