3 speed PTO and my finish mower

[ctown75]

I have a 5' finish mower on my MT160D. My tractor has the 3 speed PTO, I believe the speeds are 540(1), 720(2), and 900(3). I have been mowing this summer on 1 at 2400 RPMs like the tach indicates for the 540 RPM. Can I switch up to the second speed (720 RPM) and run my tractor a little slower? Obviously as long as the power is there would be the answer, but what would my correct RPMs be to keep the deck at the same speed? If my math is correct, I come up with 1800 RPMs. Am I right? Thanks in advance.

Scott

 

[KennyV]

You are right 1800, will work fine but do not run the rpm up while in that faster pto speed. Your mower will not like over speed KennyV.

 

[greg_g]

First, I'll preface this by assuming your mower manufacturer specifies 540 RPM at the transmission input shaft. Second, I'll state that yours is a common misconception by first-time tractor owners. You wouldn't do that on a riding mower - or even a push mower - so why do you think it will be of any benefit on a tractor?

Two reasons not to; engine life and blade tip speed. Tractor engines - particularly diesels - are engineered to operate most efficiently in the upper RPM range. You should consult your owner's manual to find out at what RPM the engine develops max torque. Any actual work performed by the tractor should be done at no less than the point at which max torque is developed. Slower than that, you can actually wear the engine out faster. What little fuel may be saved by working the tractor below max torque RPMs will usually be offset over time - by the amount of money spent on premature engine and cooling system problems.

Blade tip speed is a design factor considered by the mower designers. They go through a mathematical process to first determine how fast they blades they use need to spin for the best cut. Then they assume the tractor PTO will be putting out a true 540 RPM at/above max engine torque. Below max torque, the engine bogs down too quickly in thick grass, blade tip speed drops, the cut suffers. Anyway - given a design blade speed and 540 PTO rpm - they then design a mower transmission in the middle to make that happen. Over and above the premature tractor wear mentioned above, fooling with the blade tip equation can often result in a less than satisfactory cut.

The time tested approach is simply to follow the manufacturer's advice. When mowing, run the tractor engine at the RPM necessary to produce the mower-specified PTO speed (in this case apparently the typical 540) - then control ground speed with the transmission.

That said - if 1800 RPMs on your tractor is at/above the torque peak, then it will mow fine in the light stuff. Just expect a poorer cut when the engine bogs down.

//greg//

 

[Ranch_Hand_Supp]

Which PTO out put speed of the tractor is determined by the PTO rated speed of the gear box.



Ronald
Ranch Hand Supply

 

[ctown75]

First off thanks for all the speedy replies

Second, I'm far from a first time tractor owner, but thanks for pointing that fact out. The only first about this mitsubishi is it's the first tractor I have owned that has a multiple speed PTO.

Third- since when have diesel engines been designed to operate best at high RPMs? That's poppycock. You ever looked at a diesel tach VS at gasoline tach? My diesel truck redlines around 3200 RPM and runs down the road about 1500 where my gas truck's redline is nearly double that and runs down the road about 2300. Those are trucks obviously- but just for sake of proving a point. Of course the motor likely generates the most horsepower near the rated RPM, otherwise the rated RPM would not be there, because the place of the rated RPM is based on power specs.

The huge advantage of a 3 cyl diesel at 18 HP vs and 18HP single cylinder gas is torque- and torque is what keeps everything spinning. As far as HP goes, that 18 HP is probably up at 2400 RPM. The highest torque is probably made closer to 2000 RPM or lower. EVERY engine's peak torque is different(and almost always lower RPM) than HP- and that's fact. It is likely that this tractor makes MORE torque at 1800 than at 2400, so as far as rotational force is concerned, the 1800 RPM is likely easier for the tractor to turn than the 2400. Now obviously the strain is more when you go from the 540 speed PTO and increase that load by 1/3 to 720- so that's more work needed to be done.

I'm not stupid, so obviously if the tractor is not operating as well on the higher PTO speed and is barely chugging along at the lower RPM, lord help me I will go back to lower PTO and higher RPM. I wasn't concerned as much with saving fuel as much as saving wear on the engine. There are a reason big rigs chug down the road at 1500 RPMs- because they are aiming for 500,000 miles without a major overhaul. I haven't mowed with this new mower much yet, so I don't even know how it will act at will act in the situation at hand. I probably won't get to until next year either. I just purchased it when I sold my riding mower(which was gas and I always operated at full throttle because the book said to LOL)

I really do appreciate your input on the situation. It got me thinking about it a little more this morning. Obviously it's near impossible for you all to judge the situation via the internet- you're going 100% off of what I tell you.

All that being said- the main reason for this post was to know if I was correct on the PTO speeds on this tractor. All the selector says is :1 - 2 - 3. I was assuming on those pto speeds above. Thanks!

 

[greg_g]

Well, you asked - and I've got no dog in this hunt. So since my answer isn't the one you wanted to read, ignore it.

WRT to my statement about diesel RPMs, this is an agricultural forum (read off-road). My statement about diesels working most efficiently at/above the peak torque RPM was made accordingly. And I'm not stupid either. Having >20 years experience with both, I know quite well the differences between on-road and off-road diesels. FWIW, I'm currently operating and maintaining one on-road, two off-road, and five PTO-powered implements.

But for the record, standard PTO output RPMs are in fact 540/720/1000. So despite what you consider poppycock, I guess you got what you came for after all.

//greg//

 

[ctown75]

Now I wasn't trying to be rude, I was just saying that I think you're wrong in one of your statements. I guess I shouldn't have asked a "Can I" question, because I obviously can do whatever pleases me, the same as anybody else. I think the question shouldve been "should I". I realize now I knew the answer, just needed to talk it through in my head. I guess my point will be this: There wouldn't be a 3 speed PTO if the manufacturer's intentions were for every implement to be ran at 2400 RPM and at the first PTO setting. Am I correct there at least?

I have two diesel trucks and three diesel tractors and I know as well as you do that having 100 diesels doesn't mean you know a darn thing about them- I've known guys that've owned diesels their whole life and couldn't change a fuel filter.

Thank you for answering my question about the PTO speeds, that is exactly the information I didn't have.

Thanks and good day!

 

[radioman]

now this discussion is making me think - wait a second here -- uhh what PTO implements needs higher rpms. from there we can discuss it further. why did manufactuers put those higher RPMS if most of the equipment is 540 ? call me ignorant or whatever - i am just curious here . anyone care to enlighten me ?

 

[ctown75]

Well I thought I was on the right track but who knows! LOL

My guess is that because most of the tractors with the multi speed PTO are foreign made, that there are implements over seas(and likely here as well) set up for higher RPM. My new Agco has the option of midmount PTO for a mower deck, if i got that it would be rated at 2000 RPM- but it's rear PTO is only 540. Mowers and things like that need to spin fast(obviously). They probably keep the 540 on there for things like augers, etc.

 

[wushaw]

Doesn't CAT use on-road diesels in many of their tractors? Like the Challanger line.

On-road/off-road, does it really matter just as long as you follow the manufactures recommendations on what to do with what they built.

 

[Spudland_Dave]

Back before getting our L2900, we had a Bolens (the exact model # escapes me because I was a bit too young to remember it)...well anywho, That Bolens (Iseki) had a 3 Speed PTO as well...usually speaking we always ran it @ 540, the ONLY attachment we had that Loved "2nd Gear" was the 60" Lucknow rear blower we had on it...wouldnt blow snow to save its life at 540 RPM because of the puny 20" fan and relatively slow tip speed, but spinning it up really made a blower out of it....Tractor worked fine like that and the blower is still living behind the L2900 albeit with 6" wing extensions on each side....My dad had to build a 1:1.333 Speed Increaser using chain & sprockets because the L2900 is "handicapped" with only a 540 PTO.

If I were you, I'd try it and experiment....that being said....keep in mind your doing things that are not "OEM Approved" be prepared for what might happen....damage, etc...

 

[Diamondpilot]

I have to agree with Greg here. Yes you can run it at other pto speeds but is it the best practice. It would be like driving you truck around not using 1st and 2nd gear but instead starting off in 3rd or higher. This would put alot of stress on the moving parts and probably end up using more fuel due to the longer spin up time and higher throttle positions required to maintain a good cutting speed when in heavier grass.

Just do as the manual states and you will enjoy trouble free tractor time.

Chris

 

[ctown75]

If I had a manual- I'd be all over it. But I don't! Haha

 

[PILOON]

If I had a manual- I'd be all over it. But I don't! Haha

I do! LOL

Manual quotes:
1st=623 @2700rpm
2nd=919@2700rpm
3rd=1500@2700rpm

also:
1st=540@2660rpm
3rd=1000@1793rpm

Any how, with the above manual specs you should be able to determine your PTO rpm's.

Personally I use 2nd at about 1600-1700 rpm's for snow blowing with great results and find that I never clog my shute with wet snow and attain reasonable distance.
With 1st I'd always clog up plus merely pile the snow a mere 3-4 ft to the side, but then again the snowblower does not have a large turbine blade as most newer ones do.
It also has but 3 impellers vs current designs that have 4

The slightly higher blower RPMS have not caused any problems nor is there any excessive vibration.
(NB; I just did a complete teardown and checked all bearings etc in preperation for this winter)

 

[Hooked_on_HP]

ctown75, I think you have a good idea. Try 2nd and see how it mows. As long as you doesn't pull the motor down you should be fine. There is no reason to run the engine any higher than necessary.If you can do the same amount of work at 1800 as you can at 2500 rpms I think you are being easier on the engine. In at truck you go down the road in the highest gear you can while maintaining speed. In heavy equiptment (dozers,excavaters) you Keep the rpms up to maintain hyd. pressure.and flow.On my tractor 540 pto is 2400. If I am mowing I run about 2000 rpms.at give me a good cut at a comfortable travel speed. If I am using the FEL I run at 2400 just so the hyd. are faster.

 

[skspurling]

The issue isn't that engines are designed to work more efficiently at higher RPM's. It is due to the nature of how an internal combustion engine works that the faster the engine turns, the more power will be generated. That is generally the rule, until you get close to the redline of the engine. The design flattens or sharpens the curves, but design dosen't really determine if the low end has more power than the high end.

If you use a slower engine speed with a higher gear ratio on a direct drive PTO, you will have the same blade tip speed under a no-load condition. However, you will not have the same amount of torque or Horse Power delivered to the blades. They will bog down in thick grass or doing hard work. That is why the 540 RPM range on the tach is near the top end of the range for the engine. They place that near the top of the power and torque curves so that you get the best performance.

 

[KubotaSam]

I have a Kubota B7100 that has a 3 speed pto. I always use the second speed (780 rpm i think) when snow blowing. I also use 2nd sped if I am tilling broken ground. If tilling new ground I use lower speed on PTO. I use the slower speed on my rear finish mower.
The snow blower won't hardly work on the lower speed. It just does not blow the snow far enough. The tiller on broken ground in 2nd speed does a wonderfull job. It leaves the soil looking as smooth as a carpet. With the 5 foot RFM my tractor does not have enough horse power to use the faster speed it lugs the engine.

 

[TractorRob]

I have a 5' finish mower on my MT160D. My tractor has the 3 speed PTO, I believe the speeds are 540(1), 720(2), and 900(3). I have been mowing this summer on 1 at 2400 RPMs like the tach indicates for the 540 RPM. Can I switch up to the second speed (720 RPM) and run my tractor a little slower? Obviously as long as the power is there would be the answer, but what would my correct RPMs be to keep the deck at the same speed? If my math is correct, I come up with 1800 RPMs. Am I right? Thanks in advance.

Scott

I don't know why people are advising against doing this, as long as you are not working the engine to hard(you did state "as long as the power is there") there is nothing wrong with it. You obviously do not want to do it if it causes the engine to lug or run too hot(there will be less coolant flow at lower RPM's), but otherwise, I don't see the problem. In fact, this is the same thing as using the Economy PTO setting that some John Deere's have.

 

[skspurling]

I don't know why people are advising against doing this, as long as you are not working the engine to hard(you did state "as long as the power is there") there is nothing wrong with it. You obviously do not want to do it if it causes the engine to lug or run too hot(there will be less coolant flow at lower RPM's), but otherwise, I don't see the problem. In fact, this is the same thing as using the Economy PTO setting that some John Deere's have.

It's more of a liability thing. Especially with tillers and mowers. I believe that snow blowers are made to run at the higher RPM's any way. With the other two, you have to understand that there is a tip speed that the cutters are rated for. When you double the tip speed, any defects in the material could cause the blade/tine to break off and become a projectile. That is especially true for a mower blade. If they didn't put the tiller together exactly right, it could tear it's self apart. They design it so it shouldn't, but it might so they say don't.

Also, there is a lot more variation in speed if you run the higher gear ratio, and idle your motor down. With the 540RPM range, you may be at 560 or at 520. If you run at the 1000 RPM range and try to hit the sweet spot, you could be running 500 or 580 RPM. Then, because you are running lower on the HP/Torque curve, any time you get into a little heavier grass it will bog down even more and not have as good a blade tip speed. That would leave you with a poorer cut because the mower would tend to choke up. Not as big an issue on a well maintained lawn, but it could be.

I use mine at the speed they say to, and it works just fine. If it breaks, I can honestly say I never ran it at any other speed than what it was rated for. One less thing I have to worry about. :thumbsup:

 

[PILOON]

I have a 5' finish mower on my MT160D. My tractor has the 3 speed PTO, I believe the speeds are 540(1), 720(2), and 900(3). I have been mowing this summer on 1 at 2400 RPMs like the tach indicates for the 540 RPM. Can I switch up to the second speed (720 RPM) and run my tractor a little slower? Obviously as long as the power is there would be the answer, but what would my correct RPMs be to keep the deck at the same speed? If my math is correct, I come up with 1800 RPMs. Am I right? Thanks in advance.

Scott

On my MT180D I have been running my blower on the 720 RPM pto for years without any problems.
At 540 the snow barely goes 5 ft but at 720 it becomes a decent blower.
Mind U the fan is 3 bladed and about 16" diam as compared to better designs that generally sport 4 blades and closer to24" diam.
Downside is ice chunks tend to sheer pins more frequently but that is a minor problem.
I do not notice any unhealthy vibrations either.