OMC cobra 4.3 batwing exhaust manifold problems!

[billythekid7059]

OMC cobra 4.3 hydrolocking issue...

hello everyone I have a OMC cobra 4.3 engine in my boat. it ran very well, my buddy let me store it out on the lake for a couple months. I went to drive it it started fine drove fine. but then after I shut it off and tried to restart it it was having issues. I took out the plugs and only on one side it had water in the cylinders. I took it apart and did the intake manifold gasket and it had the same issue. it wont get water in the cylinders if i have it hooked up to my hose. it only happens when the boat is in the water. I took the exhaust off on that one side and the exhaust flap was open. should it be closed? it will go back and forth very easy. please help me.

 

[alldodge]

I took the exhaust off on that one side and the exhaust flap was open. should it be closed?

It should sit closed when the motor is not running, if that's what you mean. Also if you have this style of manifolds they should be replaced.

 

[billythekid7059]

yes those are the manifolds I have. I took that side off and there was water in the manifold. and the exhaust flap was open. I also had water in the oil.

 

[alldodge]

Those are called bat wing style and are really bad at getting water in a motor

 

[billythekid7059]

So do you think that's the cause of getting water in the cylinders? and oil in that case? is there a way I can be 100% sure? and what does the other style manifold look like? thank you for the help.

 

[billythekid7059]

Hello everyone I was talking to someone on one of my previous posts about the "Batwing" style manifolds on OMC cobra engines, He told me the "Batwing" manifolds are good at getting water into your engine. What is the cause of this and how can you tell if your manifolds are actully bad? Why are the "Batwing" manifolds so bad? Mine are off of a 1988 and this is the first issues Im having with the engine.

 

[alldodge]

The exhaust flappers are there to stop water from coming in when the boat is stopped and water comes rushing up. I'm thinking your current issue is the manifold may have a crack in it. You can fill the manifold with acetone and see if it leaks out.

Water leaks down besides the rings and cylinder walls into the pan.

The replacements look like these, but there are others and different prices
https://www.ebay.com/i/311872593697?chn=ps&dispItem=1

 

[billythekid7059]

so just fill it up and see if anything comes out?

 

[Scott Danforth]

if you have batwings, consider them bad. not all are bad, however a majority are. so why take a chance

thin casting walls and core-shift usually leads to internal crack failures which will take out your motor. some of the castings were as thin as .06"

replace them with separate manifold/elbows

 

[Scott Danforth]

So do you think that's the cause of getting water in the cylinders? and oil in that case? is there a way I can be 100% sure? and what does the other style manifold look like? thank you for the help.

yes that is the cause

you can be 100% sure if you have batwings that they are 100% problematic (actually 95%, however close enough to 100%)

here is what the conversion kit looks like

 

[billythekid7059]

okay I will be conducting the acetone test tonight or tomorrow. I will post results!

 

[Lou C]

lol. Had 3 sets in salt water over 15 years time and never had a problem and the last 2 I tested with acetone, twice after reading this stuff.

Its a moot point anyway as they have been NLA for a very long time.
​I'm so sure I'd run out and replace them with the GLM's though, they have had issues too.
​With mine I'm strongly considering trying to convert over to the more expensive but better design Merc dry joint. I have to find out if one of our local marine exhaust shops will lend me one side's parts to see if they can be made to match up. Basically you need to adapt the Merc 4" diameter risers to the OMC 3.5" Y pipe. There are adaptors that can accomplish this.....

 

[Lou C]

okay I will be conducting the acetone test tonight or tomorrow. I will post results!

​Be careful for one thing acetone is very flammable. For another do NOT get it in your eyes!
​What you need to do is prop up the manifold so its as level as you can get it. Then get a metal funnel and put it in the feed hose. Hold the funnel level and very carefully pour in the acetone. Stop when it starts to drip out the exhaust cooling ports. Then let it sit for a while. What you are looking for is acetone trails inside the engine exhaust ports. I tested the last 2 sets I have had this way, let it sit about an hr, not one of them ever l leaked. And never had water in the engine till the head gaskets blew from overheating. So some may be OK but some may be bad.

 

[billythekid7059]

Okay guys I found a crack in the manifold. The putter part by the plug. Is it possible to weld them?

 

[Scott Danforth]

dont even bother trying to weld them. they were a poor design subject to core shifts and cracking without freezing. adding the heat required to get a high-nickle filler metal to weld cast iron would mean that you end up with a crack elsewhere.

replace them.

 

[Karlomora]

Hi, I got the same problem, water in all cylinders, my is a omc cobra, 4.3 liters. I think my manifolds are 984222 model. Which other model will replace this old manifolds.

 

[aspeck]

Hi, I got the same problem, water in all cylinders, my is a omc cobra, 4.3 liters. I think my manifolds are 984222 model. Which other model will replace this old manifolds.

Please start your own thread instead of replying to an old thread.