'86 Johnson 40hp Blown Powerhead

Discussion in 'Bubba's Outboards' started by LittleRiverBigFish, Jul 16, 2007.

  1. LittleRiverBigFish

    LittleRiverBigFish New Member

    Messages:
    35
    State:
    Iowa
    boat: hole in water you throw money into...

    We were scouting some new sections of the river Thursday night and had run about eight miles upstream, picking our way along finding the channel and GPS'ing it for the ride back to the ramp. Our work done, we headed back towards home, got up on step and let the motor run. I had a new lower unit installed this spring after an incident with a stump last fall and this was the first chance I had had to see how everything was running on the top end. For the first six miles, everything was great, motor hummed right along. Trimmed it up a bit and got almost three more miles an hour on the top end, then something went poof! Nothing dramatic, no fire, no smoke just a very hollow sounding idle from the motor. Thought we had fouled a plug. Took off the cover and found a 1"x1.5" chunk blown out the side of the block and a 2" long crack in front of the missing chunk. Looking at the motor, this was on the front lower left section of the block. We were still about two miles from the boat ramp and I had my three and five year old sons with me. Luckily I had a trolling motor and two batteries and very little wind and we limped back to the ramp at 2.2 mph.

    Any idea what could have caused this catastrophic failure? The water pump was working and pumping cool water the whole trip (we checked it frequently as it was replaced with the new lower unit). There were no rods or visably ejected parts from the motor. I would have thought something of this nature would have been much more dramatic than it was. The motor still starts and runs... I'm at a loss and not looking forward to purchasing a new motor since I just put several hundred dollars into this one.:sad2:
     
  2. Mr.T

    Mr.T Active Member

    Messages:
    2,554
    State:
    MO
    I'll bet the stump had a lot to do with it. If the impact was enough to damage the lower unit, it almost certainly transmitted some of the damage up into the powerhead, weakening one ore more components. Those components failed under a heavy load. When you pull the head off, you'll probably find a broken connecting rod or piston or something similar.
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Many things can cause this. If I choose one I would have to guess but I will lean toward over reving here . The motor was turning more then it was designed to do. That is why a tach is so important.
     
  4. LittleRiverBigFish

    LittleRiverBigFish New Member

    Messages:
    35
    State:
    Iowa
    Now another question. I've managed to locate another motor, identical to the one I have. The owner bought it new on a 16' Lund in 1987. Three years ago he replaced it with a larger hp motor and the 40 has been in storage ever since. He says the motor ran well when he took it off, but it has not been started over the course of the last three years. In the pics he sent, the motor is spotless, not even a scratch on the hood, decals still on lower unit, etc.

    What should I be concerned about since it has sat for so long? I'm guessing the carbs will need to be cleaned at the least, anything else?

    He's asking $1200 which is the same price as the remanufactured powerhead I looked into yesterday.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    If it wasn't winterized when stored I would clen the carbs and lower unit oil and squirt some TCW-3 oil in the cylinders before turning her over and change the water pump. Then fire that old gal up and get back to fishing.

    Before I bought it I would do a compression check to make sure they are even or close to even on pressure.
     
  6. LittleRiverBigFish

    LittleRiverBigFish New Member

    Messages:
    35
    State:
    Iowa
    Bubbakat,

    Is a compression check something I can do on site or do I need to take it somewhere to have it done?
     
  7. LittleRiverBigFish

    LittleRiverBigFish New Member

    Messages:
    35
    State:
    Iowa
    Disregard that last question if you want, but if you have some suggestions on compression testing, I'd welcome them. I did a quick search and found some information on how to go about it.
     
  8. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Just pull the plugs out and make sure they aren't full of oil because this trick will give you a high reading when in fact the will be lower.