Head gaskets and quench

peeeot

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Elsewhere, it has been mentioned that 0.035-0.050 is a desireable target for quench, and that the current head gasket offerings are currently at least 0.025” thicker than the originals. Fel-pro publishes its MLS gasket thickness at more than 0.050”, and I just measured one I took off of a rebuilt 223 and got 0.060” with my calipers.

If the head gasket is 0.050-0.060” thick, doesn’t that make it the limit as to what quench can be attained? If so, since it is possible to buy an NOS steel beaded head gasket, is there any objection to using the old technology to maintain quench and compression? Seems like a head gasket that requires sealant wouldn’t be as reliable as the modern stuff...
 

bubba22349

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peeeot:ei3nra86 said:
Elsewhere, it has been mentioned that 0.035-0.050 is a desireable target for quench, and that the current head gasket offerings are currently at least 0.025” thicker than the originals. Fel-pro publishes its MLS gasket thickness at more than 0.050”, and I just measured one I took off of a rebuilt 223 and got 0.060” with my calipers.

If the head gasket is 0.050-0.060” thick, doesn’t that make it the limit as to what quench can be attained? If so, since it is possible to buy an NOS steel beaded head gasket, is there any objection to using the old technology to maintain quench and compression? Seems like a head gasket that requires sealant wouldn’t be as reliable as the modern stuff...

Yes the ideal quench distance is .035 to .050, but no the limit of the quench can still be changed some even if the new head gaskets are.050 to .060 thick, the Victor head gasket is one of the thinnest at about .045. Still changing the quench distance (i.e. The distance from top of pistion to block deck plus the head gasket thickness) is as simple as decking the block enough to attain your goal. This would bring the pistion tops up above the deck the needed amount to offset the extra of the head gasket thickness. Other ways to change this amount is to increase the crankshafts stroke slightly during the regrinding prosscess (offset grinding) to gain a small amount of extra stroke. Beyond that you could use slightly longer Connecting Rods by custom bushing their small end during the rebuilding process to make them a little longer and most important of all so that they are all equal length. Lastly you could use a set of custom Pistons or some off the shelf Pistons from a different application. Good luck (y) :nod:
 

peeeot

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I didn’t realize it was possible to let the pistons go past zero deck! Good to know.

Do you think using an NOS head gasket would produce a reliable seal for a mildly warmed street car?
 

Max_Effort

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peeeot":2sesfq28 said:
I didn’t realize it was possible to let the pistons go past zero deck! Good to know.

Do you think using an NOS head gasket would produce a reliable seal for a mildly warmed street car?

It’s not unusual to have the pistons protrude above the deck on some engines.

I don’t see any problem with an NOS gasket, unless it was damaged or obviously deteriorating in some way.

What is the NOS gasket made from? Composition (fiber and metal) or steel shim?

Another option is Cometic gaskets. If they already have the pattern in MLS, they can make it in different thicknesses by the amount of layers.

If they don’t have it in MLS, Cometic will make you a custom composition head gasket for around $100. I think the thinnest composition will be around .030” compressed.
 

peeeot

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The NOS gasket is a beaded steel shim. Here is an example: https://www.ebay.com/itm/NOS-1954-1964- ... SwQt9bp5eE The shop manual says to apply a layer of sealer to it at installation.

If the OEM gasket can be expected to work reliably for 50,000 miles or more than I would prefer to use it—very inexpensive and surely the thinnest option. But I will take a look at cometic. It’s nice to know there are more options than fel-pro and victor!
 

Max_Effort

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peeeot":ud5rvorg said:
The NOS gasket is a beaded steel shim.

Steel shim is the the thinnest least expensive option. It doesn't "go bad" in storage unless bent or rusted.

I use them on some SBC for the same reason, increasing compresssion and adjusting quench distance.

As long as your gasket surfaces, the head and block deck are smooth, straight and flat, a beaded steel shim is fine. The sealer is to prevent fluid seepage. Old school is loctite aviation gasket sealant. I've also used copper coat gasket spray and hylomar.
 

bubba22349

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X2 yes if the steel shim gasket is available I'd use it! Most times have used the spray copper coat on them in a pinch though have even used some Aluminun spray paint on them too. Good luck (y) :nod:
 

B RON CO

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Hi, if you use the steel shim gasket many guys paint them, as mentioned.
You also need to re torque them after you run the engine. Good luck
 

powerband

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Steel shim gaskets for 3.50" - 144/170 bore are fairly available and often sold as suitable for 200/250. The 3.68" - 200/250 bore steel shim gaskets (AFAIK) are unobtainable except for rare appearance of NOS on Interweb' sales sites.

.. got one on E-BAy (C9xx), showed up and had been folded in half -creasing it. I returned it...

I have some - used steel shim 3.68" bore gaskets, previous discussions have mentioned re-use but haven't tried..

Original STEEL shim gaskets with 3.50" bore : FELPRO 7915





I run a steel shim gasket with a D7 head cut to 48cc's BUT on a 170 (71 Maverick C9xx block) with the 3.50 bore. With 48cc chambers and steel gasket the 170 is close to 9.5:1 CR. Installed with copper coat spray, it runs great , on 93 octane for over 10 years with no weeping by engine or myself.

have fun
 
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