Belt/Gear problem

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
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Is there a reason sprockets and roller chain won't work? I'd have to check but I think #60 chain handles this load. It would be smaller simpler cheaper.
Karl
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I'm not a great believer in high speed chain drives, but I did consider them. Going by the charts I have, it could be done with a 3/4" pitch Triplex chain, but the required sprockets would be too big, and also it would have to run in an oil bath. Also the expense is more expensive than purchasing new gears.
Thanks Moray
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snipped-for-privacy@v21.me.uk says...

Look at HTD toothed belts. A 14mm pitch x 85mm wide belt on a 40 tooth (178mm pitch dia) pulley is good for 70HP at 1000RPM. There are also a few proprietary cogged belts that will give even more capacity in the same space. Gates Poly Chain is one example.
http://www.gates.com/index.cfm?location_idU7
Ned Simmons
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says...

I'll look into that. The current supplier catalogue I've got only lists HTD belts upto 55mm wide.
Thanks Moray
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Moray, There are readily available, pumps made specifically to run off of the front pto, or crankshaft. Look at any older backhoe for an example........Would be much easier a task.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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The catalogues I've seen so far only list the same style pump and gearbox combination that has been damaged, which are too big to mount in the available space. Crankshaft mounting isn't possible as the pump oil lines will be disconnected when the trailer isn't in use. The biggest problem I'm facing, is that when merecedes designed the MB-Tracs, they took most of the components from Unimogs, and very little seems to meet any off the established Tractor standards. Alot of this is because the MB-Tracs use a conventional chassis with the components bolted on. Raising the rear PTO up to the standard height above the pick-up hook has even been considered, but the prop shaft for it would then have to pass through the rear axle. Other problem is that in the UK, front PTOs are not very common, so anything to fit them is very hard to come by.
Thanks Moray
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Sounds like you ought to just mount the pump back on the trailer, and drive it with a regular pto shaft, like used on balers, etc. That way the pump would be protected by the "tongue area" of the trailer and the driveshaft (PTO shaft) has the U-joints in it to permit manipulation of the tractor/trailer. Ken.
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<Ken Sterling (Ken Sterling)> wrote in message

This has been considered, but due to the design of the trailer, the pump would have to be mounted with the PTO shaft coming up from the tractor at about a 45degree angle, which would then put it directly in the line off the 3 point linkage arms when turning corners. Although this may be an acceptable method on a normal tractor, you can't see the rear linkage very clearly on the MB-Trac when driving it (cab is mounted forward on the chassis with an aprox. 3ft platform behind it), so any contact between the linkage arms and the PTO shaft wouldn't be noticed. This method is still on the list of considered ideas, but would prefer something more idiot driver proof.
thanks moray
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What about mounting the pump in the engine bay and plumbing back to the 3 point hitch with quick disconnect fittings
Scott
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