blown head gasket cylinder head question.

[mizozuman2]

when you have a blown head gasket on one side, do you have to mill down both cylinder heads?

(do I have to mill down the passenger side cylinder head, if driver side cylinder head had the blown head gasket)

[bd]

You shouldn't need to "mill" either head.  Surfacing is not the same as milling. 

Now, stop and think about a blown head gasket for just a moment.  If a head gasket is blown, you need to determine why it is blown.  If it is due to gasket deterioration or poor maintenance, how do you suppose the opposing head gasket will look?  Tearing an engine down to the point of replacing one head gasket is almost as much work as removing the second head at the same time.  Don't "play the odds" or you may wind up doing the job twice!  Inspect the head bolts thoroughly for rust, pits, nicks, obvious stretching, etc.  If even one bolt is rusty or pitted, etc, replace all of the bolts as a set.

[77 longstep]

Look for a little crack in the head.  This often happens to cause the head gasket to blow.  Don't ask me how I know,
Greg

[mizozuman2]

There's no cracks on the heads. Either side. They're both removed. The driver side gasket in the farthest back piston has broken. (I'll upload pictures in a second of what it looks like.

[Engineer]

If there is no visible sign of deck damage I wouldn't plane the head.

99% of the small block Chevy gaskets just fail. Many times from miles and miles of detonation.

I have head gaskets fail right to a head bolt. I have put them back together with premium parts and they continued on for many miles.

[mizozuman2]

Alright, here's the gasket (Both sides of it), and the chamber for that cylinder. The only thing I see is some spots that have been LIFTED (Towards me when facing the chambers). Some of it flaked off, some of it seems to be stuck on there.












And here's the piston's. I'm fairly sure these aren't stock, and it's an .040 bore (It says 040 on the top of the pistons, anyways)



Thanks for looking.

[bd]

Clean up the head and block gasket surfaces using some 100 or 120 grit emery cloth wrapped around a hard, flat sanding block.  Then, check the gasket surface for flatness using a long precision straight edge.  If the fire ring surfaces on the head and block are not eroded (notice the shiny 'ring' imprint surrounding the combustion chamber that corresponds to the metal edge that tore and flaked away from the gasket in your image) then I agree with Engineer - you do not need to machine the head or block.  How do the bolts look?

[mizozuman2]

The bolts looked oily when I pulled them out. I cleaned them up, and they look just fine. I might get some new ones though, just to play it safe.

When you say eroded, do you mean that that fire ring is no longer visible in that area?

Thanks.

[bd]

When the head gasket failed, hot combustion gases blew past the fire ring into the coolant passages.  Over a long enough period of time hot combustion gases can etch (erode) the sealing surface of the head.  The sealing surface where the fire ring seats must be absolutely flat.  If there is a "dip" in the surface the new gasket won't hold.  So, after sanding the surface as described in a previous post, place the straight edge across the head at the location the head gasket failed and make sure there isn't a low spot or gap between the straight edge and the head surface.

[mizozuman2]

Awesome! Thanks for the info