1988 4.3 OMC Cobra guidance

[Joshpike15]

Hello to all, new here so be gentle haha. Just bought a 1988 Rinker 186 captiva. Picked it up with trailer for $2500 and it is, well what I thought to be, in decent shape. Motor starts right up every time. It had an overheating issue I found and resolved by changing the melted impeller and that fixed that issue. I changed water pump, plugs, wires, distro, points, belts, thermo just to freshen it up. Got it out on the water and did a test run. Did decent for the most part for well over an hour, stuttered at top end and felt a little sluggish. Was on the way back in and it did not want to run good at all. Worst it ever has, to my knowledge. Would not go over 2500 rmp and at 2500 it was struggling to hold on. Just did a compression check, should have done that before testing..lesson leaned, found 2,4,5,6 to have 145-150 psi...1 and 3 have 0...pulled the valve cover and hand spun motor over and all spring and rods move in sync like they should. At a little bit of a loss on this one. Oil looks great, no water there. I assume all I can do at this point is fully remove the manifold and take the head off to check conditions? Any advice is more than appreciated.

 

[Joshpike15]

Here is the passenger side with top being cylinder 1

 

[Scott Danforth]

let me guess, you have the original bat wing exhaust manifolds? those leak, cause the valve and rings to rust

other possible issue is your timing was off and you burned holes in the pistons.

 

[Joshpike15]

let me guess, you have the original bat wing exhaust manifolds? those leak, cause the valve and rings to rust

other possible issue is your timing was off and you burned holes in the pistons.

I do have the OG batwings...sounds like I just need to keep tearing it down. Hope it is something simple like that.

 

[Lou C]

The only way to narrow it down the cause is to do a leakdown test; this will tell you if it’s valves not seating vs a blown HG between #1 & 3 cyls. I had the batwings on my engine till 2017, I had 3 sets, the original, replaced in 2004, then again in 2011. I’m in salt water and have to change them approx every 7 seasons. Never had water in a cyl from them but I have heard that it can happen due to casting issues just like the Merc one piece ones used on the Vortec V6s. These can be converted to the 2 piece manifold/elbow design used by OMC & Volvo. I used Barr Marine aftermarket manifolds and elbows and Volvo Penta 90* exhaust pipes and hoses. This is the best way to do it; there are cheaper kits but quality is not as good (GLM). I installed these 4 years ago and they fit & work great.
You might get lucky and just have to pull all the accessories off, remove the intake and both heads and take em to a machine shop. I had to do that in 2017 due to blown head gaskets and water in a cyl. Installed reman heads & the new exhaust. Not a hard job really.

 

[Lou C]

This is what you can convert to after the engine is repaired. Costs approx $720 for the Barr exhaust and for the Volvo stuff, another $500 or so, the parts are not cheap. But then its one and done, no leaks, bad fitment etc. Either that or take your chances with cheaper aftermarket. First 3 pix are mine, last is not but I included it so you can see what the V/P 90* adapter pipes look like. They adapt the 4" elbow outlet to the 3.5" OMC/Volvo Y pipe. I think these let the engine breath better than the restrictive bat wings as well. This set up will fit your '88 OMC 4.3 Cobra with no alterations at all. If you upgrade to the later model Vortec engine you can continue to use this updated exhaust with it as well.

 

[Joshpike15]

Well, I found the culprit. At least I hope I did. Let me know what you all think. Thank you all for putting some time in with your responses, it was and is most appreciated!

 

[Scott Danforth]

blown head gasket and the start of a fire-slotted block

you need to clean the deck, and with a very very very accurate straight edge, check the deck between the bores. if you see light under the straight edge, you may need to get the deck fly-cut.

 

[Lou C]

Interesting pix. Wonder what caused the HG to blow?
On mine it was different, the fire rings had slits in them which allowed water into the front cyls on each side. Not enough to hydro but enough to put water in the cyls and oil. While running I don't think water was getting in but when shut down and cooled off there would be a small amount of water in #2 cyl.
Yep now you need a good straight edge and feeler gauges and really clean up those sealing surfaces very carefully. Might be able to save it.
I would for sure use Fel/Pro marine head gaskets, they sell a set for those engines that includes the HGs, the intake gaskets and the distributor gasket with sealer for the china wall area for the intake. Make sure to really clean out the cyl head bolt threads in the block (thread chaser) and clean up the head bolts, make sure they will easily thread all the way in by hand, if not consider getting a new set.
Those engines are easy to take apart aren't they?
Did you see evidence of leakage in the exhaust ports of your batwings (the ports that match up to the cyl head)?
I think its a good time to change over to the 2 piece exhaust system at this point. Then you should be good for a while.

 

[Karlomora]

Very nice information for 1988 omc cobra 4.3 liters.

 

[jbcurt00]

Very nice information for 1988 omc cobra 4.3 liters.

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