Timing a magneto

[4010boy]

Installing the magneto after it has been removed from the tractor can be done easily. as follows:
First, remove the spark plug on the flywheel side. Place your finger over the hole and rotate the flywheel in the running direction until you feel a pressure of air from the cylinder. Continue turning the flywheel slowly until the "LH Impluse" mark, stamped on the flywheel aligns with the timing mark on the tractor. In this position the slot in the coupling on the governor shaft will be horizontal.
Next, secure a short piece of wire and insert one end in the upper terminal of the distributor cap on the magneto, bend the other end around to within 1/8 inch of some metal part on the magneto frame. Hold the magneto solidly in the same upright position as when mounted on the tractor.
Grip the driving lug on the impulse coupling firmly and turn slowly in a left hand direction (counter clockwise). Stop instantly when impulse trips. Driving lugs on the impulse coupling will be in a horizontal position.
Replace magneto and gasket on the governor case, making sure the impulse coupling lugs engage slots on the governor drive coupling. A gasket must be used between bolting flanges. After tightening the two cap screws firmly with fingers, rotate the top of the magneto toward front of tractor as far as possible. Then rotate the flywheel one complete turn and line the flywheel mark "LH Impulse" exactly with the timing mark on the tractor. Now tap the top of the magneto toward the rear of the tractor a little at a time until the impulse trips.
Tighten cap screws holding magneto to governor case and install spark plug cables. Left hand plug cable must be installed in upper distributor cap terminal.

Submitted by Gary Derzinski
March 1992

[John T Nordhoff]

Richard, this procedure is "mostly" correct BUT can only yield a 50 50 chance (Depending on if its a direct drive Mag like the Wico C or X versus a gear reduction like Fairbanks Morse or Wico AP) that the Magneto isnt 180 degrees out of time in which case it could pop n bang or backfire something awful and/or kick the flywheel backwards OUCH.

The reason is on direct drive Mags like the Wico C or X they fire each 180 of revolution and fire each cylinder on BOTH TDC's, Power and Exhaust. The "tip" correctly calls for manually turning the drive until its Snaps/Impulses, BUT it does that once when it fires out the caps Top (Originally to left No. 1) terminal, and then 180 later it fires out the caps Bottom (Right No. 2) terminal. SOOOOOOO when you manually trip the impulse, theres ONLY a 50 50 chance the rotor tip just lined up and fired the CORRECT cylinder !!!!! The "tip" ASSUMES when you manually tripped the impulse it just fired the Top terminal (posed to fire Bottom 180 later) but theres an equal chance it may have fired the Bottom when you manually tripped it. If the manual trip just made her fire the Bottom right cylinder and you install the mag when the Top left is at TDC (i.e. Flywheels LHI at 3 O Clock) and turn it 180, shes next gonna fire the Top tower (to left No 1 cylinder) when its at the low end of its stroke (WRONG Weedhopper) and another 180 (total 360 full turn as called for in "tip" ) its gonna fire the Bottom tower (to right No 2 cylinder) when its at the lower end of its stroke (WRONG Weedhopper).

Of course, if its 180 out and she pops n bangs n backfires etc. one can swap the top n bottom plug wires to make her run, but thats NOT the original configuration.

ALSO the procedure may NOT work if the Mags Lag Angle isnt set approximately correct in the first place, i.e. impulse stop plate not correctly adjusted, because she may or may not Snap/Impulse when you rotate the mag backwards CCW in the govenor flange as the "tip" calls for.

ALSO the "tip" correctly calls for shorting out (or artificial 1/8 gap) the caps top tower to avoid risk of coil damage (One shouldnt dry fire those Mags) but again, how does one know its the Top tower thats gonna fire when you manually trip it ???? If unsure BOTH towers need protected by a short or artificial arc gap or else utilize a mag kill switch.

ALSO this procedure sets the static start/impulse timing ONLY but DOES NOT address the run time advance which is a function of the drive cup used (like a 25 or 35 BTDC etc.),, the mags rotational position in the govenor flange (that 10 or so degree adjustment window slot),, the points gap,,wear and tear and other minor factors.

Hey, dont get me wrong, this procedure indeed works for adjusting the static start/impulse timing (at least gets it close) its just that you have to have manually tripped the CORRECT cylinder to avoid the risk of backfire and/or flywheels kicking backwards. Such is easily accomplished by removing the cap and observing the position of the rotor tip or tips so as to know if you manually tripped the correct cylinder or not.

That's my story and I'm stickin to it until proven otherwise (Hey its sure possible, I been wrong before lol)

John "T" Nordhoff in Bloomington, Indiana Retired Electrical Engineer, Attorney at Law.

[Curious George gets ebola]

So, I think you are saying that if you are using a mag that fires every 180 degrees, and have it timed right, but you switch the plugs wires around it won't be timed right anymore. Is that right?

[John T Nordhoff]

Thats right George. If a Wico C or X (direct drive NOT 1/2 speed reduction gear drive) Mag is working and you swap plug wires IT WONT RUN. However, remember, if you install it 180 out of time (which makes it pop n bang n backfire etc) but then sawp wires, IT WILL RUN.

If its a reduction gear drive like Wico AP or Fairbanks Morse and they are 180 out, A WIRE SWAP WILL NOTTTTTTTTT CURE THE PROBLEM.

John T

[murphyImplementco]

Here is my carburetor and magneto work bench. Just finished rebuilding a Wico Model C in the work / test stand. I use a cordless drill with a home made adapter to drive the mag for testing. Two spark plugs are mounted on stand for testing.





Murphy