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Thread: Short shaft Jet on a Long shaft O/B

  1. #1
    Member dkwarthog's Avatar
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    Default Short shaft Jet on a Long shaft O/B

    I recently picked up a boat with a long shaft Merc 35 prop lower unit. Last night I picked up a seized outboard (same model but a short shaft) that has a jet unit on it.

    What I would like to do is take the short shaft mid section and jet pump as an assembly and mount it on the power head of the good (long shaft) motor.

    I've never messed with outboards too much but am relatively handy with a wrench and hammer.... Is there anything glaringly wrong with my thinking that this should work? Any gotcha's out there that I might run into??

    I've researched and done enough to be comfortable with the lower unit replacement, but I've never had a midsection apart (where the driveshaft couples to the crankshaft).

    Thanks for any suggestions or experiences you guys might have had...

    Dave

  2. #2
    Member SusitnaAk's Avatar
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    Default

    First thing i thought of would be the drave shaft length, The Mid section, Is longer, Some moters had a extenstion that could be removed, Newer ones are built short 16" or long 20'or Extra long 25" Might be easer to come from the other end. And swap out the power head?

  3. #3

    Default

    The "long shaft" vs "short shaft" is below the power head. The jet unit is a jet unit.

    Change from the bottom end, not the top end.

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    Default Do it...

    Dave,

    If the motors are the same, everything below the powerheads will swap out. Been there & done it myself more than once, & it's a pretty straightforward process. If the motors are older and have been run in salt water, be cautious when unbolting the shaft housings from the powerheads as you may have some corrosion & sticky bolts. Don't want to twist anything off. Hope this helps. Good luck!

    Brian

  5. #5
    Member dkwarthog's Avatar
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    Default thanks

    Sorry for the post and run...I was making it harder in my head than it was in reality.

    I did just like outdoorsman and SusitnaAK said. I Pulled the powerhead off both ob's, no problems...except needing some new gaskets for reassembly.

    One more question if you guys dont mind...Is it ok to just use rtv to seal the jet unit to the mid section, or is there a special gasket required?

    I got the used jet unit (with seized OB), along with a spare jet housing for $100.. Couldnt resist that deal!!!

    Should be done tonight..if I can find the motor mount gasket today...

    Thanks

  6. #6
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    Default No gasket

    Dave,

    Sounds like ya have things about whupped. There's no gasket between the midsection & the jet foot. That Merc may have a heavy seal/ring where the exhaust enters the jet, but it should be reusable from the prop foot.

    Brian

  7. #7
    Member dkwarthog's Avatar
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    Thanks brian. Looking forward to gettin her out this week...

  8. #8
    Member dkwarthog's Avatar
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    Default Update

    Just thought I'd follow up on this post in case anyone else out there is contemplating putting an old jet unit on their outboard....

    I put it all together and it ran flawless for about 2 hours, then the motor just stopped, no sputtering or coughing. A hard mechanical stop...

    Pulled of the jet foot and the impeller was jammed into the wear ring. I shimmed up the impeller and started it up. It jammed again (duh)... did it 2 more times until I realized that the drive shaft was dropping thru the bearings.

    Got it home and pulled it apart, the bearings were completely destroyed..

    I only point this out so that anyone putting on an old (used) jet can consider replacing the bearings right off the bat or else run it somewhere with no bad consequences for a while before launching in the rivers. I had a nice walk home but it couldve been serious...

    At this point Im going to replace all the bearing, seals, etc. as long as the shaft is still straight...of course they stopped making the bearing kits for the version I have so I have to retrofit it....live and learn.

    I sure had fun for those 2 hours though!!!

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