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  1. #1

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    Failure Analysis-787 RFI

    The engine in my '98 GTX-RFI shut down at WOT. It has 375 hours so I plan on replacing it but I want to determine the failure mode. I want to make sure I don't have fueling, oiling, or cooling issues. The MAG piston dome has gold colored pieces of metal that look like lava. The crank assembly rotates fine by hand but it does sound a little "crunchy". What do you think?
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  2. #2

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    On a related note-I would like to install the replacement engine myself but I don't have the tools to remove the flywheels and to check the alignment. What would be a good approach?

  3. #3
    wkuadam07's Avatar
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    Mag cylinder had no oil, i bet your oil line cracked on that cylinder. Replace the oil lines, and send the fuel injectors to any reputable fuel injection shop for cleaning and testing while the motor is out. Tools are cheap... buy them, then ebay them to get most of the money back... just keep the boxes to ship them in. You will need an alignment tool, a 787 flywheel puller, a good chain pipe wrench for the PTO flywheel, and i would recommend an impeller removal tool so that you can freshen up your pump and wear ring while you have it all apart. Did it start badly or idle rough the day it blew up? 375 hrs is pretty good for an RFI...

  4. #4

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    Quote Originally Posted by wkuadam07 View Post
    Mag cylinder had no oil, i bet your oil line cracked on that cylinder. Replace the oil lines, and send the fuel injectors to any reputable fuel injection shop for cleaning and testing while the motor is out. Tools are cheap... buy them, then ebay them to get most of the money back... just keep the boxes to ship them in. You will need an alignment tool, a 787 flywheel puller, a good chain pipe wrench for the PTO flywheel, and i would recommend an impeller removal tool so that you can freshen up your pump and wear ring while you have it all apart. Did it start badly or idle rough the day it blew up? 375 hrs is pretty good for an RFI...
    Great information! Yes, 375 hours is a lot for a 2 cycle. I bought it new in 1998 and it has been a great running boat. I will look at the oil lines and I'm going to replace the oil pump just as a preventative measure. It didn't run any differently on the day it died. I would think if there was a shortage of oil the piston would have stuck before the crank bearings seized but there doesn't appear to be scoring on the MAG cylinder. That's a good idea on having the injectors cleaned-I've never had the fuel system apart. I rebuilt the pump last fall so that is good.

  5. #5
    wkuadam07's Avatar
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    Another thing i forgot, look up how to replace the fuel filter in the tank... i'd say that would be worth your while as well... not what caused the failure, but something i would do before i put a new engine with freshened up injector in action. If it wasn't an oil issue, then the front crank seal failed and ran that cylinder lean, but this is usually a gradual problem. Crank seals going bad gradually on an RFI will amount to needing to change idle settings, hard starting, and so on...

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  7. #6
    Myself's Avatar
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    wkuadam, don't you think the cylinder would have more scoring/damage from no oil? The plug electrode also looks very crusty like possibly it's been burning off some water. What do you think?

  8. #7
    wkuadam07's Avatar
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    Quote Originally Posted by Myself View Post
    wkuadam, don't you think the cylinder would have more scoring/damage from no oil? The plug electrode also looks very crusty like possibly it's been burning off some water. What do you think?
    Piston wash doesn't look like water to me... Looks like the RFI that came to me with a broken oil pump shaft... except the ski with the broken plastic oil pump drive shaft looked just like his mag cylinder on both cylinders.

  9. #8

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    I'm trying to determine what the gold colored crust is on the edges of the mag piston and spark plug. If I had the tools to split the crankcase I would know more but my guess is the front main bearing disintegrated and the metal debris got pushed through the transfer ports.

  10. #9
    is the gold color stuff magnetic? Bearings are steel and will be magnetic. Everything else is aluminum and won't be.

  11. #10
    WICKEDSEADOO's Avatar
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    most likely bad fuel pump with dirty strainers

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