Farmall Cub

Static timing of a magneto has always been a little confusing....at least to me....as to what you actually should see with the cap off. After the process of timing, #1 TDC, rotor pointing to #1 position on cap, mag all the way against engine block, engine rotated 360 degrees back to TDC #1, then rotate mag outward until impulse trips. At that point......doesn't the rotor point a little beyond #1. (Impulse tripped). So if I had a properly timed mag, as I was bringing the timing mark around to TDC, just before the mark hit the pointer, I should hear the impulse trip. Then when I remove the cap, the pointer should be slightly past #1 tower?

I'll throw in my 2 cents... put fresh dry plugs in it or take the ones out and dry them off good, take a carb off a runner and put on it. Start it up.
Looking forward to you figuring out if this is parts or not... revitalized Bashful or will you be selling me parts ?

Harold...when I have done mine, the mag trips at the timing mark and the pulley "surges" past the mark...depending how much, I will turn it back to the mark.

Winfield Dave wrote:Harold...when I have done mine, the mag trips at the timing mark and the pulley "surges" past the mark...depending how much, I will turn it back to the mark.

Dave, that is my experience most of the time as well. The impulse on the mag is pretty strong and once it trips, the engine turns much easier! I also turn it back to the pointer. However, if you start with the mag coil rotated as far back to the block as you can get, the impulse should not trip when you are coming up to the pointer. If it does, your governor is out of time, and you won't be able to get any better timing than that without taking the governor out and triple checking its timing to the idler gears.

I also find that when I am slowly rotating the mag top away from the block of the tractor, when the impluse trips, I have to be REALLY careful not to let the mag continue rotating. That impulse is a strong sonofagun!

Mike in La Crosse, WI

I had this funny feeling that I just might have had the timing out by 180 degrees.

I tried to verify #1 TDC by:
the thumb over the plug hole method - couldn't feel it [probably fingers too cold]
compression tester - no reading
small piece of paper over the hole - BINGO
ALSO verified by watching #1 valves - exhaust, suction, compression and then the pointer was at the notch in the pulley.
and the rotor was pointing at #1 position.
So I did have it on #1 TDC !!!

Just to completely get rid of my funny feeling, I pulled the mag and set it for #4 TDC and still no fire.

While I was switching it back I checked the governor lugs to be at 8:30 and 2 o'clock positions - lining up with the punch mark on the gov case.
[they weren't this way when I originally started this - that is what led me to find the gov out of time]
And checked the marks again on the rotor gears.

Tried it again after switching back - no fire.
I even turned it over by hand and watched the valves - and #1 plug sparked when I thought it should.

Eugene wrote:One more check. Crank engine slowly over by hand until magneto snaps. Check rotor position. If not at #1 spark plug tower, roll engine over one more full turn until magneto clicks. Now move the engine crank shaft until the pointer/timing mark is about 5/8" past the TDC alignment - this should be close to the full advance (normal running) position. Now check the rotor location - should be pointing at (centered on) the distributor cap #1 plug wire location.

Checked this also.

Pulled the manifold off to make sure there was no obstruction in there.

I have been assuming this is still a 6 volt system.
Could that be the problem if it is in fact 12 volts?
I have been hooking a 6 volt battery to the coil for juice and hitting the starter with 12 volts from a battery charger/jumper.

I'm not even close to giving up yet.
Next is to pull carb from Hercules after plowing is done and try it on Bashful.

Dave, I am confused , you say mag and then you say running a jumper wire to the coil? a mag needs no jumper wire unless it has been converted to a dist.

Boss Hog wrote:Dave, I am confused , you say mag and then you say running a jumper wire to the coil? a mag needs no jumper wire unless it has been converted to a dist.

Boss...the mag is empty [no internal coil]...the tractor has an external coil...I thought the external coil needed power to function, that's why I connected it via jumper to the 6 volt battery...Am I wrong?

Dave - no, you are not wrong. The external coil requires a voltage source to work. You are using only the distributor portion of the magneto.

Observing valve function is my favorite method of locating top dead center, for ignition timing purposes. I don't watch the valves on #1, however, but #4. As the piston approaches TDC. the exhaust valve is closing and just it reaches TDC, the intake valve will start to open. I stop at that point & align the timing mark. That's TDC on #1 cyl. It's easy & totally fool proof.

Gary Dotson wrote:Observing valve function is my favorite method of locating top dead center, for ignition timing purposes. I don't watch the valves on #1, however, but #4. As the piston approaches TDC. the exhaust valve is closing and just as it reaches TDC, the intake valve will start to open. I stop at that point & align the timing mark. That's TDC on #1 cyl. It's easy & totally fool proof.

THANKS for that great tip, Gary.

Rudi...Tip of the week?

Actually that is a great tip and one that I can actually see... A very useful alternative method to finding TDC It is now Cub Tip of the Week! January 19th, 2011

I guess I should have shared this method a long time ago, I've done it this way for years, anytime I have visual access to the valve train. Glad you guys like it!

I hate to bringthis up but of you timed the mag you might have it firing just past #1 inbetween 1& 3, might try turniung the engine backwords 1/2 turn then try to start. Im probabley wrong but it a feeling I have!

I tried a couple more things today after plowing snow.

1-I watched the #4 valves as Gary mentioned above while turning the engine over by hand...the #1 plug sparked at the correct moment.
2-Sprayed starter fluid in one of the plug holes and cranked it over to see if it would fire - no go.

Would it still be a good idea to pull the carb off a runner and try it...in light of #2 above?

Or is it time to pull the head and see whats what?

Since the compression test was so good.... I really find that it didn't fire with starter fluid sprayed in directly baffling.... my only thought is really weak spark ?
Or the ignition switch isn't properly functioning...