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Gas in crankcase. Good?Bad?

Discussion in 'XJ Technical Chat' started by MrSeca, Jun 21, 2019.

  1. MrSeca

    MrSeca Active Member

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    I'm sure it's happen to all of us at one point or another on your vintage bike. You're petcock doesn't quite work and the floats in your carbs don't quite stop the gas from leaking down into the crankcase, a week later you get on your bike and voila, a crankcase filled with gasoline. I'm curious, however, if this can actually be a good thing for your engine in terms of cleaning it. Can it be harmful to the engine? Would like to know peoples thoughts? Thanks.
     
    MrSeca, Jun 21, 2019
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  2. Jetfixer

    Jetfixer Well-Known Member

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    Not real good , the gas washes the oil from the bearings . lack of lubrication cases wear to the bearings and possible scoring of the crankshaft , the pistons and rings wear as well as they rely on oil , is you run like this for a period of time this is possible issue . Best to fix carbs and petcock and CHANGE the oil ASAP.:D
     
    Jetfixer, Jun 21, 2019
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  3. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    There is also the serious risk of hydrolock and bent or broken connecting rods. And while fairly rare, a combustion event within the crankcase is possible.

    Also rmember that the transmission shares the same oil as the engine. Gears under load need an oil film just as much as their bearings do.
     
    k-moe, Jun 21, 2019
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  4. MrSeca

    MrSeca Active Member

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    I'm not saying to leave the gas in there. I'm simply saying if gas is run through the engine, drained out, and then put fresh oil in there what effect would this have on the engine itself.
     
    MrSeca, Jun 21, 2019
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  5. Franz

    Franz Well-Known Member

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    How fast does the oil pump need to rotate to create sufficient pressure to force oil through the oilways? If the oil is changed (and ignition is off) can rotating the rear wheel with the machine in gear lubricate the bearings and their journals before starting the engine?
     
    Franz, Jun 21, 2019
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  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    just turning the crank for checking shims pumps a lot of oil through the motor.

    running gas through motor with oil? gas is in no way or form a lubricant .gas will clean the oil off of surfaces
    it is not good but if it happened because of overflowing carbs drain oil. long term running will start scoring on surfaces that rely on oil

    if you want to clean crud out of the motor run seafoam in with oil
     
    XJ550H, Jun 21, 2019
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  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The key being the ratio of gas to oil. A Seafoam dose is one ounce per quart of oil (1:32). In a full oil change the added Seafoam is barely enough to noticeably raise the oil in the sight glass.
    If you noticed gas in the crankcase, the oil is too dilute to do its job in a 4-stroke engine.
     
    k-moe, Jun 21, 2019
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  8. Franz

    Franz Well-Known Member

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    I was on the motorway years ago around 1979 when my Honda CB 750K2 became a 375cc twin due to one set of points sticking open and I thought about the unburn fuel mixture not being good for the cylinders.
     
    Franz, Jun 21, 2019
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