Merc 470 engine noise in cabin

[lselmes]

I own a 1981 Glasply 2100 HT with same year Merc 470. The motor runs great and is very quiet when standing outside next to the dog house but when I get in under the hardtop in the covered area and sit at the helm its really loud. It seems that maybe the sound is somehow coming through the floor? or could there be something else going on? The dog house has typical sound/heat insulation. There is a 50 gallon aluminum fuel tank that sits under the floor in the usual spot as well. I've added some pics of my boat as well. Any input would be really appreciated.

Thanks!

 

[Eric 3.7LX Alpha 1]

Re: Merc 470 engine noise in cabin

Your gonna have to help us out a little more on this one...
Take a video of it happening.
Does it happen at idle, under way, during a turn to port.starbord, at WOT?

Rattle, squeal?
Noise can mean like ten thousand things..

 

[stonyloam]

Re: Merc 470 engine noise in cabin

Sound like exhaust noise? is it something new?

 

[lselmes]

Re: Merc 470 engine noise in cabin

Sorry for being so vague! Yeah its a hard one to describe. Its basically an engine noise that's loud only in the covered area and super quiet when you stand back out in the open area. I can also tell you its loud at idle and under way in the water or in the driveway on the muffs. The leg is completely rebuilt and there is a new gimbal bearing as well. Port or starboard doesn't make a difference in noise levels. No rattles or squeals, just kinda like what it would sound if you were to sit beside the motor with the dog house open. I will try and post a quick video clip in the next day or so when the weather clears up here in the Pacific North West.

 

[lselmes]

Re: Merc 470 engine noise in cabin

Not new. Exhaust / engine noise combined.

 

[stonyloam]

Re: Merc 470 engine noise in cabin

OK just a guess, could be you have a rusted out casting plug in the head behind #4, it will dump exhaust directly from the head and be pretty loud. With the engine running put your hand behind the head and see If you can feel the exhaust blowing out. #3 here http://www.mercruiserparts.com/Show...062&bnbr=9&bdesc=Cylinder+Head+&+Rocker+Cover

 

[lselmes]

Re: Merc 470 engine noise in cabin

Thanks for the input "stonyloam" I will definitely check that out. I was just out looking at my dog house and transom cover arrangement and noticed something I completely overlooked. The dog house seals nice and tight against the cover but I see that on each side of the cover port and starboard there is a gap that is usually filled with a separate piece of trim and I have none. So now I'm thinking maybe the engine sound is travelling through these two openings and being amplified into my covered area. I see there is also a small gap at the front/bottom of my dog house that could also allow some noise to escape and resonate in my cab. In the following image you can see the small gap at bottom of dog house and if you look carefully you can see the gaps narrow openings on the transom flap/cover....



Uploaded with ImageShack.us

 

[lselmes]

Re: Merc 470 engine noise in cabin

A little too dark to see so here's the area in question......

 

[lselmes]

Re: Merc 470 engine noise in cabin

Jeez now that I'm seeing all these possible noise escapement area's it just occurred to me that the storage area on port and starboard is open to the transom compartment area. Would this normally be sealed as well? Hope these pics help......

 

[lselmes]

Re: Merc 470 engine noise in cabin

OK so now the big question is how much can I seal off the engine compartment area without fear of overheating or am I safe with my FWC system? The only venting is the 2 louvred vents and one of them is hooked up with a 4" hose and blower.

 

[stonyloam]

Re: Merc 470 engine noise in cabin

Your engine will not overheat, but it might get pretty hot in there, and there might be a chance of vapor lock problems, so it is always wise to run the blower if you are going slow.