Motor carnage!
 

Well guys finally tore the motor down to find the reason for low compression on top cylinder. Motor ran hot and melted top piston scaring the cylinder some. Atleast its fixable and not tooooo expensive. I think im going to go ahead and replace all 3 pistons and rings and bore it to .030

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Dang. That Suxs. Get some Yamaha stickers after you rebuild. Might help. ;)


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I learned my lesson after I blew 4 mercurys up.

Ill prob run it till next winter then sell and buy me a bay boat.

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Next motor will prob be a yammy

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Get cha a suzuki :cool:;)

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Isn't this the second motor on that boat?

I don't mean this in a bad way, but if i remember correctly didn't you do some work on that motor to get it to run faster etc..

Do you think that may have contributed?

I was sure envious of the speeds you were talking about with that motor when i was comparing it to what my little 50 yammy was doing.... but now not so much...

Glad it's fixable. Happy to offer you a ride on my little tin boat some day... you just gotta show me how to bang them specks like you do... :)

I wonder what caused it to get hot? Bad oil pump/low oil, water pump?

yes i bought this motor used from a local guy and im assuming there was some type of water blockage or something for the top cylinders. bc it was pissing fine with plenty of pressure. or it may have been already hurt when i got it. im not sure. but im goin to flush it out very well and replace the water pump also. And this motor is pretty much stock so nothing contributed to it running hot but me being stupid and ignoring the alarm bc i thought no way its running hot its pissing fine. I thought it was a wiring issue that i caused

Coulda been clogged thermostat. I know the mercurys come stock with the pisser on the bottom of the head before the water even passes through the thermostat. Meaning you could be pissing fine but the whole time your thermostat is clogged and your motor is over heating. You have to move the piss indicated to the top hole on the top cylinder and plug the bottom to get an accurate reading.

I didnt know this. Mines still on the bottom hole.

sell it, buy a 150 and video it flying.

That's a great design


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Didn't cause the problem, but, someone used the wrong sealant on the block halves. Red locktite was discontinued for tht purpose 25 years ago.
Stacked Mercs are notorious for burning the top cylinder, hardest one to cool.
D

Mercury's mexican electronics are known for giving problems as well. Makes sure everything is firing properly before you start running it again after you rebuild it. Some people don't agree with gutting the thermostat but IMO you don't need one in south LA on a carb 2 stroke. Gut the thermostat and let it flow. If you plan on doing the rebuild yourself get a mercury service manual and makes sure everything is within specs.

Im going to use hondabond to put it back together.

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It's difficult for most folks to understand the purpose of the thermostat in an outboard. It is not to make the engine run cool, it is to insure the engine block runs at the optimum temperature for performance and parts expansion. It is actually to make an engine run warmer than it would without a thermostat. Mercury is notorious for galling pistons when folks do not allow the engine block and pistons to warm properly. Most Mercury outboards use forged pistons. Forged pistons have a greater expansion rate from a cool state to their heated state than cast pistons. This means that when you first start that Mercury in cool weather, the piston is much smaller than the cylinder bore. By allowing the engine to warm before takeoff, you allow the pistons to grow and properly fit the bore. If you just start the engine and blast off, piston slap will eventually cause the piston to gall aluminum and stick it to the cylinder wall.
As for the port job, there is more science to it than just grinding 1 port. If it were that simple, everyone would be QUALIFIED engine builders. There are several excellent engine builders in this area. Each usually specializes in one or two brands of motor and only certain sizes of those motors. It is a time consuming task to map out the ports and enter all the data into a good port mapping program and come up with the correct sizes to make ALL ports in that cylinder, intake, transfer, and exhaust ports work together PROPERLY! To modify one port in each cylinder is like putting a 20" wheel on one corner of your vehicle and 15" wheels on the other 3, it will roll, just not correctly. All ports must be properly and proportionately sized to work together.
D

I just don't see the need for thermostats in south la with the heat we have. I ran a 25 merc for years without a thermostat,hell I would pump straight mud through that motor. Did the same thing on my v4 evinrude with zero issues. Good podna of mine runs an old 2.0 merc 135 on a tunnel hull with no thermostat and it's still running to this day.

Quit cussing like that. Lol


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