After shoveling, snowblowing, and plowing 10″ of wet heavy snow this morning,
I told myself I was going to stay inside the rest of the day (or month), but
boredom and curiosity got to me, so I went out to the garage to look
at the 4 hp OB35A 4 hp Magneto. Compared magneto diameters between
the 4 hp and 6 hp OB64A that needs a coil, and they were the same OD.
Off to a good start, so I tried exchanging flywheel nuts. 6 hp nut was too loose
on the 4 hp crank….. and of course, the 4 hp nut would not go on the 6 hp.
Figured this was going to be a “deal breaker”, and it would have different crankshaft
taper and or diameter, but not much to loose at this point, so I pulled the flywheel on the
4 hp and slid it on the 6 hp crankshaft…. it fits!
Then removed the mag plate off the 4hp and it fit right on the 6 hp crankcase boss,
no problem. Both mag plates are stamped Model 72A. The 6 hp flywheel even appears
that it will work with the 4 hp mag underneath.
The 4 hp Eisemann coil looked good (but I’ve never had this 4 hp running or worked on it yet)
so I checked it with the Ohm meter. Reading 7.6 K across the secondaries, and .2 K on the
primary, so I think it’s worth a “go”, but it needs new plug wires for sure.
If it does work, I’ll be minus a coil on the 4 hp for when the time comes, so I may still be
experimenting with battery ignition.
P.S.- regarding the flywheel nuts, the small one is 7/16″ NF, and the the other,
between 7/16″ and 1/2″ NF. Is there such a bolt as a 15/32″ NF or something?
Prepare to be boarded!
