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:grinser010:

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.

I was getting there!! I pulled one valve cover but then with everyones suggestions to replace the exhaust gaskets I went in that direction instead...Then of course I took it to a shop. BOTH valve covers are coming off tomorrow if the shop cant determine the problem..
Of course none of this makes sense based on where the tapping noise is coming from--directly underneath the distributor!

THANK YOU!! Those are the suggestions I was looking for!

--We did pull the cap and the rotor--the rotor was broken and the cap appeared to have been scored/worn away by the rotor. If the gear has cracked teeth I wonder if it could cause the rotor and cap damage we witnessed.

What kind of problem does pulling the plug wire's one at a time isolate with these symptoms?

You can isolate the problem if it is on a certain cylinder. The noise will be less pronounced. I have had rocker studs break. Before pulling both valve covers I would pull wires to tell me what cylinder had the problem. It would back fire through the carb when the chamber ignited. Same thing if it was a rod or something with and a specific cylinder.

It will probably rule out more things then solving his problems.

The damage in the distributor is something you need to figure out. I would look very carefully at all components, pull the shaft from the distributor, inspect the lower and upper bushings in the distributor, shaft, everything. Also check the teeth of the drive gear on the cam. Something caused the damage to the rotor, that is very uncommon.

That is exactly why we did it

Ok, well my shop brought in their engine builder and after more testing including taking the oil filter apart (no issues, the oil filter didnt have any metal shavings in it) its been determined that the tapping noise is definitely coming from inside the bell housing and is most likely loose flywheel bolts. Im pulling the engine on Monday and will have a look....Its amazing to me how many things make the same sound inside an engine bay and how many hours and tests it can take to determine what is really going on.

Metal can be a great conductor of sound. Buddy of mine heard what he thought was a lifter tapping/ticking. When he got into it, it turned out to be a con rod bearing that was hammered flat by detonation and had mashed out like a penny on the railroad tracks. The tick was the bearing hitting the main journal. :eek:

Well, we pulled the motor, unbolted the bellhousing and....all the bolts were tight! We did notice that the motor mounts were loose and that one of the spring washers was sitting in the bilge...
Upon reinstalling the motor (and properly aligning the drive) the tapping noise seems to have disappeared. I havent taken the boat out and run it yet (thats happens tomorrow) so we will see how she does after a full shakedown run.

i had a similar noise issue it was my lower inspection plate on the bellhousing. got it out with out pulling the motor but was not easy.

I had a mystery ticking in Valve train.Cost me an engine rebuild. Mercury had defective valve springs early 500 H.P. The inner spring broke and sounded like a sticky lifter. Finally dropped a valve . $6,000 dollars later. Good Luck.

I'm glad the noise is gone,(maybe) but doesn't it suck after all that there is no definitive answer as to what the problem was? :angry-smiley-038: I swear, boats and women.:rolleyes:

There is a saying 'if it has tits or tires it's going to give you problems'....that needs to be expanded to tits, tires or props!:eek:

Tits, tires & tabs!!! :lolhit:

Took her out today and she ran flawlessly!! Thank god!!

Correction...she is running flawlessly BUT the tapping noise is still there. I am down slightly on power from last summer (4900 rpm vs 5100 rpm at wot) and hitting 60 mph vs 63 but otherwise it sounds and runs awesome.
I am scratching my head as to what to do at this point. Do I continue to run her? No one can seem to figure out what this tapping noise is...

Did you ever find out why the distributor had the damage?

No, according to Eastside Offshore (my shop) they said the tapping noise is clearly not coming from the distributor. I never found out why the rotor was damaged.

you need to find a qualified repair shop...
its hard for anybody to tell you whats wrong with your engine without inspecting it..

Find a repair shop that knows what they are doing...:drink:

The boat spent 2 weeks at Eastside Offshore with the owner, 2 mechanics, their engine builder and even had the factory mercruiser rep look at it. They are the performance boat experts in the Seattle area.
I also brought the boat down to a friends house and he had a good friend of his look at it who owns his own boat shop and is a 25 year certified mercruiser mechanic. Everyone said the tapping noise was coming from the bellhousing which is why we pulled the motor and the bellhousing only to find nothing wrong.

So this is not a situation where I havent had the boat to the shop.

you just have not had it at the right shop..

sorry but a good engine tech would have figured it out by now..

Heard this one at the marina last week..."If it Flys, Floats or Phuks...you're better off renting it":evilb:

Did they pull the distributor and look at it? Maybe the drive gear lost part of a tooth? Or the cam lost part of a tooth?

Mine's making noise too so I'm interested to hear what ever happened with your engine.
It really sucks that it only has 50 hours on it and you're dealing with this problem!
Please post what the problem was once you get it figured out.

OK, it sounds like an epidemic, my starboard engine has the same sound. Sounds like it is coming from the center of the engine or the starboard valve cover. I listened with a stethoscope and could not identify a location. I started to remove the valve cover tonight but with Stainless Marine Exhaust either the exhaust manifold or upper intake have to come off :bsflag:. Does not sound like an exh gasket leak, more of a metallic contact. My engines have recently been under some severe abuse due to low fuel pressure and disconnected knock sensors. The number 3 cylinder actually melted the center out of the spark plug and shot the porcelain out of the hex... oops. Slighly lower compression on cyl 3 but the others are OK (125 vs 150). My engines are 502 MPIs with 500 EFI cams, larger intake and exh valves, crane roller rockers and the boat has stellings boxes on it. Any thoughts on the source of this sound would be appreciated... As I was typing this I had a thought - PB per your posts it sounds like the ticking went away for a short time and returned, did you reinspect the distributor (cap and rotor) after the sound returned?

THATS FUNNY $HIT!!!!!

Any progress on resolving the ticking?

I had ticking in one of my engines (502) and it would come and go.Finally it would pop through the exhaust on start up but run fine just little loss of power.Long story short..I dropped an exhaust seat and it (pieces ) bounced around into all cylinders though the intake and trashed all the pistons.New rebuild was needed.So if you hear a noise ...it means something is making that noise.In my case pistons hitting nice hard pieces of a exhaust seat...

Cheap gaskets!!!

Sorry to tell you but the gaskets you are using are awful.
There is nothing worse than an exhaust gasket and riser gasket that is (simply) punched out of cheap paper gasket material.

You will need a stainless steel sandwich style gasket.

A stainless steel core, sandwiched between graphite gasket material. The stainless steel core keeps the gasket ridged, preventing blow out under high pressure, and the graphite seals the stainless core to both gasket surfaces.

Dennis Moore
Moore Performance

I checked all rocker adjustments and all was good (except for a small interference I found between one roller rocker and the stock valve cover). After clearencing the rocker arm the sound was still there so I decided to be ambitious and pull the engine. Once out of the boat with all spark plugs easily accessible I decided to build a leak down tester and check ALL cylinders before disassembly (I had early done a compression check but only on the right bank. The numbers came in between 3% and 86% leakage. The 86% was the number 6 cylinder which was in the area of the ticking sound... Hmmmm could be related. Upon disassembly I found the source of the sound, a part of the top compression ring which had broken free after the piston melted was wedged into the top of the piston and was making that elusive tapping sound as it contacted the head at the top of each stroke. Should be an easy fix, just chisel the ring part out of the piston and reassemble the engine. I should be boating by Labor Day. Oh, does anyone have an easy trick for removing melted piston from the cylinder wall?