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  1. #1

    Talking oiling diagram of a two stroke 718 rotax

    Hello all! I hope someone out there has a diagram of the oiling system of a 718 Rotax 85 HP engine, all I have is the exploded diagram of the oiling system parts, I have a pretty good Idea of the direction of flow just from the way the system is plumbed, but I would like to know about how the oiling system works (lower end anyway's) I just had an engine fail and want to ensure my oiling system is working correctly.
    Thanks in advance!

  2. #2

    Talking what? nobody can explain this?

    Hell again everyone, I figured there has to be someone who has been running these two strokes out there that can explain the oil system on the rotax two strokes (720 engine at least) I can tell by the oil line routing that the path the oil makes from the oil tank through the engine back to the tank, but is there a scavenge pump internally in the engine, or is it crankcase vacuum/pressure that pulls/pushes the oil in and out? I just had a engine seize and I'm having one rebuilt right now, I just don't want to see another failure after spending all that hard earned cash. Any help would be appreciated!!!!!

  3. #3
    Make sure the oil pump filter is clean, and working. You can check by putting it into a drill chuck and spinning it for x time and measure the oil that comes out. I do not know the time, RPM, or amount of oil for your pump. What ski is it? I may be able to check that way for you.

  4. #4
    First: Keep the Oil Pump attached to the 720 engine's Rotary Valve Plate assy. and both Oil Injection lines attached to the Banjo bolts. (which actually have tiny check valves inside of them)

    *If* you have a high speed drill you can attach the drill to the Oil Pump to drive it. To do this you must first remove the Oil Pump Drive Gear from the Oil Pump Shaft to have enough shaft to attach the Oil Pump to the drill chuck.

    ... or to make this job easier, I used a small metric coupler without having to remove the Oil Pump Drive Gear since there are just enough threads of the Drive Shaft coming through the Gear center to have something to attach it to.

    You will need to have some Oil in the large supply line which feeds the Pump and the two small lines will also need to remain attached to the outlet of the Pump so you can see the Oil "pulsing" out those two small Injection Feed lines.

    Do not plug the main feed line into the Oil Pump or it may create a slight vacuum, overcoming the Oil Pumps' ability to do it's job. No air in the Pump either, it must be bled off first by opening up the small Hex head screw under the Body of the Pump. (below the lever)

    The drill drives the Oil Pump in *reverse* (counterclockwise) and must be running fast to actually pump (pulse) the Oil.

    While driving the Oil Pump Drive Shaft counterclockwise you must hold the Oil Pump Actuator Lever Wide Open.
    A small Zip Tye makes this easy...

    If everything is set up correctly, you will see Oil slowly pulsing up through the small Oil Injection lines as you drive the Oil Pump.

    Of course, you could always just put it all back together on the engine. Pre-Mix some fuel to be safe and run the engine (on the hose at idle) while holding the Oil Pump actuator lever open by hand while watching for Oil flow through the small Injection lines.

    I assume you already replaced those Oil Injection Lines, if not.... you should, since they dry rot / crack over the years and are the primary reason for engine seizure due to lack of lubrication. The Oil Pumps themselves are pretty reliable from my experience. They are manufactured by Mikuni, like your Carbs.

    Hope this helps, sorry for the long written book but that is how it's done.


  5. #5
    "I can tell by the oil line routing that the path the oil makes from the oil tank through the engine back to the tank, but is there a scavenge pump internally in the engine, or is it crankcase vacuum/pressure that pulls/pushes the oil in and out? "

    The very large Oil Lines attached directly to either side of the engine Cases and originating from the bottom and returning to the top of the Oil Tank feed the Rotary Valve Drive Shaft/Gear Oil Bath which is in the center of the engine Cases, lays perpendicular to and is driven by the Crankshaft.

    The Oil Bath is just that, a cavity filled with Oil. There is no circulation and no scavenging pump. In essence, you could remove those lines from the Oil Tank, plug the outlet holes, and attach the two lines (full of Oil) to each other with a hose coupler and a small air pocket in it for heat expansion.

    Many racers do just that since they run pre-mix and have no need for an Oil Tank's extra weight, but the Rotary Valve Shaft Cavity *must* have a bath of Oil to run in.

    Here is a diagram of the Oil Hose routing on a 717/720 engine.


  6. #6

    Talking oil system

    Thanks to everyone who has replied, I just wanted to ensure I don't have another failure after spending a fortune on these ski's.....I bought a matching pair of 2003 GTI LE's for $6,000 with the double trailer and after having them on the water twice, one failed. the other had recently had an engine replaced,it's runs like a scalded dog..... the one that had failed, had a black cylinder case with the silver cylinders and head, a dead give away that someone had been inside the engine before, the previous owners were very confident that there was nothing wrong with them at all, well, after the local Seadoo dealer disassembled the top end, they found evidence of water damage (rust stains on the cylinder walls, and the rear con rod seized to the crank) he said this was a pre-existing condition that either the owner knew about, or the shop that serviced these knew about, or just never bothered to admit it.
    Short of actually taking it out on the water for a test, who could have known? anyway, lesson learned, at least it's been educational, I have learned more in the last two weeks about how these Seadoo's run and how to maintain them, thanks to the good folks here and on other PWC forum's!!! Thanks you all!

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