OMC exhaust flappers...Part #?

[Payne]

I need to replace the exhaust flappers in my 1990 OMC 4.3 HO. They melted in an overheat.

First, what are they really called? Exhaust seals? Anti-backwash flaps?

Second, what is the part number, if anyone has the parts book around?

Third, the teardown showed a cracked head on one bank, but not much of a crack. The gaskets showed a very minor difference between the affected cylinders, not the big blowout I was expecting. I had water in both banks, though. Is it possible that I fried the flappers, then shut down too fast and sloshed water into the manifolds? Then when it cooled, it drew water into the cylinders? Everything else looks ok, although I am replacing the thermostat as a precaution. And, yes, the impeller was shot. It was supposed to have been replaced last June when I had the shift cables replaced, but it doesn't look like it had been replaced to me (but I am not an expert by any means).

Thanks

 

[HT32BSX115]

Re: OMC exhaust flappers...Part #?

Try here and you might find what you need. Also you may have a leaky riser gasket.


Regards,


Rick

 

[Payne]

Re: OMC exhaust flappers...Part #?

Thanks, that is exactly the site I need.
Is the exhaust gasket the same as the riser gasket?

 

[HT32BSX115]

Re: OMC exhaust flappers...Part #?

Well, No.

The exhaust gasket would be the same as an automotive engine gasket. (by same i mean goes in the same place)

The riser gasket is the one that goes between the riser and the exhaust manifold and keeps water from running back into the engine after you shut it down.

If you don't have a OMC service manual. Now would be a good time to get one.

Thanks, that is exactly the site I need.
Is the exhaust gasket the same as the riser gasket?

 

[Payne]

Re: OMC exhaust flappers...Part #?

I believe I have the big one-piece manifold rather than the two piece job used in later years.

 

[Payne]

Re: OMC exhaust flappers...Part #?

Or is that what I am calling the "flappers"?

 

[HT32BSX115]

Re: OMC exhaust flappers...Part #?

I looked at Doug Russell parts and man! Those are expensive manifolds. I would check out OSCO or BARR from an aftermarket place for replacements if yours are leaking. If those are at their service life (if they're original then they're at their service life) you cannot tell when they will start leaking.

The exhaust seals don't seal that good. It's unlikely that cooling could draw water into the exhaust. The exhaust seals are there to prevent the water from 'sloshing' up into the riser area of the manifold. You may also have rust-thru in the manifolds if they're old.

That link to Doug Russell has all the part numbers there. You might want to call them to verify the model and serial numbers.

 

[Payne]

Re: OMC exhaust flappers...Part #?

Yes, they are very expensive. But they don't look bad. Very little rust inside, none outside, and no cracks that I, or a mechanic friend, can see. They must have been replaced before I bought the boat last year.
The water in the cylinders is still a bit of a mystery to me. The engine was running when I shut it down, but after 10 minutes of cooldown, it was hydrolocked.

And thanks again for the link to Doug Russel; they have a better diagram than the factory manual (it doesn't show those exhaust seals at all).

 

[skier-24]

Re: OMC exhaust flappers...Part #?

Same engine in my boat. Ran it on the trailer 2 weeks ago, all was well. Put in the water yesterday, turned over about 10 seconds, would not start, hydrolocked. Pulled plugs, blew out water. Where did it come from?

 

[Coors]

Re: OMC exhaust flappers...Part #?

My 88 Omc, that I bought from my stepson- He bought it ,used it once; the flappers were stuck wide open, he did a quick shut-down. That turned into a new reman, flappers, starter, battery, alternator, and an alarm system for no oil pressure, too hot- involving a car horn under the dash, for people that don't look at the gauges. And a redundant set of flappers on the thru hull tips.

 

[HT32BSX115]

Re: OMC exhaust flappers...Part #?

This sort of problem is caused by riser or riser gaskets leaks. If you don't have removable risers then the manifolds are leaking in the riser area. They need to be pressure checked.

Otherwise there could be an intake/head gasket leak, cracked head or block....or there's a little gremlin pouring water into your intake when you're not looking. ......another way would be to leave it outside with the engine cover off and let it rain on the carb flame arrester. There's not much else

Same engine in my boat. Ran it on the trailer 2 weeks ago, all was well. Put in the water yesterday, turned over about 10 seconds, would not start, hydrolocked. Pulled plugs, blew out water. Where did it come from?