pulled heads on 1998 johnson 115 90 degree cross flow

[awol1]

history of bad compression upper starboard cylinder 120, 120, 80, 120. Starting an overhaul of the engine anyway. pulled lower unit and changed water pump. Got curious and pulled the head on the starboard side. Here is what I could see:<br /> <br />The upper piston (bad compression cylinder)had alot of gouges and nicks and burrs around its perimeter. The inside of the head also had alot of gouges especially in the cup like portion that cylinder head sits in. The head gasket look ok. the cylinder wall seemed fine with no obvious nicks or scoring. The lower piston, head and cylinder had no obvious damage at all.<br /><br />Does this type of damage relate to a specific problem? <br /><br />thanks<br />chris

 

[Dhadley]

Re: pulled heads on 1998 johnson 115 90 degree cross flow

It almost sounds like a ring broke from coking. It usually shows up on the starboard side first. Youll know more when you get it apart. <br /><br />Coking is usually a product of propping the motor out at a lower than optimum rpm and/or not decarbing soon enough. Typically when you look at the piston the ring to the right of the locating pin will be the side that breaks first.<br /><br />Let us know what you find.<br /><br />Good luck!

 

[Hooty]

Re: pulled heads on 1998 johnson 115 90 degree cross flow

Sounds like it ate a bad rat or something. <br />Seriously, it does sound like it ingested part of a ring or reed or something but that usually scores up the cylinder wall too. Replace the piston, rings and probably the head. While it's down, check the inards carefully and see if you can figger out what's missing.<br /><br />g'luch & c/6<br /><br />Hooty

 

[awol1]

Re: pulled heads on 1998 johnson 115 90 degree cross flow

interesting, especially about the prop. when i bought the boat it came with a beautiful 4 blade ss prop. Could this prop have caused the damage. the problem is I have no tach and do not know what I am spinning at wot.

 

[Dhadley]

Re: pulled heads on 1998 johnson 115 90 degree cross flow

Its not the prop exactly - its the set up and the prop is a factor of the set up. Lets not jump to conclusions. Get it apart and see whats there to work with. While its being repaired you can install a tach. <br /><br />Good luck!