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rebuilt motor.. no oil pressure **found**

Discussion in 'The Garage' started by big83chevy4x4, Dec 10, 2005.

  1. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    updated at the bottom.

    i recently rebuilt a stock 350 (only thing not stock was the RV cam) for my cousin, dropped it in and fired it. when i was primming it, it had 25 psi pressure. when we fired it, it had 25 psi pressure, once it warmed up, it went to 0. we shut it down.

    a little history. when we bought the motor we were told that it was rebuilt and never fired (missing valve covers and intake no gasket materal on any of the surfaces, also looked very clean inside). once i got into it i knew that that wasn't true. coolant was in the block and the bores needed a hone bad. from the parts we took out, it looks like it was rebuilt at one time. the bearings were down to the copper, but clean. it almost looked as if they didn't use any lube or primed it when they fired it.

    ive been racking my brain on why it has 0 pressure. we used the stock crank, it was in good shape. the bearings were stock that we removed, i put stock bearings in (dumass me didn't check the clearances :doah: ). the cam bearings looked new, as do the frost plugs. so we did not replace those either. new melling oil pump (standard), hardend pump shaft, welded on screen.

    it is slinging oil off the crank, shown on the dip stick, we have a mechanical guage plumbed in near the distributor. i have not pulled the valve cover to see if there is oil to the rockers, there was when we primed it.

    this motor is in a s10 blazer 4x4, i really don't want to pull it, it took 2 weeks to get it in. the really stange thing is the 4.3 that we took out of it, the oil pressure was the same exact way, 25 when cold, 0 when hot. the only thing that is the same is the pump pickup and the guage. when we pulled the pan off the 4.3 to make the pan for the 350, the pick up was laying in the bottom. with the deep sump of the 4wd pan, i though i figured why the pressure was that way. (ive known the blazer for 4 years and the pressure had never changed, never heard a rod knock in all that time, and lasted all this time)

    we took a break today on it, tomorrow we are going to dig into it and find whats wrong. first thing im going to do is replace the line (have spare) and bleed it, if no change, move it to the plug above the oil filter. if we have nothing there, we are pulling the motor as something is wrong with the pump.

    in the back of my mind (because i didn't check the clearances on the bearings) im thinking the crank was turned and they put the stock bearings in, and then i did the same and thats where all our oil is going. is it possible to loose all the oil pressure through too large of bearings?

    any other suggestions?
     
    Last edited: Dec 29, 2005
  2. S. Burnham

    S. Burnham Registered Member

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    #1 i always plastiguage before i put the pan on not everyone does but it is the safe thing to do
    #2 try a different gauge.
    #3 did you use a fram or a new ac delco filter? If so remove them and try a different brand like wix. the fram and new ac filter will colapse and cut off all the oil pressure. have herd horrible stories from people coming in to the parts store.
     
  3. beater_k20

    beater_k20 Banned

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    there's your key areas to look at. there's no way to avoid pulling it back out.
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    seen this before..

    We had a lady come in with a 302 Ford motor in an old Maverick that was "just rebuilt",and had the same symptoms..decent oil pressure cold,but as the motor warmed up it dropped lower and lower,until it finally hit 0 after 20 minutes or so..and a faint rod knock could be heard at idle..

    We pulled the motor out, and took the crank out..it looked perfect,so we miked it..it was .010 undersized,just as it was stamped on one of the counterweights...but it had standard size rod bearings in the rods..:doah: the mains were .010 unders though!..

    The guy who rebuilt it even had a sales slip showing he paid for the undersized bearings,and would have shown us the boxes they came in,but he'd already tossed them out..guess they were boxed wrong..He never looked at the markings on the bearings,and usually he always did!..he was pissed at himself for not looking!.:(

    .we installed new .010 under bearings,and it was back to 45 lbs at idle when hot,and 60 at faster speeds!..cost her 450 bucks to have the motor yanked and the bearings replaced,and put it back together..she sold it two weeks later!..:crazy:
     
  5. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the filter that is on it (and the only filter i use) is a carquest filter, ive been told that they are repackaged/repainted wix.
    ill try another guage, this one isn't that old though, was replaced in the summer.

    i really hope i don't have to pull the motor, but if i have to to find it, i will. its not the pulling the motor part, its that there is bearly enough room to do anything.
     
  6. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    today we took the line off the guage and turned the pump and had no oil coming out of the line. so its not the guage.
    the motor is almost out, just taking a break now.

    after thinking about it some more, im almost positive that when i welded the pickup on, i got it too hot and killed the pressure spring in it as its right next to the pickup hole.
    im still gonna check the clearances on the crank just to make sure that its good. i have a new HV pump here that im gonna rob the high pressure spring out of the box and put it in, that is if its broke.
     
  7. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    still havn't found it.
    the crank is within spec (a little on the loose side, but ive had looser and still had pressure)
    spring in pump is good
    all the bearings are good
    the pickup is 3/8" off the bottom of the pan
    pump gears look good

    tomorrow we are putting the blowgun in the filter hole and play find the big air leak. we are also gonna put the pump in oil and spin it with a drill to make sure that it is pumping oil. everything that I could have messed up was rulled out. it was someone or something else that screwed up.
     
  8. mouse

    mouse 1/2 ton status

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    I have had an oil pressure sending unit do this to me...on a 350 chevy. It basically worked backwards. That was an electric unit, and your using a mechanical, but I would check for leaks and change the gauge.

    If it isn't the gauge, you have to be losing that pressure somewhere, and I would suggest pulling the engine to go through it carefully. It won't run long without proper oil pressure.
     
  9. 3 on the tree

    3 on the tree 1/2 ton status

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    I vote worn cam bearings. Doesn't the 4.3 and SBC both oil through the lifter galleries first??? You said the bottom end bearings were worn badly, so I would expect the cam bearings to be in similar shape.
     
  10. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the bottom end bearings are not bad, they have a few spots that are shinny, but they mic and feel just just new bearings. the cam bearings looked almost brand new (ive run alot worse and it still held pressure) when we put it together.

    weve had the motor out for a week and been trying to find the leak, but visually everything checks out. i don't want to go too deep and have to replace all the gaskets again (running out of money) but i may have to.
     
  11. 5150_BEAST

    5150_BEAST Registered Member

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    oil pressure....

    we have all been there (running out or money)but look at it at a cheaper point of view spend the money to fix it rite instead of a really expensive paper weight mocking you from the corner of the garage, learned lesson 3 years ago with a $8,000 drag engine ate itself cause i didnt shut it down when oil pres. guage was fluttering:doah: do it rite the first time and avoid the headach you will recieve after you bang your head against the wall
     
  12. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    have you miced/plastigauged the crank yet?
     
  13. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    yep, its on the high side but its within spec, .002 for the mains and .003 on the rods
     
  14. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the pump is good, it pumps mineral spirits just like the pump in my truck (had the pan off and decided to pull the pump)

    i cut the filter open and there was alot of junk in it. im thinking that it may have been plugged and caused it to loose pressure. so monday im gonna put pan back on and put some oil it in and run my primer and check the pressure. hopefully thats it.
     
  15. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I would pull the rear main cap and make sure the oil galley plug that is under there is still in place. It may be difficult to see since it sits so far down the hole it is installed in.
     
  16. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    what hole is it in and how far is in in there?
     
  17. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There is a hole next to the main bolt hole and it is probably down a good 1" or more.
     
  18. theperfectgarage

    theperfectgarage 1/2 ton status

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    I second that, 4x4 high. as I was skimming this thread it's the first thing I thought of.
     
  19. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    i couldn't see it in there (bad lighting in the garage) so we stuck a screw driver in there and it stopped just over 1" down.:dunno:
     
  20. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    after checking everything on the motor, i got curious and pulled the line out of the blazer. after i got it threw the firewall and down under the dash so i could pull on it, it didn't move. i felt up under the dash and it was tied around a wire harness and had a kink in it. after getting it out, we cut a 8" piece off that was good with no kinks, put the pan back on and stuck my primer in it and spun it. the guage read 32 or 33 psi with my 850 rpm drill and was very responsive with any flucuations with the drill, unlike before. so i bit my lip and desided to put it back in. we just need to put antifreeze in it and we can fire it, again.

    i got to thinking and thats the only way the 4.3 could have lived so long with "no oil pressure"

    so we did all that work and dug all the hiar out of our heads all for a plastic line that *thump on head* we had a brand new one in the tool box.

    tomorrow we need to get a few more parts then fire it up and see what it does.
     

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