84 Evinrude 90 HP Low comp. on 1 cyl

Discussion in 'Bubba's Outboards' started by BKS72, Jun 19, 2007.

  1. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    Guys, I'm looking at buying the motor in the subject line (sorry, haven't seen it yet so I don't have model and serial # yet). Not sure what all could cause low compression on one cylinder, but I'm thinking either rings, reeds, gasket, or (God forbid) a hole in the piston or scored cylinder walls. The guy says it runs, so that's a good sign, I guess.

    It's only a couple of hundred bucks for the motor, so I guess if it's toast I could get my money back by parting it on Ebay.

    My questions are - how do I find the compression leak? Do I have to tear it down or can I eliminate some of the options a little easier (look through the sparkplug hole for holes in the piston, etc).

    And what do you think the odds are it's repairable relatively easily?

    I know that's kind of vague, but I'd like to get this and repair and put on my boat. Any advice would be appreciated. Thanks!

    Branden
     
  2. Mr.T

    Mr.T Active Member

    Messages:
    2,554
    State:
    MO
    Sounds like you're about to buy someone else's problem...

    You could put a little raw oil in the cylinder (take the spark plug out and squirt some oil in, then put it back). Turn it over a few times to distribute the oil and recheck compression in that cylinder. If it's back to "near normal", the problem is likely worn rings.

    But it could also be a scored cylinder wall. Rings are cheap. Boring and polising the cylinder wall isn't, and requires a new piston. And if you're doing one cylinder, you probably need to do them all to keep them matched.

    I'll bet Bob and Bubba have some much more learned advice for you..
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    The only way is to pull the head and check that cylinder for scoring or broken rings. Check end play in the piston and rod.

    That motor shoul be sold at a junk price. If the cylinder is down that much and say you are lucky and get just stuck rings from carbon the okay but any tear down is going to be costly and as for the oil in the cylinder that will give you a false reading.

    I would opt out on that engine if I was looking for a runner myself.
     
  4. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    Thanks for the advice. The guy is asking a $250 for it, but if I can get him down to around $100, I may pick it up. I'm pretty good mechanically, so once I figure out the problem I should have no problem fixing it (with the shop manual and lots of posts to you guys :smile2:) I also don't know how far down the compression is yet(kind of low or no compression at all). A machine shop here only charges around $40 a cylinder to re-bore, so that's not too bad if it comes to that. I'm looking more for a project than an immediate runner. If the rest of it is in good shape and all it needs is fresh rings, I should be in good shape. If I can get it cheap enough it will make a good winter project. As I said earlier, if it's a basket case I can get $100 back out of it in parts on Ebay.

    Thanks again for the advice!
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    If you can get it for a hundred then it might be worth the trouble to make a project out of it. And also it doesn't hurt one to rebore and rebuild one cylinder and just rering and hone the others.
     
  6. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    I checked it out this evening after work. It's in great shape (other than the major internal problem...:big_smile:) and comes with controls and the factory tilt and trim is in good working order. I'm going to have to give a little more than $100 for it, but like you say, I think it's $40 a hole to get one bored last time I checked and the piston and rings are another couple of hundred if it comes to that. If it's going to be more, I can part it and get my money back. I'll let you know how it comes out. Thanks for the advice!
     
  7. Rookie12

    Rookie12 New Member

    Messages:
    1,324
    State:
    Kannapolis, NC
    Ya'll speaking of low compression made me think of a story that my uncle told me a while back about my grandpa who passed away in '05 and was the most mechanically adapted man I'v ever seen.. A friend of his had a boat that had lost all compression on one cylinder. They pulled the head and found that a bad casting spot in the intake had let water get into that one hole and burned a hole in the piston. My grandpa siad that ain'tno problem, so he got the piston on TDC and cleaned up th top of it with a die grinder and then using an oxy acetylene torch and a rod, he welded th hole shut on the piston iand cleaned it up right. They put it back together and he ran it another 2 years before selling it. I don't think they make 'em like my grandpa no more. I'm pretty good mechanically and make my livin' doin' so, but I don't hink I'm nowher near good as he was. just thought I would share!
     
  8. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    That's a great story! My grandpa was a welder and I've seen him fix things with a torch and bailing wire for rod that other guys wouldn't touch. They used to say "If Charlie can't weld it, you might as well take it to the junk" around where I grew up. Those old guys sure did know how to make things work.
     
  9. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    I grew up with spit wads and bailing wire. I still learn something every day though.:tounge_out: