Anyone know what these are or if they are necessary. Pictures were take from outside the boat while holding up the external rubber flapper on through hull exhaust . Looks like some sort of internal flapper that has burned away or been removed. My 496 is apart now due to low compression due to stuck valves. think this has anything to do with it?


Chris

that sure looks like it was an internal rubber flap, though if you also have external flaps i wouldn't think this is the reason for the problems

That would be what's left of your internal rubber flappers.

So are they needed or not?

Chris

only if you do not have external flappers, running both is ok but not necessary

They are for the Mercruiser warranty.

Correct! That's what it says in the 525 install manual. anyway. Although, I'm running just the external flaps now. The internal flaps were very noisy and kept breaking. After paying $90 two times I took them out.

If you have silent choice there will be a set of those in the top of the Y pipe also. The problem is when they go bad just like the ones in the picture did - they can drop down and partially block the exhaust pipe. This can cause a back up of water in the exhaust that can cause reversion of water into the engine. Years ago I had a problem with reversion ( milky oil under the vavle covers ) and couldn't find where the leak was. I pressure tested the headers and the engine. no leak. Just by chance I looked down the Y pipe and found the rubber flappers stuck at the bottom partially blocking the pipe. I removed the pieces and my problem went away.

I do have silent choice but I never use it. Always run through hull. I did notice my Y-Pipe flappers are the new metal type. I have heard If i put the metal type in the through hull it will clank so much it is not tolerable. I found that CP performance sells the rubber ones for the through hull for like 30.00 so I will probably go that route. This is the second motor I have had valve problems with. This one , a 496, with 120 hrs on it. Last one was a 454 mpi with 160 hrs on it. Both motors had about 60 hrs in salt. This is a 24 ft VIP vindicator with built in swim platform. Looks like a BAJA. I am starting to thing it has something to do with the boat design unless it was caused by these flappers. Both motors had the oil changed every 30 -40 hrs and always used oil recommended by Merc.

Chris

On boats with intergrated swim platforms (swim step) you have got to be careful backing down hard in reverse or when taking wave action or rollers against the transom as the trapped energy of the water slap aginst the transom, that is somewhat trapped under the platform, has no where to go, but up the exhaust outlets, having external flappers is a partial fix but remember when backing up with a little throttle applied the flappers are most likely just about wide open anyway. You can also take your tips or connection pipes to tips and weld in an anti-back-up ring about 1/2" tall and slanted 45 degrees towards the tip outlet. This condition seems to be worse in smaller boats where the transom height location of the outlets is lower( closer to the surface of the water) and the drop from the bottom of the riser elbow outlet is not very high above the surface of the water (waterline). Some brands and styles of external mufflers can help with this issue also. A little water is a dangerous thing and a little salt water is even a more dangerous thing!

Best Regards,
Ray @ Raylar