Tractor Repair: international 806 crankshaft problems, metal shavings, pressure relief valve

Question
I help my dad work on his tractors but one has us completely stumped. In the past 2 seasons we have put 2 new crankshafts and it has spun the 4th bearing each time. Now we put another one in it and it ran for a minute then the crankshaft completely froze up. We checked the engine block and have replaced the rods, pistons , sleeves, seals you name it. What do you think is wrong? We have had this particular tractor since I was 3...I'm now 28 so this has been a great tractor for a long time.  What do you think, any advice?

Answer
Hello,


  Don't know if you mean the 4th rod bearing or 4th main bearing, but here are several things that should be checked.  The oil pressure needs to be checked with a gauge.  If the pressure is low, it could be a worn oil pump, suction tube leak, wrong bearings, oil pressure relief valve, or a missing plug or bolt.  Before the crankshaft is installed, the oil passages in the crankshaft and engine block should be blown out with air to make sure they aren't plugged.  Once the crankshaft is installed, all the bearing clearances should be checked wih plastigage.  Don't rely on the size that is stamped on the bearings or on the box they come in.  Make sure the oil holes in the upper main bearings line up with the holes in the block.  Make sure the bearing caps are installed in the correct locations, are facing the correct way, and are torqued correctly.  Check that none of the bearing cap bolts are stretched, and that they screw in all the way so that they don't bottom out before the bearing cap is tight.  If it is the 4th rod bearing, I would guess a bad connecting rod, but you said the rods have been replaced already.   If there were lots of metal shavings in the oil pan from the previous failures, and if it has an oil cooler, metal shavings can get stuck in the oil cooler where they can gradually come out over time and go into the bearings, causing repeat failures.  In that case the oil cooler should probably be replaced, since it's very hard to totally clean the inside of it.  Flushing it out might not get everything out.