Noise in exhaust possible flapper

[4bait]

Exhaust Flapper noise??

I have fitted a Buick 3.8 fuel injected engine to my boat see post http://forums.iboats.com/showthread.php?t=369819

Anyway there is a strange noise coming from the rear, which I believe is the exhaust flapper, it sounds like a cross between engine pinging and a faulty bearing. It is there at all different rev ranges and gets worse as the engine warms to full operating temp. Using a stethoscope it is definitely inside the exhaust Y pipe.

I have removed the flapper valve from one side just to hear the difference and it is much better so that must be the cause. Putting it back in made the noise worse again.

What I would like to know is exhaust flapper noise normal? They do appear fairly loose inside the exhaust tube.
This engine conversion is extremly quite compaired to most other inboards so the noise is easily heard.

Cheers Andy

 

[stonyloam]

Re: Noise in exhaust possible flapper

Awesome job! Did you reuse the old shutters (flappers)? They are supposed to be rubber coated metal, if the rubber has disintegrated and fallen off due to heat and age the metal could be exposed and banging against the pipe.

 

[4bait]

Re: Noise in exhaust possible flapper

Hi stonyloam thanks for your reply,

yep they the old flappers but they appear to be in good nick, and all the rubbers are still nice and soft, but the flappers are very loose when fitted inside the Y pipe.
Is there ment to be a rubber coating where the pin goes through the flap as the pins are very loose?
The starboard side seems a lot noisier than the port side.

Cheers Andy

 

[NHGuy]

Re: Noise in exhaust possible flapper

The flappers normally have some silicon rubber bushings in the exhaust tube on which the metal pivot shaft rides. If you get new flappers they are a completely different design. I did some this year, recommend you take that approach.

 

[stonyloam]

Re: Noise in exhaust possible flapper

There should be a couple of little rubber grommets that hold the hing pin in place. The new ones are rectangular, but your Y pipe photo looks like they are round like #6 here: http://www.mercruiserparts.com/Show...1.png&inbr=1599&bnbr=200&bdesc=EXHAUST+SYSTEM Doesn't look like they sell them separately, I would be tempted to use a little JB Weld and epoxy them in place . The photo (click on part#) does show a completely different design.