Looking for old school Mack techs

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by CATsmeow, May 13, 2021.

  1. CATsmeow

    CATsmeow Bobtail Member

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    My shop recently took in a 1986 Mack Superliner with the E6-350. Customer wanted an engine tick diagnosed. found #5 cam lobes damaged to the point of no return. customer opted to overhaul the engine along with cam replacement. We did a full overhaul rods, mains, pistons, liners, heads, oil pump. We replaced the damaged lifters and inspected all cam bearings. Finish the overhaul and during run-in noticed oil pressure is low. 12 psi at idle and 30 psi going down the road. Then we began our adventure of searching for the low oil pressure issue. We pulled the pan removed and inspected the new oil pump. inspected and plastiguaged all rod and main bearings everything within spec. changed oil filters again. and installed the original oil pump thinking that the new one was suspect. test drive and same problem. We have manually checked oil pressure before and after the oil cooler to make sure it was not plugged. We have pulled and inspected the oil pressure relief, piston cooler relief and filter bypass. We have found nothing out of place. I did notice on the last test drive that the engine brakes did not work. we ran the engine with the valve covers off and we don't get a lot of oil to the top end. looking at the lube system schematic the heads get oil from the #2 and #5 cam bearings. So i was wondering if it is possible to install the head gasket upside down. looking at pictures of the head gasket it looks possible, and if it were it could absolutely be the cause of my loss of oil pressure. Any help on this would be greatly appreciated.
     
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    I have not been in one of those for a long time but:
    If it is possible to install a head gasket backwards would the rockers on one head not receive any oil?
    Does the oil pressure sensor and or line not get oil below the head gasket?
    If you run it with a valve cover off does the oil from the rockers have air bubbles? If so it is sucking air on the pump inlet.
    What about piston cooler nozzles?
    What is the acceptable oil pressure on those anyway? I know it is not high on an E7 but do not recall the 6's.
    How about a picture of that CATsmeow?
     
  4. CATsmeow

    CATsmeow Bobtail Member

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    May 13, 2021
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    From the looks of the head gasket if it were installed backwards the rockers would still receive oil but that rocker shaft. it would be as if that oil rifle had a large leak. The oil pressure reading is taken from the oil filter housing before oil gets to the rifles.
    Wit the valve cover off all of the rockers seem to get oil but it doesn't seem that it is getting very much oil.
    Piston cooler nozzles do not receive oil pressure until 35 psi when the oil relief valve for the piston coolers opens up. it has been checked
    acceptable pressure at idle is about 18-25 psi at operating temp so we are definitely below that spec.
    The spot that is circled is what seals the oil rifle to the heads. so it looks that if the gasket were reversed oil would just spill back to sump.
     

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  5. pup

    pup Light Load Member

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    If the air compressor was removed, any chance the oil supply tube between the accessory drive & compressor was left out? Just thinking about a place for an internal loss.
     
  6. BoxCarKidd

    BoxCarKidd Road Train Member

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    Then I agree it is possible.
    Saw a rocker shaft upside down on a 60 series. It had similar results. Was dumping lots of oil. Easy to see running with the valve cover off.
     
  7. CATsmeow

    CATsmeow Bobtail Member

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    had the same thought but nothing was taken off on that side of the engine.
     
  8. CATsmeow

    CATsmeow Bobtail Member

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    i,ve seen the same thing with a series 60. i will have to look but i don't think you can get the rocker shaft upside down on this engine.
     
  9. pup

    pup Light Load Member

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    I've seen a situation like this after overhaul when the wrong size main bearings were installed. The
    crankshaft mains had been turned .010 at some point in it's life. The installer never checked the size of the
    bearings he removed & just tossed in the std bearings that came in the overhaul
    kit. It behaved exactly like yours. If you still have the old bearings I'd check them. The size & part#
    should be stamped on the back.
     
  10. CATsmeow

    CATsmeow Bobtail Member

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    That was our first thought. But all bearings have been checked and plastiguaged so I know the bottom end is solid. We are quickly running out of tricks to pull out of the hat. My head gasket theory is about the only thing I can come up with but i was looking for some reassurance before I jerked the heads back off of it.
     
  11. haycarter

    haycarter Road Train Member

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