How important is the Exhaust seal flapper?

[Trevthefox]

I've been slowly fixing up an '89 460 King Cobra. Recently found the exhaust seal flappers part #0765166 broken off in the bellows. My question is, how important is it to replace these 2 flappers located at the top of the Y exhaust pipe? I know the purpose is to prevent raw water from going the wrong way into the exhaust. However, I read somewhere that Volvo advised not to replace these because they were ineffective on their engines/drives. But this is OMC and I'm debating on replacing them. Love to hear your thoughts on this.

Thanks

 

[Trevthefox]

Here's a diagram of what I'm talking about

 

[Lou C]

I replaced mine. Over the years I never had water come up the Y pipe into the cyls. Not sure if I agree with Volvo’s reasoning.

 

[Trevthefox]

Yeah I think I'll just install new seals. I'm not sure how likely it is for sea water to travel up that passage, but I'd rather not find out.

 

[HT32BSX115]

However, I read somewhere that Volvo advised not to replace these because they were ineffective on their engines/drives. But this is OMC and I'm debating on replacing them. Love to hear your thoughts on this.

Thanks

Howdy,

Welcome aboard!

Yeah,

Volvo never did produce a 460 powered engine/drive combo. They did feel that the exhaust seals were unnecessary in the SX type packages though....

It's pretty important to have those seals to stop water from getting into the exhaust. Also, If you haven't, you should also replace your riser gaskets. When you get it apart, check both the risers and manifolds for "flatness" and either have then carefully milled or sand with a belt sander to ensure a perfect seal.

Mine (in my "sig" below) actually leaked enough to allow some raw water running into the manifolds and into open exhaust valves in high enough amounts to briefly cause a hydrolock during immediate restarts. Once I let it sit for an hour or so (or overnight) it would start right up! I didn't find out about it until I removed the heads during the "Big Teardown".

I was chasing down a "LOW" WOT RPM problem that eventually turned out to be flat lobes on the camshaft (hence the teardown)


I debated replacing my "seals" when I did the big teardown.......I settled on replacing the entire engine/drive package......but that's another story!!

Cheers,

Rick

 

[Trevthefox]

Thanks Lou and Rick!

Rick I did remove both manifolds and risers and already replaced the gaskets and used gasket sealing compound. Pretty confident I got a nice seal on everything. I'm going to take your advice and replace those flapper seals. Already ordered them. Whoever had the boat before me obviously didn't look into this because both of those flappers were just sitting in the lower exhaust bellows blocking about 60% of the passage.

Thanks again!

 

[HT32BSX115]

Thanks Lou and Rick!

Rick I did remove both manifolds and risers and already replaced the gaskets and used gasket sealing compound. Pretty confident I got a nice seal on everything. I'm going to take your advice and replace those flapper seals. Already ordered them. Whoever had the boat before me obviously didn't look into this because both of those flappers were just sitting in the lower exhaust bellows blocking about 60% of the passage.

Thanks again!

Don't forget a picture! We all like pictures!

 

[Lou C]

For them to fall off the rubber must have melted. They don't fall off for no reason. That meant that at one time there was a serious overheat. How did the rubber exhaust hoses look?
Also, if the overheat was bad enough to melt the flappers, then the water tube grommets in the outdrive (these seal the top and bottom of the water tube, that carries water up from the water intakes to the impeller) could have been partially melted causing low raw water flow. If you put it together and it starts to overheat, that may be the problem. You have remove the drive and split the upper and lower to fix that. Done it myself, got some tricks to get it apart if you need to do that.

BTW I don't 100% agree with Volvo's reasoning. If I had an SX powered boat with no way to add flappers, I'd remove the exhaust bellows and replace it with an inboard style exhaust flapper on the exhaust exit of the gimble housing. This would serve the same function, keeping water from rushing up the Y pipe. Might increase noise a bit but likely safer. Just about every inboard boat with thru the hull exhaust uses something similar.

 

[Lou C]

https://www.crowleymarine.com/johnson-evinrude/parts/55682.cfm?mdl=I46RBX

parts #s 75 (2) and part 76 (plastic guide) could be melted.

 

[Trevthefox]

For them to fall off the rubber must have melted. They don't fall off for no reason. That meant that at one time there was a serious overheat. How did the rubber exhaust hoses look?
t

Hey Lou,

Thanks for the feedback. Honestly, all the hoses look perfectly fine. I'm going back out to the boat this weekend to do some more work so I'll double check everything. Those exhaust flapper seals have been shipped so that should happen soon.

This all came to be because the Port exhaust riser was noticeably hotter than the starboard after the running the engine. There was good water flow. But we decided to replace the impeller and thermostat and basically follow the water path throughout the engine. That was solved by clearing out a blockage in the riser itself. But everything else seems to be in good condition besides those exhaust flappers. I'll be replacing both bellows, gimbal bearing, and seal for good measure while I have the drive off.

Funny you mention separating the upper and lower unit. I'll be doing that this weekend. Just waiting on some parts to arrive, including those seals you mentioned. They should arrive in a day or so. I have all the o-rings as well for bearing housing too. I also have to check for correct height on the shift rod while the units are separated.

I'll send pics one I get out there.

Thanks again!

 

[Lou C]

Let me know if you have trouble getting the upper and lower apart. Then I'll show you my trick. They can seize up on one of the orings inside.

 

[Trevthefox]

Let me know if you have trouble getting the upper and lower apart. Then I'll show you my trick. They can seize up on one of the orings inside.

Love to see your trick. Rather know it before I spend hours attempting it by myself...lol

 

[Lou C]

OK the split the Cobra trick. To do this you need an outdrive stand of some kind, 3 scissor jacks, 2 bolts, 4nuts that fit the bolts and a long piece of all thread, or any steel rod that fit the hole for the trim ram rod. You put a bolt and use 2 nuts to secure it in both of the lowest front mounting holes. Then you get a long piece of all thread and slide it into the hole for the trim ram rod. Now put a scissor jack under the front 2 bolts, and one on each side of the all thread. Use some wood and c-clamps to hold the lower unit down on the stand. Jack each jack slowly and evenly and the upper gear housing will pop off. I tried everything else before imagining this in my head. I used the strongest parts of the upper gear housing, and it works even on a drive that sits in salt water for 6 months each season.
Other tips: coat those orings that seal the upper and lower with OMC/Evinrude triple guard grease. Coat all the threads of the bolts with OMC gasket sealer. This will help them not to seize up for next time.

PS this will work on a Volvo SX or Merc drive as well, same basic idea. Don't bother prying with long screwdrivers or prybars it won't work, and you might break something.

 

[Trevthefox]

Thanks Lou,

I'm going to give this a try. Sounds easy enough

 

[HT32BSX115]

Thanks Lou,

I'm going to give this a try. Sounds easy enough

If someone hasn't already told you (or in the unlikely event you don't know) be absolutely sure you refill the drive correctly (through the "FILL" port.....NOT the drain port) )
before running it.....(also ensure that the drive takes the full amount of oil)

Every year someone destroys a Cobra filling it wrong.

Also, have a close look at your oil cooler. If you (or the previous owner) have had previous impeller failures that put small fragments into the cooling water, a lot of it can end up in the oil cooler.

 

[Lou C]

https://www.crowleymarine.com/support/omc-tech-articles.html
a lot of good stuff here.

A properly maintained Cobra will last a LONG time...

 

[Trevthefox]

Don't forget a picture! We all like pictures!

Here's a pic of the broken off exhaust flapper stuck at the opening of the exhaust bellow. I haven't removed it yet, but you can clearly see how much of the exhaust it's obstructing.

 

[Lou C]

Not to make you worry but usually that signifies a bad overheat. Monitor the engine for water in cyls or other head gasket problems related to an overheat. After I had an overheat bad enough to cause that, I got 2 more good seasons then both head gaskets gave out. That led to my top end overhaul in 2017. Re-man heads, all new gaskets, upgraded from the old OMC batwing one piece exhaust (NLA) to the center riser style used by Volvo up till the dreaded cat converter exhaust.

 

[HT32BSX115]

Is this a salt water boat?

 

[Trevthefox]

Is this a salt water boat?

Yes it is.