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Rider PTO speeds

6607 Views 11 Replies 6 Participants Last post by  Richard-tx
I've searched but can't find the 800/8000/G series rated PTO speeds anywhere in the Gravely literature.

Anyone know what they are for a 800/8000/G?

How about for a 24-G?



Thanks guys..
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What I've found is that an 800/8000/G is 1200 and the 24 is 1800. Somebody correct me if I'm wrong.
I have often wondered about this as well, so today I measured my G with the laser tach.

Measured engine speed = 3550 RPM, measured PTO output shaft speed = 1015 RPM

Engine speed is 3.5 times PTO speed.

So at GRAVELY factory governed speed of 3300 RPM, PTO speed = 942 RPM

I know the 24G is different, I don't have that info.

Sheldon
Don't forget to bring your laser tach the next tme you are in Mount Airy and we'll find out.

So does it turn clock wide or couter clock wise?
I have often wondered about this as well, so today I measured my G with the laser tach.

Measured engine speed = 3550 RPM, measured PTO output shaft speed = 1015 RPM

Engine speed is 3.5 times PTO speed.

So at GRAVELY factory governed speed of 3300 RPM, PTO speed = 942 RPM

I know the 24G is different, I don't have that info.

Sheldon
Will do, we can measure all sorts of stuff!

Clockwise, just like the engine, as you stand behind the tractor. Engine input clockwise, PTO clutch shaft counter clockwise, PTO output shaft clockwise.

Sheldon
Don't forget to bring your laser tach the next tme you are in Mount Airy and we'll find out.

So does it turn clock wide or couter clock wise?
Just depends on how wide the clock is! :fing32:
Don't forget to bring your laser tach the next tme you are in Mount Airy and we'll find out.

So does it turn clock wide or couter clock wise?
Thanks Sheldon. 942 RPM, makes you wonder why Gravely choose such a slow PTO speed?
The 24g PTO spins at 1/2 of engine RPM roughly. I measure 1800 @ 3100 RPM at the engine. In other words the 24g spins at 2x the 800/8000/G PTO speed. The PTO spins the same direction as the two wheel tractors.
I don't know for sure, but I suspect it was because it was similar to to the two wheel tractors, for attachment interchange, etc.

And, for torque, which is more important than HP for these tasks,

and for safety and durablity - something designed for 3000 RPM run at only 1000 RPM will likely never wear out or put parts into orbit.

Just like the thinking behind a Checker Marathon, a 3700 lb car with a front suspension originally designed for a 6000 lb Lincoln, and a rear axle designed for 6000 lb pickup trucks.

Sheldon
Thanks Sheldon. 942 RPM, makes you wonder why Gravely choose such a slow PTO speed?
I'm pretty sure that the second hand on a wide clock turns 1 RPM ;)
Just depends on how wide the clock is! :fing32:
Torque without speed (RPM) is useless.
Speed without torque is useless.
Horsepower is horsepower. The more horsepower there is, the more work it can do.

The quote "Torque is what does work, not horsepower." is false.


Torque, RPM, and the resultant horsepower are inexorably linked by virtue of the fact that horsepower equals torque (in ft-pounds) times RPM divided by 5250.

Below are 3 engines, all rated at 7.6hp but will produce that peak hp at different speeds.
engine #1 - 7.6hp @3600 RPM produces 11 ft. lbs of torque
engine #2 - 7.6hp @2400 RPM produces 16.6 ft lbs of torque.
engine #3 - 7.6hp @1200 RPM produces 33 ft lbs of torque.

If you take engine #3 and change the gearing via a transmission so that the output shaft spins at 3600 RPM and the torque goes down to 11 ft lbs.

Want to get more work done in a set period of time? Get more power and and lessen the gear reduction.
There are two standards for PTO rpm; 1000 RPM and 540 RPM.

The first PTO standard was adopted by ASAE (the American Society of Agricultural Engineers) in April 1927. The PTO rotational speed was specified as 536 ± 10 rpm; the direction was clockwise. The speed was later changed to 540 rpm.

Newer types, supporting higher power applications, operate at 1000 RPM.

So where does that leave the 24G with it's 1800 RPM PTO speed? Gravely had a speed reducer that it sold with a snow blower that would reduce the front PTO speed by a 2:1 ratio. That is why it is recommended that the engine speed be dropped to 1800 RPM when operating the tractor without the speed reducer.

Now that I have the data regarding the PTO RPMs, that mower deck that I took a video of was spinning with a blade tip speed of nearly 30,000 SFPM with the engine at 3100 RPM. The legal limit is 20,000 SFPM. One can calculate the proper engine RPM for a given mower deck when powered by the 24G without a speed reducer and still stay within the legal limits. The 50" deck spins at about 15,000 SFPM with the PTO shaft spinning at 900 RPM. Each mower deck is different. If I recall correctly and according to my sources, the 30" deck normally spins at about 17,000 SFPM.

Personally I like having the capability of more speed. When conditions warrant it, I have that flexibility.
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