Broke the motor, what do you think?

[BigBassin78]

Here's the scenario. I just bought an 18' F/S with a 88 Johnson GT 150 VRO that has been bypassed. When I bought it, the compression on all cylinders was around 85, normal for this age and condition of motor. Took boat out for first time, cranked right up, ran like a top both at partial and full throttle, GPS with a 20 pitch 4 blade stainless prop was 55 mph, everything seemed right on. That trip put about 15 minutes on the motor, maybe a little more.

Have the boat out a second time, same thing, everything went well, running well no problems, about another 15-20 minutes on the motor, mostly at partial throttle.

Boat out for third time, about 20 minutes of partial throttle and then about 2 minutes of full throttle and PERCLUNK!! chokes and dies. Water poring out of carbs, stumbling idle, then freezes up.

I have pulled the motor and taken it apart. Middle cylinder, starboard side, ate its con rod bearing, added a new port on the intake side of the block, cracked the cylinder sleeve(hence water poring out of carbs), chewed up the cylinder head and pretty destroyed this block beyond any hope.

I have not taken the lower unit water pump out to check the impeller, I may find my answer there, but betting that wont be it. Tell tail stream was flowing well. And there was copious amounts of water poring out of the bottom carbs when I restarted the motor trying to get a little closer to the dock.

Question! what in Sam hill could have caused this? over heat? I know fuel mix was okay, had Seafoam in it too.

 

[emdsapmgr]

An unusual failure mode for sure. You won't know just what happened till you pull the engine apart. 1.Look for during your inspection: check out the crank journals. Look for pitting that may have occured some time ago, due to the engine having water residue on the journals. Once an engine winters with water on the crank, it will pit and can lead to failures like you experienced. I've seen this on VRO engines, where the tank ingested some water and was run that way-then put away for the winter. Would have been on the prior owner's watch-when he had the VRO hooked up. 2. Another thing to look for would be signs that the engine suffered a high rpm hydraulic lock. That could have occurred if a head gasket was leaking excess water into a cyl. That could also lead to catastrophic failure. 3. An extreme overheat can expand a single piston so much that it will actually lock up inside the cylinder. Another type of high rpm hydraulic lockup. If any of the rubber diverters are misplaced in the block, you can overheat one piston, even if the impeller and thermostats are functional. My one experience with this failure was that the lockup did not result in a broken rod and blown powerhead. The locked up piston did result in cracked port bridges and a scrap block.

 

[Faztbullet]

I myself have seen several good engines blow up running seafoam,,,,,

 

[thdrduck]

2 strokes can be like that. Running fine one minute and end up with a piston up your butt the next. 4 strokes run a pressurized oil system and have many more moving parts that all wear and make noise and usually give a warning before they shell out. You probably could not have prevented it, sounds like it was just it's time to go from what you said. Sorry for your loss.