How to install Outboard Pistons when rebuilding your outboards motor

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How to install outboard pistons, Check the piston ring end gap. Warm the rings then install onto the piston. Lubricate the little end bearing with two stroke outboard oil. Then lubricate the piston rings and piston skirt.

Insert the piston into the bore. Compress the rings, gently wobble the ring compressor from side to side and gently pull down on the con rod. Never force anything!!



13 thoughts on “How to install Outboard Pistons when rebuilding your outboards motor

  1. great video..ive rebuilt many outboards n other motors & i have 2 honestly say that u did everything perfectly by the book…congratulations!…

  2. I have a question4 u buddy,im rebulding a 1997 mercury 90hp,it doesnt have cyl,heads, i have to put in the pistons by the back & then drop in the crankshaft, can i still use a piston ring compressor or would i have compress the rings with a flat screw driver on my motor?..great video you are a king at rebuilding motors

  3. Hey Michael. Yes you can, you need to buy the tool to suit the motor you are working on. A dealer should be able to order the correct one in for you. Or if you have a friend with a lathe spin one up.

  4. HI there, great video. I have a 1974 40 hp Mercury. We started it on the muffs the other day and we had water squirting out of the Spark Plug on the top cylinder. Have you got any ideas on this? I am about to go home and strip the engine down. Any advice or ideas would be much appreciated. 


  5. Thank you for sharing, i just saw people change their four stroke engine in to two stroke one and my question for expert builder like you is what would they do to their piston? can it be used a four stroke piston for two stroke engine? other than the skirt height, what will happen to the four stroke piston rings when it is inserted in to two stroke cylinder?

  6. Good video , but please slow down some so I can see were the piston rings gaps are located correctly

  7. Question about seal ring gaps on 1986 Johnson outboard 90 hp. The book says place crankshaft in its block saddle with gaps facing up. I believe this is so the ends at the gaps will not snag and chip or break when setting the crank in. I see that a boat motor rebuilder posted that after the crank is in with gaps up you push the rings down into the crank grooves. He was not clear on what that means. So is he saying that you turn the rings from the top gap position so the gaps are then down into the block so the crankcase cover will not snag on the gaps when you install the cover. I see some guys saying that you need to stagger the gaps. Of course these rings are not compression rings like piston rings but are just spacers. So I don't believe it would make a difference if the gaps were offset or not. Now is there anyone out there that can for certainty say if the crankshaft seal rings need to stay with their gaps up or need to push the gaps down out of play for the crankcase cover so they are not snagged when installing the cover? Any competent comments on staggering gaps?

  8. Question for ya m8.. I have an old 1991 75hp mercury 2 stroke 3 cylinder. I was getting low power on the water after the initial run. I suspected a fuel issue and I think the oil pump went bad. I have one cylinder with no compression, when I pulled the head the piston face looks very rough with some minor chipping on the sides. The cylinder walls appear to be undamaged. Is there a way I could just replace that piston and not have to rebuild the entire motor? The rebuild kit is almost $800, for the time put in its just not worth it to me, nor is it worth buying an new power head as they can cost upwards of $2000.

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