Model H Mag timing

Hello Folks,

Good to be back working on my tractors. I need a little help. My Wico C mag impulse has stopped tripping and I can only start the H by pulling it with another tractor. I have an old Wico X mag that has a nice hot spark I want to swap out on the H but I have never timed one of these, only timed
an A & B.

Are there any tricks to timing the H since the mag is off the cam shaft instead of the crankshaft.

Appreciate the advice and help.

Gimpl

The mag is driven off the gov on all these tractors

I believe the H takes a "long lug" mag. So if you replace it keep that in mind.

Far as I'm concerned the X is a better mag anyway then the older C. To time it the FIRST thing I do is adjust the rear lag angle (four screws then rotate stop plate) to match what drive cup you have IE if its a 35 degree cup set the lag angle to 35 if its a 25 drive cup set lag angle to 25. Then install the mag and adjust by rotation so it SNAPS IMPULSES at the left piston TDC which is when the Flywheels Left Hand Impulse LHI mark is at the 3 o clock flat mark. Then I use a timing light to see what the run time advance is and as long as its in the 20 to 30 BTDC range I usually let her alone. If you dont get the mag in correct but 180 out she can run if you swap plug wires top to bottom.

NOTE some older all fuel tractors used a 35 degree cup but I prefer 25 for gasoline use.

As noted you need the correct drive cup so it fits into the slot.

I used to give Wico C and X Mag timing and troubleshooting seminar workshops at Gathering of the Green and Two Cylinder Expos but that was long ago and Ive forgotten a lot so no warranty on this.

I thought the belt pulley was driven off the cam instead of the crank on the H but the mag?????????????????? you sure???

John T

The H takes a Short Lug magneto.

Not much different from the A and B. With the mag off roll it to TDC of compression stroke for No.1 (Left) and look at the drive coupling. The slots should be horizontal. Turn the mag till it's about to fire the top terminal and install it. It will be leaning forward when the lugs engage. Then roll the mag backward slowly till the impulse trips and tighten the screws. It should fire at TDC for starting. The running advance is built in.

Thank you John T. You are right, I think I am over complicating this a bit. The pulley is off the camshaft and turns in the opposite direction as the flywheel.

I will take the old one off tomorrow night and see what I can do to get this one running again.

All the best, Gimpl

Thank you Kent, you are correct.

Sorry I was getting confused.

Thank you Mike, do I need to adjust the advance like John T talks about?

Gimpl

Youre welcome

YES INDEED you need to adjust the Lag Angle in the rear (loosen the 4 screws) to match whichever drive cup you have. If its a 35 cup set the lag angle to 35 if its a 25 cup set it to 25 WELL DUH............

John T

Hi John T

How will I know which cup I have.

I have seen them marked, maybe 6274 or 25 or 35??? If not its a matter of geometry and angles and those opening slots where the dogs come out and go back in at 250 RPM. I might figure out if I had it here but may not lol.

If I didn't know Id loosen the 4 screws and set the index mark to 4 1/2 marks to the left of top center. That will work for a 35 degree cup or a 6274 drive cup, but NOT for a regular non 6274 25 cup which would be set 2 1/2 to left.

Heres the deal and theory: If the lag angle is adjusted properly when you start time her to fire at TDC if all else is correct the mag will be pretty much straight up n down and then its run time advance will be correct. If the lag angle is way off the mag may have to be rotated a lot front or back to get start timing correct in which case the run timing will be off. It can still be made to start and run but that adjusting slot only allows for like 5 degrees either way so it just best to do it correct.

Try 4 1/2 to left and see where mag ends up when you fine tune rotational adjust it to snap/impulse at TDC (LHI at 3 o clock). If the mag has to then be wayyyyyyyyyy forward or wayyyyyyyyyyy back to snap/impulse at TDC, try the 2 1/2 to left rear adjustment.

AGAIN 10 years ago when I taught this at Gathering of the Green and Expo I had this all down but am running on memory now and haven't dug out my notes so I may be wrong as rain.

John T

Never messed with that.

I think it's usually stamped on.

Thank you again John T. Mine says 6274 and 25? so I set it at 4 1/2 and we're going to give it a shot

Gimpl

She runs. Fires on the first turn of the flywheel. Mag sits a little back from straight up and down but she sure runs great.

THANK YOU EVERYONE !!!!!

Gimpl