Changed crank, strange things happened. M/w 9002B 5hp

[olliebird]

Think I finally figured out a strange problem when I changed my crankshaft to the newer powerhead. When I tried to fire it up all I got was a backfire each time I pulled the starter rope, so I thought I would switch plug wires so I put the bottom wire which has always been on the bottom, verified by the steel band to the top plug and top wire to the bottom. Two pulls and it started, now all I did was change the cranks, both powerheads are from M/W 1956 9002B motors. In the meantime I had to change plug wires as the bottom wire which I put on the top was too short and could not accelerate the engine. well, I decided to change both wires and now cannot acquire spark on top plug and very light spark on bottom. I decided to check the points settings and found that I now have to put the piston on TDC to set the bottom plug where as I always had to put the top piston on TDC to set it. Now could it be that the old crank and the newer crank had the keyways cut 180% apart and changed the timing? That is the only thing I could come up with, any opinions from the Pro's on this?

Appreciate any comments I may receive....

 

[F_R]

Re: Changed crank, strange things happened. M/w 9002B 5hp

As a guy that makes repro timing fixtures for those motors, I can assure you that all Universal Magneto crankshafts are the same as far as keyway position goes. Could your breaker cam be upside down?

All OMC Universal Magnetos, no matter which motor, are set up so that the coil most forward on the motor is for the top cylinder. When the points connected to that coil just begin to open, the top piston will be near TDC, but not necessarily AT tdc. That varies according to throttle setting. Now that I have introduced a potential confusion, don't be concerned about throttle position when setting points, it doesn't matter. Merely adjust them to .020" gap at their widest opening on the cam.

 

[olliebird]

Re: Changed crank, strange things happened. M/w 9002B 5hp

Looked up the reply from a previous quote where chinewalker replied that some of the earlier made engines were built with the Johnson TD-20 style magneto while others used the OMC universal mag. consequently using different crankshafts as to why I had to change cranks in mine.