Re: one more compress check question?
A while back I bought a used 2 cylinder 40 horse for my kid to put on his river boat. It ran fine but never had much power. We checked the compression of both cylinders (warm) getting 75 in the top and 80 in the bottom. We thought this was acceptable since, although they seemed low, they were close to each other as Capt Ken said.<br /><br />So then we did a wet compression check by squirting some 2-stroke oil into the cylinders. Compression came up 10-15 lbs in each. But it still seemed low and indicated possible worn rings/cylinder. <br /><br />Do to the lack of power we eventually tore the engine down. To our surprise both pistons had broken rings and worn ring grooves. Apparently the outboard had sat long enough to rust the rings to the cylinder wall and on first start up they broke. The outboard ran amazingly well and for a long period like this.<br /><br />After rebuild and a little break-in we got 120 and 121. <br /><br />Moral of the story is that low compression readings, however so close together they are, can mean problems. Find out what the compression for your particular outboard should be. If your test seems low, do a wet check. If that check causes the compression to come up significantly, you may have ring trouble. If it doesn't change the low readings, you may have head gasket trouble.<br /><br />Most compression gauges are usually calibrated using the same standards within +- a few psi. Most reputable shops have their tools and gauges calibrated frequently. To find a 20 psi difference between gauges means something is defective with a gauge. Besides a small calibration difference, the other factors that can make a difference in the gauge readings are atmospheric pressures, temps, humidity, altitude changes, and cylinder temps.<br /><br />Hope this helps tgodiver. Your numbers don't look too bad. A warm wet check might tell you more.
