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Doing head gaskets on ej25. Had heads machined, but can't seem to get all the black coloration off the block mating surface.even with green scotch bite and break clean, How clean does the block mating surface have to be?

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You won’t get that off without machining. 

Block deck needs to be cleaned so there’s no old head gasket material left. I use a flat blade to do this.

Once you’ve done the blade work and are satisfied that you’ve got all the gasket off, I then wipe down with a white spirit like metho. 

Then assemble. 

Cheers 

Bennie

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Subaru calls for the use of the 3M "white" bristle discs. They will take all that off no problem. That's all we use on block surfaces. 

GD

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23 hours ago, el_freddo said:

You won’t get that off without machining. 

Block deck needs to be cleaned so there’s no old head gasket material left. I use a flat blade to do this.

Once you’ve done the blade work and are satisfied that you’ve got all the gasket off, I then wipe down with a white spirit like metho. 

Then assemble. 

Cheers 

Bennie

So your saying it okay to leave those black lines on the deck face. Just clean off the gasket material with razor blade and reinstall the head. The lines look like their in the metal, not sitting on top of the metal.

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4 hours ago, steve56 said:

So your saying it okay to leave those black lines on the deck face. Just clean off the gasket material with razor blade and reinstall the head. The lines look like their in the metal, not sitting on top of the metal.

That’s what I’ve always done. No issue. 

GD might have something to say about my method though. I’m keen to know more about this white bristle disc use...

Cheers 

Bennie

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11 hours ago, steve56 said:

So your saying it okay to leave those black lines on the deck face. Just clean off the gasket material with razor blade and reinstall the head. The lines look like their in the metal, not sitting on top of the metal.

 

Yup.

Wipe down with lacquer thinner, or spray with brake clean and let dry before installing gasket.

I personally dislike the bristle discs.  They are fast, but can damage block if used too aggressively.  even the white ones.

I am sure GD and hopefully his workers know how to use them correct, but since I do just one or 2 a month I go the slow, by hand route to clean.

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I used the 3M bristle wheels AFTER scraping with a razor and wiping.  They work really well and you honestly have to be a brainless, hairy-knuckled mouth-breather to damage the block with them.  Take care, take your time, keep the pad 90-degrees to the gasket surface and don't let the thing grab the edges of the block and yank the tool around.

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Quick update. My Subaru tech friend stopped by. Said the black lines are caused by decalcification. Said  the head gaskets would seal but could fail prematurely. 

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Decalcification? This would imply (I assume) a source of calcium. Now I'm no chemist or even metallurgist, but this seems unlikely. 

I call BullSh1t. 

Show us a picture. 

GD

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The black lines are caused by the black coating of the head gasket transferring to the block's gasket surface and adhering due to heat, pressure and micro galling.  It ain't decalcification.  Google doesn't even have a good result for "engine decalcification."

I'm with GD on this.

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4 hours ago, carfreak85 said:

The black lines are caused by the black coating of the head gasket transferring to the block's gasket surface and adhering due to heat, pressure and micro galling.  It ain't decalcification.  Google doesn't even have a good result for "engine decalcification."

I'm with GD on this.

Thanks carfreak. Do you use 

 

4 hours ago, carfreak85 said:

The black lines are caused by the black coating of the head gasket transferring to the block's gasket surface and adhering due to heat, pressure and micro galling.  It ain't decalcification.  Google doesn't even have a good result for "engine decalcification."

I'm with GD on this. Do you use the 

14 hours ago, GeneralDisorder said:

Decalcification? This would imply (I assume) a source of calcium. Now I'm no chemist or even metallurgist, but this seems unlikely. 

I call BullSh1t. 

Show us a picture. 

GD

Thanks I was hoping my friend was wrong. 

 

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4 hours ago, carfreak85 said:

The black lines are caused by the black coating of the head gasket transferring to the block's gasket surface and adhering due to heat, pressure and micro galling.  It ain't decalcification.  Google doesn't even have a good result for "engine decalcification."

I'm with GD on this.

Thanks for the explanation. That makes more sense than decalcification.

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13 minutes ago, carfreak85 said:

Looks like you had a question that you didn't finish typing?  Do I use...?

My bad. I meant to say, do you use the 3m white bristle disks like GD, or just the standard brake clean and razor blade routine.

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Both.  The razor can gouge the block's sealing surface, so it's actually better to just use the 3M wheel, then wipe down the surface.

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On 6/13/2019 at 1:13 PM, carfreak85 said:

Both.  The razor can gouge the block's sealing surface, so it's actually better to just use the 3M wheel, then wipe down the surface.

 

On 6/13/2019 at 1:13 PM, carfreak85 said:

Both.  The razor can gouge the block's sealing surface, so it's actually better to just use the 3M wheel, then wipe down the surface.

Just ordered a two back of the 3m white bristle. Can I use them with a drill or do I need to go get a die grinder.

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1 hour ago, GeneralDisorder said:

You can use a drill on high speed with the block surface setup vertically. But we use 90 degree air die grinders. 

GD

How much pressure do I apply with the die grinder to make sure I'm not damaging the block? 

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Start with very light pressure and increase as the deposits require.  Like GD mentioned, once you get into it you'll find the 3M discs are pretty hard to screw up the block with.  You'd really have to fall asleep at the wheel to do damage.

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On 6/12/2019 at 3:09 PM, steve56 said:

Quick update. My Subaru tech friend stopped by. Said the black lines are caused by decalcification. Said  the head gaskets would seal but could fail prematurely. 

A Subaru tech said that?  I dont have a problem being wrong - that’s how we learn. but misguiding/guessing under the ruse of “Subaru tech” or professional...come on, that’s not helpful. 

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