What size rotary cutter

[spd132]

Bought a 1955 Ford 640 a few weeks ago. Tractor has been restored and engine runs very strong. According to tractor data the 640 puts out 31 hp at pto. I am getting ready to buy a rotary cutter but can't decide on 5' or 6'. I measured rear of tractor and 5' would be just inside tires by about 1-2" on each side and 6' is about 4-5" wider than tires on each side. I have always heard 1' for every 5hp. My question is do you think the tractor would be ok with a 6' cutter? If anyone has experience with the 640 and cutters please let me know.

 

[tman1020]

Personally I prefer the brushcutter not to stick past the rear tires for the majority of cutting I do. Might be a different story if most of your cutting is in wide open areas.

 

[kenmac]

You appear to have the HP to run a 6 footer. If you have the means, you can add weight to the front if it gets light with Heavy duty cutter

 

[JimRB]

Remember that HP and torque are two different things. Gas and diesel engines have different characteristics. Often a diesel tractor has more torque than a gas engine given the same HP. A 30 HP diesel might be able to do more work than a 30 HP gas based on increased torque. Of course getting specs on torque might not be that easy. Unproven theory of mine about torque. I do know my low HP diesel car is really easy to drive because of its high torque. People who are used to gas engines are amazed at how peppy my 50 mpg car is.

My little diesel 870 has similar HP to your 840. My 5 foot JD brush cutter has a closed back deck which I think mulches more than an open back deck. It has to go pretty slow in thick stuff. Slow defined as 3 mph and fast cutting defined as 6 mph. Just know if you get a 6 foot deck you might have to go slow in thick grass. Of course a brush cutter with an open rear deck or cutting higher than I cut can make a difference too.

As H of D mentions, many tractors have provisions to put counter-weights on the front of a tractor. My tractor manual has a listing of how much weight for different implements.

 

[jeff9366]

Bought a 1955 Ford 640. Tractor has been restored and engine runs very strong. According to tractor data the 640 puts out 31 hp at pto. I am getting ready to buy a rotary cutter but can't decide on 5' or 6'

1. That was 31-hp/PTO in 1955. Even restored you probably have less, especially as it is gas. Your tractor is 2-WD, which is no big deal UNLESS you will mow slopes. On slopes both uphill traction and downhill braking may be safety issues.

2. If you will mow along fence lines you will want a mower a bit wider than your rear tires.

3. If you buy narrower, tractor tires will mash down some verdure before it is cut. If you will be particular about the job you will not want a mower narrower than full width of tires.

4. There is a great variance in weight within 5' and 6' Rotary Cutters, and that weight is cantilevered behind the rear axle. The 'leverage' weight can mount up fast, making the front light. So do not buy too heavy an implement. You do not want the RC to lift either the front wheels or rear wheels off the ground on a slope.

5. Recommendation:

A. Consider a "Standard Duty" 6' RC but add a good bit of weight to the front of the tractor. Keep the RC blades sharp to reduce the PTO power required to spin the blades.

B. If you will regularly mow well spaced saplings, up to 1-1/2", which is what a standard duty R/C can handle, go with 5'.

I had a well used Standard Duty (40-hp gearbox) King Kutter RC that was an excellent implement.

Why not take time to fill in your T-B-N profile? You will get responses more particular to your questions.

 

[nybirdman]

I don't believe you could handle a six ft.cutter in anything other than very light cutting.My tractor is 37 HP diesel at the PTO and can bog it down(6ft.Landpride) in very heavy long grass.I was surprised because this never happened with my 5ft'er.I was set on purchasing a 7ft.and glad I didn't.

 

[Texasmark]

I have no problem running a 6' with my 2000D (a 600 series painted blue and a later model year). You can always shift to a lower gear when the going gets rough or just cut half the width of the cutter in the tough stuff.

I like the 6' for 2 reasons.

I prefer the mower to stick past the tires for mowing fence rows and it keeps the tires out of the next round. You do have to know the overhang is back there but just watch out for it. It's just a few inches on each side.

Any time you mow you have to have some overlap to ensure a clean cut with no holidays. From a percentage point a 6" minimum overlap is a 10% loss on a 5' and 8% on 6'. The wider your safety factor the higher the loss. On a big field with many laps that 20% additional loss adds up over the time it takes to do the field.

For my uneven terrain, I find the 6' is the best width having gone from 4' to 8' with twin blades and rear tires over the years. Current is a 6' Branson med. duty (65 hp gearbox) made by Kodiak. The light duty would do fine for you as the gearbox on most of them are rated at 45 drive hp max.

Added comment: If you have a tranny driven PTO get an overrun clutch for your PTO which allows you to "disconnect" the tractor from the turning shaft on the mower when you want to throttle the tractor down or shift gears. It will keep you out of a fence, or save you climbing a tree....with the tractor. Live PTO or Independent are the preferred for me with live being preferred for drilling holes for fence posts. Tractor Supply has them.

Also, having had drag and 3 pt, I'll take 3 pt hands down.

Mark

 

[kenmac]

My little diesel 870 has similar HP to your 840. My 5 foot JD brush cutter has a closed back deck which I think mulches more than an open back deck. It has to go pretty slow in thick stuff. Slow defined as 3 mph and fast cutting defined as 6 mph. Just know if you get a 6 foot deck you might have to go slow in thick grass. Of course a brush cutter with an open rear deck or cutting higher than I cut can make a difference

I have an open rear on my 5 footer & 35 HP diesel.. I have to go slow / raise the cutter higher in thick grass . SO, smaller cutter & diesel engine ,doesn't mean you can cut thick grass fast or as close as you want. I have had my dieael engine killed several times cutting thick grass real close

 

[GManBart]

I ran a standard duty 5' cutter behind an early (late 1947) Ford 8N that was rated at 21hp (like 19 at the PTO) and it worked fine. If you stick to standard duty 6' cutters you should have no problems. As with anything, you may have to slow down a bit in the heavy stuff, but it should still handle it.

 

[GManBart]

1. That was 31-hp/PTO in 1955. Even restored you probably have less, especially at it is gas.

If the engine was properly rebuilt it should be capable of making as much power as when it was new, or at least very close (sometimes more if you're more careful than the line guys making it 55 years ago).

The thing that might make a difference is that the rating was determined with 85.7 octane (RON) which isn't what you can get at the pump now. Modern U.S. regular is normally 87 Octane, but it's the (R+M)/2 method which would make it around 91 or 92 octane on the RON scale. Higher octane makes less power except in an engine that needs it to prevent knocking, and a 6.6:1 engine doesn't need it.