78 80Hp Merc #3 20PSI compression

[WinnipegBoatMan]

I currently have run into some issues with my Merc. I regularly have my merc serviced, and this year I have a huge issue with cyl #3 with low compression, 20 PSI. All but #3 have good compression.. around 120PSI. Can this be a blown cylinder, or something else?

 

[trendsetter240]

Re: 78 80Hp Merc #3 20PSI compression

I currently have run into some issues with my Merc. I regularly have my merc serviced, and this year I have a huge issue with cyl #3 with low compression, 20 PSI. All but #3 have good compression.. around 120PSI. Can this be a blown cylinder, or something else?

20psi is very, very low. Could be a blown gasket if you're lucky. Otherwise it could be worn, broken or stuck rings in that cylinder or deep scoring on the cylinder walls.

 

[emckelvy]

Re: 78 80Hp Merc #3 20PSI compression

There is no gasket to blow on an 80 HP Merc that will cause low compression in one cylinder.

Time to tear the powerhead apart and assess damage. Be sure to address the cause of the failure if you decide to rebuild, or you stand a chance of having the same problem again down the line...........ed

 

[Faztbullet]

Re: 78 80Hp Merc #3 20PSI compression

If its a 70ish 4 cylinder the distributer is bad, this ususally takes out cylinder #1 or #3, look at "eyebrow on #1 and see if it has some erosion also. Time to rebuild.....