Nothing wrong with going beyond you comfort zone, Thats how we learn. Besides its only a v8 engine, been making them for over 100 years and millions of them out there can't be to serious. Sounds like you were right valve train. Let us know what you find, I had similar sound 'not that loud' I pulled valve covers and saw nothing out of norm. friend of mine had strange sound coming from engine compartment and it ended up to be a alternater bolt that backed out and was hitting fins on alternator.

Well, that was a waste of time!! The dealership/shop ran it and told me its a rod knock...time for a new motor!! Did they unplug any sparkplug wires which of course would prove their theory? No. Oil pressure strong? 60 PSI! Did they remove the valve covers? No. Is the engine running with full power and smooth (especially above 4000 RPM)--Yes! How did they come up with rod knock? "Its their opinion based on how the motor sounds!!"

No one that has listened to this engine run has suggested a rod knock. So glad we have experts working in the marine industry.

Like I said--A total waste of time!
Im bringing it to another shop tomorrow (an experienced one).

Remove your oil filter and split it with a chisel. Look for non ferrous material in there. I just saw your Youtube video, I think it sounds a little bit like a rod.

Also I believe that the oil pressure is made in the mains more then the rods (anyone correct me if I'm wrong)

Well I won't say the dealership is a bunch of idiots because they have heard the engine in person, I have not.

Really you need someone more experienced to get going on this motor. You did the right thing by changing gaskets, they needed it anyways.

A rod knock will come from lower in the motor than a rocker arm or pushrod, and should be easy to tell the difference to an experienced mechanic. Simply running the engine with the valve covers off will quickly confirm or deny as to whether this is a valvetrain problem. Pulling the intake should not be necessary except to access the lifters.

Yes it is possible to have full power and good oil pressure with a bad rod bearing, but it would be pretty loud and not last much longer.

Also a total rebuild is not necessary if it IS a rod bearing, just the rod and main bearings could be replaced without a complete tear down IF the compression and leakdown numbers are good since the engine only has 50 hours on it.

Just judging from the video, the noise sounds too fast to be valvetrain related. The valvetrain operates at half crankshaft speed. Noise from rockers, lifters, etc. will be very slow at idle. I'd cut the filter open and look for debris. Rod bearing doesn't sound out of the question, or possibly a piston burned down the skirt. Again just judging by the sound and it's speed relative to engine speed... at least for as well as it can be heard in the video.

Hate to hijack, but i have a similiar ticking noise w/ my port engine. The sound isnt as solid or loud sounding as the vid. I was on trailer fender & couldnt hear it while buddy in boat could. Sounds like its coming from around the water pump pulley. I changed all the fluids, filters, impeller everything looked fine. I have Gil dry exhaust so should i start w/ the exhaust gasket too?

i bet hes got a cracked piston or sticking wrist pin...that knock is DEF NOT a lifter or pushrod,as 1 member said,remove plug wires 1 at a time to see if goes away....tryed a leak down yet?
thats how i found out i had a rocker off a exhaust valve!!
poppin thru carb,isolated it to the cyl in question

Well, I brought my boat into the only performance boat shop in Seattle...The owner and one of his mechanics spent over an hour in her and there is alot of head scratching.

So, Im going to ask the experts on Offshore Only: what could cause a tapping sound directly underneath the distributor (back of motor and dead center)? A bolt loose in the bell housing was crossed off the list because the tapping noise doesnt occur when turning the motor over--only when its running. Cracked flex plate? Oil pump driveshaft?
The shop owner swears it sounds like the tapping is metal hitting the underside of the intake (towards the back). Everyone seems to agree its NOT a rod because the sound is coming from the top of the motor--not the bottom and the sound is too "tappy" and not a knock which is much deeper in the motor.
He's going to have his engine builder stop by tomorrow and listen to it but I thought I would ask everyone here if they had any thoughts.
I still have NOT removed the starboard valve cover so there could be a broken spring or broken rocker there...

Thanks guys!

--Oh, we did unplug each sparkplug wire (one by one) and the tapping noise remained. Oil looks clean too--no signs of metal. Again, strong oil pressure and she runs well at speed.

Oh for crying out loud just pull the valve covers and intake and be done with it

Pull the distributor, possibly the roll pin has worked out of the distributor gear, also visually inspect the gear for cracked teeth. Manually spin the distributor and feel for a click. Use a priming tool and spin the oil pump while you listen for the noise. Finally rotate the engine and visually inspect the camshaft drive gear, maybe a tooth is cracked. Those are the only possibilities for noise in that area. Good luck.