Thread: 25 hp Mariner / Yamaha made.. water droplets on spark plug.

Head gasket. A pin hole leak will not affect compression numbers to any noticeable extent. Water pressure will inject water into the cylinder while the cylinder is not pressurized. While pressurized, compressed gases will enter cooling system. A sporadic tell tale output is another symptom you should be looking for.

Originally Posted by sliderman

A sporadic tell tale output is another symptom you should be looking for.

By this do you mean motor running off and on with one cylinder going out like fouled plug or bad coil. Switch the coil out and new plugs and it does the same. If you look closely at the pic. top cylinder has been washed clean and the cylinder sleeve has turned about a 1/4 inch covering some of the exhaust port. I don't think this would make it leak but it will affect performance somewhat. Because if it's turned a 1/4 inch on the exhaust side it would be turned a 1/4 inch on the intake side..Thanks for info on head gasket. That basically the last fix I know of with out complete tear down

A sporadic tell tale is sporadic water output. I can't see enough of the port in the pic to say whether it has turned or not. The sleeves are ported prior to installation. If it has moved, a complete tear down is just the start of the repair.

The dropping of a cylinder is a direct result of the water entering and negating combustion. Which can't be corrected with a new coil or plug. It's just watered down fuel that will not combust.

I put the new coil and plugs on before I did a closer inspection and found the water droplets on the plug. You have to look close to see them. Best way is to run motor for a bit turn motor off. Then crank motor over with kill witch off or key off for a bit and pull plug and inspect it. I will change the head gasket out and hope for the best. As far as the sleeve goes it has turned. There is no way it should have turn but Yamaha had some trouble with this in some of there engines. I called and retired tech that I know and he said he had 3-4 do the same thing. One Yamaha motor less than a year old and dealer brought it to him to look at because they could not figure out why the performance was not there. He took the exhaust cover off and seen it was turn and covered 1/2 of the exhaust port like he has seen before. But none of these motors were leaking water into cylinders. I sent him some pictures and he seen it for sure and said that's not good but it will still run but not as it would if the sleeve was flush with the exhaust port. There is no fix. He had tried to heat the block in a high temp oven and tried to turn sleeve while hot and he could not get them to move at all. They are pressed in at the factor and should never move. Hope this post might help someone that is having performance problem with Yamaha motor. Just remember my motor has been hot and the sleeve has turned 3/8 of an inch but the ones he has inspected later model motors and not been overheated have turn enough to cover 1/2 the exhaust port.

i would think heat would expand the sleeve . i know a diesel is frozen and slid in the cylinder and when defrost it is there . steel expands when heated .

That makes more since than trying to heat it. I don't think he had a way to freeze it unless you set it outside in the middle of Feb. here in Illinois..lol. I hope it don't get that cold this year. Haven't had time to take the head off and do some more inspection on the head and gasket.

I know this might not help but I seen some spray that you can use to freeze nuts and bolts to help free them. Not sure if something like that would work or not? (The product is by CRC called freeze off)