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Technical Head gasket vs combustion chamber

Discussion in 'The Hokey Ass Message Board' started by 30tudor, May 31, 2020.

  1. I see the gasket edge is in the chamber. I scratch a line in the gasket material (rubber coating) shown as a silver line. And then lay the gasket back on the block. The bore is 4.030" the gasket is a GM 14096405. The combustion chambers have been modified. Do I modify it, or let the gods of hell fire modify it when I start it. What head gasket should I use?

    DSCN2618.JPG DSCN2627.JPG DSCN2629.JPG DSCN2628.JPG View attachment 4705346 DSCN2633.JPG DSCN2632.JPG DSCN2578.JPG
     
    Last edited: May 31, 2020
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  2. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    Well, you can't just cut or file the offending material away because the folded stainless armor edge isn't thick enough, you risk filing through it or making it too thin and weak to be durable.

    You choices are live with it, it will disrupt flow a small amount possibly but will otherwise be fine....or replace it with a gasket that has a larger bore opening.

    Somebody didn't check the gasket to head fit before modifying the head, or didn't check the gasket vs the head before deciding to put the engine together so they could get the correct gaskets.
     
  3. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,588

    2OLD2FAST
    Member
    from illinois

    Not having pressure on the " fire ring" of the head gasket ,I would think ,would lead to early gasket failure ....JMO
     
  4. This gasket would have given me about 9.5 compression, I'm thinking of going to a solid gasket and see how it fits. Thinner at .015 compressed it will raise the c/r to about 10.1. 2old2fast is right you certainly can't trim the fire ring on a composite gasket but maybe it can be shaved if it's solid.
     
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  5. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    The solid type gasket can be filed or sanded to trim it's shape. I've know of guys who would sand .060" or so out of a 4.100" bore solid gasket so it would fit an a 400 SBC's 4.125" bore(they don't make the solid shim for 400's).

    If your block has been zero decked to the piston height you won't be able to use a .015" shim gasket, minimum piston to head clearance is generally given to be .035-.045", but I've heard of guys stacking two or three of the shim gaskets to get there. Kind of the MLS gasket concept long before gasket companies jumped on the technology and started to offer the MLS(Multi Later Shim)
     
  6. This block has been decked and all the pistons and rings are in it. The depth of each piston in the hole varies from .007 to .017". The combustion chambers all measure within 3cc of 65cc. I'm waiting for the fel pro 7733sh1 gaskets.
    What gasket would you consider here?
     
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  7. Road Angels
    Joined: Mar 2, 2015
    Posts: 121

    Road Angels

    Your going to have to do a custom head gasket mod..that will for sure torch in short order
     
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  8. That's a steel shim , .015 compressed..Not gonna work @ .022 total
     
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  9. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,327

    Mr48chev
    ALLIANCE MEMBER

    Snooping around a bit brings up info that says that gasket is good for an .030 over bore. Makes me want to wander if they were put in the wrong package or damaged a bit.
     
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  10. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,020

    Mike VV
    Member
    from SoCal

    Yea, time for a different gasket, steel shim or otherwise.
    The one you have will work...for a while, but how long is the question. Not nearly as long as it's supposed to.

    Mike

    Mr48chev - The gasket fits the bore properly..!
    The O.P. stated the the chambers had been modified
     
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  11. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    Mr Gasket Ultra-Seal #1134G - .028" thick x 4,130" bore based on thickness and needing a bigger bore than the 4.100" you've got, but I can't tell from the photos if .015" in bore size per side is going to be enough for your case.

    Personally, and if you are searching to maintain a tight quench, in this case with a flat block surface since it has been decked, I'd do two stacked .015-.016" shims with a mist of copper gasket spray between the sandwich. You can trim those easily with a Dremel. Same effect as a MLS gasket without the high price for having it riveted together
    The one 7733sh1 isn't going to be thick enough on the side that is only .007" down at TDC, that will put piston-to-head too close and you risk it hitting as rpm rises and everything flexes and stretches. It the rpm ever gets away from you like a missed shift or broken driveline part you really risk bouncing the piston off the head. The .017" side would be fine with just one gasket clearance wise but I don't know if I could convince myself not to do it the same as the other side.
    Closest I've ever been is .034" piston-to-head in a 7400 rpm 383 stroker with flat top pistons, cast crank and Eagle stock style rods, it would just polish the carbon off the quench section of the pistons, it was that close.
     
  12. Why not use quality gaskets for a 400 SB? JW
     
  13. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    His problem is because the chamber in the head has been modified, clearance cut around the intake valve area for flow improvement and that has made the chamber wider than it was stock. It is now wider than the bore of the gasket.
     
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  14. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    That would work for clearance but kill any quench action due to thickness.

    The standard Fel-Pro composite gaskets for the 4.00" bore are 4.166", so they would also be big enough....but they have the same too thick for good quench problem, being .039+" thick.
     
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  15. S10_Man
    Joined: Oct 29, 2018
    Posts: 18

    S10_Man

    You might check out solid copper head gaskets. They're not cheap but are plentiful for a sbc engine. You can trim them to suit your needs and still should get a good seal.
     
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  16. I appreciate all of your advice, with the one at .007 down how thick a gasket would you consider minimum?
    I see a Mr Gasket no. 1052G has a bore of 4.140 and a compressed thickness of .020. This is a copper gasket that should be able to withstand some clearance adjustment. Too thin?
     
    Last edited: Jun 1, 2020
  17. Ericnova72
    Joined: May 1, 2007
    Posts: 421

    Ericnova72
    Member

    Cast or hypereutectic pistons and under 6200-ish rpm you can probably get by with that .027" total....I've heard of guys running .024" total with no problems but they had repeatedly built the exact same engine combo and had tightened clearance at every rebuild to find the limit...claimer circle track type engine build.

    I've never been brave enough to go below .033-.034" myself, but I always use forged pistons which require more bore clearance and they rock over more because of that.

    Factory SBC originals with the .015" gasket had the pistons down .025" for a .040" total.

    Stacking factory shim gaskets was also mentioned in one of the old Chevy Power performance rebuild books I've got, Joe Sherman and Grumpy Jenkins builds were outlined doing that.
     
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  18. As i see it the head work has increased the combustion chambers volume and the 0.030 overbore would now balance that out and a 400 SB gasket will work....whats the issue? Or is there an exact compression ratio desired? JW
     
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  19. Using block to score heads to create a limit line would have saved a lot on this issue.
     
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  20. It looks like those heads were set up for a much bigger bore. You might look into a Felpro #1003. See if they will fit the head correctly. They are 4.166" and will work on a 4.030" bore. They are .041" compressed thickness and designed for .000"-.005" (in the hole) deck height.

    The only thing I don't like on your block is the .007" to .017" piston to deck height variation.

    https://www.summitracing.com/parts/fel-1003
     
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  21. I don't like the .010" difference in piston height either, went through that a couple of weeks ago.

    A compression ratio a shade under 10.1 is what I wanted JW but it may be a lot closer to 9.3 when it's over. I'm afraid of another composite gasket (felpro 1003 and Mr Gasket 1134G) because I can't shave them at all, the solid gasket should allow me that flexibility. Keep in mind the gasket I started with just missed, there isn't much material that needs to go. Double stacking makes me nervous and 400 gaskets I'm still looking at.

    DSCN2638.JPG
     
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  22. TCTND
    Joined: Dec 27, 2019
    Posts: 121

    TCTND
    Member

    I would call that a head problem, not a gasket problem. Valve relief that's outside the bore is useless regardless of whether the gasket seals or not. Don't mean to sound harsh, just my opinion.
     
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  23. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,343

    ekimneirbo
    Member
    from Brooks Ky

    What I have always found is that when you try to make something work that was done wrong, it often becomes a series of snowballing problems. You have a block that was machined wrong. Then you have a head gasket issue thats going to affect quench if you go too thick and possibly piston to head contact problems if you go too thin. Things like this are (to me) an alarm to back up and start over.
    The best place to start is with the block. Get it machined right. Then check and see how (if) you have the correct distance between your pistons and the deck. If you don't, then if the pistons have enough material, machine the tops of them. If they don't, sell them and buy new pistons. If the heads you have don't work well with what you have, sell them and buy some that do. There must be a kazillion small block Chevy heads available.
    When you try to "make do" and compound the number of things that can go wrong.......something will. Doing things right always works best even if it requires backtracking and redoing to get there. Virtually everyone who has built a few engines has had to deal with something that didn't go as planned. Its part of the learning curve.
     
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  24. All true ^^^ this engine is being put together from a basket so to speak. A basket of parts I collected over the years and it's not working too well just yet. The heads I have given up on, they're both in plastic bags under one of my benches for the time being. I have another pair that are also vintage but were worked on by another shop and do not have the valves unshrouded. They are 291's also with big valves and they have been surfaced. I cc'd 2 chambers last night once I decided to use them and found them both to be 62cc's. I will check them all today and get them ready. And yes, the gaskets fit fine.

    The block finally measured 16, 14, 15 and 17 thousandths in the hole on one side and 07,10,13 and 17 on the other. Poor work by the machine operator to allow the taper to graduate from 7 to 17 tho' on one side. As much as I hate to say it I may live with this.
     
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