Stanley Schaefer wrote:


Are the wheels coplanar?
One of the classic failures on these is the lower wheel walks
off the shaft. This misaligns the worm wheel in the gearbox,
so it can wreck the gears, too. I eventually bored out and
re-threaded the setscrew in the lower wheel, and it has not
slipped since. When the lower wheel has walked out on the
shaft a bit, the blade tracking starts to get unstable.
The check is to take the blade off and see if the lower wheel
can move axially. Any more than a few thousandths of an inch
is wrong, and an eighth of an inch is a sure sign this has
happened.

Jon