Refurbishing stock exhaust

[DMC-81]

Today I picked up my manifolds from Precision Cycle Inc., the shop that deck planed them. They were very rough beforehand, with depressions and extra casting material protruding from supposedly flat mounting flanges. No wonder I had 3 of 6 ports leaking!

Before:
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After:
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Don, the shop owner only removed enough material to provide a completely flat surface, as expected. This was the second task that I had him do and can definitely recommend him for welding and machining work like this. He is excellent to deal with, reasonably priced, and he is a fellow Delorean owner.


I also picked up a can of POR -15 High Temp paint from Brandon. Thanks!

[DMC-81]

So, the manifold, cat, and front / crossover pipe are ready and waiting for media blasting. I got worried about media getting into the fine screen on the catalytic converter so today, I tried muriatic acid at least around both openings so I could seal them shut beforehand. It worked well, so I continued...

Before:
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After:
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I guess the cat doesn't need blasting anymore.

It looks like the only thing on this part that is mild steel is the square flange with the 4 bolts attached.

Question: does anyone know if the catalytic converter is stainless steel? It sure looked like it when I was stripping the rust off of it. The metal behaved differently than the square flange which skimmed over with light rust shortly afterwards (as you can see in the picture).

What I will paint with the POR-15 depends on the metal. Maybe I just have to paint the flange.

Also, I picked up some aluminum colored "flame proof" paint to refurb the asbestos heat shields for the starter and cat.
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[DMC-81]

Today, I painted these exhaust parts with the POR-15 High Temp. As mentioned previously, I stripped the cat with muriatic acid and I had the other parts glass bead blasted this week. To clean them afterwards for painting, I used a SS wire brush on the little bit of surface rust that formed in the meantime, then high pressure air, and finally, a liberal amount of carberator cleaner to clean off any residue.

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I got confirmation that the catalytic converter and crossover /front pipe are stainless but I opted to paint them anyway for looks. I understand that the cat can reach 1400 degrees which exceeds the tolerance of the POR -15. So, in hindsight I may not have painted the cat, just the square cast iron flange.

I was impressed by how close the color of the POR -15 High Temp Manifold Gray was to the bare cast iron. The manifold on the left has been painted, the one on the right is bare.

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Here are the parts with one coat of paint done. A half pint of the paint is plenty for multiple coats.

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I'll do a second coat tomorrow.

Thanks to Brandon for blazing the trail.

[David T]

Check the instructions. I don't think multiple coats are a good idea. One thin, even coat is all it takes.

[DMC-81]

Check the instructions. I don't think multiple coats are a good idea. One thin, even coat is all it takes.

Hi Dave,

Thanks. I always read the instructions. The can states " A second coat can be applied in 24 hours, depending on ambient temperature and humidity".

[Rich_NYS]

Looking good...!

That painted manifold totally looks like the unpainted one.

[Morpheus]

Looks great, Dana!

[David T]

Hi Dave,

Thanks. I always read the instructions. The can states " A second coat can be applied in 24 hours, depending on ambient temperature and humidity".

While a second coat "can be applied" it may not be wise to do so. In my experience, the less you do to the manifolds the better as far as painting goes. One kind of coating that is sold is a kind of bluing, it is more like a dye and is activated by the heat of the parts that leaves a thin coating so it won't rust. A thick coating won't expand and contract at the same rate as the parts and will eventually crack off. One exception to that is porcelain. That is a thick coating and can last a long time.

[DMC-81]

While a second coat "can be applied" it may not be wise to do so. In my experience, the less you do to the manifolds the better as far as painting goes. One kind of coating that is sold is a kind of bluing, it is more like a dye and is activated by the heat of the parts that leaves a thin coating so it won't rust. A thick coating won't expand and contract at the same rate as the parts and will eventually crack off. One exception to that is porcelain. That is a thick coating and can last a long time.

David, with all due respect, do you have specific experience with POR -15 High Temp? I'm guessing not, since you were unaware of the name change above. You suggested that I check the instructions. Then you still disagreed with the manufacturer's specific instructions as it didn't support your generic opinion. This product is activated by heat and it is well reviewed.

Sorry, but I discount your hypothetical comments. If you have specific experience as Brandon posted above, please share.

[DMC-81]

Today, I applied a second coat on the exhaust pipes. I stripped and painted the 2 OEM plugs for the crossover pipe as well.

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I also cleaned and honed the surfaces for the exhaust ports on the heads today, and cleaned the sides of the engine block.

Here was the driver's and passenger side before honing....

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Here is the driver's side after cleaning and honing. I block sanded them wet, with 320 grit and Gunk engine cleaner. I used a nylon brush and a blue Scotch Brite pad on the block. I still have more block cleaning on the rear of the block to do.

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Here is the passenger side, first pass. I'll hone it a little bit more...

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