I have been lurking for awhile, but decided to join to share this story that recently happened.

I recently purchased a junk boat for its running motor to swap into my boat to get me back on the water. (I will be parting it out shortly)

The motor runs like a bat out of hell.....GPS said it got my pig up to 70mph!!! 

Dont know much about the motor...its a 2 block main, but has 990's, crane golds and a decent comp cams cam. I was please to see this was a built motor, not just something taken out of a truck.

Anyways I took this thing out on the river this past sunday.....drove it up the river and floated back down then made a few passes. on the 3rd of 4th pass, the oil pressure dropped and it started to knock.

i shut her down quickly and lifted the engine cover....oil everywhere....bilge pump is pumping milkshake into the river like a BP well.

I float down the river back to the ramp, put it back on the trailer, take it back home and put a cover over it and call it a day. defeated and broken.

Monday I started to get it ready to be pulled out of the boat to see what happened. I pulled off the passenger side exhaust log and there it was....a 1" hole where the drain plug was supposed to be. somehow it walked its way out and emptied the pan into the bilge. This pan is a 10 qt doolly pan with a 1" drain plug on the front and a drain hose on the back. I used the drain hose to change the oil during the motor swap. never checked this plug......so again, i stopped what i was doing, put the cover back on it and called it a day. I figured it was bad. it had to have been.

so last night I got back to it and pulled the motor out....got it flipped over and started pulling rod caps and mains. the crank is in excellent shape. not a sign of anything bad. the bearings are a little burnt but overall dont look to bad.

I got a new set of bearings on order and all the gaskets n crap. might as well replace the timing set while im at it too.

so call it what you want, but I think my boat is cursed for something so odd ball to happen, and I got dumb luck to come out of this with no major damage.

 

I think you're lucky that you caught it before you did too much damage, hopefully some new bearings and you'll be golden.
BTW, welcome to the fray....

I have a similar story. Thought it was a rod bearing, it happend to be a push rod tip worn down and the the exhuast vavle wouldnt open so it was just back fireing but sounding like a knock. have the motor torn down rite now and am replacing the damage parts, (3) and doing all new bearings and a hone job to be safe. I got real lucky too. best thing you did was shut it down and float back. I had to float 2-1/2 hours when mine broke and the wife was going nutz cause it was dark, ( she worries about the river sharks, piranas, snakes, eals, coyotes, rats and croks lol) f-n wemon. saved me thousandas in parts and may have sunk the boat if I didnt shut her down when I did. if you didnt it would have been big $ to rebuild.

always shut your boat down if you hear or suspect anything off. check what you can reach while on the water and do a full inspection when on the trailer.

I would go through the valve train to see if something is damaged. Check the lifters, rockers, push rods, valves & springs and cam. If you heard knocking then most likly something failed. DO NOT OVER LOOK THAT. find the reason for the knocking you heard, you dont want to have to pull the motor soon as you drop it back in. not having oil can destroy or mildly hurt every part in the motor in minutes. Pictures for us too please. the more the marrier. and one of the genius's on her may be able to tell witch part you need to replace. Are they roller lifters? or what kind? check for a flat or worn cam lobe. use a micrometer if you can.

 One thing I do Is check the oil before every ride and befor iI leave for every trip. I cange the oil as soon as its not golden brown anymore, like every 10 20 running hours. I'm anal about that.

Welcome to the site and sounds like a nice boat. looking forward to see if anything broke or got warn so others can know what to look for if/when it happens, lol me or them.

Post pictures of it while you tear it down, helps for reasembly and us forum junkies love pictures. If its not to late, see if you have any loose rockers b4 you remove them, that could explain the knock. I have a weird feeling you have a flat cam lobe. thsoe lifters are not the best (no offense). I would up grade to a sloind roller lifter & camset up if you have to replace those. Inspect the shit out of the rockers, lifters, and cam.

After years on the race circuit I have found on oil lines even with push lock fittings will come off. Now some will say BS however have seen it and had it happen to me. So I add clamps to the lines and safety wire all fittings. Same goes with water fitting they also fly off. I check mine every time I go out to be sure, engines are too expensive to replace. Call it preventive maintenance, just my .02 cents.