Evinrude 225 cylinder compression test

1989 Evinrude 225 hp V6<br /><br />I need help on how to do cylinder compression test, the allowable range and max difference between cylinder values.<br /><br />Thanks<br />tornillo

Re: Evinrude 225 cylinder compression test

The following are thing's I've snipped from this and other forums to guide me. None of it is my personal opinion - except that as a novice, I followed this general guide and it worked for me.<br /><br />--------------<br />Compression test<br /><br />What you’re looking for is any difference in compression between cylinders to determine if something is wrong with one or more cylinders. Therefore it’s most important to be consistent in the test from cylinder to cylinder regarding warm vs. cold, removing spark plugs, open vs. closed throttle, number of revolutions, etc. etc.<br /><br />You're also looking for changes from season to season, so pick a method and stick with it.<br /><br />Get a compression gauge that screws in to the spark plug hole, not with a rubber stopper type of fitting.<br /><br />Calibrate the gauge per instructions if available.<br /><br />Some recommend a warm engine. Others say it doesn’t matter.<br /><br />Remove all plugs. Others say it doesn’t matter.<br /><br />Disengage the lanyard if you have one. That'll disable ignition and minimize danger of exploding fuel. Use another method of disabling ignition if necessary.<br /><br />RE: open vs. closed throttle, two opinions:<br /><br />“On a 4-cycle motor you need to open the throttle to minimize the vacuum restriction when intake valve opens and the piston "sucks" in the air to compress. On a 2-stroke motor, the exhaust port is open during the bottom travel of the piston and the slow cranking speed allows the cylinder to fill until the exhaust port is covered, and some air comes thru the intake ports. You can check compression with the throttle open or closed and still get the same reading."<br /><br />“The main reason I check compression at wide open throttle is if your carbs are not exactly synchronized (meaning you have the same vacuum readings on each one), it will give you a slightly different compression reading for each cylinder when checked with the throttle at idle. You eliminate this when you check it at WOT. And, since all manuals I know say check it that way, you can then compare your results to what they publish.”<br /><br />Give each cylinder at least 5 compression hits. (count them) Try to give the same to each cylinder. <br /><br />Cylinders should read within 15% (I’ve also read this as 15 lbs.) of each other. <br /><br />“Acceptable” compression varies for each engine. The service manual may or may not give this spec. There are well-functioning engines with as low as mid-80s and as high as mid-150s, so it really depends. Many OMC engines had only 100psi from factory, so 85 – 90 might not be so bad. <br /><br />If all read low but equal, the engine is worn evenly – and only overall performance can tell you if it’s not acceptable compression.