Oops. 77 Evinrude 35hp overheated

Discussion in 'Bubba's Outboards' started by Mr.T, Sep 25, 2005.

  1. Mr.T

    Mr.T New Member

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    Well, apparently my dad didn't get the lower unit installed correctly last week after looking for the shifting difficulty that I asked about here previously. The tube that takes water from the pump to the engine wasn't connected and (quite predictably) the engine overheated just a few minutes after we started it. Neither of us noticed the lack of a tell-tale stream until it was too late.

    Got the engine cooled down and fixed the water tube but then couldn't get the engine to start again *except* when we pulled the top spark plug out -- it would run on the lower cylinder, but not with the top plug installed. Both cylinders were getting a good spark and we used new plugs, so it's not the power packs as far as I can tell.

    So where do we start? The whole cylinder head is horribly discolored from the heat, so I suspect there's quite a bit of damage.

    Head gasket? Piston rings? Just take it to a shop and take our lumps?

    Thanks...
     
  2. Bobpaul

    Bobpaul New Member

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    Do a compression check. Very important.

    An over heat might cause a blown head gasket

    If the compression check comes out bad, remove the head and inspect the gasket and pistons surfaces for damage.

    With any luck it'll just be the head gasket.
     

  3. Mr.T

    Mr.T New Member

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    Thanks for the reply. Compression was about 30 lbs in each cylinder. Squirted some 30wt oil in each and it went up to around 175 lbs, so I'm thinking frozen piston rings?
     
  4. Bobpaul

    Bobpaul New Member

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    Pull the head and be sure.

    Look for scored cyl. walls.
     
  5. coach

    coach New Member

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    the 77 model 35s will blow a headgasket before it does any damage to the engine,,,, usually.............. i use to carry a spare gasket cause it would happen frequently if u didn't pay close attention to the water intakes staying clear of bread wrappers and such.............
     
  6. Mr.T

    Mr.T New Member

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    The cylinder walls were scored pretty good - dad's going to take the head down to a machine shop and see if they can hone the cylinders; if not, I guess we'll have them bored and use the .030 overbore pistons. It's getting more expensive as the minutes pass...
     
  7. Bobpaul

    Bobpaul New Member

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    Adding oil to increase compression is usually a sign of scored walls.

    It's nearly the end of the season. Are you sure you want to put alot of money in it and still have a 77' engine.
     
  8. Mr.T

    Mr.T New Member

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    Don't really want to spend a lot on it, but I don't know where I'd get a replacement engine for the price of the repair. It's an old, beat-up boat and I can't see spending $3k on a newer model engine for it.
     
  9. Mr.T

    Mr.T New Member

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    Just talked to my dad - he says there's a local shop that has a 1990 25hp Johnson with the lower unit gears tore up but "guaranteed to run" for just $200 -- the guy at the shop says we can use the lower unit from our 35hp engine and it'll all work just fine. Certainly seems like a better option than spending $300 for parts on an old engine.

    Anyone know if it's really possible to swap the lower units like that between a 1977 and 1990 Johnson?

    I told dad to take the lower unit over to the shop and if they can get it installed and put it in a tank to test run it, that he should go ahead and buy the thing.

    And did I read somewhere that you can turn a 25hp into a 35hp by just changing some parts in the carburetor?
     
  10. Mr.T

    Mr.T New Member

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    Well we bought the 25hp engine and are planning to swap the powerhead onto the old 35hp frame. Apparently the lower unit isn't a simple bolt-on replacement, as the shift rod is different between the 1977 and 1990 models.

    Is there anything else we need to look out for when performing this transplant surgery?

    Thanks
     
  11. Bobpaul

    Bobpaul New Member

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    If the 90' 25 runs good, it seems like an easier fix to get a lower unit for it.

    I wouldn't think a 90' powerhead would fit a 77' midsection. You've already seen one instance where the shift shaft is wrong.
     
  12. Mr.T

    Mr.T New Member

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    Well, much to my surprise, the '90 powerhead was a bolt-on match for the '77 so it looks like we're in business. Provided, of course, that the engine actually starts and runs like the shop owner says it will. There's a little bit of work in getting the wiring harness changed over - the '90 has a couple additional wires that we need to deal with, but we'll get that taken care of.

    We're thinking of making the old 35 hp power head into a winter project - we'll get it rebuilt, along with the lower unit from the 25hp, then swap powerheads back and have two engines come spring, possibly to sell one or the other and try to recover some of the parts expense.
     
  13. Mr.T

    Mr.T New Member

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    To conclude the story:

    The 1990 25hp powerhead bolted onto the 1977 35hp frame and after the wiring issues were taken care of, it fired right up.

    So for $200 we got our engine up and running again - certainly a lot less than it would have cost (or rather, will cost when we get around to it) for the parts and machine shop labor to switch to the .030 overbore pistons.

    Of course, the blue powerhead looks pretty goofy sitting on top of the white body... But the cowling will cover that up just fine.

    As an added bonus, we now have a working electric choke -- the 1977's choke solenoid had been removed and discarded by some previous owner.

    Thanks, Bob, for the wisdom here - I suspect I'll be back for more when we get ready to overhaul the old burned-up powerhead...
     
  14. Bobpaul

    Bobpaul New Member

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    I'm sure pleased it worked out for you. I wouldn't have thought the two would be interchangeable, because of the difference in age.

    That's the advantage of having them both on hand and being able to compare them.
     
  15. JERMSQUIRM

    JERMSQUIRM New Member

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    il-waynesv
    thats a neat story. sure was luck im guessing. i wouldn't think it would have been that easy either. glad it worked out. mine shucked a clutch this year and in term shucked two props and a pinnion gear in the diagnostic process. B/P SAVED MY BUTT. clutch $71 , pinnion gear $110 , and third prop at $139.00 x3. labor $0. did it myself. having s fella to guide ya through the process= priceless.