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Technical oil pressure drop

Discussion in 'The Hokey Ass Message Board' started by SJ13, Sep 9, 2015.

  1. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

    recently built 351w 11:1 compression motor @ 1st it was holding steady 50+ lbs oil pressure now after break in & oil change {btw no major metal shavings in oil or filter} the pressure rises to mid 40s but after warming up @ 2500 rpm it has less than 20 lbs and @ an idle it has only about 6 to 8 lbs ... I know that the engine has to come back out to be fixed and I am definitely not happy about that , I was seeking a little insight on what this may be ... weak oil pump ... journal plug ... spun bearing ......
     
  2. lippy
    Joined: Sep 27, 2006
    Posts: 6,825

    lippy
    Member
    from Ks

    How much bearing clearance did it have to begin with when it was rebuilt? Lippy
     
    turboroadster likes this.
  3. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    What are you using for a gauge? Try another..
     
  4. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    Oil pressure loss is mainly main or cam bearings. But the first thing check if the oil pump is tight. I have found more than one loose pump or pickup after a rebuild.
     
    Last edited: Sep 9, 2015
    loudbang likes this.

  5. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

  6. blowby
    Joined: Dec 27, 2012
    Posts: 8,661

    blowby
    Member
    from Nicasio Ca

    Sudden or gradual drop? Was it alright before the oil and filter change?
     
  7. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

    it had gradually started to decline before the oil change but over the last 6 weeks and about 500 miles it has dropped to 38 lbs on start up no major noise and doesn't run erratic
     
  8. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    I was under the impression this drop was right after break in. I'm thinking abnormal bearing wear. Are you sure the main caps got back in the right places?
     
  9. blowby
    Joined: Dec 27, 2012
    Posts: 8,661

    blowby
    Member
    from Nicasio Ca

    You could send an oil sample out for metal analysis, however as you say it's likely coming apart.
     
  10. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

    will post follow up when time permits , Thanks for your input and genuine concern, on the positive side while this beast is sitting in the garage I can do some other things that in my haste to get on the road before summer I neglected this beast was in storage for many years and had a few minor problems with wiring but with new life and some voltage through them they are starting to awaken, lots of small things that are taken for granted and are just an hour or 2 and a few $$$ here & there cant fix as fall & winter approaches and before spring comes she will be more road ready than she has been in over 20 years
     

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  11. agreed, mains possibly
     
  12. its not gonna make noise yet, the parts are riding on a thick film of oil thats seeping out, if you keep driving and give it more time and a smidge more wear, it will start the not happy noises in the bottom. I would be checking it out instead of waiting and driving it.
     
  13. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

    no more driving for sure its not worth taking the chance on destroying the motor
     
  14. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Just a few things I'd do, especially on a fresh engine...

    Pull the oil filter, cut it open...what does it have in it?

    What's the oil look like (drained in a clean pan)?

    Put a good mechanical gauge on it and compare, should be able to find a port somewhere on the engine, no need to run a line into the car, mount one up, etc...

    I mean if oil is good (no shaving slurry) filter is good (no metal particulates embedded in it), live with a comparison to the mechanical gauge.

    Otherwise (as you've mentioned you're not going to run it again), pull the engine and tear it down...but I like my approach better, before pulling the engine.
     
  15. BnG Engine
    Joined: Jul 1, 2015
    Posts: 60

    BnG Engine
    Member

    Oil pump bypass spring? Oil galley crossover plug, but you'd have lifter noise if it was this.
    Lots of things it could be, but since you're going to take it apart take lots of pictures as you do.
     
  16. AHotRod
    Joined: Jul 27, 2001
    Posts: 12,216

    AHotRod
    Member

    What brand of oil filter is on it?

    What Brand and type of oil is in it?

    Is it a flat tappet camshaft or Hydraulic roller?


    We only use Wix filters....... period.
     
  17. SJ13
    Joined: Dec 9, 2014
    Posts: 62

    SJ13
    Member
    from PNW

    it has mechanical gauge & stock dummy light , hydraulic roller , Royal Purple 30 WT. oil , Fram PH8A filter , break in oil was ran into a new drain pan and I inspected it ,cut filter apart and looked & each fold and no noticeable chunks of metal just tiny specks
     
  18. I had a motor drop to no measuring on the gauge a few years back and found the oil pump bypass stuck. if it stuck or got a little piece of crap holding it a little bit open it would still make pressure but not as much.
     
  19. AHotRod
    Joined: Jul 27, 2001
    Posts: 12,216

    AHotRod
    Member

    Find who sells Wix Filters in your area, and get a Wix 51515 filter and put on it. We have found so many engines with Fram and cheap, store branded filters having pressure issues. The poor quality construction is one thing, and the 'flow rates' are low.

    I would also try a 10-40W or 20-50W oil, we only use Brad Penn 30W break in oil on the initial break in of all new engines, Then, depending on the engines bearing clearances, they get Brad Penn 10-40 or 20-50 (unless they are the new GM LS or Ford and Dodge late model engines).
    We also always check every engine with "our" shop pressure gauges and then compare to what has been installed in the car. Many times we find variations.

    This is what we do for our customers, sometimes you can save them, sometimes it's to late.... but it's always worth a try.
     

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