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Old 09-30-2007, 03:26 PM   #1
TreyS
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Question What should I do to clean mating surface?

Hello,

I recently blew my head gasket and had the heads resurfaced. It now has a mirror finish. What I need to know is what is the best way to clean the block's mating surface so it too is ready for a great seal once I reassemble everything. Right now there is old head gasket residue on it.

I appreciate your suggestions.....
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Old 09-30-2007, 09:14 PM   #2
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First clean the old gasket with a razor blade

Then sand it with 220 grit. If its aluminum do it by hand. If its anything else you can use a cookie wheel.

Then clean with brake cleaner.
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Old 09-30-2007, 09:44 PM   #3
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Thanks. The block is an 04 STi so it is aluminum. When you say "cookie wheel" do you mean a sanding disc on an air tool?

Thanks!
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Old 10-01-2007, 08:06 AM   #4
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Quote:
Originally Posted by TreyS View Post
Thanks. The block is an 04 STi so it is aluminum. When you say "cookie wheel" do you mean a sanding disc on an air tool?

Thanks!
Yes but do not go near aluminum with the cookie wheel. An amateur mechanic can and will destroy the block / heads with an air tool. It will be ruined and no you probably cant fix it. You can even ruin an iron block if you grind down too much.
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Old 10-01-2007, 09:23 AM   #5
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Sounds like a light duty scotch brite pad may be a better choice.



Quote:
Scotch-Brite™ Light Duty Cleansing Pad
Soft, non-woven fibers and mild abrasive clean most surfaces gently, but thoroughly. Ideal for stainless steel, chrome, copper, porcelain and ceramic.
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Old 10-01-2007, 12:46 PM   #6
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I have a flat steel block I can either wrap with sand paper or you those adhesive disks. Any very flat thing will do but you can usually find drops for pretty cheap at a metal supplier or even a machine shop. I would recommend against using scotchbright since you don't know if the surface is flat. If you use a know flat sanding block any low spots on the surface will show up. I'd use 800grit paper and WD40 as a lubricant while making a figure 8 across the surface.
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Old 10-01-2007, 02:23 PM   #7
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Good info!!

Thanks!
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Old 10-02-2007, 04:18 AM   #8
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I've been using a bench mounted wire wheel to clean my block and the mating surfaces. Haven't gone near the deck with it though to avoid my freshly honed bores, but the outside is coming up nice!

I bought a wire wheel that you put in a hand drill today and attacked the bits I couldn't reach with the bench brush, but need a real small one to get into all the tight spaces...

I noticed a little bit of rounding on some of the edges but nothing to really worry about.
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Old 11-06-2007, 11:55 PM   #9
Patrick Olsen
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Late last week I picked up an assembled short block from a machine shop. I didn't really look too closely at the head mating surfaces as it was getting dark, but they said they were already cleaned. Now that I've put the engine on my stand and have taken a look, though, it doesn't look to me like they were. The machine shop's an hour away, so I'd rather just do this myself than spend 4hrs driving to/from the shop to drop off and then pick up the engine.

So, any tips on cleaning the head gasket mating surface of the block on an assembled shortblock? Obviously I don't want to get any mung into the cylinders. My thinking is that tilting the engine on the stand and cleaning the face that's pointed down towards the floor (so gravity helps keep stuff out of the cylinders) is a start.

Thanks,
Pat Olsen
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Old 11-07-2007, 12:07 AM   #10
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I'm using a flat sheet of glass (window) with sand paper glued on it. A few drop of oil also on the sand paper. (split block half)
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Old 11-07-2007, 01:37 AM   #11
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Quote:
Originally Posted by TreyS View Post
Sounds like a light duty scotch brite pad may be a better choice.

Even regular scotchbrite would be fine if you're careful. I have a box of this light-duty stuff, and it's really only good for scrubbing counters.

Whatever you do, don't use a putty knife or anything steel for that matter. If you leave any steel in there, it can create galvanic corrosion down the line and cause you to end up with leaks.
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Old 11-07-2007, 02:38 AM   #12
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Quote:
Originally Posted by TreyS View Post
Hello,

I recently blew my head gasket and had the heads resurfaced. It now has a mirror finish. What I need to know is what is the best way to clean the block's mating surface so it too is ready for a great seal once I reassemble everything. Right now there is old head gasket residue on it.

I appreciate your suggestions.....
I used lacquer thinner, works like a charm.
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Old 11-13-2007, 07:39 PM   #13
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600 grit wet sanding paper, a bondo board, some saran wrap and some vaseline.
Smear Vaseline around the top of the bore, stick a cylinder of saran wrap to it to where the saran wrap is just below the deck, slowly, smoothly and straight sand with the bondo board with the 600 grit wet with wd40, go one direction across the deck for about 15-minutes, then intersect that direction at a 60* angle and do the same till it's nice and smoooth, clean with brake clean when done.
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Old 11-13-2007, 08:11 PM   #14
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Take it to a machine shop and have them shave a few thousandths off. Shouldn't be much more then $100 and it gets the mating surfaces perfectly flush on the block and heads.
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Old 11-13-2007, 10:13 PM   #15
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do it by hand..i usually have bits of 220 or 440
that i use.
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Old 11-13-2007, 10:34 PM   #16
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i use little scotch brite-like pads on an air angle drill, use the fine stuff. got mine at harbor freight for like $3-$5. i then finish up with 600 wet sanding paper on the hard to reach areas. If you do this go slow, i turn the speed on the air tool down a bit so i cant remove material.

but ill try laquer thinner next time......didnt think of that.


~Josh~
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Old 11-14-2007, 12:06 AM   #17
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DO NOT USE SCOTCH BRITE!
It's not simply that it's aluminum oxide but it's fragile "sponge" that come art easily and little bits get everywhere unlike sand paper, this especially true when using a small air rotary tool.
Contamination with this stuff will chew up any surface in your engine.
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Old 11-14-2007, 12:07 AM   #18
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Quote:
Originally Posted by MY99 2.5GT View Post
Take it to a machine shop and have them shave a few thousandths off. Shouldn't be much more then $100 and it gets the mating surfaces perfectly flush on the block and heads.
This is the best way.
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Old 11-22-2011, 11:31 AM   #19
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Bump for more answers to this, preferably from people who did it successfully and ran without headgasket or other issues....
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Old 11-22-2011, 12:29 PM   #20
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we have a round flat sanding stone that i used on my block. we usually use it to clean tgv and intake manifold surfaces. still running and no problems. I did it to my moms leggo as well when i put new headgaskets on it. just make sure you blow everything out real good when your done.
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Old 11-22-2011, 12:36 PM   #21
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Quote:
Originally Posted by MY99 2.5GT View Post
Take it to a machine shop and have them shave a few thousandths off. Shouldn't be much more then $100 and it gets the mating surfaces perfectly flush on the block and heads.
+2

Itís the only way to do it properly, the surface finish of the mating surface should be > 35 RA (I believe that is what most MLS head gasket manufactures suggest) - do it right and save yourself the heartache later.
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Old 11-22-2011, 01:00 PM   #22
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When you talk about taking the stuff to machine shop. Can they do it safely/cleanly without disassembling block or the heads?

Basically I have a block and heads that I want to put together without disassembling anything. Both block and head are low mileage and do not require messing up with.

They also should not require decking, which as I understand involves removing more material (and I believe the allowable amount to be removed is very low). My plan was to clean them, use straight edge/feeler gauge to check if they are true, and put together.
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Old 11-22-2011, 02:25 PM   #23
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Quote:
Originally Posted by Built Industries View Post
the surface finish of the mating surface should be > 35 RA ...
I've tried searching and haven't had any luck. What is RA? I've seen the term used in a number of threads about head gaskets, but I haven't been able to find what it means and what it's a measure of.

Thanks!
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Old 11-22-2011, 02:39 PM   #24
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Old 11-22-2011, 03:04 PM   #25
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It has a lot of a fail (scotch brite for example), but I thought it's better to bump an existing one than to start a new one (with new fail).
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