I want to run this by you guys before I tear into the engine further...
My 73 140 HP Mercruiser is getting water in the #4 cylinder. I removed the riser and the gasket was sealing well, so no leaks there. The manifold had a puddle of water in the bottom of the exhaust passage (not from removing the riser) so I pulled the manifold to investigate. #4 exhaust port was rusty while all the others exhaust ports looked nice and sooty black. I hooked up the compressor to #4 cylinder and could hear/feel air escaping from the exhaust valve,,, and I "think" I hear hissing out of the water pump outlet. It was getting dark and I didn't have time to seal off all water ports to the engine, to see if the water jacket was pressurizing, tomorrow...
My question right now is, would #4 exhaust valve leaking cause reversion and water to be pulled back into the exhaust and then into the cylinder?
Background, the engine was completely rebuilt 3 years ago and has been running good, until the last couple of trips where it would start missing after idling for 20-30 minutes while trolling. At the end of the last trip it started missing (dropping a cylinder) every 5 minutes while trolling so I headed home.
I went through the carb today and found nothing, had it idling smoothly in the driveway for 20 minutes when it dropped a cylinder and started missing, bumped the RPM to 1500 RPM to clear it up and it started stumbling a couple minutes later. Pulled #4 plug and found water... :faint2:
I figure I need to block off the cooling system tomorrow, to see if the water jacket builds pressure while pressurizing #4 cylinder. Then remove the head to investigate if it's a blown head gasket, hosed valve, cracked block/head. (Even though I'm in the desert I've been draining the engine, so I doubt it's freeze damage.) Probably need to fill the manifold with acetone too, to see if it has a crack. Manifold and Riser replaced 5 years ago, freshwater boat.
My 73 140 HP Mercruiser is getting water in the #4 cylinder. I removed the riser and the gasket was sealing well, so no leaks there. The manifold had a puddle of water in the bottom of the exhaust passage (not from removing the riser) so I pulled the manifold to investigate. #4 exhaust port was rusty while all the others exhaust ports looked nice and sooty black. I hooked up the compressor to #4 cylinder and could hear/feel air escaping from the exhaust valve,,, and I "think" I hear hissing out of the water pump outlet. It was getting dark and I didn't have time to seal off all water ports to the engine, to see if the water jacket was pressurizing, tomorrow...
My question right now is, would #4 exhaust valve leaking cause reversion and water to be pulled back into the exhaust and then into the cylinder?
Background, the engine was completely rebuilt 3 years ago and has been running good, until the last couple of trips where it would start missing after idling for 20-30 minutes while trolling. At the end of the last trip it started missing (dropping a cylinder) every 5 minutes while trolling so I headed home.
I went through the carb today and found nothing, had it idling smoothly in the driveway for 20 minutes when it dropped a cylinder and started missing, bumped the RPM to 1500 RPM to clear it up and it started stumbling a couple minutes later. Pulled #4 plug and found water... :faint2:
I figure I need to block off the cooling system tomorrow, to see if the water jacket builds pressure while pressurizing #4 cylinder. Then remove the head to investigate if it's a blown head gasket, hosed valve, cracked block/head. (Even though I'm in the desert I've been draining the engine, so I doubt it's freeze damage.) Probably need to fill the manifold with acetone too, to see if it has a crack. Manifold and Riser replaced 5 years ago, freshwater boat.
Better than $300...