FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: rcodecj on December 14, 2011, 10:23:45 AM
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Is there a .020 head gasket that will work on a 390 with aluminum heads?
I'm thinking they would have to be a steel shim or copper, and I guess that doesn't work on street engines or what?
My pistons are .019 in the hole and the engine originally had a .020 steel shim type gasket but that was with iron heads.
Would Cometics maybe be able to make a .020 head gasket similar to the Fel-Pro 1020?
Thanks.
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.027 is as thin as cometics go when i inquire a few months ago, solid copper may be possibility
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That would be an improvement over the Fel-Pro.
Hopefully they don't require a freshly decked block, as mine is original untouched.
That would give me .046 quench which would be great compared to .060.
I guess I should call them to see what it looks like.
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I see the Fel-Pro 1020 gasket bore is 4.4.
Is that necessary?
Since the standard 390 bore is 4.050, maybe go with a 4.080 gasket to further reduce volume?
I seem to recall that you want the head gasket larger than the bore by some amount to create a squish area for better combustion. Thoughts?
I hope I can get a steel core laminiate gasket from Cometic at .027, that would be great.
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Should be no problem getting that Cometic gasket; I just got a .027" set of Cometics for one of my SOHC projects. On a factory block, you might want to put a little copper spray (Copper Coat is one brand, I think) on the gasket, just to ensure a good seal. But it is probably not necessary. And I run Cometics on the street regularly, so that shouldn't be an issue for you.
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So Jay, what's you take on OEM type 100% steel head gaskets with aluminum heads?
The cylinder head makers seem to frown on them for all the reasons they normally list but....I do know of some who have successfully done so for exactly the same reason as our poster gave....keeping quench to a minimum with an undecked block.
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I used a set of Cometics on a 410 build with Edelbrock heads. The decks were messed up and the block wasn't bored yet so I had no way of dummying it up to measure the deck height. I had the decks squared decked, and once the block was bored and torque plate honed, line bored, etc. I dummied up the assembly to check deck height and piston to valve clearance in case I needed to flycut the pistons... before I had the assembly balanced.
The pistons turned out to be .014 in the hole, instead of re-decking the block for zero deck for an additional 100 bucks, and using the normal .041 thickness 1020 Felpro gasket, I left the block alone and used the .027 Cometic to get it where it would be happy. I used the 4.160 bore gasket for the 4.080 bore. The reason for that was the Edelbrock heads have a chamber that is 4.160 wide and I didn't want the 4.080 bore gasket to be hanging out under the head (in the chamber).
You can get lots of different gasket thicknesses from for the FE and with bore sizes of 4.080, 4.160. 4.250 and 4.400. I always wondered why the didn't do a 4.310 also..... maybe custom. They open up the gasket bore bigger where the intake valves would direct the flow cone, or where the blocks would be "notched" or relieved, for large valves... a little more than I think is needed, but they probably know more about this stuff than I do!
With the difference it bore diameter and the thickness of the gasket there really isn't that much difference in CC volume to get too concerned as far as "loss" of compression. Use one that works best for your combo... lots of choices!
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How can the Edelbrock head chamber be 4.160 wide? I'm confused. ???
I would think 4.080 on a 4.050 bore would be okay but I don't have my heads off yet.
So you think I need it to be .080 larger than the bore?
Thank you for the information though.
I calculated the change from 4.4 bore gasket to 4.08 bore gasket on a .027 gasket to change compression from 9.06 to 9.14, maybe I did something wrong.
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So Jay, what's you take on OEM type 100% steel head gaskets with aluminum heads?
The cylinder head makers seem to frown on them for all the reasons they normally list but....I do know of some who have successfully done so for exactly the same reason as our poster gave....keeping quench to a minimum with an undecked block.
I've never tried that, but I'd be a little concerned about the relative movement between the head and the block causing leaks over time. That said, if I really needed a .020" head gasket, I'd try it too!
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I had very small water leaks on this engine with the Mr Gasket head gaskets. They are from the whole engine gasket kit. They are all white some kind of composite with no webbing and a small steel ring on the inside of the bore. I had the same leaks on my 460 with this style gasket and used a Victor Reinz gasket and it cured the problem. I don't know why I didn't remember that when I assembled this engine. I now keep a list of every part I use so that doesn't happen again. The mind kind of went about the same time as the close up vision!
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I do know that minor brinelling or spalling to the heads and water leaks are the most common questions, yet folks do run them with spray copper coat or aluminum paint (VHT type header paint) to prevent leaks. Hey, it is only .007 difference (OEM Ford @ .020 versus Cometic's @ .027) yet the Ford gaskets are often still available from Ford, Summit, Jegs and are much cheaper. But, I'll admit the block deck had better be dead flat and quite smooth.
http://www.network54.com/Forum/74182/thread/1167345504/1167371351/Question+on+steel+shim+headgaskets%2C%2C%2C%2C%2C%2C
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Is the Cometic gasket we are referring to an mls gasket?
If so they do not recommend a sealer.
Here's a link to faq: http://www.cometic.com/faq.aspx#q2
They also require a surface finish of 50 RA, whatever that is. I know it's roughness average, but what is stock?
It looks to me like they must have a fairly smooth surface to seal.
Hmmm, I'm starting to worry about water leakage with a stock undecked block.
I would be inclined to use the copper coat despite what they say. :-\
XR7, did you use sealer?
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That's what I'd do, too. The Cometics are MLS gaskets, but use the copper coat anyway. Done it quite a few times, with no problems. Especially if you are re-using the head gaskets.
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I think I will call Cometics after I pull the heads to see what issues there may be with the combustion chamber size/location side to side as far as dimensions go.
Then I will decide a bore diameter for the gaskets.
My Edelbrock heads are Barry R stage X heads with 2.2 intake and 1.71 exhaust valves.
There may have been some unshrouding of the combustion chamber for the bigger valves, I don't know.
I know bore diameter of the gasket won't mean much, but as long as I'm ordering a custom gasket I may as well get as much compresion as I can.
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Is the Cometic gasket we are referring to an mls gasket?
If so they do not recommend a sealer.
Here's a link to faq: http://www.cometic.com/faq.aspx#q2
They also require a surface finish of 50 RA, whatever that is. I know it's roughness average, but what is stock?
It looks to me like they must have a fairly smooth surface to seal.
Hmmm, I'm starting to worry about water leakage with a stock undecked block.
I would be inclined to use the copper coat despite what they say. :-\
XR7, did you use sealer?
Yikes, trying to 'show' a 50 RA finish is tough here on the 'Net...LOL! Generally, a factory deck for any older engine design (FE, Cleveland, 385 BBF) is rougher than 50. Note the link:
http://www.enginebuildermag.com/Article/1459/common_mistakes_to_avoid_when_resurfacing_cylinder_heads__blocks.aspx
Keep in mind though that Cometic will likely supply a MLS gasket with the proper surface coating (see the article, they specifically mention this) ) to handle even a rougher OEM factory finish. And heck yes, if you need to order a copper gasket set, get the proper bore size to minimize cc inflation as that's the whole purpose of this exercise in minimizing quench.
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How can the Edelbrock head chamber be 4.160 wide? I'm confused.
Because that is what they measure out of the box, on bare or assembled heads, when they machine the chambers for the seats, the outer walls are cut at the same time or just part of the normal machining process. That is before the valve job, if there was any "un-shrouding" done... it will be even wider. Your chamber is wider than your bore, you will see when you take it apart. Having said that... there are plenty of 390's running hard with Edelbrock heads.
You have pretty big valves for a 4.050 bore... I was thinking your bore was 4.080. I am guessing your exhaust valve is very close to clipping the bore.
I did not use sealer when I first put it together, all decks were fresh machined and smooth, Cometic doesn't recommend sealer. I have re-used Cometic's on the same engine before, then I do use copper coat before assembly after I have cleaned everything up, as best I can. No problems sealing to date. In your case... I would most certainly use it.
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As far as Cometic head gaskets go I am changing course and just going to go with the Felpro 1020.
It won't run as good, but it'll run a bit better than it did and hopefully not leak.
This shortblock and the iron heads that were on it are going to a friend anyway.
I can live with it as is until I build the other motor (428)
Sometimes I sweat the details too much, but that's part of the fun.
Thanks for the help guys.
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You have pretty big valves for a 4.050 bore... I was thinking your bore was 4.080. I am guessing your exhaust valve is very close to clipping the bore.
I wanted to make a correction so people don't go out and use 1.71 valves on a stock bore 390 base on my comment.
My exhaust valves are 1.66.
Sorry for the confusion.