Engine Oil pump failure

Good afternoon, folks,

I've been away for a long time, and my tractor has been working well.  Until 2 weeks ago.  Just for the record, I had posted some time ago about oil pressure loss on a friend's tractor, which seems to be due to significant overheating.  But now I have a problem with a different tractor… my own.  So, 2007 Jinma 274, Yangdong Y385T engine, 800 hours.

So I was clearing snow, not working it hard (although I had been the previous day for a few minutes) when the oil light came on.  Long story short, the engine oil pump shaft snapped in two where the shaft enters the rotor.  I'll send photos in another post, but the shaft had been contacting the housing, and was worn down.  There was no sign of foreign material in the pump causing jamming.  There was also no sign that a bushing ever having been in the lower part of the housing, which allowed the shaft to wobble resulting in the shaft wear.  There was a bushing at the top, next to the drive gear.  Happily, I popped the main bearing caps, the con rod caps, and pulled the camshaft and saw no evidence of unusual wear. 

Now, to repair this requires splitting the tractor so you can remove the engine and tear it down.  After several days of work (of course, accompanied by a huge ice storm just to make it more interesting) I started it up yesterday… and the oil pressure went to about 50% of normal, and dropped to about 25% of normal over about 15 minutes.  No idea what I did wrong, but it looks like a complete disassembly is once again in the works.  Drat. My first reaction was to head to the liquor cabinet.

The question is, does anyone have intimate familiarity with these oil pumps?  Is there supposed to be a bushing in the bottom of pump?  The second problem is a new mystery, but the first failure remains a concern that I would like to understand better.  Personal experiences, anyone?

Thanks in advance,

Mike (Prairie Dog)