D7-3T pony motor

1.) Diesel engine must be engaged when the starting engine is running so it has coolant circulating through it, or it will eventually overheat.

2.) Fuel contamination of crankcase oil: If the carburetor leaks down, from the bowl, it can literally fill and overflow the crank case oil, assuming the sediment bowl valve is left open so it can drain from the fuel tank. Solution: drain the carburetor bowl, on the Zenith carburetor, there should be a threaded hole at the bottom of the bowl, take the plug out, install a petcock and use a long hose to safely drain off the gasoline after the diesel is running. You can also let the starting engine run out of fuel, shut off the valve at the sediment bowl, but I prefer to drain it, because it takes too long for the starting engine to run out and I know the bowl is dry, meaning NO gasoline can leak down. If you let it run out, the bowl still has some fuel in it. I'm not sure what inside that zenith carb causes this, I'm sure this was not so prevalent when these were new, other models are suceptible as well, but as things age who knows, that carburetor is quite simple, easy to clean out and rebuild. This is important, gasoline thinned crankcase oil will cause these starting engines to fail quickly, always check the oil level and make double sure it's not thinned by any gasoline, smell and feel the oil. It happened to me once, and it overflowed the crankcase out the dipstick tube, glad I detected gasoline in the oil before running it. To me, even that little left in the bowl if you let it run out of fuel, while your running the tractor, it could possibly leak down, cumulatively contaminating your crank case oil over time, which is why I take no chances and know the oil is clean everytime beacuse I drain the bowl. Just my preference to take care of mine like this, others may disagree, but after seeing a crankcase overflow with gasoline, I take no chances, not cheap to re-build these, even worse after it has a catastrohphic failure.

3.) Keep the oil clean and change it regularly. Those crankcase sump plugs are a real joy to get at, one of mine has some strange copper tubing looping both plugs together, and I've never been able to get them off, so I have to clean the immediate surrounding area, (using a water hose to eliminate dirt and dust getting blown around. Clean the track, the frame rail, wipe down everything nearby, then pull the side cover and use a drill pump to extract the oil, clean the crank case with a NON-LINT type of rag or similar, I usually just soak up the remaining oil at the bottom of the sump, don't want lint or foreign materials inside the crankcase. It's really hard to get to those sump plugs, need to make a special tool or something to get to it from underneath, even though it's so close when your standing against the track. It's probably why the oil does not get changed often on these, which is not good. I'd love to hear how others deal with this one, seems a lot easier to take the inspection cover off, just make sure nothing can get blown or fall into the crankcase.

4.) Fuel Supply: these old steel fuel tanks rust nicely inside, coffee grind size rust particles, it's good to clean out the interior of the steel tank, refinish it with products designed to coat the inside. For example you can strap it to your lawn tractor while you mow the lawn or something similar that rotates and fill it with crushed stone, it will polish up nicely, then do what you have to to coat the inside with a product meant for the purpose. When not re-furbished, a high sediment bowl screen will help keep fuel flowing as rust settles, these starting engines like lots of fuel. Also check and clean the screen at the end of the fuel line where it connects to the carburetor and keep the carb cleaned, adjusted etc.

5.) Spark: these came with either Eismann or Bosch magnetos, have to keep them in good working order to make good spark, same rules apply for all magnetos, good to check the spark and see what it's doing. Mine for example seems to have a weaker spark on one cylinder, possibly needs to be re-magnetized or some other work, the other side is hot. Remember to use solid conductor spark plug wires and don't use champion spark plugs, they seem to perform badly from what others say about them. Also know how to time the magneto to the starting engine in case you need to work on it, read in the serviceman's reference book, funny how it does not tell you what cylinder is No. 1 ( it is the cylinder closest to the radiator that is #1 and there is a mark on the starting engine flywheel behind the inspection cover to line up with #1 top dead center compression stroke, you can also use a cork in that spark plug hole to identify compression stroke, it'll pop out). It's good to know how to do this in case you have no spark and need to quickly repair or swap a spare magneto onto it. I was stumped by this the first time I had to do it, but can recite how to do it in my sleep now LOL !

6.)When the diesel fires: The starting engine disengages from the diesel via centrifugal force, the pinion latches disengage the pinion gear and it retracts from the diesel flywheel, so as the diesel starts to fire, at a certain rpm (see your servicemans reference book) it will disengage. There is a procedure listed to adjust the speed by turning a screw on the pinion. If the diesel disengages at the first pop of a cylinder, you can hold the lever until it's running, meaning you can manually release it in a pinch, but you should adjust it properly per the book as it should stay engaged until the diesel has enough rpm to disengage it without holding the lever. In reverse, if the latches on the pinion release too late, the diesel can and will overspeed the starting engine, which could cause it to fail. I'm not 100% sure, but I assume the throttle lever connected to the governor controls the speed of the motor, so that needs to function properly,( I've never learned how that works actually so don't quote me) There is also throttle linkage latch on these. For safety, you can manually operate the throttle, I hold the linkage when I move the compression lever up to run, so that when the diesel fires, there is no chance it can overspeed the starting engine, it wants to sometimes, so I just move the throttle linkage back so it idles back down, as the latches release. Theres a lot to pay attention to when starting one of these in my opinion and this particular adjustment is important.

Also be safety minded at all times, you're standing or kneeling on a track, if that tractor is in gear or can pop into gear, once that diesel fires, you have to cut fuel or air to get it to stop, the throttle linkage on mine is really stiff in the down direction, bluntly, you cannot quickly shut it down. There is differing opinions on safety for these, when running and stationary, the master clutch should be engaged and the 5 spd & foward reverse levers placed in neutral, apparently there is no way they could vibrate into gear due to the interlock mechanism. (someone please correct me if this is wrong) With the master clutch disengaged, it could get bumped into gear or left in gear etc., which does not seem possible with everything spinning, apparently it is possible though maybe more so when things are worn. All that's left is that master clutch to engage and it's a runaway. Operators instructions for these state to disengage the master/main flywheel clutch when starting, speed selector and fwd/rev in neutral There will be extra drag if you have the flywheel clutch engaged in cold weather, so you don't have a choice there but to disengage it, making less work for the starting engine. Only reason I mention this, don't fire up one of these in a hurry or without paying attention to what you are doing, they do not forgive you for making dumb mistakes, just a safety reminder. Operators instructions seem clear enough to follow here.

7.) Cold weather starting: It's nice to have that starting engine in good working order, to my amazement I have fired mine off with just the hand crank, but it has to be in good working order to do that, the electric starter sure is a nice thing to have. As an example, one of mine is a true low hour tractor, the diesel probably has the compression it had when it was new, in warm weather as soon as you move the compression lever to run, not even a pop, it's literally just running. In the cold, that starting engine lugs right down, say 20 deg F or a little lower, with the lever in Start position and in Low gear,( most have the 2 spd auxillary transmission, older ones do not) The starting engine stays engaged and I let it run in Low, every few minutes after letting it loosen things up in there, I'll move the lever up to Half, repeat and then move it to Run, depending on how cold it is, it often really lugs down and or stalls out if you shift to High. In real cold, start off in Low on Start, then move to Half and or Run. This is where you really need to have that starting engine running at its best, good spark and fuel. Mine for example, the diesel has good compression and it's possible I've got weak spark on one cylinder, so the starting engine really bogs down in colder weather as soon as I move the lever to Run, and have the trans in High, but eventually it catches up, takes time though. It just seems like a heck of a jump from the Half position in real cold weather. It appears that this 2 cyl vertical 20 something HP starting engine is barely enough for the D-8800 4 cyl. probably the weak spark. The D8's of the same period are basically the same diesel engine D-13000 with 2 more cylinders. That compression seems real tough to overcome, hard to figure how electric start conversions work in the cold weather without a block heater. The beauty of the starting engine is that you can get oil pressure to register on the gauge before you give it fuel and compression. I'd also think that if one these motors was well worn, it may be a harder to start in the cold, rpms and compression create the heat needed to fire off, sometimes you have no choice but to give a small dose of starting fluid to them when bitter cold, something I don't like to use very often on any motor for that matter. I've never had to use it on this low hour tractor, have fired it off in the teens without much trouble. I remember my dad starting the older one which I still have, (have a pair of 4T's same as a 3T for the most part)and I think he used to turn the fuel on too early, plumes of white smoke in cold weather, kinda looked cool as it cleared out, but I think that fuel just washed the cylinders and made a lot of smoke, mine smokes a little, tosses a few smoke rings, but clears quickly, even in the cold weather, warm weather, no white smoke, fires off clean with a little black soot/carbon in the smoke is all.

Another thing about this particular starting engine is many tractors used the same starting engine. I believe it was the first one or one of the first that caterpillar built to be used with their new diesel engines, early diesel Forty's Fifty's and Sixties had them, RD series diesel tractors had them, RD6's RD7's & RD8's, early D6-2H's 3 cyl diesel tractors had them, as did D7's until the mid 50's D7 17A series is where it went to the later style I believe. D8's had them until after the 2U series ended, 13A's 14A's and 15A's prior to H series D8's had them if I am correct, so I would think many of them are still in salvage yards for parts, complete running units come from those who change to direct electic start, and many are still in use on the older tractors still in use by collectors or those still in service. Also Cranes, Marine Applications, Power Units and Compressors using the same caterpillar diesel engines the tractors had, also used this same starting engine.

I know a lot of people still have these, and have been at it much longer than I as far as that goes. I'm not an old timer nor an expert, but it's what I've been able to learn so far about them, hope this helps, it's kind of long, but good information for anyone new to these.

Thanks for the pony motor discussion. I realize now that my 3T has several of the problems mentioned.
1) When I crank the Pony motor,it never fires first on #1 (always fires on #2).
2) I have to clean the gas/oil mixture from #2 plug as it is shorting the spark plug. This problem is probably due to gas in the crankcase.
3) This is the first discussion I have heard where there is no 2-speed trans between the pony and the flywheel. My dozer doesn't have this item.
4) There is evidence of a water pump on the pony motor but parts are gone.

5) Would anyone hazard a guess as to the model this is. The serial # is unreadable.

I almost forgot to mention the 2 spd trans, hard to figure how they started these without one, the pony certainly would run awhile, and you'd have to use that compression lever carefully as it warms things up, no doubt the starting engine has to be in excellent shape to work in real cold temps without that 2 spd trans.

If you've got gas in the oil, I'm not sure what in that zenith carb lets it drain down, but I can tell you if you run it like that with thinned oil, sooner or later it could let loose, assuming it thins the oil and the main bearings fail, I have all the remaining parts of one that let loose, tossed a rod, someone I know who had a '53 D7 3T, nice shape, he converted to electric start, and gave me the parts which I could use as spares, the rest of the motor was junk after that, except maybe the head, would have liked to have seen what it did, I just found the 2 spd trans, magneto and some other odds and ends.

I don't know how a water pump could be fitted to the starting engine, the diesel motor drives it directly. Not sure which way it circulates, but there is a pipe in front of the starting engine and one on top of the head between the spark plugs, the only way water is circulated is when the diesel is spinning.

The serial number tag is illegible, must be the one on the back of the tractor above the final drive case, but behind it stamped into the steel should be the same number, carefully clean the paint of, don't grind it off or do anything to distort the stamp marks.

The serial number is also on the left side rear of the diesel engine block to the right of the starting engine, that tag might be legible, but should also have the s/n stamped behind it. These were built from 1944-1955, in '53 they were at around 20,000 built and the series ended just over 28,000 built.

One of the sawmills nearby uses a 13000 to power the mill, and it's getting tired, hand crank pony, no electric start and no 2 spd trans if I recall, more of a pain to get running in the cold, than in the summer he says, was looking at replacing it, could probably freshen up the one he has.

The two speed pony transmission was an option up to sr. # 3T4389 . This would also indicate the range of your missing serial number.