86 Evinrude 70HP need help with compression problem

Discussion in 'Bubba's Outboards' started by my4x4awd, Aug 2, 2006.

  1. my4x4awd

    my4x4awd New Member

    Messages:
    105
    State:
    TN
    This might be a little long but I really need some help with this. Let me first say I have built engines including autos and mowers but never an outboard. I bought the project boat and the 70 HP Evinrude had not been run for a least a year. The head was off the motor. The shop the previous owner had it at, said it needed rebuilt. The cylinder had a little scuffing like deposited ring or piston material. Looks pretty normal for a 1986 and even still has some cross hatch from the hone. The cylinder didn’t appear to be heavily damaged I installed the head and did a compression test all plugs out. My gauge top 135 mid 95 lower 135. The compression readings at the shop today with a three plug machine, top 120 mid 85 lower 135. First shop said engine bad, has to be rebuilt. This based upon the scuffing.
    Second shop said probably can hone mid cyl and re-ring and lower was high because mid was low. Don’t get that! Now, he wants $250 to pull apart to look and then tell me what it will take. Here are a few questions.

    Would de-carbing help or pulling the head and soak the rings with seafoam?
    Does the power head have to be removed to get the piston out to inspect the cyl walls?
    Cant I mic the walls and just re-ring.
     
  2. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Craig those 70 h/p in that year and on up until 97 had some serious heating problems. Order you a manuel and tear that engine down and rework it the way it needs to be done. If you can pull a wrench and with a good shop manuel you can bring that old gal back to life. If the middle cylinder doesn't have any wrinkles in the wall then you might get by with a good ring job. But with that engine I don't think it will do any good to decarb because of the issues it had from the get go. OMC did a recall on those engines for the upgrades and if that one wasn't carred in for the upgrades then that is what happened , she over heated most likely several times.

    I do have the service bulletins for that engine upgrades and if you want them I would be more then glad to e-mail them to you.
    The reason I know this about this engine My brother has one and we did a complete rebuild on it last fall and did all the upgrades.