Run a PTO with a Diesel engine - PTO w Donkey Engine

[Andrew Brousseau]

Hi Guys and Gals, I own a large PTO driven mixer wagon. I want to run it with a diesel engine so I can load it with my tractor, otherwise I would need 2 tractors! The guys at LuckNow told me that the PTO needs 60hp to run it. It's a 500rpm PTO.

I am looking at Mercedes engines. The 2.4 or 3 L versions should have enough hp.

I think the max torque is at 2400rpm, so I need to gear it down also. I'm wondering how much hp I'll lose in the gear down.

Thoughts?

 

[PHPaul]

There will be some loss through the gear train, but the increased torque from gearing it down will more than make up for it.

Looking forward to seeing how you make out with this!

 

[Soundguy]

too bad you can't find a ratty old tech big iron tractor.. bad tires.. or no steering..e tc. and just use it as a stationary engine.

 

[CNC Dan]

I am looking at Mercedes engines. The 2.4 or 3 L versions should have enough hp.

I think the max torque is at 2400rpm, so I need to gear it down also. I'm wondering how much hp I'll lose in the gear down.

Get a manual car transmission from a junkyard that came with the engines and you should be able to select the ratio you want. Get the driveshaft too.

 

[BHD]

just a old standard tractor with PTO would be the easiest system. and most likely a lower cost, in the end.

 

[Norm W]

Using the drive shaft and transmission would be great if the rotation were the other way. A PTO runs clock-wise when viewed from the end. A car transmission runs counter clock-wise except in reverse. That leaves one gear (reverse), but probably close to the correct speed. I don't know how long the counter shaft will hold up under a sustained load.

 

[Renze]

With automobile engines its allways a bit tricky, their torque curve isnt very favourable. 2 weeks ago i went to a maize chopping event with classic machinery. There were guys with MB-trac of 160hp, with the Mercedes OM 352 truck engine, 160hp at 2500rpm from 5.8 liter. There was also a Zetor 12045 with a 6.8 liter naturally aspirated engine, with the pump turned open. The Zetor could drive a higher gear on the 3 row chopper than the Merc because when you depress the clutch, the header of the chopper is still taking in a big stream of maize: So when the MB-Trac driver would push the clutch to relieve the engine, when it came under its peak torque at 1800rpm, the maize still coming into the chopping drum from the header would stall the engine. The guy with the Zetor chopped anywhere between 2000 and 1200rpm because the engine kept a constant torque and would chew through the tall patches.

When using an automobile engine, i would at least go for the 3 liter engine (i assume you mean the OM 617 inline 5 at 85hp) because with the OM 615 (70hp) you're getting in the danger zone with the torque curve, when a bale of straw hits the mixing augers.

Next to that, automotive engines arent built to operate at peak hp for extended periods of time, you may blow a head gasket or just wear it out very soon. In the Ram truck the Cummins 6.7 is doing 400hp or so, but in tractors its used up to 250hp. Thats the difference between continuous tractor duty, or intermittent automotive duty.

 

[BHD]

another option could be a old truck with a governor, on the engine, take the drive line and use it to operate a PTO shaft, it would be much easer to adapt. some old school busses got next to nothing in our area.

 

[muddstopper]

I wouldnt worry about running the merc engine at 2400rpms for extended times. Face it, that is pretty close to what it turns when running 55mph down the highway. As for gearing. 2400rpms/500pto rpms=4.8:1. Maybe a bulldog truck transmission will get you there in first gear, dont know. Might find a 5"1 gear box, or simply just use a couple of sprockets to do the job. The gearing will result in multiplying the torque and hp at the ptoshaft, by the same amount as the gear ratio, but thats not taking into account friction losses and other ineffecientcies that will come with additional drive forces. ie, centrifical force, chain drag, bearings, etc. Still, the car engine should work just fine for your project. Bog down can be overcome by using a large flywheel, such as found on old hay balers. This would need to be mounted similar as on the haybaler and be on the pto shaft and not the flywheel of the engine. The large flywheel should provide enough kinetic engery to keep the engine rpms up when it gets the shock from a load of material dropped into the mixer.

 

[Andrew Brousseau]

Wow so many responses, thank you all.

That's a good point about the rotation of the PTO. Just reading a little here ( W123-240D-Getriebe/en ) the gearing of the reverse on Mercedes can be from 3.9 to 5.6. I am wondering what the ideal rpm is for one of these diesel engines..

I had considered finding a tractor that was in bad shape but that had a running pto. Looking for a 60hp tractor though means I'm looking at spending about $5000

Renze, those are some good considerations. You said " So when the MB-Trac driver would push the clutch to relieve the engine, when it came under its peak torque at 1800rpm, the maize still coming into the chopping drum from the header would stall the engine." Why did the MB chopper have to relieve the engine?

muddstopper, so lets say its a 4:1 ratio, and the pto needs 60 hp, does that mean I could use a 15hp engine then gear it down and it would be 60hp at the pto? The 15hp doesn't sound strong enough though. So if I had a 60hp engine, geared down it would be 240hp? The engineer at luck now told me that I need a 60hp to run the mixer. He was probably referring to the tractor so that means that the drive on the pto really needs 240 hp. Ok that makes sense to me.
I am thinking that I will do my own gearing. I like the idea of the flywheel too. I think it will be 80hp Mercedes engine, geared about 4:1, then a belt tensioner to engage a shaft with a large flywheel on it, which is then connected to the pto. Any thoughts on the engaging mechanism?
The fly wheel is a double edged sword, it will keep the mixer running when material is dumped in, but it will also be a hinderance for the engine when its starting up. Worst case scenario is if the mixer is stopped with about 10 yards of material in it. Then the engine might have trouble starting both the fly wheel and the augers. What if I had a belt tensioner or centrifugal clutch between the engine/gearing and the fly wheel, and a centrifugal clutch between the flywheel and the pto? Now its getting more complicated, but still doable.

Or would it be better to have the centrifugal clutch between the engine and the flywheel, and then the tensioner/clutch to engage between the flywheel and the pto. I'm just thinking of a situation where the augers get bogged down, then the clutch would disengage?

 

[Renze]

Why did the MB chopper have to relieve the engine?

because the MB-trac doesnt have a powershift (modified 16 speed truck transmission), and crop varies in height within the length of the field. There is a delay in crop thickness and engine lugging because it takes a few seconds for the crop that gets grabbed by the header, to reach the chopping disk. So when you hit a good spot of crop and the engine dropped below 1600rpm, the torque curve fell down so quickly that the seconds that the heavy crop flow endured, were enough to stall the engine.

Automotive engines are usually tuned for peak hp at high rpm, not for lugging... however the OM617 was used in commercial vehicles too, and has about the same displacement as 60hp industrial engines.. With the OM617 you'll be o.k. because the torque curve is quite flat for an automotive diesel. It has no turbo, so it doesnt have any lag when it has to take up an intermittent power peak.
http://wiki.mercedes-benz-classic.com/index.php/W123-300D-Getriebe/en

Oh, and if you worry about it being able to get the momentum going: why not use an automatic transmission behind it ? I would just put an oil cooler on the transmission and it will be fine.

 

[muddstopper]

I am not familar with mixers so I can only guess at requirements. As for 60 hp tractor to run one, I suspect that the tractor is rated at 60hp at the PTO. At least that is how my last tractor hp was rated. The would lead me to suspect that with proper gearing, you could get by with a less hp rated engine to accomplish the same thing. Dont take my word for it tho because I am just guessing and could be guessing very wrongly. I would think that 240hp would run a very big mixer.

Your requirements of 60hp and 500rpms suggest a torque requirement of 630ftlbs of torque. Meet this requirement with what ever engine combination, hp, and rpm and gearing mix you can comeup with and it should work. A 15hp gas engine turning 3600rpms geared at 7:1 would only give you 153ftlbs of torque and, because of gearing, it would be similar to a 105hp, and the correct rpms, the torque would be on a fraction of what you actually need.
Horsepower Design Equations Formulas Calculator - Torque Rotating

 

[CNC Dan]

The gearing will result in multiplying the torque and hp at the ptoshaft...

Torque will multiply up, and speed divide down, but not the horsepower, that will remain the same less losses to friction.

 

[muddstopper]

Torque will multiply up, and speed divide down, but not the horsepower, that will remain the same less losses to friction.

Thanks for clarifying, I wasnt sure on that.

 

[CNC Dan]

Thanks for clarifying, I wasnt sure on that.

It can be easy to get lost in the numbers sometimes.
I try to remember that power is RPM x torque. So you can have the same power with a wide range of speeds, or torques.

 

[Sysop]

I had considered finding a tractor that was in bad shape but that had a running pto. Looking for a 60hp tractor though means I'm looking at spending about $5000

It should be mentioned with a tractor that isn't moving it's own weight will be able to supply the full amount of PTO power to the PTO shaft, and many horsepower requirements provided by large implement manufacturers are simply to ensure you have a large enough tractor to handle their machine safely (many don't require the horsepower as much as they do the average size & weight of a given horsepower class). Was the fact this will be a stationary setup part of their consideration when they said you needed 60HP? Being a stationary setup that is only used for mixing you may be able to get away with a 40 horse and reduce the cost.

 

[BHD]

Had another thought,

take a truck or pick up with a working cruse control, lock up the differential, and make a bolt on PTO shaft to the wheel hub,

If I am figuring correctly, a 33 inch tall tire. 33 tall tire x 3.14= 103.62 inches, or 8.63 feet, 5280 (mile) / 8.63, 611 rpm at 60 mph 540 RPM that would be approximately 53 mph on a trucks speed-o-meter, the cruse control would act like a governor,

About the only modification would be to lock up the differential. and make the adapter.

 

[hophornbeam]

Andrew,
I liked to jerry rig machinery as much as the next guy, but I can't help but think all your effort to eliminate a second tractor is going to cost more than an older tractor. JMHO

 

[Sysop]

Andrew,
I liked to jerry rig machinery as much as the next guy, but I can't help but think all your effort to eliminate a second tractor is going to cost more than an older tractor. JMHO

At least if you count the value of your time in making it work. Some folk view their time as "free to them", in which case I'm interested to watch and provide sideline idea assists on whatever OP chooses to do.

 

[hophornbeam]

Sysop, I understand that in the farm community, or even anyone, we usually value our time extremely low in an effort to make gains, sweat equity I call it. However, unless the donkey engine(s), transmissions, reduction gearing, etc, etc, are sitting in the back shed waiting to brought to light there is a cost. Hey, I wish the guy luck on his endeavour and look forward to seeing the creation too. I just wanted to suggest that before the blinders get too restricted, consider the option that at first seems less favourable. For all I know, one day he may find himself stuck with his one tractor and wouldn't a second tractor look good then.