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Old 06-02-2011, 01:11 PM   #1
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Default MLS (Cometic) Head gasket and Roughness Average - Discuss

With my Cometic head gasket slated to arrive on Tuesday I'd like to get the block and head surfaces as smooth as possible but how smooth is "smooth". Cometic head gaskets require a RA50 or smoother whatever that means.

My head is smooth enough that I cannot feel anything with my fingers or my fingernail when I run it across the surface. However, my block deck has machining marks. When I run my fingernail across it I can feel it "zip" across the machining marks. This cant be good and i'm not looking forward to sanding it down with the block already assembled in the car.

Thoughts?
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Old 06-02-2011, 01:18 PM   #2
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In the past on other cars I've done HG on, as long as there is no raised debris on it thats stuck on and it's flat, it was fine. Cleaned it with scotch pads and a block of wood with 1000grit paper and ran it in one direction to smooth it down a bit. Never had a leak.
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Old 06-02-2011, 01:41 PM   #3
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Originally Posted by falcon View Post
In the past on other cars I've done HG on, as long as there is no raised debris on it thats stuck on and it's flat, it was fine. Cleaned it with scotch pads and a block of wood with 1000grit paper and ran it in one direction to smooth it down a bit. Never had a leak.
Well looks like i'm not going to be able to avoid sanding this block then. How in the hell am I going to keep metal out of the oil galley?
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Old 06-02-2011, 01:55 PM   #4
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1000 grit sandpaper shouldn't create large metal flakes. Tape over every hole in the block, sand it down and use a vacuum to suck up any shavings before removing the tape
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Old 06-02-2011, 06:52 PM   #5
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How the **** is he supposed to tape holes and sand it?

Anton, try a machinist's stone, one of these:

It's a sharpening stone, part number 4474A4, if the imagine doesn't work, I can't seem to find it anywhere else.

Put a few drops of oil on the block, and just hone it like you'd wax your hood, smallish, fast circles. Then just wipe it down a million times, until your cloth comes off clean. This'll help maintain the block's flat surface much better than sand paper would.
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Old 06-02-2011, 07:17 PM   #6
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Well looks like i'm not going to be able to avoid sanding this block then. How in the hell am I going to keep metal out of the oil galley?
Ive had some places actually have a farly rough surface intentionally but I didnt ask why they did it. I used the spray on permatex copper stuff just because I think it would help with any imperfections.

Bob
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Old 06-03-2011, 03:16 PM   #7
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Ive had some places actually have a farly rough surface intentionally but I didnt ask why they did it. I used the spray on permatex copper stuff just because I think it would help with any imperfections.

Bob
This is exactly what i was hoping to hear. People can tell me that I need to polish my block deck and head all day long but as long as people have gotten by just fine without doing that then i'm not going to worry about it. I'll definitely spray the gasket with the copper stuff.
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