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Results 1 to 5 of 5
  1. #1

    Default 1991 Mercury 115HP 4cyl/2 stroke

    Greetings,
    I found a boat with a 1991 115hp (4cyl/2 stroke) in reasonably good shape, except for one thing. He claims the engine started running rough, and he immediately returned. It was determined the oil injection line right beneath the oil tank that goes into the carb came off. He was told he lost a cylinder. I checked the compression and the second cylinder from the top is flat.

    Do I need to be concerned about other damage? How much would it cost to fix this problem? The engine has a lot of new parts, and I am interested in pursing the boat.

    Is the 4cyl/2 stroke 115 Mercury basically a good engine?

    Thanks,

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,026

    Default Re: 1991 Mercury 115HP 4cyl/2 stroke

    If crankshaft bearing was damaged it could be an expensive repair.------If you can repair it yourself it might be worth it.-----------If not pay as if you are buying just the boat and hope for the best finding another motor / used powerhead.

  3. #3

    Default Re: 1991 Mercury 115HP 4cyl/2 stroke

    Quote Originally Posted by racerone View Post
    If crankshaft bearing was damaged it could be an expensive repair.------If you can repair it yourself it might be worth it.-----------If not pay as if you are buying just the boat and hope for the best finding another motor / used powerhead.
    Probably good advice. With the plugs out the engine turned nice, but a main could still be damaged. I would like to understand why only the one cylinder is dead? Scored cylinder wall? Why not others?

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,026

    Default Re: 1991 Mercury 115HP 4cyl/2 stroke

    Last one I took apart just a few weeks ago ( freebie powerhead ) had one scored piston and mainbearing rollers that appeared welded together.-------------Outboard owners are notorious for lack of proper maintenance and a plugged / partially plugged carburetors means lean running.-----That leads to less oil going into one cylinder. that leads to higher temperatures and the piston expands till it jams. Higher temperatures means the oil burns off the parts and there is then little or no lubrication and the motor is finished.

  5. #5
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,026

    Default Re: 1991 Mercury 115HP 4cyl/2 stroke

    A 4 cylinder 2 stroke like that is really 4 seperate engines with a common block and crankcase.---------Each cylinder has it's own carburetor , crankcase and ignition.------Therefor you will often find multi cylinder motors with good cylinders and one complete junk.------Lack of care of fuel systems is a big cause of this.----It is said that outboards rarely wear out , they end up as junk because the owner made one of many mistakes !

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