'86 Evinrude 70HP - Hole in piston w/ cylinder damage

[bshellrude]

Well... Just last Friday I thought I'd done my homework and found a mint 1986 Chaperral 16' w/ 70 HP Evinrude. Bought it immediately as Open bows seem to sell like they're going out of style.<br /><br />Long story short, took the boat out for the first time for 2 hours on the river, only to lose power while at WOT . Limped back to the dock and got it loaded back up. Upon checking compression (Which I know now should have been done in the first place), found 100 up top, 90 in middle and 25 on the bottom. Obvious problem right? Pulled off the head to find a hole on the outer edge of the piston (Apparently most probable cause from pre-ignition or detonation... from what I'm reading, PLEASE correct me if I'm wrong). Any how, in the process of pulling the power head, which for a first timer is interesting (Have background in auto but not marine).<br /><br />After all that, question is this... Cylinder in question has what appear to be ridges (as opposed to valeys) in the cylinder wall. Is it possible to correct this with a simple honing? It may be obvious to some of you that after having only 2 hours in my newly aquired boat, I'm wanting to get it back in the water as soon and safely (for the engine) as possible. Other option I looked in to was to get that cylinder re-sleeved w/ new piston and simply re-ring the other two.<br /><br />Looking for as much advice and/or comments as possible.<br /><br />Please help!

 

[voodoo]

Re: '86 Evinrude 70HP - Hole in piston w/ cylinder damage

Probably an overheat..is it on the exhaust side ..could be water leak too or bad cooling part.<br />The ridges are bits of aluminum piston, acid scrub will help remove them and if a hone is all that's needed (if you can feel the scratch it's too big) why not. Go oem piston to ensure the right fit if not boring.<br />If only 1 cylinder is smoked look for lean condition ,gummed carb, air leak etc..<br />If it's an 86 motor think about the VRO too.<br />I had an 86 70 vro...scrap metal now

 

[bshellrude]

Re: '86 Evinrude 70HP - Hole in piston w/ cylinder damage

Thanks for the info voodoo! Much appreciated.<br /><br />So, perhaps that's what the beeping (Sounded like sonar) comming from the console may have been? Overheating? Very strange, twice while out on the boat the console started making the sound described above, although it does not match with anything I've read as far as warning alarms. It started very slow, as if like sonar there was an object far away, then sped up to become very rapid, then slow down again. Very odd... Any how...<br /><br />If it was in fact overheating, would there not have been some sort of evidence of a problem? i.e. lack of good strong stream from p-hole? Evidence on the head gasket and around the head and cylinders of water leakage (deposits)?<br /><br />Not sure which side is the exhaust side. If when standing at the back of the engine facing forward it's port side, then yes, that's where the "chunk" blew off.<br /><br />However, like you say, only 1 cylinder is smoked... and thinking lean condition on that cylinder.<br /><br />As far as the VRO... heard some people say they disconnected the oil line and just mixed gas. Suffice to say, at this point I'd rather not leave anything to chance... <br /><br />Thanks in advance!<br />Ben

 

[voodoo]

Re: '86 Evinrude 70HP - Hole in piston w/ cylinder damage

that is the exhaust side, <br />I would change the water pump too.<br />You say new to you, I would rebuild/clean the carbs while you have them off You will need to mix your gas after new rings why not remove the vro and keep mixing.