Reply to neil:
Mike, could you consider getting your shells retinned if you can't find new stock?
Yes Neil, in fact just this morning I spoke to a very clever guy here in Melbourne about possibly doing this, he said it will cost around $US150 per bearing, but the crankshaft needs to be in good condition. My crankshaft has old water stain damage unfortunately, and I'd really love to avoid having to dismantle the engine to clean up the crankshaft, it's already been ground to 30 thou under, this tractor will be lucky to do 5 hours a year.
It's a interesting problem Neil, when the engine oil is cold the oil pressure is a steady 34 pounds, both when slowly cranking the main over with the pilot motor, and when the diesel fires up, but within 20 minutes of starting the diesel, and the engine oil slowly warming up, I can see the oil pressure slowly decreasing on the guage, at high idle it's still 10-15 pounds, but at low idle it's only around 1-5 pounds, that's too low for my comfort.
I'm running 40W oil in the motor, and had the pressure relief valve screwed in as far as it will go, I dismantled the oil pump a week ago and it looks great, I can see how someone has been in there before and reconditioned it. I measured the conrod bearings on 2 cylinders with plastigage and got 13-14 thou wear, so they are at maximum wear, hence I thought if I could find some new bigend bearings I should help improve that low pressure at low idle.
I'm just confused at how I've got a beautiful 34 pounds when cranking the diesel motor over with the pilot motor when the oil is cold, then almost zero pressure when the oil is warm, unless the diesel is running above low idle. There is some minor wear on the oil pressure relief spring from rubbing within it's bore, and I'm aiming to replace that.
Thanks for your input, appreciate it
Mike