Replacing Risers/Elbows and Exhaust Manifolds on a Ford/OMC Cobra 5.8 Ltr

[KM7]

I'm replacing the risers/elbows and exhaust manifolds on a Ford/OMC Cobra 5.8 Ltr

I started this with the post: "Overheating Possibly Caused by Restricted Thermostat Housing Port". Now I know that the thermostat housing may have been contributing to the overheating but I will change the risers and the exhaust manifolds. I wanted to start a now post with a better subject.

This a 1991 motor from a 1992 Four Winns boat with a 5.8 Ltr Ford and OMC Cobra. The exact motor model number is: 584APLRGD.

I have already got the risers. Next I'm looking for the exhaust manifolds. The part numbers are P/N 3852347 Replaces 0914898.

I wanted to show pictures of the old manifolds now that they are off. I also took pictures of the mounting surfaces on the block.
Any comments or observations?

 

[KM7]

Here are pictures of the starboard side. Any comments or observations?

 

[Bondo]

Ayuh,.... You've got alota cleaning to do,.....
Once cleaned, then inspections can be done,....

 

[KM7]

Ayuh,.... You've got alota cleaning to do,.....
Once cleaned, then inspections can be done,....

I think that you mean cleaning the block, right? You had earlier said that the exhaust manifolds must be replaced. What would you suggest for cleaning the engine block and the mounting surface?

 

[Bondo]

Ayuh,..... I use rol-lock abrasive discs on my right angle die grinder,...

 

[KM7]

Picture please. Wouldn't you have to be very careful not to go too deep and create a low spot that doesn't seal?

 

[KM7]

Picture please. Wouldn't you have to be very careful not to go too deep and create a low spot that doesn't seal?

 

[Bondo]

Picture please. Wouldn't you have to be very careful not to go too deep and create a low spot that doesn't seal?

Ayuh,...... The idea is to remove any residual gasket material, 'n obviously care must be used,.... there should be clean iron, before the new gaskets are installed,.... I believe the allowable variation is .003",....

I have big air in my shop, so my die-grinders are air powered, but in the video, he uses electric power,....

 

[Lou C]

Yep the .003" variation is what I saw, and used when I did mine. The studs OMC used make it a pain to clean the exhaust ports but on the other hand the quality of the fasteners was good, so I never had a problem removing the manifolds for replacement, no broken/rusted/rounded off bolts etc.
The hardware I got with the Barr exhaust I put on some years back is also good.

 

[Lou C]

You might do OK with a one of those straight razor scrapers, brand new sharp blade, but used at a very shallow angle so as to not gouge the cast iron. Put some paper towel balled up in the exhaust ports to keep out bits of debris.

 

[KM7]

Bondo and Lou, thanks for the tips. Should I soak the gaskets with a Goo- Gone or something similar for a few days to soften them up prior to trying to remove them and cleaning up the surfaces? I could also start with a hard plastic scraper/putty knife and then only use a razor blade as needed. Would you recommend removing the studs to gain better access to the mating surfaces?

Thanks

 

[Bondo]

Bondo and Lou, thanks for the tips. Should I soak the gaskets with a Goo- Gone or something similar for a few days to soften them up prior to trying to remove them and cleaning up the surfaces? I could also start with a hard plastic scraper/putty knife and then only use a razor blade as needed. Would you recommend removing the studs to gain better access to the mating surfaces?

Thanks

Ayuh,..... Double nut them to remove 'em, not with vice-grips,.....

 

[KM7]

Yes, I'd use the double nut method to remove them.

 

[Lou C]

here's an old pic of mine from 2011 the 2nd time I changed the manifolds, I got it good enough with a razor blade, also Permatex (IIRC) makes a gasket remover spray that helps. I didn't remove the studs and the gasket sealed fine.
My later model style system uses bolts only, so no more studs, but I still have them in a bin of spare parts!

 

[KM7]

I'll find that Permatex gasket remover. Thanks for the tip.

 

[KM7]

I have been able to get the old gaskets off the heads. There is another post on just that.

I have located new exhaust manifolds by Barr for a good price. I will go to the shop tomorrow to be sure that they fit. I do know that they only use 4 mounting bolts. Mine has all 8 from left to right: Long, Long, Short, Long, Short, Long, Short, Long. The Barr manifold has: Blank, Long, Blank, Long, Blank, Long, Blank, Long. Also, the water comes into the Barr manifold from the top. On mine, the water comes in at a pipe-like piece on the bottom.

Anyone have experience with this?

 

[KM7]

Here is a picture of one of my exhaust manifolds and a Barr manifold I can get tomorrow. See the discussion above about the differences:

 

[Lou C]

When I converted mine from the OEM OMC Batwings to the later 2 piece style the attachment points were different but the gaskets sealed up fine. They only get about 26 ft lbs of torque so it there are differences in the attachment points it’s not likely to make any real difference.

 

[KM7]

Thanks Lou. Did you have to change the hose from the thermostat housing to the manifolds?