Re: V4 rebuild 84 crossflow 100hp Photos of old parts
The wrist pins show some sign of heat distress, with the bluish color on them. The sides of the pistons are scuffed and a couple of the top rings have let go. A combination of too much heat and not enough lubrication. A couple of things to look for regarding the failure: 1. Check the rubber water diverters by each cylinder in the block. It's hard to see that area from the pictures you posted. If crud/debris builds up in that area, it will restrict water flow and can overheat one cylinder-even though the powerhead overheat horn did not go off. I'd check the wrist pin area of each rod for any similar heat blue color, like on the wrist pins. 2. There is some slight coking around the rinsets. That carbon buildup will prevent the cooling incoming fuel/oil charge from reaching to top ring from the back (intake side of the crankcase) side and the top ring will run hot and eventually break in half then disintegrate and blow through the combustion chamber then out the prop. It's good to run a can of Bombardier Engine Tuner through a crossflow engine every 100 hours, or annually-to reduce the carbon buildup on the pistons. 3. I'd pull apart your carbs, esp those that feed the two bad cyls. Pull out the jets, esp the high speed ones. Check for debris or restrictions, like dried fuel or small bits of black disintegrated fuel hose. If a cyl runs lean due to insufficient fuel flow/delivery, it will overheat and trash a ring. Is this a commercial model? I see you are running the QL16V plugs, normally found in the commercial engines. The recreational engines normally use the L77JC4.
