Late 70's Mercury 850, Low Compression

[winded2002]

I have a late 70's Mercury 85HP with low compression on the top cylinder. There is also very little water coming out of the pee hole. I was told that the water pump probably failed and the 1st cylinder over heated. Has anyone heard of this? Is this serviceable?<br />The other cylinders run good and have good compression.

 

[rickdb1boat]

Re: Late 70's Mercury 850, Low Compression

That is probably exactly what happened. And yes, you can have the cylinder bored out(If clearance allows) and install a new piston and rings. And of course, replace the water pump!

 

[jumfleet]

Re: Late 70's Mercury 850, Low Compression

i have a 1973 65hp, and i think i have the same problem. did ya get it fixed. mine runs, but the idle goes up and down, like boggs out then goes high and continues to do that until it dies, and then dont wanna start after that

 

[Really Old Guy]

Re: Late 70's Mercury 850, Low Compression

i have a 1973 65hp, and i think i have the same problem. did ya get it fixed. mine runs, but the idle goes up and down, like boggs out then goes high and continues to do that until it dies, and then dont wanna start after that

STOP! Do no run it. You are going to ruin what is left!
Fix your pump and start repairing what is left!

 

[oldgradywhite]

Re: Late 70's Mercury 850, Low Compression

When though motors over heat the first thing to go is the top cylinder. Don't run it. replace with water pump.