Head gasket question

[Robert M.]

I am looking to purchase a pair of head gaskets for my '70 L46. It has been bored .030 over. The GM 10105117 composition gasket is .028" compressed, which what I'd like. The GM catalog says that this gasket is for 4.00" cylinder bores. My deck clearance is .025"

Is this gasket acceptable with my .030" over bore, or should I seek a differnt one?

[Duke W.]

Re: Head gasket question

Run the numbers through the CR calculator. You want it to be no more than 10.5.

Use 2.4 cc for piston dome volume and read the instructions to get the sign right.

If your heads have not been milled or the chambers ground, use 64 cc. If they show evidence of post-Flint machining, measure the chamber volumes.

You can use different available gasket thicknesses to determine what it takes to get it to no more than 10.5.

Let us know what CR and gasket you end up with.

http://www.csgnetwork.com/compcalc.html

Duke

[Robert M.]

Re: Head gasket question

I should have stated that the gasket in question would be if I used flat top speedPro 631-30s. Compression would be 9.97 if I did the calculator correctly. My concern was if the gasket is too tight for the .030 over bore.

[Clem Z.]

Re: Head gasket question

I should have stated that the gasket in question would be if I used flat top speedPro 631-30s. Compression would be 9.97 if I did the calculator correctly. My concern was if the gasket is too tight for the .030 over bore.

if it does not over hang the cylinder bore it should be fine

[Joe C.]

Re: Head gasket question

I am looking to purchase a pair of head gaskets for my '70 L46. It has been bored .030 over. The GM 10105117 composition gasket is .028" compressed, which what I'd like. The GM catalog says that this gasket is for 4.00" cylinder bores. My deck clearance is .025"

Is this gasket acceptable with my .030" over bore, or should I seek a differnt one?

Robert,

I saw what your problem was earlier this morning. But thought that I'd reply now, because your intent may have been misunderstood.

After looking at some head gasket listings, it appears that GM lumps many of their head gaskets as "standard bore" (which is, actually 4.0005" in your case). In looking at their (generic) pictures you'll notice that the bore config is not a perfect circle. You might have to look at an actual gasket to be sure, but I'm willing to bet that the vast majority of head gaskets intended for non-race applications, actual diameter is somewhere between 4.080 and 4.125". Most other manufacturers specify actual bore diameter.

In calculating actual C/R, the actual gasket config should be taken into account. The effect on C/R would be computed as the annulus of gasket void area between the deck and the head surface. e.g. For a .040" overbore and gasket of 4.125" and .029" comp thickness, this would be pi r squared outer x compressed thickness minus pi r squared inner x compressed thickness, or 3.1417 x (0.085)(0.085) x .029

Specialized racing gaskets (ie, copper) may enable purchaser to specify exact bore diameter.

Joe

[Robert M.]

Re: Head gasket question

I will most likely use flattop pistons, so I am not concerned about exceeding the 10.5-1 that Duke reccomends as an upper limit.
By using the GM 10105117, I want that little bit more compression, 9.97-1.
My concern is that part of the sealing ring might overhang the bore just enough to possibly fail, a blown gasket. While the catalog says it's for 4.00 cylinder bore, is it really for that, and that only?

I suspect some one here has used or tried to use one on a .030" bore.

[Duke W.]

Re: Head gasket question

I should have stated that the gasket in question would be if I used flat top speedPro 631-30s. Compression would be 9.97 if I did the calculator correctly. My concern was if the gasket is too tight for the .030 over bore.

Most mfgs state the gasket bore diameter. Another GM gasket I know of is 4.080". You might just have to buy them and measure.

The CR calculator as you probably saw needs the gasket bore diameter to accurately compute the CR.

Duke

[Joe L.]

Re: Head gasket question

I am looking to purchase a pair of head gaskets for my '70 L46. It has been bored .030 over. The GM 10105117 composition gasket is .028" compressed, which what I'd like. The GM catalog says that this gasket is for 4.00" cylinder bores. My deck clearance is .025"

Is this gasket acceptable with my .030" over bore, or should I seek a differnt one?

Robert-----


I think that the GM #10105117 will be just fine with a 0.030" overbore. However, I would not use it, anyway. This gasket is a lower quality, composition gasket and IT REQUIRES RETORQUE. The latter is a big pain on a Chevrolet as you have to remove the exhaust manifolds to do it right.

I'd highly recommend using a Fel-Pro #1003 for your application. This is a bit thicker with a compressed thickness of 0.041". However, it's a very high quality, "bullet-proof" gasket. Compressed volume of this gasket is 9.1 cc and bore size is 4.166".

[Duke W.]

Re: Head gasket question

A couple of projects I'm familiar with have successfully used the Victor Reinz 5746 composition gasket, .026" compressed, 4.100" bore diameter.

I don't think it needs to be retorqed. You should be able to buy it at NAPA.

Duke

[Clem Z.]

Re: Head gasket question

you can use GM# 3830711 steel shim gasket and they will not needed to be retorqued and it is .026 compressed

[Duke W.]

Re: Head gasket question

The 711 is okay if your block and head surfaces have no measureable warp.

It's my understanding that it may be discontinued, but some dealers may have remaining stock.

If unavailable, he ROL 31600 polymer coated steel shim, .024" x 4.09 is a good substitute.

Duke

[Clem Z.]

Re: Head gasket question

[quote=Duke Williams (22045);342574]The 711 is okay if your block and head surfaces have no measureable warp.

duke every one says that BUT i can remember when i was a lot younger putting 12.5:1 pistons in used SBC engines with the stock shim head gaskets with out any sealing problems. i just used high temp aluminum paint as a sealer. maybe i was just lucky.

[Michael H.]

Re: Head gasket question

[quote=Clem Zahrobsky (45134);342610]

The 711 is okay if your block and head surfaces have no measureable warp.

duke every one says that BUT i can remember when i was a lot younger putting 12.5:1 pistons in used SBC engines with the stock shim head gaskets with out any sealing problems. i just used high temp aluminum paint as a sealer. maybe i was just lucky.

I agree Clem. I've never had any problem with the original steel GM gaskets, even if the head isn't dead on flat. These things are a bit flexible.
The light coat of aluminum paint is important though.