Posted by John T on August 05, 2009 at 06:26:41 from (66.244.97.31):
I been puttin this off but its kinda froggy outside and I have a little time so will lay just a bit of Wico C and X Mag timing talk on yall cuz theres been a lot of cornfusion lately. I wish once more to give my dear departed friend Duane Larson and Glen Schueller down in Texas credit for helping me with this topic over the years and prior to giving my own first Mag Seminars. Just a few definitions this time:
LAG ANGLE ? Its how much (in degrees) the start/impulse timing LAGS behind the run time advance.
HOW IS IT ADJUSTED ? By loosening the 4 rear screws holding the stop plate in position and rotating the stop plate. NOTE Rotating the stop plate AFFECTS START/IMPULSE TIMING ONLY NOT RUN TIMING
WHERE SHOULD IT BE SET ? Think about it, if the run time advance is say 25 BTDC and the tractor needs to start at TDC, THEN THERE NEEDS TO BE A 25 DEGREE LAG ANGLE DUH How to set it will have to come later, it depends on which cup is used.
WHAT DETERMINES RUN TIME ADVANCE ? (Thats over 220 RPM when the impulse assembly stops functioning) Its PRIMARILY a function of which drive cup you have (like say a 25 or 35 advance cup),,,,,,and the rotational adjustment position of the mag in the flange (about a 10 degree window). Its SECONDARILY the points gap and wear n tear n slop in the drive cup and driven flange and bearings/bushings etc. NOTE rotating mag in the flange AFFECTS BOTH START/IMPULSE AND RUN TIMING
I FIRST set my lag angle adjustment if needed and then set the start/impulse timing (so she snaps right at TDC) either by stop plate adjustments and/or fine tuning by rotating mag in the flange and then use a timing light and for a parade use tractor if shes anywhere near say 20 to 30 BTDC I let it go. IN MY OPINION 35 IS WAY TOO FAST FOR GASOLINE it was more for Distillate tractor fuel use in older tractors many of which were equipped with C mags and 35 degree drive cups. My friend Duane who was more precise and particular FIRST used a timing light to get his run time advance EXACTLY where he wanted it, marked its location in the flange, and then removed the mag however many times it took and re adjusted the lag angle (stop plate rotation) so she snapped/impulsed right at TDC.
Enough for now, theres all sorts of info on lag angle and edge gap n other "stuff" but I wanna get outside n adjust up the rear brakes on my RV since I just put new pads up front and turned the rotors wooooooo hoooooooo
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