Is that right as the mag turns 2 degrees the engine only one?
If the mag runs 1/2 engine speed, surely the engine will turn 4 degrees for 2 magneto degrees
Lucas Mag' Earth Brush Holder Thread
- Thread starter cinquecento
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Is that right as the mag turns 2 degrees the engine only one?
If the mag runs 1/2 engine speed, surely the engine will turn 4 degrees for 2 magneto degrees
Whoops. Divide by 2, multiply by 2, what's the difference? Yes, 2 degrees magneto is 4 degrees engine.
I would have thought that with all the gears, backlash,imprecise magneto's and the atd that near enough is all your'e ever going to get with a vincent anyway. Perfection is great but is it realistic for a 60 year old machine, for that you really want a crank mounted modern electronic system.
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I've only timed two bikes with a strobe, both Triumphs and both with camshaft mounted breakers so only 3 gears in the train instead of the 4 of the Vincent. However, the backlash wasn't an issue for either because the engine rotation removed it and so the timing marks didn't vary, i.e. both were better than a degree. As for the ATD, timing is done with it mechanically locked in the fully advanced position so it bumps up against the same hard stop every time. So, the only reason I can think of that there would be a problem of timing variability in operation with a Vincent is if they are somehow manufactured much worse than Triumphs.
Having said the above, I don't lock magnetos myself when installing them. What I wrote earlier is that if you were going to lock them, you should lock them in a way that was reproducible. Another point is, even though backlash isn't an issue in operation, it is an issue to be concerned with when setting the static timing.
There are four gears that are driven in the Vincent gear train for the ignition. The driver is the crankshaft half time pinion gear. The key word is driven. A driven gear train mass when accelerated by the increase of its mass during RPM increase takes up each gear back lash in progression, half time to idler, idler to cam, cam to breather ,breather to ATD. some of the gears has only mass in its acceleration rate and some have its mass plus
lode . The reverse takes place when RPM decreases ATD to breather gear and so on. In real life the ignition is in constant change to ATD changing timing like a vary drive changing the gear ratio and the back lash changing the gear ratio during acceleration and DE acceleration.
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I have no idea what this means?? Nothing is gaining or loosing mass anywhere on the bike, other than the loss of mass due to oil slowly leaking out onto the road.
As long as the engine is spinning at or greater than the ~2000 rpm the ATD is "locked" in its fully advanced position so it isn't a factor. If the crankshaft could somehow abruptly come to a halt the other gears in the timing chest would continue to rotate slightly until they took up the backlash. This would alter the timing by that small amount. However, since your crank just came to an abrupt halt, this particular issue would be moot.
Short of such an abrupt halt the rotational inertia of each of the gears in the timing chest is very much less than that of the crankshaft. Because of this they respond much more quickly to changes so if the crank starts decelerating the other gears will have no trouble following this change and the same faces of the gears that were driven before are still driven, i.e. the backlash remains taken up and the timing doesn't change.
