Rebuilding this outboard because it had compression of 30 on # 3. All the rest of the cylinders tested good. Found a piston on the net p/n 742-34125a and decided to tear it down and rebuild. After cleaning all the pistons I noticed number 1 & 2 were defective as well, grooves, stuck rings, busted grooves. Very apparent that there were detonation problems. Tried to find 2 more but they want $200 a piece for them and I only paid $106 for a brand new one on ebay. I remember getting a powerhead for $1000 years ago so hard to rationalize.
It makes me wonder if pistons from the 1969 125 mercs or 1970 115 mercs would work. the 1968 piston was the only year they made it, which tells me there were likely problems with them, why else would Merc reengineer a piston for the sake of 1 yr. They went from a convex high rise to a concave high rise, and they used the new design for years. I can't believe they reengineered the block as well and I believe the 115 block is identical. Also of note is they changed the timing from 34 btdc to 23 btdc between the 1968/69 125 and the 1970 115 merc which is is a 30% adjustment, very significant, makes me wonder if this was because of detonation problems on the 125. I have read in forums that on the 115 merc there was even recommendations to go to 20 btdc because of the changes in gas octane.
I would appreciate any advice on this topic, I'm loathe to quit now.
It makes me wonder if pistons from the 1969 125 mercs or 1970 115 mercs would work. the 1968 piston was the only year they made it, which tells me there were likely problems with them, why else would Merc reengineer a piston for the sake of 1 yr. They went from a convex high rise to a concave high rise, and they used the new design for years. I can't believe they reengineered the block as well and I believe the 115 block is identical. Also of note is they changed the timing from 34 btdc to 23 btdc between the 1968/69 125 and the 1970 115 merc which is is a 30% adjustment, very significant, makes me wonder if this was because of detonation problems on the 125. I have read in forums that on the 115 merc there was even recommendations to go to 20 btdc because of the changes in gas octane.
I would appreciate any advice on this topic, I'm loathe to quit now.