Small Outboard Cylinder Compression Test

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This video shows you how to perform a cylinder compression test on a 6 hp Johnson Evinrude OMC Outboard Boat Motor

If you have a different understanding of what typical compression ranges should be please leave a video comment. I specifically didn’t mention an acceptable range is for cylinder compression in the video in case I was wrong and someone corrected me (with an explanation).

From my research, cylinder compression values that people say are “acceptable” for these low horsepower outboards seem to vary. They not only vary from the reporting individual but from manufacturer to manufacturer. For instance, a fully functional Mercury 25 Hp cylinder compression value may be significantly different than that of a Johnson 25 Hp. Its also rather hard to find where a manufacturer will say the compression range should be from XX psi to XX psi. What I have found unanimously is that the relative compression values between the cylinders should be within 10 psi.

This source says modern two-stroke outboards should be in the 90 to 105 psi range.

https://www.boatus.com/magazine/2016/...

However if you watch the end my video you will see that my 1979 Evinrude 6 Hp cranks easily cold ( 2 pulls) with 60 psi compression

This source says the older two stroke outboards below 25 Hp should be between 75 and 85 psi.

http://www.pochefamily.org/outboard/C...

This source below seems to confirm with my understanding that 60 psi in older outboards can sometimes be OK.

http://aomci.org/forum/viewtopic.php?...

Bottom line, if I was buying an older outboard I would probably want to see compression values above 75 psi ESPECIALLY if I couldn’t see it run.

Let me know what you guys and gals think in the comment section.

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