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  1. #1

    polaris 780 oil question

    I just recently bought 2 skies polaris 780 and Seadoo spx. The Seadoo has 2 stroke oil running into the bottom end of the engine from the tank, but I'm not seeing anything supplying the bottom end with oil on the polaris. The Seadoo was adapted to premix but left the tank on for the bottom end supply of oil. The polaris is set up for premix gas also but oil tank is gone. So my question is can someone steer me threw how the bottom end get its lubrication. Or point me to a diagram somewhere that explains it. Thanks very new to this any help would be great.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Arrow How does oil get into a Polaris PWC 2-stroke engine?

    Welcome

    The SeaDoo engine is quite different from the Polaris engine. Be sure to learn how that SeaDoo engine works.

    Lubrication of the Polaris 2-stroke marine engine is similar to many other 2-stroke reed valve engines, but this is different from the rotary valve SeaDoo.

    The lubricating oil enters the Polaris engine alongside the intake air and the atomized gasoline. Below the carburetor all three ingredients first flow into the crankcase via the intake reeds, where air turbulence from the spinning crankshaft flings the oil mist everywhere.

    The crankcase uses uses roller bearings which are partially exposed to the oil mist and also receive oil via drain/drip holes that feed the main bearings. As the engine runs the airflow pulses from the crankcase up into the combustion chamber between power strokes. Some of the oil mist also gets sucked up, that oil then burns along with the gas-air mixture during the next power stroke.

    The only difference between the stock Polaris OEM oil injection system and the pre-mixed oil-in-gasoline system is in how the oil gets delivered into the engine's intake air stream. The actual lubrication inside the engine is the same.

    The Polaris oil injection system uses an oil pump to mildly pressurize the oil and push it through small oil hoses to oiling nipples on or below each carburetor. The oil then dribbles down inside the air intake tract towards the crankcase intake reeds. The oil gets carried along and distributed by the violent airflow that occurs with every air intake pulse/suction as the engine runs.

    With pre-mixed oil in the fuel tank, the oil arrives inside the carburetor dissolved in the gasoline. As the mixture gets drawn out through the carbs and down into the engine the gasoline evaporates and leaves the oil behind to lubricate.

    From the crank case onwards the oil works the same and gets consumed the same as the engine runs, regardless of how the oil got into the engine.

    Most Polaris engines (except early 1990s) came with variable flow rate oil pumps. The oil pump has a link to the throttle such that the oil pump reduces the oil flow at low throttle openings and increases the oil flow rate when the throttle is squeezed hard. The engine needs very little oil at low to medium throttle levels so the variable rate system not only reduces exhaust smoke, it also reduces carbon accumulation inside the engine and minimizes the amount of oil you need to buy for a given amount of riding.

    In contrast, pre-mixed fuel always delivers the same proportion of oil regardless of throttle position. The typical ratio is 40:1 fuel to oil, so there is one ounce of oil going into the engine for every 40 ounces of gasoline burned.

    You can find a lot more info by clicking my signature links. Lots to read and learn!
    Last edited by K447; 02-19-2014 at 06:39 PM.

  3. #3
    Aw thanks. I've been scratching my head about this for five days now.

    So if I am reading this correctly, the oil pump only delivers the oil to the carbs and mixes it at that point and then air fuel and oil enter the crank case together. So with premixing you are just combining the fuel and oil before the carbs, but after the carbs the oil and fuel always enters the engine mixed whether you utilize the pump or premix.

    In other words there is no straight 2 stoke oil or other oil of any kind flowing throughout the crankcase. Right?
    Last edited by K447; 02-19-2014 at 06:38 PM.

  4. #4
    BlueFishCrisis's Avatar
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    Quote Originally Posted by Un-cowJ View Post
    Aw thanks. I've been scratching my head about this for five days now. So if I am reading this correctly, the oil pump only delivers the oil to the carbs and mixes it at that point and then air fuel and oil enter the crank case together. So with premixing you are just combining the fuel and oil before the carbs, but after the carbs the oil and fuel always enters the engine mixed wether you utilize the pump or premix. In other words there is no straight 2 stoke oil or other oil of any kind flowing throughout the crankcase. Right?
    Correct. In a premix setup, the fuel is mixed with the oil in the fuel tank and passes through the carbs. With the factory oil pump it is added at the carbs. Either way, it is mixed in the bottom of the crankcase and distributed through the motor along with the fuel.

  5. #5
    Got one more for you guys. There seems to be oil under the motor. I cleaned some up, but it seems to to be more yellow than blue or green.not much just a small amount seems to come back after its been fired. Does the bottom of the case have some sort of drain.and why's it yellow not bluish green. This motor only has 34 hrs on it. The engine compartment is immaculate, new everything it seems.just curious if the leak is bad news or normal.

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Un-cowJ View Post
    Got one more for you guys. There seems to be oil under the motor. I cleaned some up, but it seems to to be more yellow than blue or green.not much just a small amount seems to come back after its been fired. Does the bottom of the case have some sort of drain.and why's it yellow not bluish green. This motor only has 34 hrs on it. The engine compartment is immaculate, new everything it seems.just curious if the leak is bad news or normal.
    I would start by thoroughly cleaning under the engine. It may just be old oil and such caught between the hull ribs.

    2-stroke oil comes in many colors. Who knows what people have used in the past.

    There are three crankcase drain plugs on the engine. Down very low on the left side of the crankcase (when looking down at the engine from behind the watercraft). The drain plugs are rarely removed unless rebuilding the engine. Hard to get at when the engine is installed in the hull.

    Try shoving a clean white cotton rag (t-shirt) under the engine. With some effort you can push the cloth in from one side/end and pull it out the other. I have used a painters stir stick to good effect as a push tool. The cloth should absorb the liquid and you can get an idea how much was under there.

    Sometimes spilled oil will hide under the gas tank. When the hull tilts up the oil runs under the engine.

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