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  1. #1

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    MSX 150 HIGH oil pressure..

    Hi, Ive recently rebuilt my MSX 150 because of too low oil pressure (broken oil hose, turned the crankshaft, conrod etc to crap).

    This evening I gave it a go for the first time after rebuilt.
    Ironically this time the oil pressure was too high.

    Cranked with ig. coils and injectors unplugged to build up some oil pressure, got up to about 3bar then plugged it all in again.
    Fired up right away but the oil pressure was speeding up to at least 7bar, pulled the lanyard immediately. Gave it 3 more shots but same result, my pressure meter stops at 7bar and I think that it would get past that mark without problems.

    Couldnt hear any wierd sounds or anything from the engine, checked all the hoses and all looks good.

    In the overhaul Ive changed the pto end conrod and all bearings on the crankshaft and balanceshaft. The crankshaft was rebuilt.
    The oil cooler was also changed.
    Measured all things that could be mearured when I was at it, incl. the oil relief spring and piston.

    Do anyone have a clue what could be wrong with my engine?

    Thanks, Conny.


  2. #2
    ripcuda's Avatar
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    Howdy Cmizzer!

    Sorry to hear of your previous misfortune with your MSX 150. I too just finished a rebuild of my MSX 150 (had a warped block from bad overheat).

    How are you measuring oil pressure? Sounds like you have a gauge... where are you hooking it up?
    I've never had a gauge on my engine... so don't really know what pressures it operates at. I never see any oil pressure idiot light... so I assume it's all good.

    Here's what the service manual states:
    Oil Pump Specifications
    OIL PUMP TYPES = Trochoid
    ROTOR TIP CLEARANCE (PRESSURE) = N/A
    OIL PRESSURE RELIEF VALVE = SPRING FREE LENGTH = 2.7″ (69mm) / PISTON O.D. = .43″ (10.9mm) /PISTON LENGTH = 1.10″ (27.7 -- 28mm)
    OIL PRESSURE = 21 @ IDLE -- 80 @ MAX PSI (1.5 -- 5.5 BAR)
    Is it possible too much oil causing over pressure? Do you know the correct oil check procedure?

    Wish I could be more help.

    Cheers!

  3. #3

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    Hi, I got my gauge hooked up on top of the oil tank. Built an adapter and longer banjo so I can fit the oil hose and the adapter for my gauge. Tried this on another working ski and it worked on that one, it showed about 3bars on the rev limit in reverse (~3400rpm).

    I filled it with 3,5 litres, since the whole system was dry it shouldnt be overfilled.

    Thanks

  4. #4
    ripcuda's Avatar
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    That's a clever spot to tap for oil pressure... high pressure... comes right off the side of the head.

    Did you measure crankshaft bearing clearances? I wonder if they were too tight how that would affect oil pressure.

    Another thought would be when you sealed the block halves together... possible that some sealant squeezed out into the oil pump area and is clogging something. Having just done this myself in the past month... I remember having to be careful of sealant squeezing into the oil relief valve cavity and the oil pump housing (end of counterbalance shaft). I suppose if enough had oozed out where it shouldn't be... and hardened... it could clog somewhere. This would really be a pain though... not sure how you would be able to determine or fix it without pulling the engine.

    Are you using a new oil filter? I suppose a badly clogged on could cause issues... but I doubt the pressures your seeing.

    I'd still be sure to confirm you have proper oil levels. With a cold engine, start, run 20-30 secs, stop, pull dipstick, wipe, insert (do NOT screw in), pull, read. Should be just barely on the stick or up to 'MIN' mark... but not above.

    Good luck. Cheers!

  5. #5

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    Yes all the bearings were checked and within limits, and I checked the oil level. The oil filter is also new. Now ive pulled the engine and torn it halfways apart, the block halfes and head is still togheter. I took out the oil relief piston and spring, oil filter and high pressure pump. All the oil channels are clear. From the oil supply fitting on the side to the pump its all clear, also from the pump to the filter housing, from the filter housing trough the block up to the oil feeding hole on the cyl head its all clear. No sealant in the wrong place to be found.

    I checked the relief spring, it should be 69mm but its 70mm. The piston o.d. should be 10,9mm but its 11,05mm. Could this be my problem?

    I also fitted a better gauge before i took out the engine and the pressure was 7,1 bar @ 3400rpm.

  6. #6

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    Conny,
    There were a few problems with the piston diameter being too large and /or galling on the piston that causes the piston to seize into the bore. The piston should move freely thru the entire length. The piston & spring is the only thing that controls oil pressure. RipCuda is 100% correct about making sure you clean all the crankcase adhesive out of the oil pressure relief area. I dont think you can get too much oil pressure from tight rods & main bearings, but I have never seen this problem. If the bearings are too tight, they usually just spin and destroy themselves.. haha..
    Better to set the rods & mains on the "loose" side.

    Regards,
    Randy

  7. #7

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    Thanks for the quick reply. The piston and spring were changed for new ones in the last rebuilt and the piston moves freely the whole way. I can take out the copper cylinder that the piston moves in with a sprewdriver easily but that shouldnt be a problem i think. But its a straight channel from the oil pump to the hole in the cyl head so my problem is probably in the spring or piston. I was hoping to find some sealant in any hole so i could see the problem right away.. If aint someone have any other ideas i probably put a new spring and piston in and hope for the best, it sucks that i doesnt found anything concrete.

  8. #8
    ripcuda's Avatar
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    Well... that tad longer spring could raise the pressure the relief kicks-in at. But you are way above stock pressures... so I can't imagine that 0.1mm extra spring length resulting in that much higher pressures.

    So unless there is some issue with the high pressure pump (on the PTO end of counter balance shaft)... which in my mind a problem here would probably lower pressure not raise it... but I'm unsure. Seems there could be a blockage in the high pressure oil circuit somewhere. The piston bottom squirter orifices or passageways in the block somewhere.

    Wish I had more ideas. Good luck.

    Cheers!

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  9. #9

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    Now its up and running again, bought a new oil relief spring and piston. Cant tell what was wrong with the old one from just laying in a box over the winter. Just wanted to let you know. Now im looking forward for the 15h break-in period to be over! Thanks anyway for the help!

  10. #10
    ripcuda's Avatar
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    So a new oil pressure relief spring and piston fixed it? Glad to hear you got it sorted out.

    Can you describe your 15hr break-in period? Is this a Polaris or Weber recommendation?

    Cheers!

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