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Leroy

Info on retrofit. for a 20 hp to a 7117

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Leroy
This mowers original 17 horse engine died a broken rod death. I have bought a 20 Hp onan . Does anyone know if there is any issues with this replacement ? I have not recieved it yet , just trying to be prepared. This one has a oil cooler and a air cleaner that is different from the 17 hp engine so i am aware of those two items. My concern is the hydro tranny may not be able to handle the extra ponys. I have no need to whind the engine out . but in case it gets done by a teenage son will it burn the hydro out? Leroy

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HubbardRA
I doubt that a fully functional hydro unit is going to notice the three horsepower difference. Only time to worry about this is if you were dragging a tree stump or pulling a heavy trailer that would take everything the engine has to move it. Normal operation, the hydro is never heavily loaded, unless your son is trying to pull wheelies with the tractor by suddenly changine from reverse to forward. I have a 61 Wards that came with 7.25 Hp and it now has a 14 Hp engine, with the same 3 speed tranny. It has been used for tractor pulling for over 15 years, and has gone from 7.25 to 10, to 12, and now 14 Hp. We sheared a woodruf key in the diff, and cracked the old-style removable left hub. This all happened in the first year of pulling. No problems since. These are tough tractors, and it takes lots of abuse to break them. I wouldn't hesitate a bit in making the swap, if I were you. Rod H.

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powermax_paul
I agree with Rod. If you put the tractor under the same loads you did before, then you're not using any more HP than you did before. You might have a little more flywheel inertia with the Onan. Anyway, most hydros have relief valves for load and acceleration that'll prevent any damage to shafts etc. I also agree that these tractors are pretty tough and Simplicity probably used the same hydro in the 7119, 19 HP tractor.

Paul Kjorlie, The Norwegian

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Al
Hi, I agree. The strain on the hydro comes from the load, not the engine. You can "stall" hydro with a 12 hp engine. Stall is stall. If you put 100 hp in front of it the engine will still turn the pump 3600, the same as a 12. Do not slow the engine down. Most of these engines are designed to be run at 3400 to 3600.Running at part throttle can cause the valve seats to come out. Valve seats come out from excess heat that is usually caused by 1 of 2 things. 1 mowing at part throttle, or 2. plugged fins or restricted cooling. Restricted cooling can be a result of inadequate OEM testing for heat recirculation. Briggs doesn't always warranty valve seats coming out because they say it is caused by customer misuse for the above reasons. Note that Simplicity went to lifetiime drive belt warranty on many of the tractors, because Cub made a big deal about "THE SHAFT". The hydro usually uses around 2 hp and the mower from 10 up. Cub uses a shaft for the hydro and a belt and mule drive for the mower that eats all the power. Why not put the straight belt where the load is and a belt to the hydro. When this campaign was on our local Deere dealer advertised: Don't get the SHAFT. The Cub dealer returned: You will love getting the shaft from us. I say to heck with the shaft, MOVE UP TO A SIMPLICITY. Good Luck, Al Eden

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UCD
Leroy I have a 7790 Diesel rated at 18 1/2 hp. more like 25 hp. I have 75 lbs weights on each wheel plus the tires are loaded with chloride. the hydro has taken everything I have thrown at it and comes back for more. I have moved 38' camper trailers with it pulled, pushed or dragged cars and trucks into my garage with it. I blow snow wide open forward to reverse and back to forward my brake lining is just like new because it has never been used. The tractor has survived 17 years of very hard use. So i don't believe 3 extra hp. is going to hurt any at all. This & $1.00 might get you a small Coffee Maynard aka/UCD

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Leroy
Maynard I'm impressed. It sounds like you have a very good machine there. I am now attempting to line up the replacement motor with the old tranny shaft. Seems the Onan has different hole size on motor than the old motor. So the tranny to motor interface has to be developed. I have gotten two 4 inch 3 ply rubber disks ready for drilling or punching. Is there a better way to ensure a sure fit. my goal here is to illiminate vibration before it starts. Leroy

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