Omc stringer vs cobra exhaust manifolds

cup of Joe

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I just ran water to the hose inlet and stuck a rag in the 3.5 out let and water was pouring into my exhaust ports.
This is on a 1985 4.3 omc stringer,
Looking in EBAY are are some listed as OMC Cobra that have the same manifold castings as my stringer

Port 984221
starboard 984222

will the gray cobra manifolds fit my stringer?
the casting numbers are the same as my silver stringer manifolds
thank you
 

Scott Danforth

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if the casting numbers are the same, paint color doesnt mater. however I personally would stay away from the bat-wing manifolds. especially used off of ebay. most have the casting flaw that leads to failure, or they have already failed.

I pointed you in the other thread to the updated manifolds and elbows.
 

Lou C

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I think those batwings were used on the last year of the Stringer drive, 1985-1990 were the years they were used. While I never had a problem with the ones I had (3 sets over 15 years worth of salt water boating), I agree with Scott I would not trust an engine to a set you got from ebay. I tested both sets I had with acetone, neither leaked but I would not sell them to anyone because they were each used in salt long enough that they probably would have failed in a year or 2. Just do the Volvo style center riser conversion if you want to not have problems. Yes it costs more but then you don't have to say, 'oh I wish I listened now I have water in a cyl and sticking exhaust valves'!
 

cup of Joe

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Thanks Scott and Lou, I found A set of batwings the set for $ 350. from a local boat repair shop.
They have a set a batwings with castings numbers the same as my old ones so they should fit ,RIGHT??????
All that matters is they are not cracked now, I'm selling the boat
Monday I'm going to put water into the hose inlet and jam a rag in the outlet , to check for internal leaks to the ports.
Id rather sell this boat in good running condition than selling it knowing there is a problem.,
I'm just glad the block is not cracked.
Thanks again for all your help.
 

Maclin

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Ok, makes sense now. I had been following this and was scratching my head a lot :)

I suggest using acetone or similar solvent type fluid, because that will leak through cracks that standing water won't. Good luck!
 

Scott Danforth

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Best to skip batwings. Lou is the exception with his luck testing his batwings often prior to replacing them. The design is flawed and core shift made tge internal walls super thin, many failed within hours of being new

However its your boat. Everyone has told you to buy new. I personally believe used manifolds are like used underwear. Especially used batwing manifolds. Not worth the risk
 

cup of Joe

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Thank you all for your input.
If I was to keep the boat I would by new style manifold, But I'm just want to sell the boat in good running condition.
I know the old manifolds have cracked on the inside, and I can't sell the boat as is.
Have a local boat shop that has the same manifolds for sale for $350 for the set.
The cast number on the manifolds are Port 984221 starboard 984222.

So if the numbers match, Then they should work RIGHT???

I just want to sell the boat and get the money I put out to get it in good running condition.
Again Thank you all for your input.
I would rather stay with inboards.
 

cup of Joe

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Maclin and lou How do I use acetone to test the inside for a crack?
Plug the inlet hose connection and pour the acetone in the outlet and shake it around?
Please fill me in.
thank you
 

Maclin

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Wouldn't need to shake them around. Just look at the exhaust ports and see if the acetone has seeped through after a few minutes.
 

Maclin

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Not sure, but you could do the water thing first just to get an idea of the volume it would take.
 

cup of Joe

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The water thing was just to put hose to the inlet turn on the water and plug the outlet with a rag.
Then the water pour into my ports
 

Maclin

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To use the solvent, plug one end of the water jacket and turn the manifold up and pour the solvent in and wait a while. If there are cracks in the water jacket you will see wetness in the exhaust passages.
 

Bondo

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The water thing was just to put hose to the inlet turn on the water and plug the outlet with a rag.
Then the water pour into my ports

Ayuh,.... Look into the end ya stuck the rag into,.....

You'll see 2 or 3 or more little ports when the water mixes with the exhaust stream, after the downturn, but before the actual exhaust outlet,....

Bein' the junk batwing manifold/ risers they are, they can't be pressure tested,...
A manifold from a 2-pc. set can have a flat plate bolted to the flat riser gasket surface, to hold pressure,....
 

Lou C

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The way I tested them with acetone was to prop em up level on the ground & connect the feed hose with a funnel. Hold up the funnel and carefully fill with acetone till it runs out the 4 exit ports in the rear. Let it sit for a while and watch for wetness in the three exhaust ports that match up to the exhaust ports on the cyl head. If you see wetness they are junk. If not then at least they don't leak now. Be careful with acetone its highly flammable. I had a bad overheat back in '13, while I was waiting for a tow in I pulled out my IR temp gun and checked the manifolds (375*F!). Took em off and tested them and they were not cracked and was able to use em 2 more seasons!
 

cup of Joe

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thank all of you for your help and replies.
Monday I will go to the local boat shop and test them.
Again Thank you.
 

cup of Joe

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I will have to do the test all over. With the
hose's connected to the out let I did not see the
2 or 3 or more little ports when the water mixes with the exhaust stream,
after the downturn, but before the actual exhaust outlet,....
I did not know what Bondo was talking about till I took off the 31/2" hose from out let.
 
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Lou C

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Here's a pic of the exhaust ports. The used one was used for 5 1/2 seasons in salt water in this pic, see how one outlet is clogged. Second pic is the center riser exhaust, see how much bigger the water passages are? Less prone to clogging....
 

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cup of Joe

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Thanks Lou, Yep That's how I did it .
Plus I plugged the exhaust out let and the water out let so the acetone could fill to the top.


Batwings2.jpg
 

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Lou C

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The other thing I noticed with these is after being used in salt for a while, the rust in the aft portion travels backward to the top of the riser section. With vibration, you can get rust flakes falling down into the exhaust ports which is not good! Take a small hammer and tap along the top section lightly and see if you see rust flakes in those three exhaust ports that match up with the ports in the cyl head. If so I would not use them even if they do not leak.
 
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