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V8 Flapper Valve

alreadygone

Contributing Member
"Saturday morning attempted to

"Saturday morning attempted to start 250hp 1998 350 chev. Engine locked, pulled plugs and water came out of 3 on port bank. Began teardown and found destroyed flapper below exhaust elbow. Pretty certain that's where water ingressed. Where can I find part # and order?

Bob"
 
"Bob,

I believe you are cor


"Bob,

I believe you are correct on your diagnosis. You can buy those at most well stocked boat repair shops.

Dean"
 
Bob.
You may have or may not


Bob.
You may have or may not have found the cause. Everyone thinks those fllapper valves keep water out of the exhuast.
They do not seal that tight.

Stop and think about how close the engine needs to be to the water line for water to come back into the engine through the exhuast manifolds.

The dead rise of the engine would need to be very low
putting the engine at or below the draft line on the boat in order for water to get over the rise on the manifold.
This flapper could be the cause but the exhuast manifold having a cracked water jacket could also be the cause.

We had one that drove us nuts for a long time because it only locked now and then. What was happening is the engine did not stop on the compression stroke everytime.
This engine had been replaced because it had frozen and cracked the block.
A check of the manifolds showed no problem but the one manifold was cracked inside where it could not be seen.

Anyway this is something else to look at.
 
"Have purchased new shutter va

"Have purchased new shutter valves. Will install this weekend. Old ones so destroyed I can't tell, does bump, tit,whatever you call it on valve go up or down inside housing?

Bob"
 
"Bob, FWIW I agree with Charli

"Bob, FWIW I agree with Charli. My flappers destroyed themselves a decade ago. The Mercruiser guy said it was optional to replace them. Never did, without issue. On the other hand, I had a freshwater lock up when boat was on trailer. It was a riser gasket (aftermarket) that went bad. That is where I would look."
 
"BoB,
If it dieseled when you


"BoB,
If it dieseled when you shut it off the motor will suck water back up the exhaust if the flapper is not working properly. I have first hand knowledge"
 
"Motor is in a 78' housebo

"Motor is in a 78' houseboat. Can't hear motor when starting or stopping. After getting valves in place, noticed throttle cable had play. Was running near 2k after using throttle. Was dieseling when shut off untill I adjusted cable & set idle rpm.

Engine is running fine now!!

Thanks,

Bob"
 
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