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What should I do with the purchased of 1999 25 Hp Johnson Outboard

M

Mercury800

Member
Hello,
I just picked up 1999 25 Hp Johnson Outboard. I saw it ran in the barrel a minute so I bought it. I did compression test and all 95/93/95 psi in all 3 cylinders. At home in barrel, it ran for a while and I saw the smoke came behind the CDI box. I removed the CDI and saw a crack in the block. I also removed the cylinder head to see if it had the crack on the cylinders but all the cylinders looked good. Mechanic said that BJ weld should cover the crack.
What is your opinion? Should I tear down the block to inspect? If I tear down the block, I may do a quick honing on the cylinders.
 

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How about the compression for this outboard? I have 1980 70Hp Johnson, 115/120 psi on each cylinders. Is 95 psi too low for this 25 hp ?
 
Up on far inspection, there was a BJ weld before on it the crack in the picture was the BJ weld. I have removed all the old BJ weld and applied high heat BJ weld (400F). I left it overnight for curing. I started the engine next day and it ran OK. It could stay running longer when it got warm up. So it looked like BJ weld fix the problem. But I don't think BJ weld would last long so I plan to tear down the engine in next winter time and do proper aluminum welding. I found on the web there are low temperature aluminum welding rods which I could weld at home with a propane torch.
I have removed the head and check the cylinder wall, the cylinder walls looks good but I could not get more than 94/91/93 psi on the compression test.
But it runs OK.
 

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I have used that Aluminum brazing rod.-------A wee propane torch may not have enuff heat for work on a large piece like that.----Heat travels away quickly on aluminum.
 
racerone said:
I have used that Aluminum brazing rod.-------A wee propane torch may not have enuff heat for work on a large piece like that.----Heat travels away quickly on aluminum.
Click to expand...
At my work, we have the guy who could do MIG aluminum welding. I may ask him to do me a favor.
I just bought a power head seal kit so I am ready to tear it down any time. Should I replace the piston rings as well at the same time since a light honing will be done too.
 
Rings are about $50 for each cylinder.----I would measure gaps before ordering new parts.----Oh-----I have about 10 of these motors for parts / rebuild.----I know what they look like inside and out.
 
Hi Racerone,
Is mine compression acceptable? Rings are too expensive #0437283 - Piston Ring Set, Standard $50 per hole.
What should I need to watch for when I tear it down? This is my first 19XX outboard. I have a couple 18XX OMC and they are reliable, cheap replacement parts and easy to work on it.
 
If you think rings are BIG $$$---try the ignition parts.-------Repaired one last fall for a new owner.------Previous owner gave up after he could not find a shop that knew how to diagnose it.----New powerpack was defective.----I installed a used pack and motor fired right up.
 
After looking at the cost of ignition parts, I feel lucky that mine has spark and runs. Otherwise, replacement of these parts cost almost the cost of the whole motor!!!
CDI parts are a bit cheaper but still expensive to replace.
 
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