Magneto adjustment??

[ScottyG]

Some of you may recall that I was having problems timing my Cub last year. I finally became so fed up that I pulled the governor and adjusted the gear, regardless of the timing mark until I got the timing to be close. I just chalked it up to engine work that someone did in the Cub's history with a careless reinstall as to timing.

Well, now that I've delved into engine work myself and made sure that all timing marks were lined up, I still can't ge the magneto to time properly. At TDC, the magneto coupler does not line up to the governor, at all. I always have to adjust the magneto and every time, I get a spark that is about 30 degrees advanced. Rats.

My question is with the old style magneto's, the kind with the square coil on top, is there a way to adjust the rotor gears so that the timing is proper? I'm talking about a way to pull on the rotor and reset it to get things right? Or... is it possible that someone could have reinstalled something in the magneto incorrectly. Keep in mind that I'm aware of the gears just underneath the rotor. The smaller one is keyed so you can't mess that up and the rotor gear is correctly synced mark to mark.

If this magneto isn't self adjustable, would all of you recommend just pulling the rotor gear and line things up until I can get a TDC spark?

Thanks.

[John *.?-!.* cub owner]

Scotty, getting the rotor correct is only part of the problem, the points have to open at the right time, and truning the rotor won't affect that. There is no internal adjustment in the magneto unless someone has pulled the impulse coupling plate and put it back on without the woodruf key installed. I know you have checked it, but is sounds like the idler or governor gear are not rihgt. Missy was that way when I got her. The person who rebuilt her had told the owner the mag was bad, and sold him a distributor rther than retiming.

[Eugene]

Your magneto may be working properly. The magneto operates at full advance except during engine cranking rpms.

To check the internal magneto gear timing. You need a Ohm meter. Remove the covers. Connect the ohm meter so that it reads the points opening and closing.

Rotate the magneto backwards. The points will open then close. You need to set the gears (timing) so that the rotor points to #1 spark plug tower just as the points close. You also need to check the magneto drive coupling. Usually the slot in the magneto drive coupling gear is in the horizontal position when the engine is on #1 cylinder TDC.

Clear as mud.

Eugene

[ScottyG]

Eugene,

The coupling is almost horizontal on the magneto so that correlates with what you're saying however, the governor is not horizontal at TDC. It's about 1/4 past horizontal. John, I'm absolutely positive I've timed the idler gear correctly. Checked and double checked before putting the front cover back on. I'll start the engine and see how it runs at full rpms. As I recall last year, the engine wouldn't smooth out unless I physically skipped a few of the governor gear teeth to get the spark closer to TDC.

[John *.?-!.* cub owner]

I have the magneto off one of my tractor now working on it. If you turn the enigne so #2 has jusut fired and # 1 is just beginning the compression storke, the drive lot should be approx. vertical, and the rotor should be at about the 11 to 11:30 position.

[Eugene]

Scotty: From you description you have the internal magneto gears timed correctly. However you can double check using the ohm meter.

I have not had the Cub magneto apart. I have had the IH H4 and the FM J4 completely apart. The internal timing marks were missing on both mags. I reassembled them using the ohm meter trick.

John. I'll defer to the vertical position of the slot in the govenor gear. I just installed the distributor in the NOS block engine and I'm thinking the slot was dead on horizontal. - it is on Allis Chalmers.

Scotty: Once you get the engine running, time the engine with a timing light and check the number of degrees in the advance. The lag angle (advance) for the J4 is 13 deg. Scotty, you stated that you have a 30 degree advance. Could it be possible you have the wrong magneto?

Eugene

[Mag Man]

Some times you have to trip past #1 on the mag becuase of the way the trip works. Then install the mag and turn the motor reverse with the crank well past the timing mark and then go back to timing mark and set the mag to trip. I would not mess with the rotor timing .You will end up with a ill running hard starting cub. Usally when there times right you can look at the cap and see that there burning off to one side or the other and then adjust the rotor to compensate but that takes a few hours to see usally . You need to fix the main problem first.
JON

[ScottyG]

Thanks guys. I'll keep trying and let you know what I find out. I was a little burned out last night after messing around with it for a few hours. I'll probably put it down for tonight and pick it up tomorrow... or then again... maybe not

[ScottyG]

Not beat a dead horse but, process of elimination here...

With engine at TDC, where should the governor gear (coupler) be pointed? Mine is in the 2:00/8:00 position so, about 1/4 before horizontal.

[ScottyG]

Also,

Is it possible for the governor coupler to be assembled incorrectly. Not the timing gear, the coupler.

[ScottyG]

Just a followup question as I'm still scratching my head here after being in the shed for another hour. I have the old style J-4 mageneto with the square coil cover. This however is not a magneto sparked engine. It was converted to battery ignition. Could this be the reason my spark is not occurring on TDC? Should something have been changed when it was converted to battery ignition?

[Mag Man]

No either or the J4 mag or the distributor. Did you do what I said and trip the mag past #1?
JON

[ScottyG]

Hi Jon,

Yes, I've tried working with it at each place before trip and after. It seems that it wants to be rougly 20 - 30 degrees advanced or 20-30 retarded. This happened to me before I tore the engine apart last year. I finally compromised and adjusted the governor gear until I got it close to TDC. Don't know why but it worked.

[WKPoor]

Scotty, Some time ago I posted on rotor timing when I was looking for a way to adance my mag. Therefore I know that can be a problem area. You may have been right on your first post in that if the rotor timing is off you will never get it right. By the way I talked to a tractor puller last weekend who mentioned that playing with the rotor timing is what some guys do to get the advance I was looking for.

[John *.?-!.* cub owner]

Here is the position of the drive slot at TDC. Note the drive turns on a one to one ration with the engine, so it will look the same averytime a piston comes to TDC. The only difference will be which end of the slot is to the right.