Trouble with 65 Hp Mercury

[cdnboatguy]

Hi everyone:

I recently got started working with marine engines.
I have a 65 Hp merc outboard. Not sure on model number but can get it if its important?
I discovered the cooling system was not functioning. "After it got very very hot."
I tested the compresion after discovering the heating issue. I think I caught it in time.
Cylender compresion is as follows
Bottom: 150LBS
Middle cyl: 135LBS
Top Cyl: 130lbs
After replacing the water pump propellor I put the boat back in the water for a test. It now doesnt fire on the top cylender when in the water.
All cylenders fire when out of water.

I suspect my problem is in my plug wires and or distributor.
I have replaced the plugs as well

Can anyone tell me if I am on the right path? or should I be looking elsewhere??

thanks in advance

 

[jebeebe]

Re: Trouble with 65 Hp Mercury

I would take the top plug out and inspect the piston for metal flakes or detination signs. (coroded piston surface). The top piston is usualy the one that goes first on these engines. Furtherest from the water source. I had a 60hp that the top piston had most of the rings gone and the remaining pieces welded in the groves. I wa able to hone the cylinder and go with a standard piston with only a tiny scratch left in the wall. Most of the nasty was on the surface. With pistons at 100.00 a piece (including rings) it won't be a cheap fix, but will probably be nessessary. I had to replace all my pistons as the old pistons were 3 ring and the new was 2 ring and I had over $500 when I got done, but it purrs like a kitten now. Be sure to replace the impeller or better yet the whole pump ($65 ) as this is the source of your whole problem. Lots of luck...................Jerry

 

[cdnboatguy]

Re: Trouble with 65 Hp Mercury

Thanks so much for the post.
I did check the pressure in the top cylinder and i did hold for a long time (10 minures no pressure loss. so I dont suspect a bad cylender. Am I wrong in this assumtion?
It sounds to me lke you feel my top piston might be shot?
can you confirm this for me.
Does the high PSI on all the cylenders not suggest they are in good shape?
What about the fact that everything fires when not in the water?

Thanks again for all your help?

 

[jebeebe]

Re: Trouble with 65 Hp Mercury

If it held compression that long you didn't fry the cylinder. Mine didn't have any comression. I'm not sure what to tell you. It doesn't sound like you have serious problems dollar wise. You could have a top cylinder running too lean. This will cause heating problems as it would not be getting lubrication. You could try spraying a mixture of premixed fuel in the top carb while cranking. Dont use starting fluid as it will burn the walls as it has no lube. If it fires on the top cylinder you will need to rebuild the carbs. I took mine apart and soaked them over night and reassembled them and adjusted them by the book and it runs so good I didn't adjust them after I got it going. I suspect the carbs are what did my top cylinder in. Could have been sand in the water pump too. Good to hear you have compression on that cylinder. Good luck.............Jerry