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  1. #1
    Veteran Member Mechanos's Avatar
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    Default Partial overhaul on Yanmar 3TNE88

    As I'm using my 955 more and more lately and getting comfortable with it, I'm starting to push it more and work it hard. I've noticed that there is what seems to me to be way too much blow-by gasses coming out of the breather tube. I have no history of the engine, how it was used, how it was cared for, or how many hours are on it. All I know it that the engine sat for a few years without being used. I've ordered a compression tester and will check the compression when it gets here. Based on what the test yeilds, I may be looking at a partial overhaul this winter. Might just be worn rings or it might need to be bored. Could also be valve related... just won't know until I get into it. If I have to get into it, I'll have the head, valves, valve guides and valve seats checked out as well.

    Right now, the engine still starts easily and has no noticeable power drop off when worked. I've dug out and moved about 70 yards of dirt in about 12 hours of use. A friend of mine thinks that a compression test at this time may be premature and says that the excess blow-by gas may be a result of the engine sitting for an extended period and that rings my free up or reseat after some use. That would be nice, but I'm not too hopeful.

  2. #2
    Elite Member Tx Jim's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Quote Originally Posted by Mechanos View Post
    As I'm using my 955 more and more lately and getting comfortable with it, I'm starting to push it more and work it hard. I've noticed that there is what seems to me to be way too much blow-by gasses coming out of the breather tube.
    How much oil does engine burn?? If it were my tractor and had been sitting for several years but didn't use a lot of oil I'D RUN IT a while before thinking about an overhaul.

  3. #3
    Veteran Member Mechanos's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    It's only been run hard for about 14 hours. Too soon to tell. But, yes. It will get run some more. I'm in the middle of a project, so I need it. If I do anything, it wouldn't be until this winter.

  4. #4
    Veteran Member Mechanos's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Quote Originally Posted by BUBBAX View Post
    for your engine internal concerns, would you consider, AN ENGINE OIL TEST, before your winter inspection ? thank you for your earlier project postings for your engine conversion [855/955] project. happy tractoring mechanos.
    ps... would you think a 855 engine, be fitted into 755 john deere without too many modifications, or parts needed, to complete this engine conversion ? thanks again.
    Sorry, I've never actually seen a 755 in person. I don't have any insight on that one.

  5. #5
    Veteran Member Mechanos's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Update. Check oil and its down about a quart. I've already put one quart in it since I started using it, so this would make a little less than two quarts consumed in 12 hours of use. Doesn't seem to be lacking in power at all, normal exhuast... no blue smoke, just a black puff under load. The only indicators that something is amiss is the excess vent gasses and the oil consumption. Oil is already starting to turn black.
    Last edited by Mechanos; 10-13-2012 at 11:34 PM.

  6. #6
    Veteran Member kuboman's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    That is fairly heavy oil consumption for an engine that size. I would still work it hard for a while but a better than even chance it will not improve.
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  7. #7
    Veteran Member Mechanos's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Yeah. It's a guessing game right now. I have a compression tester and adapter on order that should be here any day now. When it comes in, I'll be able to do a compression test and a leak-down test. Hopefully that will point me in the right direction.

  8. #8
    Elite Member Tx Jim's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    A qt of oil to every 6 hrs of operation will cost about $.70 per hr. of operation. Rings,rod brgs & gask. set = *Subtotal 377.75 USD plus head work and labor .
    AM877967 PISTON RING ASSEMBLY ADD 65.98 USD 197.94 USD
    MIA880563 BEARING ASSY, CRANK ADD 14.87 USD 44.61 USD
    AM878183 GASKET KIT, HEAD ADD 135.20 USD 135.20 USD

    I'd still run it a few more hrs keeping a watchful eye on crankcase oil level. I'd probably try adding some Marvel Mystery oil also.

  9. #9
    Veteran Member Mechanos's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Thanks Tx Jim. I do plan on running more since I'm in the middle of a project and I'm not alarmed enough to pull it out of service. My parts prices are a quite a bit less since I can get the parts for this engine directly from a Yanmar distributor... this engine is not bound by the OEM agreement with JD. Still, it's a significant expense.

    What's your thoughts on the Marvel Mystery Oil? Maybe a stuck ring?

  10. #10
    Veteran Member kuboman's Avatar
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    Default Re: Partial overhaul on Yanmar 3TNE88

    Marvel mystery garbage!!!!! It won't fix anything, maybe mask some symptoms for a while. If you could put it on a steady load that puts it close to max output for several hours and run a slightly lower viscosity oil it may loosen the rings if that is the problem but more than likely there is permanent damage that only an overhaul will cure.
    L5740 LA854 loader
    L3130 LA723 loader sold
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