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  1. #1
    boudin's Avatar
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    300LX Spun Bearings - Root Cause

    I picked up a nice condition, low hour 300LX a few weeks ago. Owner said the ski just stopped in the middle of the lake with a big puff of blue smoke. Owner had done a recent oil change with Royal Purple (I don't know the weight).

    When I got the ski back to my shop, I noticed the oil was overfilled and also the oil catch on the bottom of the air box was full. I had to pull out nearly 2 quarts to get it to register correctly on the dip stick, and another 1/2 quart drained out of the airbox.

    Disassembly revealed that all five main bearings were very worn or spun, as well as the rod bearings. Case and crank were trashed.

    I have since sourced a good condition case/crank, and have new OEM bearings, and everything else I need for reassembly. I have cleaned/checked the oil pump for wear, oil cooler (and tested the thermostat), also cleaned the intercooler (which was a bit oily), SC seems fine, got injectors cleaned/tested, did a valve job (lapped) while I had the head off/checked lash. Honed the cylinders; pistons look good. Pulled the jet pump (which the owner did rebuild, but it looked fine). I can't find anything else wrong.

    I've rebuilt about ten normally aspirated 15F motors, and pretty confident in reassembly. However, this is my first SC motor rebuild.

    I have heard that severe overfills of oil can lead to loss of pressure. Thoughts on what could have caused such catastrophic damage? Just looking to determine root cause.


    -Greg


  2. #2
    Check the pop off valve on the oil pump. Once the get some debris ran through them they like to stick. You can also pressurize it to see when it cracks open and then back the pressure off to see if it fully seats.

  3. #3
    boudin's Avatar
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    I checked the oil pressure relief valve per the shop manual. Made sure when depressed it came out on it's own, and there were no rough spots. Seemed fine. I did not pressurize it, and don't see that procedure as a checkpoint the book. How much PSI should cause it to open?

  4. #4
    I usually just use a leak down tester and clamp the pop off on the end. You can see/hear exactly when it cracks open, then back the air pressure off and make sure it 100% seats. Typically I notice they'll open fine but won't seat fully closed after a bad engine failure. Its not in any shop book, just what I've done in my builds. Click image for larger version. 

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  5. #5
    Let me out of here......I need to go on Greenhulk!
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    Did you check the cam journals ? The bits of bearings/aluminum usually end up making a new home there.

  6. #6
    steve45's Avatar
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    I'm guessing (and I'm no expert) that when the oil was overfilled that much, it got up to the crankshaft area causing it to foam.

  7. #7
    Pain is fear leaving your body.... rlovebk's Avatar
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    FYI: I have seen more SC motors trashed and issues related to the use of Royal Purple then I can say.

  8. #8
    boudin's Avatar
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    Thanks for the responses, folks.

    @TMiller, the cam journals look good; I guess the oil pickup screen did it's job. There was a lot of small bits of bearing material in the bottom of the pan, though.

    @steve45, yes that is what I'm thinking as even the crankpin journals and bearings were marred.

    @rlovebk, wow on the Royal Purple. Will research this. I almost always use Pennzoil myself.

    Overall, ended up missing ordering the oil pan gasket, and partzilla is still taking +1 week on shipping, so waiting for that. I do need to do the pressure check on the relief valve that @mwhc recommended.

    -Greg

  9. #9
    boudin's Avatar
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    Quote Originally Posted by mwhc View Post
    I usually just use a leak down tester and clamp the pop off on the end. You can see/hear exactly when it cracks open, then back the air pressure off and make sure it 100% seats. Typically I notice they'll open fine but won't seat fully closed after a bad engine failure. Its not in any shop book, just what I've done in my builds. Click image for larger version. 

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    I could not get my leak down tester to fit, but was able to use just an air gun and compressor and it looked like just shy of 100psi, and then when pressure was moved down it sealed again. Ski is back together and after warmup I’m seeing approx 59 psi at 3000 rpm. Idle 25 psi, and revving to approx 7k hits nearly 100psi, but no higher. Does that pop off sound right?

    -Greg

  10. #10
    Yea and usually once the valve gets a full heat soak in it, it will pop off a touch lower and close a bit slower.

    I have a billet aluminum reusable oil filter with a different bypass system in it and when the oil is cold I can see 130+ psi. Its typically around 65-75psi warmed up, wot with amsoil 10-40.

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