1986 mariner 4cyl 50hp

[buzmacdowell]

the top and bottom cyl compression is 90 & 100...the middle ones are 125....I'm gonna take the head off Sunday a.m. if I can get it off and rotate the motor and have a look....What can I expect to see? I did squirt some trans fluid in the top jug and it came up to 125...then started dropping after a few rotations ....the fuel pumps on the carbs were put together all wrong...got plenty spark...re worked the carbs & pumps...the motor is really clean and I thought it would be a simple fix for my friend....pumps plenty of water but won't run very long under 2,000. If I can rebuild it where is the best place to find some parts?Thanks, Buz

[delawarerick]

Can you pull the head or is it one piece? The head is part of the block I think like the inline6's.

[crossflow 1]

There is no head just a water jacket cover.

[delawarerick]

Before you go into the engine try decarbing the motor if you have a carboned up ring or a sticking ring this will help.

[buzmacdowell]

Maybe I can see something if I take off the port covers that are behind the coils & switchbox...I just want to see if there is damage or if I can push on the rings....If I decide to rebuild the motor...can I reassemble the motor one piston rod combo at a time or do I have to fit all at the same time? I don't have the type ring compressor that they show in the manual....

[Steve2ManyBoats]

You can't do one hole at a time. You have to install the whole assembly - rods, caps and bolts, pistons and rings for all 4 holes. Then you need the special ring compressors from Merc to install the whole shebang. You can try it without the special ring compressors (I did it a few times back when I was a young, broke commercial fisherman} but you're guaranteed to break a few rings in the process.

Your plan to take the intake port covers off and look for scuffing and ring tension is a good idea. As others have said, this motor has no head, just a water jacket cover around the spark plugs. That motor should be over 125 psi, since it's a crossflow and not a looper like the Merc V6s.

By the way, the the older 4 cylinder 44 cube Merc/Mariner is one of the finest motors ever made. I had a 1975 50 that lasted over 5,000 hours while I was commercial shellfishing. It never actually never did die, the water jackets eventually corroded to the point that I couldn't seal them anymore, no matter how creative I got.

Steve2ManyBoats.

[delawarerick]

Before I did anything try a decarb and after it stalls pull the plugs and shoot the decarb in the holes and let it sit what do you have to loose. I have been working on a v4 crossflow had 125 and one was 107 now all are 125+. That's $12 later and a few hours. Rick

[buzmacdowell]

You can't do one hole at a time. You have to install the whole assembly - rods, caps and bolts, pistons and rings for all 4 holes. Then you need the special ring compressors from Merc to install the whole shebang. You can try it without the special ring compressors (I did it a few times back when I was a young, broke commercial fisherman} but you're guaranteed to break a few rings in the process.

Your plan to take the intake port covers off and look for scuffing and ring tension is a good idea. As others have said, this motor has no head, just a water jacket cover around the spark plugs. That motor should be over 125 psi, since it's a crossflow and not a looper like the Merc V6s.

By the way, the the older 4 cylinder 44 cube Merc/Mariner is one of the finest motors ever made. I had a 1975 50 that lasted over 5,000 hours while I was commercial shellfishing. It never actually never did die, the water jackets eventually corroded to the point that I couldn't seal them anymore, no matter how creative I got.

Steve2ManyBoats.I took the port covers off...and the top piston has some pretty small scratches on the piston towards the bottom ...and a few very slight ones on the rings.....really doesn't look that bad....pushed the rings and got them to move easier...then after putting the plugs back in and squirting inside the ports and plug holes with X-traguard lubricant ...to soak in the cylinders...I turned the flywheel by hand....and I can turn my 2.4mercury v-6's easier....maybe that's a good sign....we did brake the bottom little end of the port cover off....so we need to get a new gasket and cover...those phillip head screws were very easy to unscrew.....I was surprised...maybe somebody has already been in there......