New Flapper rattle at idle?

[turand]

So, I just replaced my flapper, or depending on how you look at it, installed a new one after the prior one disintegrated.

Anyway, I've noticed a consistent rattle that seems to be coming from the exhaust pipe. I put my hand on the pipe where the flapper is and I can feel a vibration consistent with the rattle I hear.

Is this normal? I don't feel or hear anything once I get mildly above an idle RPM.

 

[wshekar]

Did you pull out all of the older flapper pieces? Is water coming out the back of boat?

 

[turand]

A very fair question. I am 95% positive I did remove the old flapper. I did a bellows job earlier and the season and I am pretty positive I remember discarding the most of old flapper. When I replaced the flapper (from the boat side), all was left was the suspension rod and the rubber ends.

To add some context, I am hearing this noise, on the muffs (not on the water). So there should be nothing washing back up the exhaust, right?

 

[wshekar]

I asked if you see water exiting the boat to determine if a flapper is blocking the water. A water blockage may back up the water in the exhaust. I would also think the water lessens how much noise the flappers make.

Did you replace both flappers? I still wonder if all the pieces were removed.

 

[turand]

Ah sorry, I missed that. Yes, there is water coming out, in the same amount & velocity before the swap. I only have a single exhaust, so my understanding I only have a single flapper.

 

[Scott06]

So, I just replaced my flapper, or depending on how you look at it, installed a new one after the prior one disintegrated.

Anyway, I've noticed a consistent rattle that seems to be coming from the exhaust pipe. I put my hand on the pipe where the flapper is and I can feel a vibration consistent with the rattle I hear.

Is this normal? I don't feel or hear anything once I get mildly above an idle RPM.

normal yes mine taps on one side, other side is silent…

 

[Searay205]

Sadly yes, they rattle and even the new ones will rattle after a short time. Exhaust gas is actually pulsation so the little flappers bounce up and down. Should turn into white noise for you after awhile where you don't even hear it or idle up.

 

[turand]

Thanks folks, I've put so much work into rehabbing this boat and engine, I think I'm being a bit too picky about all the noise the engine should naturally make, thanks.

 

[Eric 3.7LX Alpha 1]

You never mentioned what year and engine/drive you have...
In Service Manual #1 which covers 1963-73 it mentions your issue. It may be covered in newer manuals also... not sure. Here is the page from Manual 1

 

[turand]

Interesting! Mine is a 1986 Mercruiser 140 (181), Alpha One Gen I. When I checked my service manual, it makes no mention of any inspection or rattle noise like this, it just goes straight to a replacement procedure.