1995 merc 115 inline 4 compression

hareymike

Cadet
Joined
Aug 24, 2016
Messages
14
Local dealer just did a service on my motor.
They checked compression, results were 160,165,165,170 psi.

I was kinda shocked. The motor is very clean, the whole boat looks mint for such an old boat.
But are those numbers possible.
They said the inline 4 115hp motors were high compression.

The place I bought the boat from a year ago did a test and they got from 130 to 136 on there test.

any feedback appreciated.
Mike
 
Last edited:

hareymike

Cadet
Joined
Aug 24, 2016
Messages
14
I figured it was high. It has low hours, but didnt think a 165 was possible.
I even called back and they just said its a tight engine. This is a very large well known mercy. dealer.
kinda surprised at the no.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
I had the 90 triple and had the service manual that covered 60 triple Jets through 4 cyl 125. The serv manual specified 120 and added that one could expect problems below that number......didn't say it wouldn't work, just that it might not and don't get your shorts in a wad if it doesn't perform to your expectations. Most folks pay more attention to cylinder to cylinder tolerances in the 10-15% (depending on who's talking). On the absolute value lots of things can give you a false reading whereas on the cyl to cyl, whatever problem you had measuring one should carry over to the rest; uncalibrated gauge, bad rubber seal, engine not prepared properly, sloppy workmanship,you name it.
 

hareymike

Cadet
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Aug 24, 2016
Messages
14
Im not going to sweat it. Was just curious why it was so high. The numbers last year, although lower, where good also. And yes new water pump last year by another dealer.
 

Johnson110

Chief Petty Officer
Joined
Dec 31, 2003
Messages
640
Have the same motor with the oil injection hooked up, it runs good I know it is the 2+2 design but not going to get crazy worrying about it, Going to do the water pump this year just brought the boat last year. I say as long it is running strong just enjoy it !
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Have the same motor with the oil injection hooked up, it runs good I know it is the 2+2 design but not going to get crazy worrying about it, Going to do the water pump this year just brought the boat last year. I say as long it is running strong just enjoy it !

Over the years, after growing up with the alternate firing OMC twins, I became fond of the multi cylinder engine's smooth idling characteristics. That put me in the Merc. corral and have pretty much been there ever since, especially loving my '88 115 6 cyl tower of power. When Brunswick came out with the 2+2 I couldn't believe it but the guys that work on them and set them up say that you can't tell the difference when the second pair kick in at around 2500 rpm. Well maybe not, but I tell you, I can tell the difference between a 1,2, 3, 4, and 6 cyl engine.

Good luck with it and this response was directed at your comment "I know it is the 2+2 design but not going to get crazy worrying about it". That would be my response too.
 
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