1996 Johnson 115 HP V4 - Low Compression one hole

[StrangeBrew]

I recently purchased a 1996 115HP engine for my 20' Potter. I had my mechanic mount it on the boat this week and asked that he perform a compression check. Reads 110 psi on 3 and 60 psi in the 4th. He tried a decarb, but no change. The strange thing is that the motor sounds very healthy and there is no unusual smoke. He looked in the cylinder and there did not appear to be any scoring etc. Do you think I need new rings? Do you think I can run her for the season and repair next season? Everything I have read says that all cylinders should be with 10% of each other and not more that 15 psi out from the others. If she runs (haven't tried under load yet) whats the danger of running with a cylinder thats only reading 60 psi? Should I just do rings or try to run her for a season as is? How much is a ring job roughly? Thanks

[3rdday]

It probably wont run well under a load, un-equal pressure may be put on the crank. That is a great engine, great electronics on it. Right now the issue may be rings, if you run it you may cause other problems, cylinder damage, block damage, piston, piston rod, crank, head etc. May as well replace all of the rings, while you have the block apart. have someone take a micrometer to that cylinder also.

[StrangeBrew]

Thank you for the info.. I will have my mechanic do the rings this week. Thanks again.

[eggsuckindog]

Even though you decarbed it the rings on that one may still just be stuck since no damage is apparent. You would need to pull the head and soak that cylinder with something they get from the manu. Mine had some stuck rings and soaking with this stuff broke them loose. Not sure what it was but you could call Mike at American Marine and he could tell you - worth a shot before pulling it all the way down 727 938 9796

[76Red18]

Marvel Mystery Oil has worked for me on a couple of froze up motors.

[Blue197320]

wont ATF sometimes help un-freeze a motor or motor parts??

[Bigshrimpin]

Powertune is the best decarb . . . but at 60psi something else is wrong . . . I doubt it's just a stuck ring.

[eggsuckindog]

Mine was only 80 - it is something they buy from Merc or Rude, broke it loose in a couple hours - not a standard item

[Fr. Frank]

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]

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.