magneto drive cup

[1944bgardner]

I was not satisfied with my spark while hand cranking and after searching and reading(learning). I suspected an issue with impulse spring. I was alittle nervous to remove magneto and screwing everything up but glad I did now. Before I pulled magneto I hooked up timing light, degreed flywheel,checked timing. Spark right on TDC running timing was 40+ degrees, I only marked to 40. After pulling magneto found drive cup nut just laying in governor housing. Drive cup 6274 is 25 degrees. Drive cup has a chunk worn where it contacts stop plate, would this be enough to increase timing that much? Almost forgot 44B handcrank wico X.

 

[Duane Larson]

1944bgardner,
Your drive cup moved out when the nut loosened up, and wore the drive cup and probably the impulse plate. You can see the effects of a worn drive cup on my website under 2008 GOG talk on magneto - go to slide 31.

It is possible that by putting on your drive cup with a good nut, and tightening it, the drive cup will be pushed down far enough on the impulse plate (where the drive cup meets the plate) that you will not see much of an effect. You can measure this with your timing light. Otherwise, check the drive plate for wear, both where the drive cup rests on it, and where the drive plate fits over the flat on the magnetic rotor. Both places are a source of wear, and both serve to advance the timing. Both the drive cup and impulse plate are available new, if you need to go that route.
Duane Larson
http://jd2cylservice.com

 

[John T]

Where that drive cup slot/window opening (where yours is chipped away some) mates into/with the mags driven flange can affect the run timing butttttttttttt I dont see enough to change things from 25 to 40 degrees!!!!!!!!!!!!! (Ima thinkin a broken spring and perhaps a driven flange NOT in place on the rotor shaft flat and the chipped drive cup slot could have contributed to that too fast 40 BTDC NOT the chip ONLY, see below)

The positioning of the driven flange onto the flat on the rotor shaft sure affects timing, if it were out of place (not tight onto) relative to the rotor shafts flat cuz the nut was missing NOW THAT COULD REALLYYYYYYYYYYY AFFECT TIMING. If the spring is broke the driven flange versus drive cup position can be jumping around also

The run time advance is a function of the drive cup,,,,,,,wear n tear n slop in the cup (and its window opening) and driven flange,,,,,,,,,the rotational position of the mag in the govenors flange,,,,,,,,,,,the points gap n wear n other things BUT 40 BTDC IS WAYYYYYYYYYY TO FAST especially when using gasoline

I think I would get a new drive cup n spring and get it all reinstalled tightly onto the rotor shaft n see where youre at then. I'd set the run timing more like 25 BTDC certainly NOT 40

Of course, the govenor gears postion to the cam gear can affect things, if all else is correct, when the left piston is at dead TDC (Flywheels Left Hand Impulse at 3 o clock) if the cam to crank and especially cam to govenor are allllllll in time, the open female slot in the govenor shaft end (where mag mates) should be flat horizontal fore n aft, is yours ?????????

Once youre sure the govenor is in time, Im thinking a new drive cup and new spring will enable you to get more like 25 BTDC then 40

Hey, the mags mechanical components IS NOT my thing, Im better at its electrical aspects, but this is my best shot until a real mag expert arrives to our rescue (Yo Duane !!!)

John T

 

[1944bgardner]

Thanks for the information, Duane I have your website already bookmarked, has been a big help. Unless I'm calculating wrong, flywheel 60.5", 20 degrees=3.3611,25 degrees=4.2013, 30 degrees=5.0416, 35 degrees=5.8818, 40 degrees=6.7222. I verified TDC #1 comp stroke LH impulse, pulled petcock to see piston stop, it lines up with a previous stamping on flywheel. I will start with new drive cup and see what I get, spring looks good to me, will post back with results. Thanks Jim G