78psi Compression Good?

[beerman57]

The 1962 OMC 10hp I rebuilt, 78 doesn’t sound like much to me, but it idles good and got 23mph on my 13′ FC Skipper.

[1946zephyr]

I say it runs good. As long as the numbers are even, then you’re good. Some compression guages read lower than others.

[aquasonic]

How long has it been since the rebuild?

[fisherman6]

I just recently picked up a ’61 10hp amd it’s just under 80 on both cylinders. Even more recently picked up a ’59 Sportwin and it’s about 78 on top and 80 on bottom. Seems about normal judging by my very limited selection. I hope I can get 20+ out of either or both of them in any of my 14 footers. Heck the 9.5hp that came out after the 10s were even lower compression. Lucky to find one of those in the 70s at all. Most seem to run mid to high 60s for compression.
-Ben

OldJohnnyRude on YouTube

[beerman57]

I just finished the break-in yesterday. I have 2 compression testers and whenever I compared them, they read the same. The one I used today is the screw in type with the schrader (sic?) valve just below the gauge, the other one is a Snap-on with the rubber cone that you hold firmly in the plug hole.

[fleetwin]

Seems about normal for the 10hps….Funny how they seem like they have a lot more compression when you are yanking on that recoil rope!

[1946zephyr]

Yea, the last 10hp I tested was around 80psi, so I think you’re good.

[Author]

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