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Discussion Starter · #1 ·
Did the University of Nebraska ever test a Gravely PTO for horsepower output?

I glanced through some of their PDFs, but I didn't see anything Gravely:

http://tractortestlab.unl.edu/nebraskatractortestlabpublications

And it doesn't have to be UofN - I'd be interested in any other authoritative measurements of the power of a Gravely PTO.

For instance, if you've got something like a Professional 12, with a Kohler Magnum 12, and a quick hitch, then what portion of the 12HP makes it out to the PTO?

11HP? 11.5HP? A full 12HP?

Similarly with a G or an 8000 or a 9000 or anything else Gravely [even the old L's].

Thanks!
 

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Haha, I just searched the UNL tests yesterday! I was wondering the same thing. I found a David Bradley, but no Gravelys.
 

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That would be neat to know. Maybe someone should look into doing the tests now eh? or at least lend some Gravely to U of N.
 

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If you go back through the threads, awhile back I posted a "confidential" circa 1958 Gravely tech bulletin where they did a Dyno test against another engine. Very interesting.
 

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I have been looking around and found gear driven not hydro tractors from 150+ HP to 30HP the difference between engine HP and PTO HP is around 82% to 88%. So if you use 85% a 12HP should be around 10HP at the PTO. If someone has a roller pump out there and a pressure regulator ( and alot of free time on there hands ) you could see how much pressure you could develop before stalling out the tractor and then look at the PTO HP requirements adjusted for operating speed of the pump.

I had a homeaid spray outfit that used a 5HP engine and a roller pump and it worked fine at low spray pressure 30 - 50 PSI but when you cranked it up it would stall the engine right away.
 

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Discussion Starter · #8 ·
how much pressure you could develop before stalling out the tractor
I don't know as much about the earlier Gravelys [my Dad traded in his old Gravely when he upgraded to his 5665], but on the Kohler-era tractors with which I'm familiar, there's a PTO clutch which kicks in if you stress the PTO too hard [such as if you get a small log stiuck between the blade and the mowing deck].

Meaning that on the 5665, the PTO clutch tends to "stall" before the engine stalls.

So I guess that you'd first have to remove the PTO clutch if you wanted a test like that to work?

PS: Maybe there are some Gravely documents which describe the tolerances for the PTO clutches?
 

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I don't know as much about the earlier Gravelys [my Dad traded in his old Gravely when he upgraded to his 5665], but on the Kohler-era tractors with which I'm familiar, there's a PTO clutch which kicks in if you stress the PTO too hard [such as if you get a small log stiuck between the blade and the mowing deck].

Meaning that on the 5665, the PTO clutch tends to "stall" before the engine stalls.

So I guess that you'd first have to remove the PTO clutch if you wanted a test like that to work?

PS: Maybe there are some Gravely documents which describe the tolerances for the PTO clutches?
A quick search shows this engine produces 19.8 ft lb of torque

http://www.grainger.com/Grainger/KOHLER-Gas-Engine-6VMW2?Pid=search

Gear reduce the speed to 1000 rpm, the torque goes to 71 ft lb. Far beyond the clutch capability of 35 ft lb.

The extreme difference allows for errors in my math and assumptions.

Why did they bother with a 12HP or larger engine? :dunno:

Surely it was not for the needed wheel torque.
 

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Why did they bother with a 12HP or larger engine? :dunno:

Surely it was not for the needed wheel torque.
Higher RPM, perhaps the smaller engines available at the time may not have produced the required torque.

I prefer the Gravely engine, properly tuned I feel it is defiantly a good performer. I know some have had issues, saying it does not power a 40" deck very well, I have disproved this time and time again. I feel a lot of people having issues with L's are using Tractors that are not properly tuned, have incorrect governor setup or not installed altogether, worn/poorly adjusted magnetos, worn/poorly adjusted carburetors, incorrect valve adjustment and of course a flat out worn engine that has been worked hard for 40-50 years. The gravely engine produces a lot of torque and is designed to last a log time, how many small engines of the time actually had a full flow, filtered pressurized oiling system?




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Higher RPM, perhaps the smaller engines available at the time may not have produced the required torque.

I prefer the Gravely engine, properly tuned I feel it is defiantly a good performer. I know some have had issues, saying it does not power a 40" deck very well, I have disproved this time and time again. I feel a lot of people having issues with L's are using Tractors that are not properly tuned, have incorrect governor setup or not installed altogether, worn/poorly adjusted magnetos, worn/poorly adjusted carburetors, incorrect valve adjustment and of course a flat out worn engine that has been worked hard for 40-50 years. The gravely engine produces a lot of torque and is designed to last a log time, how many small engines of the time actually had a full flow, filtered pressurized oiling system?
I am in the nay-sayer category, as I never had the opportunity to operate a Gravely-engined machine that I thought had enough power.

10 HP Kohler is nice, 12 HP Kohler is better.

The 10 HP Magnum Kohler will loose speed in a hurry in too tall grass pushing a 36" Multi-Mower.

That engine is in perfect tune, and new blades on the mower.

Note: DISCLAIMER!! My comparison is the 24G cutting 72", which goes through the same height grass with ZERO effort.

I guess 16 HP allows you to have a way out of tune engine, and still get the job done.

There is no weight disadvantage to having a higher HP K-Kohler, might as well enjoy listening to that big puppie "talk"!! :fing32:
 

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A guy in another thread is trying to develop an Earthscvator (SP?).

http://www.mytractorforum.com/showthread.php?t=416218

Was one of these ever developed for a Gravely?

THAT is an attachment that would test the torque of a Gravely.

All that loose dirt and wide blade could really load the machine!! :bananapow
I think the problem would be the small tires of a Gravely two wheel not having enough tractive power, I have seen though where a very talented person made a 4 wheel scraper/grader out of an L, seems to work exceptionally well.


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I am in the nay-sayer category, as I never had the opportunity to operate a Gravely-engined machine that I thought had enough power.

10 HP Kohler is nice, 12 HP Kohler is better.

The 10 HP Magnum Kohler will loose speed in a hurry in too tall grass pushing a 36" Multi-Mower.

That engine is in perfect tune, and new blades on the mower.

Note: DISCLAIMER!! My comparison is the 24G cutting 72", which goes through the same height grass with ZERO effort.

I guess 16 HP allows you to have a way out of tune engine, and still get the job done.

There is no weight disadvantage to having a higher HP K-Kohler, might as well enjoy listening to that big puppie "talk"!! :fing32:
To me it's all in how the engine makes torque, the Kohler engines make their torque at a higher RPK, with out a doubt the Gravely powered L's are NOT the best cutters, I have done a lot to get my L to be a good performer with a 40" deck, having a properly operating governor can make all the difference in the world. The Kohler powered Gravely has a much better engine for hi RPM grass cutting.


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A quick search shows this engine produces 19.8 ft lb of torque

http://www.grainger.com/Grainger/KOHLER-Gas-Engine-6VMW2?Pid=search

Gear reduce the speed to 1000 rpm, the torque goes to 71 ft lb. Far beyond the clutch capability of 35 ft lb.

The extreme difference allows for errors in my math and assumptions.

Why did they bother with a 12HP or larger engine? :dunno:

Surely it was not for the needed wheel torque.
If you take that 71 ftlbs of torque and figure loss through the machine it drops to 60 ftlbs and if you consider that no engine can stand to run 100% and figure 75% then you get 45 ftlbs and then if you figure a saftey factor into the clutch so it won't slip and overheat....so maybe anything over 12 HP is overkill and was made to appease the higher HP that people have come to expect of riders and such today.
 

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It all comes down to a properly operating tractor. An L can do amazing things if it is running right and it doesn't have to be run at full bore. A Kohler 8 powered Pro 8 can do the same things with a good operator and it does not have to be run wide open. Same can be said of a Rapid M with a 9 HP Subaru engine. Running an engine wide open does not generate full torque on a modern engine. And it is torque that gets the job done. Torque on an L is doubled at the PTO. Torque on the later engines is tripled. But due to engine design differences, both will have about the same at the PTO. When you get to a bigger engine, you just have more breathing room and the engine recovers quicker under the same loads. I never run an L or other two wheeler at full RPM but allow the governor to have plenty of room to work.
 
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