Not sure if it uses spur gears or helical gears. It is not planetary set. It
is a hydraulic gearbox in that there are clutches that are engaged only when
the engine is turning. You can shift these gearboxes from forward to reverse
at full throttle supposedly with no damage (the manual advises against it for
safety reasons, but says it can be done in an emergency). The gears are rated
for full power in either direction. A few different ratios are available,
from 1.26:1 to about 2.8:1. Most of the gears have a "down angle" output
shaft (8 degrees down relative to the crankshaft) and the output shaft is
also offset about 5 inches below the crank. Some gears are available with a
parallel offset output (just 4 or 5 inches offset below the crank, no angle).
The ratios for these are more limited.

Jon

 
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