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?