1996 Johnson 115 HP V4 - Low Compression one hole

Fr. Frank · #1 05-18-2008, 10:33 AM

60 psi on one cylinder could easily be nothing more than stuck rings. However, head gaskets are relatively cheap, so pull the cylinder heads and visually inspect the cylinder walls and piston tops for scoring and carbon build-up. Examine the piston cap ridge (edge) for erosion or scoring. Turn the crank to move the pistons down in the cylinder and feel the cylinder walls for ridges or scratches.

If you find scratches or erosion, rebuild the powerhead.

If the piston and cylinder walls look and feel good, tilt the motor up and spray the inside of each cylinder with Quicksilver PowerTune. Don't be stingy with the stuff, use a whole can. Let it soak in overnight.

Reassemble the cylinder heads using new gaskets. Start the motor and let it run in gear at the dock or underway at 1500 to 2500 rpms for an hour or so, intermittently spraying more PowerTune into the air intakes. Don't shortcut this process.

After doing this, recheck the compression. If it was just stuck piston rings, your compression should now be improved.

gofastsandman · #2 05-18-2008, 01:32 PM

I`ll second that. It`ll smoke like a civil war battlefield. That`s normal. Don`t to forget to spin the engine with the plugs out to evacuate the cylinders of the powertune. Liquids wont compress and you don`t want to bend a rod or worse.

StrangeBrew · #3 05-19-2008, 10:24 AM

Thanks Frank and Go Fast Sandman. What do you mean by "spin the engine with the plugs out"...Not sure how to do that?

gofastsandman · #4 05-19-2008, 07:32 PM

Thr spark plugs removed and turn over the motor to evacuate the liquid as it will not compress and "hydraulic "the motor. Trim down for this.
GFS

Fr. Frank · #5 05-21-2008, 09:01 AM

Have you tried this yet? We'd love to hear that everything came free and you're up and running.

StrangeBrew · #6 05-23-2008, 10:01 AM

I did spray the cylinder with the PowerTune...It's been sitting since Sunday. I plan to run it this afternoon and check the compression again...Keeping my fingers crossed. I will let you know what happens. Again, thanks for the info!

gofastsandman · #7 05-25-2008, 06:49 PM

I would spray all the cylinders! Even compression across the board is what you want. I`ve only been a lucky owner for a year and have learned much from this site. That`s what it`s all about. Learn - share. Rinse and repeat as necessary.

Thx to all who make the sacrifice on this glorious Memorial Day,
GFS