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Missing Flapper On OMC 2.3L Cobra

D

DavidW2009

Regular Contributor
I removed the exhaust riser and exhaust couplings in order to inspect the flapper and install a new riser gasket as preventative maintenance.

The riser unbolted with out a problem and inside it looks very good. The old gasket was not leaking, but was rock hard and "petrified". It took some extra effort to scrape it off the surfaces.

When I looked for the flapper, all that was there was the shaft on which the flapper pivots. The shaft was in good condition. I got a flashlight and looked down the exhaust connector that goes to the outdrive. Didn't see anything.

I poked around with some extra long needle nose pliers, but came up with nothing.

Two things come to mind:
1. Some mechanic removed it for some reason.
2. The flapper was exposed to raw, uncooled exhaust gasses and melted off the shaft and is wadded up somewhere down near the outdrive (have not removed outdrive yet).

I have never seen a flapper, only in pictures. I have no idea of what material they are made. Someone with experience clue me in on the material and what could have happened to the flapper?

Thanks.
 
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By doing some reading on the 'net, but not having seen a flapper, I've determined it is probably made of rubber, with some flapper designes having stainless steel substrate plates imbedded.

I now suspect the old flapper is indeed melted and partially blocking the exhaust flow to the propeller. I have way too much water coming out of the slits in the exhaust bellows and not enough coming out of the center of the prop.

So the outdrive will have to come off. If the debris can't be removed from there, the lower end will have to be dropped.

I haven't looked yet, but I'd like to find a replacement flapper that is made of S.S., if such a thing exists. Rubber for a flapper, upstream of some relatively small exhaust ports? Bad idea, imho. But it may also be the only material viable in that place.

I'm also thinking of a way to back flush the exhaust system as far as the lower rubber coupling, to see if I can dislodge the old flapper. That may not be possible with a garden hose flow and pressure.
 
you can get a new flapper from this site ,you can also get the ss clamp too . i know cause i just replaced mine . they are made of rubber with a piece of ss in the center . when you purchase youll recieve 3 i guess a pair with a spare. costed me around $68 easy to install for me because i had the engine and bell housing already removed. for you i dont know youll have to ask one of the experts but i think if you dont remove the engine you could get to it by removing the drive and the intermediate housing . im not sure wich is more painfull. either way just a heads up .. get the bell housing gasket too youre gonna need it to reinstall. good luck....dimitri
 
On the 2.3L it looks relatively easy to change. The manual says it's easy. No engine or bell housings to remove. Take off the riser, the rubber connectors and it's right there in plain view.

I plan on removing the outdrive this weekend. First time I'll be trying this on anything. I'm going to try lifting it off with a small boom hoist on wheels. Then check for pieces of the old flapper. The 2.3L has only one flapper.
 
Easier to just rest the fin on a piece of wood and 'wiggle' it loose and out, it is not that heavy!
Make a small stand to put it on (supported on the cavitation plate), in case you need to split it to get the remaining flapper out.
 
I think Dimitri was giving you the procedure for a Stringer drive and not the Cobra. I think you will have to pull the drive though to get whats left of it. You can man handle those drives like mentioned above, nice to have an extra pair of hands to grab the driveshaft once the u-joints clear.
 
correct bob , i wasnt paying attention. had i noticed it was a cobra i wouldnt have said anything. im sorry if i confused you david ....dimitri
 
Yea, u probably want to pull the drive & split it to make sure u get all of it. There may be pieces lodged in the water tube, which can cause an overheat. That drives is not that heavy, & splitting it is no big deal. The hardest part is getting it past the o-rings when u try to pull it apart. Just wiggle it back & forth until it breaks loose. And, I think u have to remove the trim tab. I'm not sure about the 2.3, but on my 3.0 u can leave the anodes.
 
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Removed outdrive this evening. (First time pulling any kind of outdrive) Used a 2-ton roll-around hoist and an eyebolt in the dipstick hole. Worked fine.

Kracker, I did have to wiggle it back and forth. It was slow going, but once free, it came right out. You are right, that unit really doesn't weigh a lot. That I found interesting.

I did find a sizeable chunk of melted rubber blocking the exhaust passage in the outdrive. I saw no stainless steel plates, though.

Tomorrow, I'm going to run garden hose water thru the outdrive exhaust passage(s) and see if the flow is better.
I'm not sure that one piece of rubber is all that's there.

Good news is the drive bellow is like new. No water in there. No rust on the u-joints. There was some minor surface rust on the spline. The gimbal bearing is well greased and smooth like new. The u-joints are well lubed and looked like new.

The exhaust bellow is shot and needs replacing.

Thanks all, for the input on this thread.
 
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Hey, no sweat. I'd remove the water passage housing just to make sure that none of the pieces are in there, & the screen. But, you'll need a new gasket. When u reassemble it, it's not a bad idea to put a little liquid gasket sealer on the rubber seals that attach to the water tube. They like to fall out of place when you're trying to put it back together. The manuel says that it's not needed, but I do it anyway. While u have the drive off, I'd also check the gimbal bearing/ engine coupler alignment. You'll need the alignment tool. But, it can save u a big headache when it's time to reattach the drive. If it ain't lined up, you'll never get it back on.
 
Wouldn't a driveshaft without the u-joints, work as an alignment tool?

Say if I bought an old, discarded outdrive, and removed the driveshaft, and used it as an alignment tool?

Wouldn't that work?
 
DavidW2009 said:
Wouldn't a driveshaft without the u-joints, work as an alignment tool?

Say if I bought an old, discarded outdrive, and removed the driveshaft, and used it as an alignment tool?

Wouldn't that work?
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No. I know u probably want to get it back together & back on the water. But, if it's not lined up u will have trouble. Here's what u can do. Without attaching the housing gasket, try to set the drive back in. If the alignment is correct the drive will slide back on fairly easy. If it doesn't, & u have to fight with it to get it past the studs, then u know that the alignment needs to be adjusted. If it goes on, pull it back off, put the gasket on & button everything up. You're home free! Good luck with it. P.S., I bought the alignment tool on ebay a few years ago, cost me like $50. The tool is a must have if u do your own maintenance.
 
kracker,

I'm going try what you suggested tomorrow. Doing a trial-run putting the outdrive back on, without the new gasket.

Today, I ran water thru the exhaust passage in the outdrive at a rate of 12 gallons per minute. Virtually every drop came out the prop with no signs of backing up or blockage. If I had seen the water starting to back up, I would have known there was a blockage.

I also figured out the melted piece of rubber was actually not inhibiting the flow of exhaust water that much. I still found no stainless steel pieces, so I figure the previous owner's mechanic had removed them and didn't bother with putting a new flapper in.

One thing I found on the spline was hardened grease, caked on. It took a screwdriver blade to dislodge the chunks from the spline. I think this is the cause of the drive being moderately hard to slide out.

Thanks again for your feedback.

BTW, I've never taken this boat out on the lake. It's a project boat. The transom is rot and needs to be replaced. I have floated it on the trailer at a ramp, and ran the engine for 30 minutes to see what problems showed up. It ran well and didn't get above 160 deg F..
What really surprised me was the transom did not leak one drop, as rotted as it is. I may take it out on the lake one time before pulling the engine and outdrive for the transom repair.
 
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Flapper 1.jpgFlapper 3.jpgFlapper 2.jpg

This is what I found tonight when i pulled my outdrive off . A little while back, i took the manifold off to replace the gasket and noticed that the flapper valve was missing , well needless to say i found it tonight!
 
boatin_bob:

From the Ebay link: "Engine Alignment Tool for MerCruiser Sterndrives including Pre-Alpha "R", Alpha One "MR", Generation II, all Bravo's, Volvo SX and OMC Comba. This Tool is similar to P/N 91-805475A1 which used to be P/N 91-57797A3."

This will work with a standard Cobra?

Yes, I need an alignment tool, the drive does not go in very well.
 
What is the flapper for? Is it common for it to disintegrate and cause problems?

Inquiring minds would like to know.

Thanks. Scott B
 
The flapper is basically there as a safety device, normally the exhaust water and gases will cause it to pivot open under normal conditions however if you get into some rough following seas or come down off plane in a hurry there is a chance that the water can rush back up through your exhaust and into your engine cylinders causing hydro lock or worse. The flapper will pivot down thus closing off most of the exhaust to prevent this. They normally last for several years but if you have cooling problems like a bad impeller and the engine over heats then the exhaust gases can be hot enough to melt them since there is no water to help cool them.
 
Hmm, that is very interesting. I wonder where I could find more information about the flapper valve. My father-in-law recently bought a boat that needed a lot of <a href="http://www.kh-engines-and-storage.ca/">boat repair</a>. We took it to a lake and it kept dying on us. I wonder if this way part of the problem. Thanks again!
 
Janie,you should start your own thread.With all the info.Make model,year etc.
Then a description of what it's doing.Along with any thing thats been done.
The profile,fill it out.You might be close to someone who can help.J
 
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