85/120 Evinrude compression 120 and 150psi

[Luna Sea]

Finally got around to doing the compression test. Both starboard cylinders read 120 and both port cylinders read 150. Anyone know what the compression for a 1985 120 hp Evinrude should be? Runs good enough for the season, I guess. But should I be looking into any ring free additives or anything?

 

[Terry H]

Re: 85/120 Evinrude compression 120 and 150psi

120psi sounds about right for that motor...Maybe someone had a warped head on the port side and had it milled...if it runs good I wouldn't be too concerned...just a Thought

 

[ledgefinder]

Re: 85/120 Evinrude compression 120 and 150psi

I've gotten 130-135 on V4s (115s and a 125 hp) from the late '60s and early 70s, and 120-125 from a 1989 88SPL. The 88 clearly had an added layer of metal to the head to lower compression for the more recent gasoline. Of the few V4s I've tested (5) I haven't seen any higher than 136.<br /><br />That being said, the common belief is that compression variation across all the cylinders should be small - ideally with 5 psi, although I have a Merc manual that says within 20 psi is OK.<br /><br />Could be that you have carbon buildup in two of the cylinders, or that your gauge or measuring technique is different than mine (higher voltage battery, etc.). <br /><br />I'd treat it just the way you are - run some ring-free tuner & not worry about it much for this season. If you're worried/curious, it's not a big deal at all to pull the heads on those V4s and take a look.