I have a 1988 357 with the silent thunder platform. Both engines are out for rebuild and I needed measurements to order new headers for my trs setup. I pulled the rubber hoses off the thru hulls and it looks like it may have had rubber flappers inside at one time, there's not much left after 21 years. Anyone have any knowledge of these and are they needed ?
Thanks

They should be stainless flap's,,,and i would put some on in because of reversion @ boatramp or backing up to the dock .................. just much safer.

The pieces that are left are riveted in and are rubber coated. Pieces are in the center of the thru hull pipes, flappers are gone. Just wondering if anyone knows exactly what was in there. Thanks

I know what was in there because I was just inspecting mine on my '92 last week. The pieces that you see are more than likely the hinge component that allows the flappers to, for lack of a better term, flap. The flappers that were there were also covered in rubber to keep them quiet. Not sure where yours went unless the rubber came off, which does happen, and the flappers rotted out.........I suppose that could happen?? Maybe there are pieces inside your Silent Thunder box? Are all 4 of your exhaust tubes showing the same? Sounds like maybe they were removed at some point....though not sure why....?

I would expect what ever still exists on yours will need to be removed and replaced with entirely new assemblies.

I think you can get the Flaps from Stainless Marine ....Bad news you might have to remove the box to replace the old flaps
What I would do is just ad the external rubber Flaps on the Cast fittings thru the transom .......m

http://stainlessmarine.com/myProducts.CFM?CFID=1370994&CFTOKEN=35fe85b5522b42 8-2B666823-E74E-38BD-7463B7656A3A5CF3&parentcategoryid=49%7CExhaust%20S uper%20Flaps%20%2D%204%20%26%205%20S%2FS%20Exhaust &productID=34&showDetail=1&categoryID=49|Exhaust%2 0Super%20Flaps%20%2D%204%20%26%205%20S%2FS%20Exhau st&vendoridtodisplay=0&filterFor=&collection=

All 4 look the same. These are installed from inside the engine compartment, not on the box side. These must have been center hinged, but with only a thin piece of metal with a little rubber left, it's hard to imagine what they looked like.
I doubt if this style is still available from Formula. The picture above looks like the way to go, but the box needs to come off. Never did it, how heavy is it ? Can you get the gasket for the box ? This stuff is getting old like me...mm

Yes, that is correct. I'm on the same page.

I would bet they are probably still available.

Check out Quicksilver part number 12674.

Thanks, but did you mean 12647 ? This is the water shutter, but not sure if it is the part I need, installs differently. Still searching...

I know what part you are talking about, our local marine supply had them in stock. They are a butterfly flapper that hinges on a rod in the center of the thru-hull stack. If I recall correctly they, are like 45 bucks a pair (twins, 90 bucks)