So I did a compression test on my motor tonight and two cylinders are at 100 psi and two are at 60 psi. Has anyone had any success with ring free working to increase cylinder pressure? I would hate to pull the boat off the water for the rest of the year. Come October it will be out of the water and i can tear into it then if need be. A second question is what would ibe looking at on average for a rebuild on it?
On those V-4 engines you can pull a bypass cover easier & cheaper than you can pull a cylinder head. You can see a problem better too. Better way to check for stuck rings. Six 3/8" headed bolts hold them on. They are on the port & starboard sides of the block. I would start with the starboard side. You didn't say which cylinders were low, but usually it is the starboard cylinders #1 & #3 that will stick the rings the worst. After you get the cover off you can see the side of the piston & rings. A small screwdriver can be used to push on the rings to see if they will move in and out in the piston grooves. If they are all gummed up they are stuck. You can buy BRP/Mercury Engine Tuner or Power Tune which can clean this up. Ring Free will keep the engine clean, but will take awhile to get it all out. Put the tuner in the ports before putting the bypass covers back on. Also put it on top of the Pistons thru the spark plug holes. Leave it in for 24 hrs, but not much longer. You need to start the engine after that and run it a minimum of 15 minutes to get it out of the system. It is corrosive. You can do the process again with a warm engine which is even better. Just remember you have to run the motor after it sits!
This is all predicated on you not finding any piston damage when you open the bypass covers. If you do have to rebuild replace all 4 pistons. These motors (as all 2 strokes) have a history of dropping dow pins (hold the rings in place). When that happens the rings rotate & get clipped by the port openings. Good luck with you decarboning.
In addition to what the O.P. said, if the 2 low cylinders are on the same side, you may have a blown head gasket. A leaky gasket between 2 cylinders can cause low readings in each; it's just suspicious that 2 cyliinders have the same low reading.
I did forget the head gasket which would be a good call, but now that we know opposite sides it looks more like scored cylinders? Maybe lean carburetor or such. Still looking through the bypass covers is better for first clance. You should see the scores on the piston. Then you can pull the head. Either way the engine will have to be pulled apart. Hope that helps.