2011 Mercury 75HP 2 stroke compression readings

[gboy99]

So maybe I have too much time on my hands but I was looking at the service book of my 2011 Mercury 75Hp 2 stroke outboard and I noticed the last compression reading (taken last week) for cylinder 3 was 130psi. From new it was 140psi. Below are the readings taken during scheduled services since new. Do I have cause for concern? For what its worth engine has done 80hrs.

	1	2	3
2011	145	140	140
2012	140	145	140
2013	145	145	140
2014	140	140	135
2015	140	140	130

 

[fastjeff]

I'm equally anal and do the same thing. Those readings look great.

Jeff

 

[gboy99]

I'm equally anal and do the same thing. Those readings look great.

Jeff

Thanks Jeff.

 

[galamb]

Just before OMC went down the drain (and got bought out by Bombardier), they sent out a guideline to their service centers.

The point they were trying to make was that far too many motors were being rebuilt due to "far too stringent" guidelines.

They suggested that a 10-15% compression drop from new factory spec should be considered to be "well within" the service life of a motor, provided that the readings are within 10% across all the cylinders. At readings "beyond" 20%, particularly if non-uniform, then a rebuild should be considered.

From your best to worst you have a difference of what 7'ish %

So I'm with Jeff - I wouldn't be complaining at all with those numbers.

 

[gboy99]

Thanks Graham.

 

[papyson]

it is good that you took these readings as you have a reference if later in the lifetime of the motor you have a problem...you will not be chasing a non existent gremlin...