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Subject: oil pressure

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gary broom    Posted 06-16-2020 at 09:11:03 [URL] [DELETE]        [Reply] [Email]  
  • oil pressure
  • just laid in a new crank on my 8n and oil pump wont pick up prime. any suggestion s?

    Bruce(VA)    Posted 06-16-2020 at 09:20:45 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • did you pack the pump w/ assembly lube?

    did you insure the pick up tube was firmly attached?

    did you replace the gears in the pump?

    gary    Posted 06-17-2020 at 08:52:05 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • pump was producing 35 psi when i tore it down to replace badly worn crank. i packed the pump body with engine assembly lube and the tube with new gasket was firmly attached. took new pump to machinist but he said the pump was fine. this happened when i originally rebuilt motor, hence wasted crank.

    Bruce(VA)    Posted 06-17-2020 at 08:59:38 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • " took new pump to machinist but he said the pump was fine. "

    Did he actually measured the face width of the gears?

    Which leads to another question. You said " took new pump ...."

    You can't just install a new pump on an N engine w/o align boring the block. Did you do that?

    gary    Posted 06-17-2020 at 09:10:08 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • no, block wasn't line bored, but it had 35 lbs oil pressure at start up. it just won't pick up prime. Last time i borrowed an old oil filter canister that was modified to allow air pressure to force oil down into the pump. that worked, but not before doing damage to crank and bearings. The man i borrowed the canister from has since passed away.

    Bruce(VA)    Posted 06-17-2020 at 11:34:04 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • I'm getting confused here on the sequence of events.

    Is this the order of what happened?

    You rebuilt the engine, it only had oil pressure after you filled the lines w/ air, and it ruined the crank as a result.

    Next, you replaced the crank, installed a new pump, did NOT align bore the engine?

    Is that what happened?

    Did you plasitgauge the rods/mains?

    gary    Posted 06-27-2020 at 14:33:13 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • i will try one more time. I have rebuilt this engine twice. First time would not pick up prime and i contacted a man who worked on these tractors all the time. he had taken a remote oil filter and put in an air fitting. Then you put oil in the canister and connect it to the brass fitting on the side of the block where the oil feeds the oil pressure gauge. after removing the line to the filter from the brass block, you connect the line from the canister to the brass block and force oil backwards into the engine. this primes the pump and problem solved. i only needed to do this once and even after an oil change it would pick up prime. unfortunately i had already ruined the crank and bearings. Jump ahead to this recent rebuild and again the pump, even packed with assembly lube would not pick up prime. I made my own contraption to force oil into the engine and viola! 10 pounds on the starter. I only ran it a few seconds, as i have to go to a party. tomorrow i will top off radiator and set timing. The question remains why will this engine not pick up prime by itself? Also you do not need to line bore the engine for a new oil pump, only ream the new bushing.

    TheOldHokie    Posted 06-28-2020 at 08:23:44 [URL] [DELETE]        [Reply] [No Email]  
  • Re: oil pressure
  • Also you do not need to line bore the engine for a new oil pump, only ream the new bushing."

    The oil pump is part of the front main bearing cap and main bearing caps are matched sets that are manufactured and bored in situ on the block they are mated too. They will not interchange with another block or each other and must be installed in the exact position and orientation in which they were bored. That is a fundamental precept of engine building regardless of make or model.

    If you replace the oil pump on an N series tractor you have to align bore the block to match the new cap to the block and other two main bearing caps. Failure to do so will result in an out of round and misaligned front main bearing housing which throws the crankshaft out of alignment on all mains. Failure to rebore and/or hone the block and caps is a real easy way to ruin a new crankshaft and main bearing set.

    If you replaced the oil pump and did not align bore/hone the block and caps there is a real good chance your bearing failures and oil pressure woes are caused by front main housing out of round and misalignment problems.

    If I were you I'd revisit that very critical area before you chance reaching another set of bearings and crankshaft.


    gary    Posted 06-28-2020 at 10:52:42 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • i did not replace the front main bearing cap, only replaced the gears and bushing and reamed to fit. The problem was the pump wouldn't pick up prime and i wasted the bearings and crank as a result. I used an old oil filter canister filled with oil and an air fitting to force oil backwards through the bearings and into the pump. this primed the pump, but it was too late for the crank. Fast forward to this rebuild where i replaced crank and bearings. Was going to replace pump gear set again, but machinist said it was fine and it would provide 30 pounds at start up, but when warm would drop to 2. I was ready for the pump to do this again, so i tried to build oil pressure with the starter with no plugs installed and no joy, so i tried the same trick with another oil filter canister, and it primed and i was able to get 10 pounds on the starter. When i started it i got 25 pounds at idle. I will set timing and top off fluids tomorrow and see what i get off idle. I even packed the pump with assembly lube and it still would not pick up prime

    TheOldHokie    Posted 06-28-2020 at 19:00:23 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • OK - you did not replace the pump - you replaced the pump gears. Did you measure the face width of the new pump gears? Read this thread over on YT - similar problem solved by measuring the clearances to identify the culprit:

    Bad Replacement Oil Pump Gears


    gary    Posted 06-27-2020 at 14:35:11 [URL] [DELETE]        [Reply] [Email]  
  • Re: oil pressure
  • BTW, 25 pounds at idle.

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