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Subject: 8N losing oil prime

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Greg Davis    Posted 07-22-2020 at 20:47:54 [URL] [DELETE]        [Reply] [Email]  
  • 8N losing oil prime
  • Side distributor 8N. Total rebuild of the engine. The oil pump was rebuilt by a machine shop that rebuilds lots of these pumps. (We rebuilt it first and thought we had done something wrong, took it to a machine shop and let machinists rebuild it to only get the same results). We checked the "pickup" tube with a smoke machine for finding vacuum leaks on cars and no leaks anywhere on the pump or pickup tube. If the tractor sits just a few minutes after being cut off, it looses prime. When primed it holds about 10 PSI at an idle and 25 to 30 with higher rpms. Suggestions???? We are at a loss. As a side note when the gentleman bought this tractor the oil pressure gauge was just trashed from age and not working. When the engine was taken apart the rod bearings were terrible. We suspect this engine had the "no oil pressure" issue to begin with and the previous owner didn't know because of the bad gauge. Could the oil pressure relief plunger valve and spring have anything to do with it? We just don't know what to do next

    TheOldHokie    Posted 07-23-2020 at 03:30:17 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N losing oil prime
  • Check the new pump gears. There are a raft of bad rebuild kits on the market and I hear this story a lot. First thing I do when I get a new kit is measure the face width of the pump gears.

    The narrow gears should measure .561/.562 and the wider gears should be .724/.725.

    The gears in the defective kits are about .010 undersize and will bypass badly giving exactly the results you have.

    TOH

    Greg    Posted 07-23-2020 at 05:40:33 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N losing oil prime
  • I hate to take it back apart again, but it may require that. The machine shop that built the pump is the one that Just 8Ns uses on a regular basis to build their pumps if that makes a difference. I don't know where they get their parts. I would assume Just 8Ns since they are in the same community not too far apart but you never know.

    TheOldHokie    Posted 07-23-2020 at 06:47:41 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N losing oil prime
  • If it isn't working I don't see any way around taking it apart again. Within the last year (or there about) Just8N's was selling the same defective oil pump kits (Atlantic Quality Parts)as everyone else. The kits were cheaper than Tisco/Sparex/A&I and many of the retailers were distributing them. I spent a while on the telephone with Derrick getting a resolution for the four I purchased from them. Quite possible the machine shop is sourcing their own parts or had an Atlantic kit they got from Just8N's on the shelf. I just ordered two kits from Just8N's and I will be checking them the minute they show up. A couple weeks ago I got a pump to rebuild and the guy supplied his own parts. You guessed it - junk gears. No guarantee your problem is the gears but....

    TOH

    Greg Davis    Posted 07-23-2020 at 06:57:42 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N losing oil prime
  • So, where should I order the parts from? What is the best brand name rebuild kit to buy? Tisco/Sparex/A&I? I totally agree with what you are saying and appreciate your advice very much. I do find it ironic that it probably (we're not 100% sure) wasn't pumping beforehand which ruined the rod bearings and it had what appeared to be the original pump (and gears) in it. Again, thanks for your advice.

    TheOldHokie    Posted 07-23-2020 at 07:54:42 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N losing oil prime
  • I just ordered from Just8N's and I have no idea what brand I will will receive. As I said as soon as I get them I will measure the gears to be sure. I have the last of 3 "no-nsme" kits on the shelf - plain cardboard box with Made in Turkey printed on it and I don't recall where I got them. Those kits were all fine. This has been going on for over a year so maybe things are beginning to get corrected but I still check each and every one I get regardless of brand.

    Failure of the oil pump to self prime has been a problem with these engines for a very long time and is not always related to defective replacement gears. That issue is just a new wrinkle to a long standing issue. Here is a thread from a few months ago that is eerily similar to your post. The problem was resolved the old fashioned way - thorough and accurate measurements:

    Oil Pump Losing Prime

    TOH

    Greg Davis    Posted 07-23-2020 at 08:18:56 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N losing oil prime
  • Wow! The other guy had very similar problems. I see no way out, but taking it apart again and trying another kit. Thanks so much for your help. If they gentleman wants to send the pump to you for rebuild, how do we get in touch with you? Thanks for all your help!

    TheOldHokie    Posted 07-23-2020 at 08:29:38 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N losing oil prime
  • I'd suggest measuring what you already have before throwing new and unknown parts at it. My contact info is on my website: windyridgefarm.us

    TOH

    Greg Davis    Posted 07-23-2020 at 08:40:37 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N losing oil prime
  • We will certainly measure what we have. Thanks again!

    TheOldHokie    Posted 07-23-2020 at 09:17:04 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N losing oil prime
  • You are welcome. Free advice and worth every penny you paid for it ;-)

    TOH

    Greg Davis    Posted 08-03-2020 at 12:29:04 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N losing oil prime
  • Update: We took oil pump back out of the tractor and the owner took it to the machine shop that put it together. The machinist opened the oil pump up in front of the owner. Gears were .10 under. The owner went to Just 8ns and picked up a new kit for the oil pump. The gears in the new kit were correct on the micrometer according to the numbers you gave us. The machinist was glad to get the information. He had another with the same issue. Now to install the pump on Saturday morning. I'll try to remember to let you know if this works. It should be the cure. Thanks for all your help!

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