Broken Piston

[Eric Eberlin]

I've been working on this old 1966 80 horse evinrude trying to get all cylinders working and after posting a couple of questions finally pulled the head to find the #4 piston has a piece missing on the exaust side edge. About 1\16 x 1 inch. It amazes me that I had 85 lbs. of compression. Whats the cause ( sticking rings ?) and does anyone know if I can get to the rod bearings without totaly disassembling it? Thanks

 

[bshellrude]

Re: Broken Piston

Eric, I would imagine that the setup is the same as mine (i.e. late 80's 70 Horse). I just did a complete rebuild, exact same problem (i.e. Blown piston on exhaust side). Indication that I've gotten from a number of people is that it could be:<br />A) Lean Mixture due to gummed up carb<br />B) Incorrect Timming at WOT<br />C) Air Leaks in the intake/carb/fuel system<br /><br />Good Luck...<br />Ben

 

[bshellrude]

Re: Broken Piston

Oh, and my experience was that a complete tear down was both necessary (in order to get proper torque on the crankcase halves, as well as intake) and recommended as you generally should do what you can to ensure that the same condition no longer exists when running after the rebuild.<br /><br />How badly is the cylinder scored?

 

[Eric Eberlin]

Re: Broken Piston

The cylinder is scored but I wouldn't say its severe. Thanks for the input!

 

[bshellrude]

Re: Broken Piston

I would imagine you might get away with a simple hone. Depends how deep the scoring is. My case was pretty horrible... gouges were so deep that the cylinder had to be bored 0.030.