Pony Motor Hard To Crank

Unfortunately, I let my D8800 motor sit too long without starting (around 2 years) and decided to get back to it. I changed the oil in the pony motor and gearbox and changed spark plugs and fuel filter. When I started trying to turn the Pony's crank, it was almost impossibe to move. I took the spark plugs out and tried it and it was no problem to crank. Put the plugs back in and it was the same. I squirted some ether in the top of the filter and although still hard to crank over, it did stat and run for a few seconds on those fumes. I decided to take the carburetor off and order new overhaul parts from the local CAT dealer, all of which had to be ordered in.
While waiting on the carb. parts, I disassembled the carburetor and noticed that the little piece of rod linkage (CAT part number 9B4820) that operates the top shutter is missing! How long that has been missing is a mystery. It is out of sight behid the carburetor when installed. All the illustrations show that part installed so I am pretty sure it is necessary to have it. I think I can fabricate one and maybe I can more easily start the pony when it comes time. It is virtually impossible for someone to have taken it. I am attaching a picture to show the rod I am talking about.
My big question now is have I done the motor harm by keeping on turning it over after finding it hard to turn over? I am hoping a bearing hasn't seized to the crankshaft and spun, but it does run a few seconds on ether.

You said that it turned easy with the spark plugs out. If a bearing was spun it should crank hard with the spark plugs out as well, as the drag on the bearings would still be there. Does not sound like a spun bearing to me. A shot of lubricant in the plug holes to lube the cylinders may be a good choice. Probably not a bad idea to clean the carb either. Can't help with the missing part but someone will chime in.

Thanks for the reply. I originally squirterd some oil in both cylinders and cranked it through several revolutions originally and after putting the plugs in and tried to start it the first time, I wondered if I had put too much oil in there and had a "liquid lock" so I put suction in the top of the cylinders with a hose in case I had too much in there but none came out. It sure won't hurt to try the oil again. I wondered also if the 90 degree gear arrangement in the cranking shaft might not be getting enough lubricaton...?

Putting in the oil did a couple of things.......first it helped lubricate the piston and rings in the cylinder.........That was what you wanted I guess.

Then it also helped seal the compression rings, so less blow-by during cranking and higher compression pressure in the cylinders.

Finally, it takes up space inside the combustion chamber which can really increase the compression ratio even up to the point of hydraulic lock if you were really heavy handed😆

If it turns over easy without the plugs in there, I would not add more oil unless I thought the compression was so low it wouldn't run without it.

I have had one on a D6 that wouldn't start at all from lack of compression until I changed the diluted oil. It immediately cranked up and ran after that. MIght have been luck, but the oil in the oil pan seems to have a big effect on starting of the horzontal opposed ponies at least.

D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time😄