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  1. #1

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    787 hard start, rough idle, backfire during starts, burns oil off then runs great

    I have this single 787 in my Challenger boat... 3 years ago in the spring during de-winterizing I could not crank the engine. Turned out it was hydro-locked with injection oil that leaked through the oil injectors and filled the engine crankcase. Since then i disconnect and plug the oil injection lines with a rivet during Winter storage. Fast forward to this Summer...if the Boat sits for 2 weeks without running, it is extremely hard to start. It will fire a couple times then backfire through the exhaust. After many (up to 10) attempts to start and a few starts the motor eventually seems to run on 2 cylinders first intermittently then steadily after burning off some excess oil for about 3-5 minutes. Then Idle returns to normal, acceleration and top end are excellent. I can now shut it off and return in 2 days and it starts right up and runs great.(with minimal initial smoking). It almost seems like a plug is fouled until the Oil is burned up then BAM!...it runs like a top. It never backfires once the rough start bad idle is gone. Anybody experience this or have any input?? Obviously I need to replace the Oil injector check valves. Will this solve my issue?? Is there something else going on here? Carbs are rebuilt, fuel lines new, engine pulls hard when running fine...


  2. #2
    The oil was not leaking through the injection, but rather the worn rotary valve seals on the crankshaft. The correct way to fix this is to install a rebuilt crankshaft.

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  4. #3
    Tool Bag water worx's Avatar
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    Yep time for a rebuild.

  5. #4

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    My knowledge of this engine is very little. I have rebuilt carbs and exhaust valves but that is it. I do not understand why the Crankshaft needs replacing, could you please explain. I have read some similar posts here recently that speak to the RV seal being bad vs. crankcase seals. I do understand that the RV gears reside in an oil bath . Is this oil bath replenished with the 2 oil lines at the RV?? Where does the oil injection mix with the fuel? Can oil flow freely from the oil tank through the oil pump into the crankcase under normal circumstances? Sorry to sound uneducated but this is all new to me.
    Quote Originally Posted by Wire4Money View Post
    The oil was not leaking through the injection, but rather the worn rotary valve seals on the crankshaft. The correct way to fix this is to install a rebuilt crankshaft.

  6. #5
    Rotary valve sits in oil bath. 2 large oil lines from tank to bottom of engine. Oil bath is sealed from crankcase with seals on crankshaft. When they leak, it fills the crankcase with injection oil. Since the seals are part of the pressed together crankshaft, a rebuilt crankshaft is needed.

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  8. #6
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    if you can manage the logistics, clamping off the oil feed line to the RV when not in use can reduce the issue to just a pain. there are some messages in the forum regarding the use of transmission seal softener to also extend service life.

    while the right way is replacing the crank, it's a pricey proposition on an older engine

    don't use brand x injector oil after replacement, this is why ( from what I've seen) the seals fail prematurely..that and using starter fluid and hydro locking the eengine

  9. #7

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    Thanks for explaining this to me....man thats frustrating, I just rebuilt the pump/wear ring/berarings and it was running so good...a damn oil seal wrecks my happiness!...lol. I have only used Rotax injection oil since I purchased the boat in 2003. The logistics of clamping those 2 lines is not appealing...just re-attaching them to the nipple when summerizing is a total PITA...takes me forever to accomplish...lets just say that I am not as slim an nimble as I used to be. Being that I am in Canada does not help as the shipping for an SBT rebuild is not palatable...

    Quote Originally Posted by nmpeter View Post
    if you can manage the logistics, clamping off the oil feed line to the RV when not in use can reduce the issue to just a pain. there are some messages in the forum regarding the use of transmission seal softener to also extend service life.

    while the right way is replacing the crank, it's a pricey proposition on an older engine

    don't use brand x injector oil after replacement, this is why ( from what I've seen) the seals fail prematurely..that and using starter fluid and hydro locking the eengine

  10. #8
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    I'm with you on the not so slim and nimble

    you can try the snake oil method since you need a hail mary on this one.

    you'll from this thread its a common problem on these older two stroke engine now that they are reaching the end of their service life

    given your lack of nimbleness going with the looped oil line method isn't going to fly.

    try this:

    http://greenhulk.net/forums/showthre...=1#post2487991

    btw, more is NOT better in this case as you'll be sharing the softener additive with the injector oil

  11. #9

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    I am willing to try the softener additive...what could I possibly loose? Also, when you talk about a loop in the 2 oil lines for the RV could you please elaborate. Is this to make them more accessible to clamp off? Is the purpose of those two RV oil lines attached to the check valves ONLY to supply lubrication to the RV gearing? Where does the oil injection for the gas occur?
    Quote Originally Posted by nmpeter View Post
    I'm with you on the not so slim and nimble

    you can try the snake oil method since you need a hail mary on this one.

    you'll from this thread its a common problem on these older two stroke engine now that they are reaching the end of their service life

    given your lack of nimbleness going with the looped oil line method isn't going to fly.

    try this:

    http://greenhulk.net/forums/showthre...=1#post2487991

    btw, more is NOT better in this case as you'll be sharing the softener additive with the injector oil

  12. #10
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    read some of the "full of oil" threads, the loop method and management is described numerous times. you can use a good amount of seal softener by looping the rv lines, but you MUST keep an eye on the oil level. let it run out and your engine will fail

    there is a smaller oil line from the oil tank that feeds the injection pump. injection takes place at the rotary valve

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