81 Evinrude 25 HP - Didn't Start

[cchildr84]

Recently I did some maintenance work on my 81 Evinrude 25 HP; change all lower unit seals, replace waterpump & housing, new thermostat, and replaced the neutral start switch becuase there wasn't one on there when I bought the motor used. Long story short I got everything back together, did pressure & vacuum tests on the seals and everything was good. So I put the motor in a clean trash can full of water to test it out, and when I hit the start switch and as the starter was engaging and turning the motor over, after a few seconds there was this noise that sounded as though somewhere on the motor there was a release of pressure. As though as the motor was turning over there was pressure building up and after X number of revolutions some sort of gasket blew or something. It did this twice, so I called it quits with trying to get it started. Any idea what this might have been.

 

[gm280]

Re: 81 Evinrude 25 HP - Didn't Start

Recently I did some maintenance work on my 81 Evinrude 25 HP; change all lower unit seals, replace waterpump & housing, new thermostat, and replaced the neutral start switch becuase there wasn't one on there when I bought the motor used. Long story short I got everything back together, did pressure & vacuum tests on the seals and everything was good. So I put the motor in a clean trash can full of water to test it out, and when I hit the start switch and as the starter was engaging and turning the motor over, after a few seconds there was this noise that sounded as though somewhere on the motor there was a release of pressure. As though as the motor was turning over there was pressure building up and after X number of revolutions some sort of gasket blew or something. It did this twice, so I called it quits with trying to get it started. Any idea what this might have been.

Oh I really hate to hear that. I too am rebuilding an OB and haven't tried YET to crank it up because I'm still finishing up building a new engine wiring harness. But I do feel sorry for your situation and will most certainly watch this thread to see what you do find out as your problem. I can't think of anything that would be causing that sound or situation... It does sound like it is building up pressure and at some point blows it out... SMH!

 

[Eyeballsdeep]

Re: 81 Evinrude 25 HP - Didn't Start

Did it sound like it was even trying to start? id do a compression test first. i have no idea that sound you heard could have been. i mean all these engines are, are just big air pumps i dont see any reason for air to build up unless somthing was pluging the exhaust Can you try to pull start it and see what it sounds like. Unless it sounds like metal on metal grinding I wouldn't worry about damaging anything. You should hear a thunk thunk when you pull it over. Should feel even in compression. I'm pretty curious myself as to what this is.

 

[cchildr84]

Re: 81 Evinrude 25 HP - Didn't Start

Yeah, it did sound like it was trying to start and right when it sounded as though it was reaching that turnover point, poof. Well, when I first bought the motor, I did a compression test using the electrical system; i.e. starter switch and hooked up to a battery and compression was around 90 on top and 82/83 on bottom. After this I did a compression test using the rope start and both cylinders were around 60 psi. I've got a quote to overhaul it, in the event that is needed so I'm saving up for that. So we'll see what happens.

 

[jasper60103]

Re: 81 Evinrude 25 HP - Didn't Start

Your compression numbers didn't sound that great to begin with. Did you run this motor when you bought it?
In any case, good luck.

 

[cchildr84]

Re: 81 Evinrude 25 HP - Didn't Start

Yeah, to a degree. Like I said it didn't have the neutral start switch on it when I got it, and one of the previous owners bypassed it so it would only start while in gear. It turned over fine each time, but there was no water coming from the pee hole when I tested it, so I didn't really get to drive with it on my boat. After getting into it, I now realize why know water was coming from the pee hole, as the overflow nipple was broken off from the exhaust cover, and the thermostat was in peices when I got to it. When I had the lower unit off I hooked a hose up to it and ran water through the engine and with the overflow nipple replaced water was coming out the pee hole with no issues.

 

[cchildr84]

Re: 81 Evinrude 25 HP - Didn't Start

Well, just for fun I took the cylinder head off this weekend. Once off, not knowing anymore than I do about engines, I thought the cylinder walls looked pretty good. See picture below. I did notice that the bottom cylinder didn't appear to have any fuel/oil in it, not sure why that is. Aslo, there was a little bit of rust in each cylinder but not much, not sure if this is common or not. I sprayed them down with some PB blaster until I can get it in the shop to be looked at. Also, notice on top of each piston there in an indentation. What might have caused that. Would it be from the ignition of the spark and fuel. Your comments are appreciated.

 

[cchildr84]

Re: 81 Evinrude 25 HP - Didn't Start

Well, as I got to feeling around deeper into the cylinder last night, in cylinder #2 (bottom) I felt some scoring. Looking at it, there is kind of a white residue, which I'm thinking is plastic from the overflow nipple. Reason I say this, is because when I bought the motor (used) the original overflow nipple wasn't even connected to the exhaust housing. At some point the plastic threads had melted, and so I'm guessing that the material that melted somehow got through the exhaust housing and into the ports. Hopefully this can either be honed away or bored enough to eliminate the scoring. My only oversize options are 0.020 or 0.030. What do you guys think?