Compression Test Question - 93 Evinrude 120

[bgiles]

I'd like to perform a compression test on my 1993 Evinrude 120 just to see how it's doing. My Seloc manual indicates to remove all the plugs and "ground" each spark plug wire.<br /><br />Is there anything else that should be done to prevent messing up any other components such as the Power Pack etc. Motor runs just fine but I am curious since it is getting up there in years.<br /><br />Does anyone have any experience to what I should expect in the way of numbers for this particular motor.<br /><br />Thanks in Advance<br /><br />Bruce

 

[mikeyzx2]

Re: Compression Test Question - 93 Evinrude 120

just pull the kill switch...<br /><br />good compression numbers are 100+, more importantly though the numbers should should be within 10-15 of each other.

 

[DJ]

Re: Compression Test Question - 93 Evinrude 120

Make sure you have the engine on "muffs" with water connected and flowing. That will save the water pump.

 

[TimMattson]

Re: Compression Test Question - 93 Evinrude 120

After a compression test and it passes,you can use vinyl coated plug pliers to pull the plug wires off one at a time while running on muffs.<br /> The idle should drop each time a wire is pulled and then a crack or snap as the spark jumps the gap upon re-installing and the idle should return to normal and smoothen out.No change means that cylinder is not affecting the engine and may have a weak coil,pack or a wire out.<br /> Run some engine tuner into(shoot into the primer valve fitting) a warm engine while on the water and let sit 15 minutes.Then run hard to blow the carbon and crud out of you combustion chambers and to prolong the engine life and improve power.<br /> Tim M

 

[rodbolt]

Re: Compression Test Question - 93 Evinrude 120

while the cyl drop test may be ok for an old point type ign, the 120 looper ign can generate voltages in excess of 60KV . I dont reccomend unplugging the coil wire from the spark plug unless you are ready. it can create a problem.<br /> that voltage is gonna try to go someplace a better method is to use a sparktester, which can be homade or buy the spark KV tester.<br /> is there any particular reason you wish to test compression ?<br />if the motor idles well and turns its recommened RPM odds are in your favor all is well with the cylinders sealing ability. once compression starts failing its rapid, usually within a few minutes. its not like a car motor that will get lower with age.

 

[R.Johnson]

Re: Compression Test Question - 93 Evinrude 120

Compression (pressure) guage's can read all over the map. I have a shop full of them, no two of them are in agreement. You are looking for a differene in pressure, that being less than %10. On a 2 cycle engine, the high reading cylinder can be the one that is bad, I have found this more than once. The most accurate measure is a leak-down test. That not only give's you an accurate reading on the guage, you can here the leakage past the cylinder, and out the exhaust , and intake port's.

 

[bgiles]

Re: Compression Test Question - 93 Evinrude 120

Hi Guys, thanks for the information, to answer Rodbolts question <br /><br />is there any particular reason you wish to test compression ?<br /><br />The answer is No reason, motor idles just fine and runs at the recommended WOT rpm's no problem. I have too much spare time during the winter months, you start reading some of the posts with compression reading's etc etc and say to yourself - UMH - don't know what mine are.<br /><br />Based upon your responses, I'll just leave well enough alone - Good point about the Water Pump though, I would not of thought about that one.<br /><br />Thanks Again<br /><br />Bruce