Timing 50 B

If it is equipped with a magneto, static timing can be done with either the CENTER or FIRE mark, depending on how the magneto is arranged prior to mating to the engine or what procedure is used to verify it after it is mated. If the engine is running and the timing is checked with a timing light, the FIRE mark should be used. For distributor ignitions, static timing uses the CENTER mark and dynamic timing checks with a timing light uses the FIRE mark. Take your pick. It depends on how you are doing it.

Rod

If I recall correctly, using the timing lug under the small mag cover and the FIRE mark, as you suggest, requires going past the impulse coupling trip point and backing up in reverse rotation to make the rotor and lug line up at the fire mark. In other words, during normal rotation, when the FIRE mark is reached, the rotor will stop prior to lining up with the lug as the impulse coupling winds up. When the coupling snaps at CENTER, the rotor position winds up being past the lug. When the engine starts and gets up to speed, the impluse coupling is no longer active and the rotor then lines up with the lug at FIRE.

I beleive that should be timed so points close as rotor passes #1 at TDC when the snap advance ativates.

If you have any other suggestions please let me know. This is making me very crazy. I have had the mag off and on so many times today I can do it in the dark. By the way, this mag was rebuilt by a local shop, but I did find the points set at .040 not at .020, so I did not trust they had it all correct as far as the timing went.

Thanks again, Ted

You are correct, the point gap should be 0.020. The work of the local shop is wrong. If they got the points wrong, they probably meshed the cover wrong also, although I am surprised you got it started at all if that were the case.

Usually it is the fiber driven gear where the "C" timing mark is difficult to see. The metallic drive gear usually has one tooth where the corner is knocked off, called a "dog eared" tooth and is reasonably easy to see. That's the way my FMJ is but I have heard about others where the marked tooth can have a spot of paint on it. Check again, using a magnifying glass for any indication of a marked tooth on that drive gear. Even if both marks are visable, it is sometimes tricky to assemble the large cover correctly since you loose sight of the marks as the cover is placed. I have found the best way is to have the drive gear marked tooth pointed straight up and the driven gear "C" pointed straight down while the cover is very carefully slipped into place. I have never tried it the way you are suggesting. I am not saying it won't work. My concern is impulse coupling windup messing things up. The rotor will only line up exactly with the timing stud (while the crank is at FIRE) when the impulse coupling action is out of the picture - e.g. engine running. That's why the FMJ instruction references turning the mag backwards when mating to the engine under the Advanced Spark Position Method, using the timing stud and the crank FIRE mark.

Hopefully someone who has done this without benefit of the internal timing marks will respond with a suggested method.

If Steve at B&B drops by, he'll see this thread and have some good input I am sure, since he rebuilds these mags all the time.

Here's something you can try:

1. Rotate crank to FIRE mark when #1 piston is coming up on compression. The two drive recesses in the governor drive gear should be nearly horizontal at this time.
2. Rotate the mag impulse coupling backwards until it can mate up with the distributor drive gear with the mag adjustment slot somewhere in the middle of the adjustment range. This assures that the windup of the impulse will not effect anything. Since the impulse rotates at crank speed, there can be only two different positions where it can be mated to the engine at this point; the correct position and one that is 180 deg out.
3. Line up the rotor with the timing lug and carefully install the main cover to the mag.
4. See if you get a spark at #1 terminal when the impulse snaps somewhere near crank CENTER with #1 on compression stroke (it could be a little before or a little after the CENTER mark). If so, you should be good to go and can fine tune using a timing light later. If not, then start over by re-mating the mag after turning the impulse backward 180 deg (crank at FIRE and #1 on comp same as before) and re-install the cover with the rotor lined up with the timing stud again.

I am not sure if one tooth off on the internal timing can be compensated for within the normal mag adjustment range. I do know that the engine should start and run even if the timing is not precise. I have never used a timing light to fine tune anything but I have always had those internal marks to use. I always use the Impulse Coupling Trip method of mating the mag to the engine when the crank is at CENTER with #1 on compression. That seems the easiest method for me. So I never use that timing stud at all.

Thanks again, Ted