Exhaust manifold mating surfaces - how clean

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NotCruzing

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Discussion starter · #1 · May 26, 2025

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How clean do the mating surfaces of the exhaust manifold need to be?

Each of the 4 oval "passages" are pretty clean for about 1/2 inch diameter. Otherwise, a bit rough as shown in photos below.

We used a plastic scraper, red scotch-brite, and brake cleaner. Have new GM gaskets for both sides. The engine block side came out "almost pristine".

Thank you for your tips and comments.

 

15cruzediesel

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#2 · May 26, 2025

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I have always used a wire brush on a drill.

 

Cruzing12

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2nd 2012 1.8l mt 220,000km

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#3 · May 26, 2025

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Yeah brass wire brush on a drill. The steel is pretty resistant


Aluminum has always been a razor blade ran at multiple angles

 

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NotCruzing

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Discussion starter · #4 · Jun 2, 2025

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Thanks gents.

We found a brass hand brush in the basement. About 15 minutes of brushing cleaned the surface up pretty well.

We did look for a brass wheel for a drill; all the stores we visited sold steel brushes with a brass "coating"; the wires were magnetic (and the packaging never mentioned brass).

However, we found a brass wire cup brush on Amazon (Weiler 14311) for $28 but didn't want to wait for it (or spend the money lol).

 

15cruzediesel

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#5 · Jun 2, 2025

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NotCruzing said:

Thanks gents.

We found a brass hand brush in the basement. About 15 minutes of brushing cleaned the surface up pretty well.

We did look for a brass wheel for a drill; all the stores we visited sold steel brushes with a brass "coating"; the wires were magnetic (and the packaging never mentioned brass).

However, we found a brass wire cup brush on Amazon (Weiler 14311) for $28 but didn't want to wait for it (or spend the money lol).

Click to expand...

I've always used steel on cast iron with no issues. Light pressure medium drill speeds.

 

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NotCruzing

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Discussion starter · #6 · Jun 4, 2025

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Finished the oil cooler project. Everything about that was painful. Several neighbors dropped by to cheer us on.

Engine runs much quieter too. I assume for the engine-manifold mating surface cleaning. And for sorting out the 3 flange studs. The 02 bung threads were a mess, so a thread chaser probably helped seal that better too.