no compression on top cylinder???

[neversinksmith]

early 80s merc 70 hp 3 cyl. no compression on cyl 1, top cyl. the other 2 are around 125psi. guy said he was running the engine and heard a pop then putted back to the dock. does this sound like head gasket or sucking in air from bad top crank seal? did not seize up. thanks guys

 

[ondarvr]

How do you know it didn't seize, it can break a ring, sore the cylinder, hole a piston, etc.

The crank seal wouldn't have anything to do with it, possible head gasket if that model year has one.

 

[racerone]

There is no head gasket !---And the top seal has no affect on compression in the cylinder either.------Remove bypass cover on the motor and look at the piston and rings.

 

[neversinksmith]

ok what I meant was the cylinder cover gasket and as for the top crank seal I was referring to an air leak that caused and over heating issue on cyl 1. it didn't seize because the engine kept running after he heard the pop and was able to drive back to the dock. no hole in piston. ​bypass cover is under the power board correct?

 

[ondarvr]

Even without coming to a stop the same damage can be done. The seal is in the crankcase below the piston, the compression takes place above the piston.

 

[neversinksmith]

uuuuugggggg I'm not intending to debate what a seized piston is, and thank you I do realize that a piston can cause damage to a cylinder. I'm simply trying to give you all as much info as I can. ​so your saying that that's not the crank seal under the flywheel and a bad crankseal cant suck air into the engine and that cant cause a lean condition and that cant cause an overheating issue???

 

[ondarvr]

You asked if the crank seal could cause the low compresion in #1, well, we'll sort of, now that I re-read the question, the leaking seal could cause the lean condition that could cause the damage and lead to no compression. But that wouldn't be the first place I looked for a cause.

 

[neversinksmith]

got into engine. ring broke off top piston. meltdown... ​went to pull carbs and realized the whoever pulled carbs last time to clean them never tightened the bolts that anchor carbs to powerhead. like 6-8 full turns out from seated. gona split cases and see how bad she looks inside