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  1. #1

    Smile for seadoo pros!RFI question

    I know everyone has seen the hole seadoo 787 motors have in rear of piston at the transfer port to allow lube of rod bearing.Iwas thinking on RFI modells since the injector is spraying directly on rod top end bearing,seems like this would flush any lube oil from bearing as oil is not mixed on injector side but on air intake side.seems like this could cause problems though I havent seen small end bearing failure on rfi yet.Also I know it doesnt help but hurts to add oil premix to DI engines, would an rfi engine benefit since fuel is injected below piston as in carbed model??thanks in advance>Marvin


  2. #2
    Tool Bag water worx's Avatar
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    The fuel is NOT inj below the piston,it is inj at the top of the piston just before the exhaust port is closed.

  3. #3
    thats for a direct injection engine not a seadoo rfi if you look at where the injector is in side of cylinder and pointing down in the rear transfer port if it injected fuel the only time it could inject on top of piston is when piston is near btm of stroke It might inject then But I'm pretty sure it doesnt,and why would it be angled down??towards btm of transfer port??I havent seen much on the injection timing and crank position when they fireetc.and am curious as to reasoning thanks>Marvin

  4. #4
    Tool Bag water worx's Avatar
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    Quote Originally Posted by water worx View Post
    The fuel is NOT inj below the piston,it is inj at the top of the piston just before the exhaust port is closed.
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

    You may doubt me, but it is fact.

    From Seadoo manual...."It is called a semi-direct injection because fuel is injected directly into cyl while the transfer & exhaust ports are open."

  5. #5
    RumRunnerRon's Avatar
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    Quote Originally Posted by water worx View Post
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

    You may doubt me, but it is fact.

    From Seadoo manual...."It is called a semi-direct injection because fuel is injected directly into cyl while the transfer & exhaust ports are open."

    +1 Worx to premix the rfi direction of air flow would have to be able to reverse somehow. The injector sprays into a (basically) one way passage for air flow. That is why the oil is injected on the throttle body side of the engine. Air and oil are then sucked through the bottom end and subsequently the oil is distributed properly to the crankcase. Oil will never get to where it needs to go by spraying it (essentially) on the output side of the intake to the cylinder.

  6. #6
    I dont doubt that explanation its only that for exhaust port to be closed when it injects the position of piston would not allow fuel to inject above piston looking at cylinder with a piston in it.I noticed this when fitting piston and rings in a cylinder on bench.The original question should have been when in the stroke does the injector fire?Is it at btm of stroke with exhaust port open?? i just didnt know why the injector is angled down it all depends on the time int the stroke that the injector fires,I guess that the upwards flow of air in rear transfer port causes the fuel charge to disperse upwards,it just seemed very strange that thetransfer port hole thru the piston extends port timing,it just seemed very strange that it let the injector point at the rod bearing.I suppose at 6600rpm the fuel and air /oil is thouroughly mixed.If injector was pointed up,half the charge would wind up out the exhaust.[I] should rephraSE the original question to does anyone know the poisition of the piston when injector fires?? I didnt mean to start argument I was only wanting to know,thanks much>Marvin

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    Fast-XPL's Avatar
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    Hurts to add premix to DI?

    I've done a search and can't find anything regarding this. Please elaborate why it's not good to run premix on a DI. I'm in the process of breaking in my newly rebuilt DI and I'm running premix. I'd like to know what problems I can encounter.

  8. #8
    RumRunnerRon's Avatar
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    Quote Originally Posted by Fast-XPL View Post
    I've done a search and can't find anything regarding this. Please elaborate why it's not good to run premix on a DI. I'm in the process of breaking in my newly rebuilt DI and I'm running premix. I'd like to know what problems I can encounter.
    Apparently from the discussions I've read it's not good on the injectors to run the oil through them. I'm going to assume you are still using the oil injection. To not be would be costly.

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    Fast-XPL's Avatar
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    Quote Originally Posted by RumRunnerRon View Post
    If you are premixing a DI how are you planning on providing lube oil to the crank bearings? The oil still has to travel through the crankcase the old fashioned way. DI injects above the piston there fore you will not be getting any oil to the bottom end.
    I'm running both premix and oil injection. I always broke in my carb'd motors with double oil and assumed it was ok on a DI.

  10. #10
    Fast-XPL's Avatar
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    Quote Originally Posted by RumRunnerRon View Post
    Apparently from the discussions I've read it's not good on the injectors to run the oil through them. I'm going to assume you are still using the oil injection. To not be would be costly.
    Good point, hadn't thought of that. I guess I'll get the premix out and hope I didn't damage anything. Sure does run good though.

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