I have been thinking about this problem for a couple weeks now, and have so
far not found an ideal solution. Any input would be very gratefully
recieved.

The scenario- Currently got a timber trailer with crane mounted on it. The
hydraulic power is supplied by a PTO driven pump with gearbox mounted on the
tractors PTO shaft. Now due to the tractor it's mounted on (MBTrac 1000),
the PTO is alot nearer to the drawbar than a conventional tractor.
Originally the pump was mounted onto the PTO via a PTO extension shaft, but
this had the problem that if the tractor went up a steep slope, the pump
would hit the trailer chassis and snap the tractors PTO shaft.
This was remidied by doing away with the PTO extension, grinding a bit of
the top flat off the tractors pick-up hook assembly, which allowed a flat of
the pump gearbox to sit ontop off the pick-up housing, eliminating the
possibility of it coming into contact with the trailer.
This has worked fine for a few months of intermittent use, but last week the
end off the PTO shaft snapped off, allowing sufficient room for the gearbox
to be spinned around and the gearbox casing smashed.

What we would now like to do, is to mount the pump onto the front PTO shaft,
which is never used. The current gearbox was geared so that the pump ran at
aproximately 2000rpm with an input speed of 540rpm (aprox. ratio of 1:3.76).
Now the PTO can be run at 1000rpm, which means a ratio off 1:2 can be used.
The pump output that the crane dealer specs is 76.9litres per min at
3500psi. Now given these figures I work the horsepower required at 2000rpm
as 51hp allowing for 80% pump efficiency (worse case), with required torque
off136lb-ft.

Originally I had thought about using V-belts, but due to limited space
around the front PTO, pulley size is limited to 7inches diameter, which
would require the use off A-section belts. Having gone through the various
calculations/charts, this would require 6 belts to transmit the required
power, and would not realistically fit in the available space.

I have also considered using a timing belt, but also due to the limited
pulley size, these would not be able to transmit enough power.

So I am back to using gears. My current idea is to utilise the gears out the
previous gearbox, and build a new casing, with the pump mounted on the
opposite side compared with the original gearbox, to allow for the front PTO
turning in the opposite direction. I may have to swap to using smaller
gears, and possibly altering the ratio to 1:2 due to space limits.

Do my belt results seem plausible?
The geabox would be construced by machining two plates to accept
bearings/seals, welding sides onto one off the plates, and bolting the other
plate on. Would this provide acceptable results?

Thanks In Advance

moray