Re: 0 compression on one cylinder 1996 Johnson 115
Model numbers are key here. OMC made two distinctly different 115's this year. The looper used Orings in place of the head gasket, so it's likely that you have the older crossflow type engine. So, a closer examination of the 0 compression cylinder is in order. Likely the rings have lost their ability to make compression. With the head off, put the 0 compresson cyl at top dead center. Those pistons do move somewhat inside the cyl liners. You can slightly move the piston by hand around inside the cyl, looking closely at the top ring. Would be interesting to know if it is still completely intact, or is broken and missing. You did not mention that there was any damage or pitting on the crown of the piston or the head face. Maybe not. In any event, you will need to replace that ringset, hone that cyl. At that point of complete teardown, you might as well repl all the ringsets. I went through this same single cyl "no compression" scenario a number of years ago on a V6. The skirt of pistons accumulated excess carbon, preventing the cooling gas/oil mixture from getting to the rings. While the two rings did not break, they overheated inside one cyl and stuck inside the block at about 4000 rpm's. Result: 0 compression. I received no warning horn, as the block was cooling normally-just not the combustion chamber. So, you are headed for an overhaul. One thing to check when you have the block apart. Visually check the intake and esp the exhaust ports area to make sure the ribs between the ports are not cracked.
