70 hp mercury thunderbolt lo compression on bottom cylinder

[todd281]

I have a 70 HP (3 Cylinder) Ser #s 4571652 - 5579016 that has low compression in the lower cylinder. This is the engine that has two carbs, and the reed valve block is inside the engine around the crank. I am wondering if anyone has got inside one of these engines. I am thinking that perhaps one of the reeds is bad, and that is causing the low compression . but I am not sure if that is possible . this engine has sat a few years, but I was told that it was running good when stored. I have sprayed some penetrating oil in the cylinders and let it set for a few weeks but no change. thanks for any help

 

[racerone]

Sorry, the reed valve has nothing to do with compression in the cylinder !--------------About the only thing that causes low compression is a scored / damaged piston.--------And before you ask , no there is no head gasket on that motor either

 

[todd281]

yea I knew about the head gasket. I just was unsure on how that reed valve system worked in this engine thanks for the reply

 

[GA_Boater]

What are the numbers? Is the motor running or not running?

 

[tallcanadian]

When you say low, how low?. My 3 cyl 65 Merc was the same thing. I used sea foam treatment and the compression come up a bit. Stuck rings I'm assuming. However it's a short term fix. Idle will be rough and motor won't run strong. Probably looking at an overhaul.