I have a rebuilt Merc 454 that makes a tapping noise above about 1600 rpms when in the water. Out of the water (on muffs) the sound is not quite as loud, but the sound is stilll there. With the outdrive off I can't seem to hear anything like the tapping up to at least 3000 rpm, and the motor runs a bit smoother. My question is does this sound like a possible valvetrain issue, a bottom end issue, or a coupler/flywheel/whatever issue? I'm leaning towards coupler since it only happens when the outdrive is on, but think it could also be something else that doesn't appear until the engine is under load. I would LOVE to not have to pull my engine, but...
Even though it's a new reman motor I think there a chance it could still be internal. At one point during the winter my boat cover failed and allowed water to drip into the carb and fill the oil pan. Luckily there was oil in the pan and nothing rusted, but the water may have been in there during a 3 day snow spell we had. Dropping the oil pan and pulling the heads didn't reveal any visible damage. This makes me wonder if something did happen in the bottom end. Later, when I attemped to start the motor for the first time, it backfired a couple times and blew out an exhaust gasket. Turned out that I had the distributor 180 degrees out. This makes me wonder if the backfires bent a pushrod or messed something up in the valve train. Who knows. Any ideas?
Even though it's a new reman motor I think there a chance it could still be internal. At one point during the winter my boat cover failed and allowed water to drip into the carb and fill the oil pan. Luckily there was oil in the pan and nothing rusted, but the water may have been in there during a 3 day snow spell we had. Dropping the oil pan and pulling the heads didn't reveal any visible damage. This makes me wonder if something did happen in the bottom end. Later, when I attemped to start the motor for the first time, it backfired a couple times and blew out an exhaust gasket. Turned out that I had the distributor 180 degrees out. This makes me wonder if the backfires bent a pushrod or messed something up in the valve train. Who knows. Any ideas?
