I have a 70hp 3cyl. Evinrude. I had 120, 120 and then 90 on cyl. 3. I went into rebuild. Broke ring on cyl. 3. honed all cylinders, replaced rings on all pistons, all new gaskets and seals. Turned over, same compression readings. Well, ****. I bought a 70hp Johnson close to the same yer for like 100 bucks. I needed some parts off of it anyway. I tested its compression and the readings were the same. Now, today i opened it back up, and swapped my cyl 3 piston with cyl 2. Re tested compression. now cyl. 2 and 3 are low. So im thinkin ok cyl. 3 piston is bad. but still dosent explain why a good piston wouldnt have compression in cyl. 3. So i measured cyl size, and for taper and out of round. all 3 cylinders check the same. not exactly the "3 inch" cylinder but its 1975. So im wondering why on both of these engines that cyl 3 dosnet hold compression? am i missing somthing? is this a common problem? I need help badly. I just finished this boat , new paint, interior trailer lined, tires, i wanna get it running now.
