43 omc knocking under acceleration but idles and sounds amazing

"4.3 had been sunk and engine

"4.3 had been sunk and engine filled with water. three oil changes, new plugs, ran awsome. 2hr cruise and tapping started,after a short run up to 4200rpms, limped to shore,set valves/rockers? Idles and sounds great again.Now there is a loud knocking from bottom of motor.We removed the outdrive to take it out of the equation and tightened loose (very loose) motor mounts. awful noise only when reving it up. should I start looking for another short block and does it have to be "marine"? top end compression is all six @ 160lbs. Am I sunk again or could it be something else...help please!"

Any drop in oil pressure since

Any drop in oil pressure since the knocking started??? Try running the engine at the RPM that causes knocking and then disconnecting and reconnecting one spark wire at a time to isolate the noise to a particular cylinder. If the noise stops when a particular cylinder isn't firing you have have found the bad cylinder. My first guess would be a rod bearing....especially if there is a drop in oil pressure.

"Steve, unfortunately i have t

"Steve, unfortunately i have to agree with Bob.You did not say how long the engine had been under water but what probably happened is that the water and oil mix became very viscous and and even though you made oil changes the flow of oil to the main and rod bearings was restricted and caused a rod bearing to overheat and spin on the rod itself destroying it. Might have been a good idea to have pulled engine and dropped oil pan and pull distributor and flushed and primed the entire system before running"

"thanks guys... but that is wh

"thanks guys... but that is what seems so strange.we didnt have the bottom knock until we set the valves, which was definatly the noise I heard when I had to limp her to shore. still has excellent top end, good oil pressure, same as before our little trip. no noise at idle and sounds awsome... could we have over tightened a valve? or knocked off a wire or could something else create a knocking noise under revs."

"is it possible that we did so

"is it possible that we did something when setting the valves. thats the only reason why I shut the baot down that day. Ran excellent for an hour and a half at about 2700 rpms, then 1min at 4200 and I smelled what I thought was burning gear oil and backed it off to an idle. found out that the guys had left the power steering cap loose and my fluid leaked out. thats when I heard the top end knocking. seemed strange and jumpy going in and out of gear when pulling her to shore. but never had this bottom knock till my buddy set the valves. Could he have over tightened and caused this knock? thanks"

"There's a real easy to se

"There's a real easy to see if you have an internal failure before pulling the motor.
Buy a proper filter cutter like this.

http://www.krcracing.com/images/Oil%20filter%20cutter%20KRC-1201.jpg"

Cut the filter open and look in the pleats. If a rod bearing is going, there will be iron in the filter - a magnet will help you see how much.

I cut 100% of all filters I ever remove from any tractor, boat, car.
Partly because I like to recycle the metal parts, but it's a free look inside the engine."

"Steve, when the valves were s

"Steve, when the valves were set, was it done while the motor was running or done the dry method. if running when done you only need to adjust the valve your doing just until the tapping stops and then go 1/4 turn more. The book calls for 1 complete turn, but thats to tight for me 1/4 turn works fine.If its a lower end knock still sounds like a bearing failure. The only other thing that could make a knocking sound is if a flex plate was broken, not sure if marine engines have an actual flywheel or a flex plate bolted to the crank for the coupler, if flex plate check it out."

"boats use a solid flywheel, a

"boats use a solid flywheel, and by removing the drive, I think any coupler issues were pretty much eliminated unfortunately.

I agree the valve set methods are goofy. I always set mine with a compression gauge.
I crank the motor, tighten the rocker nut until compression falls off, then back it off until rocker starts to rattle, then split the difference.
It's foolproof.

Having the valves misadjusted on a car is no big deal and all of those methods in the manuals are for cars.
On a boat, improper valve setting can destroy an engine rather quickly which is why I like to watch compression.
"