Gasket gap ins and outs

[turbohunter]

Ok, first let me apologize for this study in minutia but sometimes I can't let things go.
One of the things that bothered me when I pulled my truck engine down was the large ring around the top of the cylinder. At the time I had some pretty bad oil control problems which have gotten better but persist a bit to the present day. Getting back to that ring I began to wonder about the area of the gap between the cylinder head and the top of the cylinder. How does that gap affect the burn in the cylinder? Is the area of the gap worth thinking about concerning compression? I hate that it is not a perfect burn chamber and gathers garbage in that gap. Are the sharpe edges more prone to cause predetonation?
I did the math on the area contained in the gap and indeed it seems like not much of a big deal to me but I'll let those more experienced talk about it. I used an example of a .030 over 390 with a 1020 Felpro headgasket. Gotta be tons of those out there.
Here is the math I used
Bore x bore x gasket thickness x 12.87
This gives you the area in cc of the gasket, so if you do the area of the gasket bore and the cylinder bore then subtract the area  of the cylinder bore from the area of the gasket bore you end up with the area of the gap. So it ends up being 10.215 minus 8.783 equals 1.432. So a cc and a half of space in the gap.

The pic below drives me nuts. Which is why I asked Ryan to build a new gasket.
So guys check my math and would you comment on the above questions? Am I just solving a problem that's not really a problem? I almost want to pull my engine down again to check all this out.

[CaptCobrajet]

I wouldn't fret on that minor volume.  You can easily overcome that by milling .007 off the heads, in terms of compression ratio.  I have never seen evidence of detonation around that "ring".  Healthy engines will build carbon there, and it helps to self-heal the space.  Not trying to be critical, but your engine seems to have a huge oil problem.

Since your pic shows it with great clarity, check out that little tab on that 1020 gasket that's hanging over in the water hole.  That tab is responsible for rusty decks when using 1020s.  It is just enough to seep water between the gasket and block, and it traps there and chews on your block until the next teardown.  1020s work good when they don't do that.  Some blocks don't have that situation, some do....

A nicely honed cylinder and some better rings, tight valve guides, and Viton seals will dry that baby up.  Also pull your pcv hose.......if it's full of oil, re-examine your baffling.  If that hose is dry, look closer at you intake gasket seal on the bottom......intake fit, etc....just my two cents......

[turbohunter]

Thank you very kindly Blair.
That is an old picture that gave me the idea about a new set of gaskets. I have since pulled the engine down and regasketed the deal.
Yes that deck was deplorable. I'm sorry if I was not clear that that was an old picture. The idea of the thread was about the gap between the head and block. I used that picture because it illustrated very well the amount of space (in width) between the head and deck using that gasket. I pm'd you the other day about a new gasket that I will send you to check out that fixes some of those problems like the tab that you laid out.
You answered a couple of my questions, one about detonation and one about not worrying about the volume in that space. Let me ask you this. Let's say you are a wackadoodle (me) that is really bothered by that space and the volume. You deck the head to make up for any volume you might give away but if you use that same gasket (the 4.400 Felpro) you still have a space. Wouldn't you rather see the gasket right close to the edge of the cylinder and the head chamber?

Like this.

[Heo]

I rather have the new gasket

[CaptCobrajet]

Yes.  You never want gasket hanging over into the chamber.  I like to be .030 or so bigger than the head.  It will squeeze in there some when compressed.  One can also carefully chamfer a block to more closely match the gasket/head........

[scott foxwell]

I just spent almost two hours yesterday getting my (expensive) Cometic 4.08 bore head gaskets to not hang in the bore. Every cylinder had to be trimmed on one side. It was almost as if the dowel holes weren't in the right place. Very frustrating.

[turbohunter]

Aha. That's kinda what I was looking for.  .030 or so larger than the edge of the head, cool.
That sounds perfect.
Now having said that, on the iron Ford heads that Ross and I have sized so far the 4.250 gasket does hang out a bit on the top (head side) so the bigger size bore 4.350 that I will send you when built may be just the ticket for that.
As I've said in the past I've been running the 4.250 gasket (because I didn't know any better at the time) on a 4.125 bore and D2 heads for a couple years now with no problems yet.
Here's a pic of the 4.250 gasket and a C3 head.

[turbohunter]

I just spent almost two hours yesterday getting my (expensive) Cometic 4.08 bore head gaskets to not hang in the bore. Every cylinder had to be trimmed on one side. It was almost as if the dowel holes weren't in the right place. Very frustrating.

I'll tell you this Scott, we're working very hard on fit. It's a big problem. Especially with all the different blocks, Ford and aftermarket.

[turbohunter]

Hey Scott let me ask you a question. The Cometic being a layered gasket, obviously you're asking for problems with it hanging in the cylinder. Now imagine that gasket had a big old nasty fire ring around the edge and it's a street car with let's say up to 550 hp. You worried about the gasket? Not saying it's right but.......

[scott foxwell]

Hey Scott let me ask you a question. The Cometic being a layered gasket, obviously you're asking for problems with it hanging in the cylinder. Now imagine that gasket had a big old nasty fire ring around the edge and it's a street car with let's say up to 550 hp. You worried about the gasket? Not saying it's right but.......

With 550hp I'd say yes. You're obviously investing some time and money in this engine. I would not compromise anything in the combustion chamber. With a stock rebuild, maybe not but it still isn't right.
Fortunately there is a big percentage of the cylinder that is covered by the quench part of the chamber. I'm not so concerned if it hangs over a little in that area. It's pretty much out of the way. I just don't want anything hanging inside the combustion chamber area.
The nice thing about the Cometic is you can trim the edge of the chamber area and as long as you don't get into the embossed ring, you're fine. You can't do that with a traditional crimped fire ring like you have with a composite gasket. I really didn't like the shape of the 4.08 Cometic gasket. If I had more time, I'd work with them on making some changes.

[turbohunter]

Absolutely get it. I'm just kind of amazed that mine is still working well.
As I said before I have half a mind to pull mine apart just for fun to see what's up.
I haven't used Cometics so I'm not familiar but I'm learning on a steep ramp.
I have you all to thank for that.

[scott foxwell]

Absolutely get it. I'm just kind of amazed that mine is still working well.
As I said before I have half a mind to pull mine apart just for fun to see what's up.

With the smooth edge of the composite fire ring, I don't think the problem would be as bad as the MLS.

[turbohunter]

Agree

[TorinoBP88]

There are different shape gaskets, some round, some d shaped or Pentagon shaped to better match the chamber.

Gaps usually carbon in over time.

[turbohunter]

There are different shape gaskets, some round, some d shaped or Pentagon shaped to better match the chamber.

Gaps usually carbon in over time.

Yes sir you are correct. In fact the company that SCE acquired (SPM) made some of those. If I remember correctly they are a steel sandwich type composite. I'm actually having some of that old stock sent to me to check out. Another example of none round bores would be steel shims. Obviously these have all worked in the past (and nowadays) but the way we are tuning up our oil systems these days (for instance hv pumps) we felt like a new style composite with great components would have a place in the street driven FE world.

As far as the gaps filing over time. Yes, but if it's me I'd rather have a nice mechanical fit that came darn close to the edge of the chamber/bore. That measurement of .030 that Blair mentioned seems like that would make a happy clean cylinder.