Correct PTO RPM for bush hogging?

[gemutlich]

Fellas I swear the search and advanced search here mess with me just for the sport in it... Flipped back through 13 pages of posts in this vintage ford forum also and couldn't find an answer.

Proofmeter cable arrived today and I installed it - happy to see the 'meter works, probably hasn't in a few years.

I'm sure the old boy who had used this tractor and mower to bush hog the last 50 years or so just used his ear and didn't need some silly tach to tell him what RPM he should set at to spin the mower at the right RPM.

I don't have that experience yet, and until just a couple hours ago my Wife and I were just kinda winging it when we mowed.

Ground speed we can figure out, my question is: What is the correct engine RPM to maintain while mowing that ensures the (Ford 90-I) bush hog is turning at it's safe, designed speed?

Heretofore we were in standard range using 1st or 2nd gear depending on how tall the grass was. Now that we're able to drop the Sherman unit into underdrive (and overdrive), maybe there's another gear that would suit us better?

Picked up a nice little mowing job for tomorrow but some of the stuff is 7' high. Would like to go into it at the right Engine RPM and in the right gear so as to keep the mower in it's sweet spot RPM.

Thanks guys, appreciate your help.

 

[vvanders]

I'm assuming it's not a live PTO? On our Ferguson TE-20 it's at 1500rpm since the gearing is 2.75 once you find out what that is should be simple to find RPM -> PTO speed of 540.

 

[gemutlich]

Thanks, 'Vanders.

I may have just answered my own question just by looking at an old pic of that proofmeter.








*EDIT* And now that I've started this thread, I see all the way at the bottom of the screen there's a collection of "Similar Threads" which further discuss the engine/pto RPM's and ground speed

 

[vvanders]

Yup, looks like 1500 to me.

Good news is someone else who owns a 641 that someone has tinkered with can use this for a reference in the future(like many TBN threads).

 

[gemutlich]

...Good news is someone else who owns a 641 that someone has tinkered with can use this for a reference in the future(like many TBN threads).

Roger that.

 

[Soundguy]

yup, it's actually marked on the PM..

you do realize that using a sherman to reduce ground speed, ALSO reduces pto speed.. right?

the sherman simply replaces the transmission input shaft.. thus if you lower the input speed to the transmission, you lower the output speed of anything comming off of it.

about the only thing this gains you is engine rpm. In other words, you can go to underdrive, then raise the rpms past normal pto rpms, to get ground speed and pto speed back up. you are traveling at the same speed as normal, but in a higher rpm range on the engine.

 

[Soundguy]

I'm assuming it's not a live PTO? On our Ferguson TE-20 it's at 1500rpm since the gearing is 2.75 once you find out what that is should be simple to find RPM -> PTO speed of 540.

live or non live make -0- difference on pto rpm...

 

[gemutlich]

Dang, SouNdguy, I'm sure I'd read that somewhere but had forgotten (about the effect the Sherman unit has on pto rotation speed).

Feeling kinda dumb right about now, lol

Thanks for clearing that up (brush hog pun...) for me.

Now the question I have, is in std range at 1500 rpm in 1st gear won't the ground speed be a little fast to mow that tall heavy stuff?

 

[Soundguy]

depends. tall stemmy weeds cut easier than tall lush grass. So, much of it depends on the material you are cutting. Also, no law says you have to take full width bites. say you have a 5' mower and the stuff is just too stiff to mow a whole row width. Instead, drive down the new row with only half the mower on the row. Sure, takes 2x as long to cut, but you can 2x tough stuff. Lastly.. your rpm number is just a blade tip speed issue. you can certaintly cut at a faster speed. if you can give the engine throttle, and it takes it, then it's not lugging.. if it's not lugging, your not hurting it. I have drove an old 8n down a pasture that had 7' tall ragweed and dog fennle. I was standing on the running boards and every now and then could see over the top of the weeds. I had the throttle maxxed, and could maintain rpm in 1st gear. I stopped every 15 minutes to clear a 2" layer of weed fluff that would collect on the radiator each pass.

If you can keep the rpms up and not stall / lugg.. you can cut it.

Remember, if 1st/normal / 1500 are too much.. try under/1st, and 2000.

 

[gemutlich]

Roger that