Long story short, I rebuild the pony, which included having machine work to bring the cylinders and crank to standard. Got it running but was overheating within a f ew minutes. Infrared thermometer showed 220 temps. Only ran for a few minutes at a time, with total of 15-20 total run time, all at idle or mid-throttle. Pulled pony to check for obstructions and no blockages found. I'm wondering if the overheating could be caused by air trapped in the manifold. While I had the manifold off, I noticed the #2 rod was close to the cylinder wall while approaching TDC. I measured and it is approximately .055 inches at point of closest approach. Two questions, 1) any ideas why I'm experiencing overheating? 2) Should I be concerned about the close proximity of the rod to the cylinder wall?

you don't say where you are measuring the 220 degrees from....what part of the engine....block, heads etc?? air in the coolant system could definitely create overheating...or a restriction that is not allowing proper flow...or low coolant level...etc....

-sometimes the spark timing can affect the engine/exhaust temps negatively....too late and fuel is burning in late in exhaust system raising temps...

-i think your .055" rod to cylinder wall/ block clearance is fine...

Hi CY1,
it helps immensely if you give us a Serial Number so we can give you the correct full data.
Air trapped in the pony top manifold indeed does cause overheating in the pony.
Early machines did not have an air bleed tap on top of said manifold or on a link pipe elbow--early ones did not, but I lost my data in a computer crash for where to drill and tap the hole in the manifold to retro fit an air bleed tap to stop this occurring.
Hopefully someone can help out.

Scan below shows location of a said tap on the smaller horizontal ponies.

Cheers,
Eddie B.

Hi Cat Yellow1,
When you are running the pony motor are you turning the main engine at the same time, as the cooling for the pony motor relies on the water circulating in the main engine.

Regards

and oh another thought....a plugged exhaust muffler or restriction in the exhaust tract can also create crazy overheating...

Hi all, thanks for your replies. I was rushing to post this while multi tasking, so sorry about the missing info. Also had problems with posting the pictures, not sure why they posted like they did. Eddie, the SN is 4U1826, and it does have the bleed valve on the manifold, but I forgot to open it while I was filling the coolant in the radiator. I did open it after the fact, so for the most part I did have coolant in the manifold. I know the previous owner rebuilt this in the past from 3 other ponies, so it's possible he put a newer manifold on if this model originally didn't have the bleed valve. Kittylover, temps were taken in the area of the top of the head and and the manifold within a couple of inches from the head. When I pulled the manifold, the manifold gasket was stiff and stuck to the block in the area of the coolant passages on both sides. I ran the pony about 6 or 7 times for just a few minutes each time, and at idle to break it in. I first noticed the overheating when the new paint started smoking on #2 cylinder side of the manifold near the elbow that connects the coolant to the diesel engine. Shut down immediately and monitored with the infrared thermometer afterwards and shut down when it reached about 220, which only took a couple of minutes. The last two times that I ran the pony I was turning the diesel and there was no change in the temps. I've just replaced the fuel line from the tank to the transfer pump and added an inline filter, plus changed the fuel filters, so I need to get the air out of the system before the diesel runs. Also, when I pulled the pony, most of the coolant was trapped in the pony and had not drained when I drained the radiator. In hindsight, I should have drained it using the valve below the pony on the diesel engine. Thinking there was a blockage in this area, I blew air through the opening on the bellhousing and had good airflow coming out of both the radiator fill and the drain, so it doesn't look like there were blockages there, but I was still curious on why that didn't drain through the radiator. My gaskets should be in today, so I'll get it back together and try it again this weekend. I've been chatting with Neil, who has been extremely helpful (thanks Neil), and he suggests the timing issue too, so that's one of the things I have left to check.

I was a little concerned about the rod clearance, so thanks for the sanity check on it.

Hi Team,
it is the early J series units that did have the bleed valves.
Mag gear is keyed to its shaft--only way of changing the timing is to move one gear tooth or adjust the the mag points gap.
Often the points gap can be set to an incorrect gap due to confusion with which brand magneto is fitted to the pony--some run 0.014" 0.018", with these the ideal is 0.016"
Some other brand mags can be 0,020" which if set to say 0.014" will be advanced and kick back.

Even so if water is present in the pony manifold it should not be burning the pony manifold paint.

If the Diesel temp gauge bulb in the main engine head can be loosened then air can be bled there from the main engine head--if the bulb seems stuck do not try further to remove and so ruin it.
Suggest to remove the thermostat and drill say a 3/32" hole in the side plate beside the valve to allow air to pass and bleed thru from the main engine block and head and see what you get.

Have encountered difficulty in the past with air trapped in the diesel head and it gets pumped into the pony manifold causing issues.
For some unknown reason some engines can be difficult to purge of air and another be OK.
Cheers,
Eddie B.

Thanks Eddie and Neil for your comments. The mag is a Bosch. I hate to admit this, but I just remembered that when I first tried to start the pony after installing it would not fire. I swapped the plug wires on the mag and it fired right up. Thought I might have had it 180 out of time, but I was pretty sure I had everything lined up correctly. When I pulled the pony back apart, I confirmed that the mag gears were lined up (M - M) and the crank gears were lines up (C - C), but it was running with the #1 wire on the #2 side of the mag and vice versa. Below is a video that I just uploaded taking temperatures with the infrared camera.

Hi CY1,
just to re-cap, when looking from the operators seat No 1 Cylinder on the horizontal ponies is the rear or left cylinder.
It is possible that the rotor in the magneto is half a turn out.
Cheers,
Eddie B.