WICO C mag question

Thanks,

Ideally if all is new and theres no wear when the mag is mounted dead center straight up n down (NOT forward or backwards any at all) the 25 degree cup would fire her 25 BTDC and the 35 at 35 BTDC and she could be fine tuned from there for more or less advance

Remember, the rear lag angle stop plate adjustment ONLY affects start timing NOT run timing. Movement of the entirr mag out front in the flange affects BOTH

John T

• Restoration Site, John Deere

1) The "Lag Angle" refers to how many degrees the mag lags in timing when starting (spring winds n trips) versus when shes running. Thats determined simply by the rotational mounting relationship of the drive cup to the shaft (and where the shaft is i.e. the entire mags rotation in the flange). The mag fires when the cam opens the points, and when they open depends on the rotational mounting position of the drive cup to the shaft. The older C mags often had a 35 degree cup cuz they were mostly for all fuel in which case one could set the run timing more advanced since the distillate burned slower and then when they ran more on gasoline it burns faster and on many Wico X mags intended for gasoline they used only 25 degree drive cups. Sooooo oo Wico made a way to adjust the rear impulse stop plate so with any drive cup the start impulse trip setting would still allow them to start at TDC yet run at whatever advance the cup and where the entire mag was rotated (loosen two flange mount bolts) would allow.

2) The actual Lag Angle (how much start timing lags run timing) doesnt change (its fixed by the drive cups mount) when you adjust the rear impulse stop plate, ONLY the start timing is changed then.

3) When you loosen the rear screws and rotate the impulse stop plate, youre adjusting ONLY where the impulse trips i.e. its START TIMING..... ..... NOT the Lag Angle and NOT the run timing.

4) When you loosen the 2 mag to flange mount screws and rotate the entire mag, you change BOTH the start timing and the run timing BUT NOT THE DIFFERENCE BETWEEN THE TWO (thats the fixed lag angle)

5) What youre actually doing when you loosen the 4 rear screws and adjust the stop plate to those 2 or 4 index marks, is setting the start timing relative to whatever drive cup you have so the mag can SNAP n fire at TDC or wherever you want to set it i.e. your ONLY setting the start timing, youre NOT changing the lag angle youre NOT changing where she will run at over 250 RPM (run timing).

So Glen or Duane do I have this all correct??? Youre the guys who helped me prepare my Wico Seminar at the last GOG so if Im wrong its you guys fault lol lol just kidding

John T

The drive cup determines when the points open, it turns the shaft, and a 25 degree drive cup would theoretically open them at 25 degrees BEFORE the horizontal (when female slot in governor shaft is fore n aft flat horizontal and pistons at TDC) while a 35 degree cup opens them 35 degrees BEFORE the horizontal. I can look at a mag where the points just break open and where the drive cup is and physically about tell if its a 25 or a 35 cup

AGAIN, adjusting the rear stop plate ONLY changes the impulse start time while rotating the entire mag up front adjusts BOTH the start and run timing.

HERES MY CORRECTION THEN I guess then it could be said when you adjust the rear impulse stop plate youre changing where she starts at versus where she runs at and since I called that the LAG ANGLE (difference in start lagging run time) I reckon you are actually adjusting the Lag Angle which I just swore youre NOT changing. The correction would be where she runs at DOES NOT CHANGE by adjusting the impulse stop plate cuz at over 250 RPM thats not in the picture BUTTTTT T I guess you can and are adjusting the lag angle afterall when you adjust the stop plate cuz that does change the difference in where she starts versus where she runs BUT THE DRIVE CUP AND WHEN IT OPENS THE POINTS dont get changed by the rear stop plate adjustments is what I should have said EXCUSEEEEE EEE MEEEEE EEE LOL

Off to the auction hope I havent totally cornfused yall by now

John T

John T

The easy way I remember it is a 25 means you go 2 1/2 marks past center and a 35 goes 3 1/2 marks past.