what is a pony motor?

[Anonymous Poster]

The way I understand it, a pony motor is a small motor that gets the larger main engine started. How does it work specifically though? I have heard about vintage tractors with this feature, but have always wondered how it works. Does anyone have a picture of a pony motor mounted on a tractor? Is "pony motor" the correct term?

 

[Robert_in_NY]

That is what it does. You get the little motor spinning quite fast then you pull a lever which engages it to larger motor to start spinning the gears. The larger JD 2cylinders had these as a option and they mounted so that they really didn't stick out like you would think. They were mounted under the sheetmetal and blended in nicely.

 

[Egon]

Pony motor:
Correct terminolgy.
Probably not used anymore but in the past it was a small gasoline engine that would be used to turn over the main diesel till it started. This little gas engine would start easily exspecially in cold weather. Almost all the "Cat Equipment" had this feature, as I recall. Also called a pup motor. Most diesels of the past era had one.
Egon

 

[Redtractorman]

A pony motor is a small 4 cylinder(on John Deere's)engine .For deisels you started this first as soon as it warmed up a little,you pulled a lever and it engaged the deisel and spun it while it also had the exshaust hooked to it to warm the deisel and them you turned the key and they deisel started up.I had a 720 and it would start at 10 below this way.

 

[Anonymous Poster]

I appreciate the information. I wonder specifically what happens when the lever is pulled though. What type of mechanical connection is used between the two engines? Is it a belt connection that goes from loose to tight? Is it a one way clutch type connection? I think that some of the old technology was very clever in a lot of ways, and some of it interests me.

 

[RonL]

Yamaben

I think you will find a lot of interesting information on the VanNatta logging site.

RonL

 

[Egon]

If memory serves me correctly the Cat equipment had clutch to gearing. Two levers. one clutch and one for gearshift. The pup motor had to warm up before being able to turn over the main diesel. Almost all of them worked this way. Don't think any used belts that I recall.

Egon

 

[MJB]

On the Caterpillar equipment I am familiar with, the pony motor drives the main engine by way of a pinion gear just like a normal electric starter. There would be either two or three levers to operate the pony motor. On the two lever units one lever was to engage the drive pinion into the ring gear on the main engine. This would be done while the pony motor was warming up. Once the pony was warm the second lever would engage a clutch between the pony motor and the drive pinion to turn the main engine. On the three lever models the third lever would allow you to select either high or low gear on the pony motor. Once the main engine started it would automatically kick out the drive pinion from the pony. In cold weather the pony motor may have to turn the main engine for 20 or 30 minutes before starting. The pony motor shared its cooling system with the main engine and the exhaust pipe from the pony was routed through the intake manifold for the main engine in order to warm it up. This was a great system for a few reasons. First the main engine never started without first building up oil pressure. Second, since it took some time to start, the operator had an opportunity to check the machine over and grease fittings while waiting for the machine to warm up. Thirdly, time was on your side. The longer the pony motor cranked, the more likely the main engine was to start. This is just the opposite of electric starters. In many ways the old equipment was actually designed better than the stuff being built today.

 

[Anonymous Poster]

Thanks a lot for the information. That was the description I was holding out for. Some day I might just lose my mind and try to find a vintage tractor. Thanks again.

 

[Robert_in_NY]

I was just checking my JD parts CD and they call the pony motors "Cranking Engines". It ties in direct to the main engine and works just like MJB said the CAT's do.

 

[Anonymous Poster]

MJB has nailed it down for you. The term "motor" and "engine" are actually interchangeable, believe it or not, and the instruction books usually referred to the little beasties as "cranking engine" or as "starting engine". I grew up in California and out there all of our big tractor power was on tracks so we farmed with Caterpillars. Using the starting engines was a great benefit because as MJB pointed out, it gave you time to do the little maintenance duties while the diesel was being cranked. The Cats also had a lever by which you could hold the intake valves open and thereby make it easier for the starting engine to get the diesel rolling over. What I would do to make it easy on myself was crank the diesel with the compression "on" (labeled "run")until it was warmed by the heat of compression, and then flip the lever to compression "off" (labeled "start"), crack the main throttle, then flip it back to "run" and the diesel would fire up. I also held the throttle open for about three seconds in the very early stages of the cranking period to get a little bit of fuel in the cylinders to help warm the diesel up. Those tractors blew some great smoke rings when you cranked them. None of our cats had batteries; all were hand crank to the starting engines and then on to the diesel. Suberb machines in so many ways! Dave

 

[n6ckv]

If you get a copy of Randy Leffingwell's book titled "Caterpillar" you can read the starting directions for various "Cats".
He starts with the 110hp Best oil-fired steam traction engine, the user is cautioned to allow 1 1/2 hours for the starting procedure.
The directions for a 1930 era D6 describe starting with a "starting engine" (pony motor). The last note is to allow the engine to idle at half throttle for 5 min, and full throttle for 5 min before appling load.
The directions for the Challenger 75 is; turn the key, start the engine, and idle 5 min to warm up.

carl

 

[Anonymous Poster]

Wow.....a three-cylinder RD-6.....that REALLY takes me back. Those engines turned VERY slow, like maybe 720 RPM. Speaking of Cats.......we just watched the movie: "Grapes of Wrath", Steinbecks novel-turned movie about the dust bowl; and in that film there were some vintage Caterpillars. It showed what I THINK was a group of Caterpiller Diesel Sixty-Five's,and later on, an RD-8.....that's the one with the vee tapered dashboard and the "slide bar" shifter with two different reverse gates. What a treat it was to see them in new condition! Dave

 

[torch1]

On the Caterpillar equipment I am familiar with, the pony motor drives the main engine by way of a pinion gear just like a normal electric starter. There would be either two or three levers to operate the pony motor. On the two lever units one lever was to engage the drive pinion into the ring gear on the main engine. This would be done while the pony motor was warming up. Once the pony was warm the second lever would engage a clutch between the pony motor and the drive pinion to turn the main engine. On the three lever models the third lever would allow you to select either high or low gear on the pony motor. Once the main engine started it would automatically kick out the drive pinion from the pony. In cold weather the pony motor may have to turn the main engine for 20 or 30 minutes before starting. The pony motor shared its cooling system with the main engine and the exhaust pipe from the pony was routed through the intake manifold for the main engine in order to warm it up. This was a great system for a few reasons. First the main engine never started without first building up oil pressure. Second, since it took some time to start, the operator had an opportunity to check the machine over and grease fittings while waiting for the machine to warm up. Thirdly, time was on your side. The longer the pony motor cranked, the more likely the main engine was to start. This is just the opposite of electric starters. In many ways the old equipment was actually designed better than the stuff being built today.

Great description and if I may add a few comments.

The number one way to shut these engines off is to shut the fuel valve off and not the magneto switch, if you use the magneto switch the gas in the carb can drain into the starting engine crankcase and dilute the oil and over time cause a bottom end crankshaft failure. ( the oils does not get checked often and gets to be more gas than oil, very expensive to repair) This does burn a bit more gas, but gas is much cheaper than parts.

Also on the Cat pup engines, some have a two speed transmission, make sure the pup engine is in high gear when you go to start the main diesel, if you do not, the main diesel will not turn fast enough to start and it just sits there and cranks but never starts.

Being a mechanic by trade these are engines, not motors, motors are electric. Therefore we have Pony Engines, Pup engines, Donkey engines (Australia) and starting engines, no motors here unless they are starting the starting Engine.

These things are indeed a viable option and in the north at -40C or F they are king.