TR2/3/3A Point Gap?

[karls59tr]

Is it possible to set the point gap correctly "after"the timing is set?
Some say you can use a timing light instead of static timing the engine. Is this done by backing the Vernier dial on the Dist out one section to get the 4degrees BTDC needed. How would you know where the correct mark on the crank pulley would be to use the timing light. Is there a measurement in "inches" BTDC that could be marked on the crank pulley?

 

[bobhustead]

No, unless you have previously set the gap and the timing and accidentally got the gap and dwell on the new points exactly as the old. To get a dynamic timing mark, you would need to calculate circumference of the pulley and divide by 360 to get the arc length of one degree. (Randall has done this for us in another thread). Then determine the degrees of advance for your actual idle speed, mark that distance from the factory zero and time away, then hope that your worn out distributor's advance curve will be right at other speeds. Go static. It is easy and it works. Factory recommended it. I time by ear and it works fine.
Bob

 

[Geo Hahn]

The reason you want to first set the points gap and then do the timing is that the gap affects timing. As you (typically) go from a too small gap to the correct gap the timing is advanced slightly -- the points open sooner with the bigger gap.

Yes, you can set timing at 0° and then use the vernier to set the advance. I like this method because I know where I am (and want to get back to) if I have occasion to change the timing on the road (inferior gas, high altitude, etc).

Of course any timing setting is an approximation and the ideal advance can be dialed in once you try it on the road.

 

[TR3driver]

IIRC 4 degrees is roughly 3/16" at the rim of the pulley. If you want a permanent mark, use a 3 corner file to cut a small notch, then fill it with white paint.

As Bob said, the problem with dynamic timing is that the stock advance curve starts way down low. The factory spec allows for as much as 2 degrees of centrifugal advance at 400 rpm! I believe they did that so the timing could be quite late while hand-cranking (which reduces the chances of kickback, broken arms and so on), but up where it belongs for normal operation.

Might be worth double-checking. I seem to vaguely recall that the book is wrong and the marks on the vernier are not exactly 4 degrees. I always touch up the timing with a road test anyway, so I don't pay much attention.