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Hot Rods GM small block 400 oil pressure problem

Discussion in 'The Hokey Ass Message Board' started by paleot, Jul 28, 2021.

  1. paleot
    Joined: Aug 29, 2011
    Posts: 228

    paleot
    Member
    from louisiana

    Rebuilt small block 400 had good oil pressure, after running for break in lost oil pressure. No knocks or rattles both sets of rockers pumping oil fine. dropped pan and changed oil pump no change. things I have checked hidden oil gallery plug is there,all plugs in oil gallery behind cam gear and the back of block plenty of oil pressure at oil filter. all new cam bearings installed at good machine shop.Motor has been run for a long period with no damage, just no pressure out of oil pressure sender hole. what in the world can it be?
     
  2. the gauge? try a known good one
     
    dirty old man and Fogger like this.
  3. Oil pump drive shaft? Distributor gear meshing with the cam? You pulled the distributor and ran the pump with a drill?
     
  4. iagsxr
    Joined: Aug 26, 2008
    Posts: 158

    iagsxr
    Member

    If the rockers are oiling I'd try another gauge.

    When you say the hidden oil gallery plug you mean the one under the rear main cap?
     

  5. kevinrevin
    Joined: Jul 1, 2018
    Posts: 117

    kevinrevin
    Member
    from East Texas

    ”...no pressure out of the oil pressure sender hole.."
    Have you removed the fitting for the line to the gauge? Is there something clogging up the line or below the fitting?
     
  6. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 1,324

    19Eddy30
    Member
    from VA

    Any oil leaks showing ?
    Gm block or after market?
    Is cam a small base circle?
    Diagnose problem without running the engine.
    What distributor are you using?
    Distributor also completes oil circuit.
    Oil ports on rear of block near rear cam plug & under timing cover.
    Have you try oil port up @ front of block near top of timing cover ?( I think all sb have , not @ shop to verify)
    There is also a oil port under head @ rear , top of block deck , I seen not installed some times .
    Like previous post above , take a old distributor & make a priming tool , and you have to use the housing to complete the oil circuit , use drill watch oil flow @ push rods / Rocker
     
    Last edited: Jul 29, 2021
  7. "No pressure out of the oil pressure sender hole". Are you making that assumption based on no pressure showing on your gauge or did you actually remove the fitting and check with either a primer or by starting the engine? A buddy used teflon tape during the install of his oil pressure gauge and then started having issues with fluctuating oil pressure. Turns out there was a flap of teflon tape blocking the hole in the fitting. Sometimes it would cover the hole, sometimes it wouldn't. Removed the flap and all was well.

    Warning ... when starting an engine with no fitting, you will get a VERY strong stream of oil if pressure is reaching that port. I forgot that fitting when my engine was on a test stand and the oil hit the ceiling of the garage :D:rolleyes:
     
    Last edited: Jul 29, 2021
  8. Deuces
    Joined: Nov 3, 2009
    Posts: 21,250

    Deuces
    Member
    from Michigan

    Some folks don't know how to use Teflon tape on a pipe thread....:rolleyes:
    I use that stuff all the time.... Never a problem!....;)
     
    egads likes this.
  9. paleot
    Joined: Aug 29, 2011
    Posts: 228

    paleot
    Member
    from louisiana

    Every thing mentioned in previous posts has been checked, GM block only thing I don't know about is the small base circle cam.Oil line fitting has been pulled no restriction there. This motor is in a street stock dirt track car, the owner has ran the motor for several hours with no noticeable damage.Pan was pulled new oil pump installed no shavings in pan pulled rear main when changing pump hidden plug is there. both sets of rockers are definitely oiling .
     
  10. iagsxr
    Joined: Aug 26, 2008
    Posts: 158

    iagsxr
    Member

    Circle track motor so it has the oil restricted to the top right? What's it have for restricters in it?

    You snag the o-ring on a restricter and plug the pressure port?
     
  11. iagsxr
    Joined: Aug 26, 2008
    Posts: 158

    iagsxr
    Member

    That and I'd have already ran a mechanic's wire down the pressure port then started the engine with nothing screwed into it
     
  12. gary macdonald
    Joined: Jan 18, 2021
    Posts: 134

    gary macdonald
    Member

    Oil pan too close to the pickup ?
     
  13. Still not sure if oil is coming out of sending unit hole near distributor. What is status?
     
  14. malibumonte78
    Joined: Nov 17, 2011
    Posts: 265

    malibumonte78
    Member

    I am fighting the same issue right now. Fresh rebuilt 400 no oil pressure at hot idle after break-in. Tried going with a 15W40 oil and that didn't help. Switched gauges to a vintage Stewart Warner gauge and it was reading around 20 psi at hot idle so we thought we were ok. Bought a new gauge to match the others in the car and it read low, replaced the line in case it had a kink and it still read low. Tried two more gauges and they all read low. So I guess the old SW gauge was the one that was wrong. Pan wont drop in car so I am about to pull the motor to look at the bearings and see how they look and was thinking about trying a HV HP Oil Pump. I hope you get yours figured out so I can get mine figured out too!
     
  15. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,504

    2OLD2FAST
    Member
    from illinois

    Have you guys tried checking the pressure at the port above the filter or the port above the timing chain ?
     
    egads likes this.
  16. Wrench97
    Joined: Jan 29, 2020
    Posts: 469

    Wrench97

    That passage is a straight shot from the oil filter.
    SBC oil passage.jpg
     
    iagsxr likes this.
  17. jaracer
    Joined: Oct 4, 2008
    Posts: 1,218

    jaracer
    Member

    A HV HP oil pump will only mask the real problem. You need to figure out where you are losing oil pressure. I've got an old 350 daily driver with a mechanical gauge and it has about 15 psi hot idle and 45 at any speed above about 40 mph.
     
  18. iagsxr
    Joined: Aug 26, 2008
    Posts: 158

    iagsxr
    Member

    I wasn't picturing the oil path correctly.

    If it has oil pressure at the port above the filter and not at the top of the block it can only be the hidden galley plug or a physical obstruction in the port.
     
  19. paleot
    Joined: Aug 29, 2011
    Posts: 228

    paleot
    Member
    from louisiana

    jagsxrr first thing we did was check the plugin the hidden galley, it is there.
     
  20. paleot
    Joined: Aug 29, 2011
    Posts: 228

    paleot
    Member
    from louisiana

    pprather, no oil coming out of sending unit hole! both sets of rockers oiling big time. the guy that owns the car has ran the motor for several hours against my advice. when we pulled the rear main down to check hidden gallery plug rear main is perfect no damage at all.
     
    pprather likes this.
  21. paleot
    Joined: Aug 29, 2011
    Posts: 228

    paleot
    Member
    from louisiana

    born to lose we pulled sender NO OIL!
     
  22. gary macdonald
    Joined: Jan 18, 2021
    Posts: 134

    gary macdonald
    Member

    Is the oil pan too close to the pickup . Did you use a pan gasket or just sealant ? Is the oil pan sump dented or bowed on the sides ? Factory oil pickup installed properly?
    Remove pan , remove plugs , put 5-6 qts in a 5 gal bucket with oil and place the oil pump pickup in the bucket of oil and crank motor . Youll see if and where its leaking , fast .
     
  23. 33 cdan man
    Joined: Sep 15, 2016
    Posts: 163

    33 cdan man

    I had a rear cam bearing that wasn't positioned properly. Had pressure when cold but as the oil thinned pressure dropped off.
     
  24. Kevin Ardinger
    Joined: Aug 31, 2019
    Posts: 351

    Kevin Ardinger

    Are you sure it doesn’t have standard bearings on a .010 under crank? Or .010 bearings on a.020 crank?
     
    Desoto291Hemi likes this.
  25. Joe H
    Joined: Feb 10, 2008
    Posts: 1,096

    Joe H
    Member

    It wouldn't have oil at the rockers if it was loosing oil in the bearings, the rockers are last in line for oil, and it sure wouldn't run for a couple hours without pressure. If nothing else, screw in a mechanical gaugs in every port that has oil and see if you get any readings.
     
    Desoto291Hemi likes this.
  26. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,444

    Johnny Gee
    Member
    from Downey, Ca

    Remove sender or oil line fitting then prime with an oil pump primer while poking hole with a wire to see what happens.
     
  27. hemihotrod66
    Joined: May 5, 2019
    Posts: 435

    hemihotrod66
    Member

    Change the pressure relief spring in the oil pump...
     
    Elcohaulic likes this.

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