150 johnson-water damage #6 cylinder

[mocity1]

looking for help.I just bought a used boat that had a 150 johnson 6cylinder o/b that i took to a great mechanic to get a opinion on,was there held the gage myself and had 87 psi on all cylinders.The boat belonged to a elderly man that had passed and had been sitting up a couple years.I took it out and it ran great,had a good pee stream but ran a little hot at idle,cooled off good as i sped up.took it in to get a waterpump i thought, when i found the #6 cylinder had no compression and took the heads off and seems water got in it and pitted the piston and broke the rings etc.the other cylinders seem fine.the motor was rebuilt two years ago so the mech. is going to bore out the #6,replace waterpump and thermostats,clean carbs.,etc...Any ideas what could have caused this as the head gasket looked fine.I really don't want to rebuild if i don't know what caused it...

 

[emdsapmgr]

Re: 150 johnson-water damage #6 cylinder

What year is this engine? Is it a crossflow or 60 degree looper? Completely different blocks. From your compression readings, I will guess it's a late 80's crossflow flatback. If so, it is possible to get water into the exhaust chest from the inner exhaust cover. Possibly leaky inner cover gaskets. Once water gets into the exhaust chest, it typically moves down (affects) into the bottom cyls. I've also seen inner exhaust covers which develop leaks due to casting porosity or salt corrosion. Shine a light on the back of the inner cover and see if you can see the light from the other side. Or lay it flat and put some water on it to check for leaks. The water issue may not be the only problem. Piston crown pitting is usually from an overheat/lean condition, possibly from lack of fuel/lube to that cyl. You may want to pull that carb apart that feeds that bad cyl, remove the jets, visually check them (esp the high speed) for any possible restriction. If the jets are clear, check the rubber water diverters by #6 cyls to make sure it is still correctly placed and not restricting water flow. (see pic.) This type of overheat usually won't sound an overheat warning horn.

 

[mocity1]

Re: 150 johnson-water damage #6 cylinder

This is a 1985 crossflow.....thanks