Here's one for the N experts

(quoted from post at 20:55:54 10/05/17) Customer and a friend, brought me a 1949 8n front mount dist tractor a while back and
and asked me to get it running, said it had been in his family every since new,was a
very low hours tractor that had been sitting a long time but they could not get it
started.He really did't want to spend a lot of money on it, but would like to see it
running again. It had been converted to 12 V. We checked all the usual stuff,got fire,
rebuilt carb. We got it started and it had NO oil pressure. We removed the relief valve
pumped it full of 90 Wt. and started it again. No oil pressure. Finally decided to pull
the pan to see if pick-up tube was broken. Every thing looked good.Pulled oil
pump,disassembled it. Looked new. Pulled main caps. Could tell they had been dry but no
damage. Saw a little rust in a couple of the cylinders. Pulled head, knocked pistons
out, no ring groove. Miced crank. Good condition.Everything in the engine was 100%
original Ford. Ordered a set of rings ,rod and main bearings and oil pump kit. Honed
block, rebuilt the oil pump( remembering I have all the Ford tools to do this little
job),definitely not the first one I ever did either. Plasti-guaged everything and put
her back together. Filled her up with 30 wt and started her up. Guess what NO oil
pressure. Shut it down. Did the old primer trick fired her up and horray 20 Lbs of oil
pressure. A measley 20 pounds. Changed the gauge and still 20 pounds. Changed the relief
valve and spring,18 lbs. Shut her off and let it set for half hour lunch break and fired
her up, No oil pressure. Primed the pump again and 20 pounds again. If the tractor sits
for over 30 minutes it looses it's prime.We have pressure checked the suction tube. The
pan is back off the oil pump is disassembled again and I don't know what the next move
really is other than dig a hole and bury the sucker. I have way more time and parts in
this thing than I ever charge for but I hate to give up. We have rebuilt 4 tractor
engines in the last month and this one has caused more problems than all the rest put
together. Anyone else ever had a similar problem?

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• [*:5c312955be]Some signs of wear on the housing walls but nothing that looks gross. Clearance seem to be reasonable[*:5c312955be]Known good pickup tube that I can visually monitor during operation[*:5c312955be]Prime the pumps and they pump fine[*:5c312955be]Let them sit for "short" periods of time and they will hold prime and pump again[*:5c312955be]Let them sit longer and they lose prime and won't pump. Some will hold for a few hours, some will hold for half a day or so - even longer - but they eventually lose prime[*:5c312955be]No visible indications of leakage or any other unusual behavior[/list:5c312955be]All I can do based on that is speculate. If you look at how the pump is shaped you can see that the bottom of the pumping section is below the oil pickup tube opening and the shaft/bushing on the driven gear. That means there will be a small puddle of oil trapped there that cannot drain back into the sump. The bushing and/or shaft could be worn to he!! and back and oil would still be trapped in that area. I believe it is that oil that maintains prime across run cycles and as you can see from the picture below there isn't going to be a lot of it. I have also come to the conclusion that pumps that won't hold prime are simply worn to the point that the small volume of oil held in that area is not sufficient to maintain an oil film (suction) long enough to completely refill the pickup tube. At startup the oil is pulled around the gears spreading it along the worn walls, the film is lost because there is not enough volume to fill the voids cused by wear, and the oil in the partially filled pickup tube drains back into the sump leaving you with a running engine and no oil supply.
  
  In other words - these pumps are slap worn out and the only real fix is to replace them with a new or known good one with all that entails. I've seen so many of these I have started telling folks that contact me with oil pump problems to bite the bullet and replace the OEM pump with a NEW late 8N style (3/4" gears) pump whenever the do an overhaul. Replacing the pump is an added $300-$400 overhaul expense but at 65 to nearly 80 years old most of the original pumps are simply at or very near end of life and it's a lot easier and cheaper to do it up front than it is to fix it after the overhaul has been completed. Making the oil pump part of a main bearing cap was a truly bad design but in all fairness the Ford engineers probably never dreamed they would still be in use after that many years. I am afraid that is just one of the realities of owning an N-series tractor.
  
  TOH
  
  
  

(quoted from post at 07:48:13 10/06/17) TOH, thank you very much for your input. The only question is. Can the pump be replaced
without having the block and new front bearing cap line bored? I would not think the
tolerances would be close enough to get by without line boring. Your experience and input on this please.

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