My MLS head gasket came with a note that cylinder head and block deck should be new or freshly machined to use MLS .027 gasket. My new BPE heads were milled to 60 cc chambers. My 4K mile block I cleaned the hell out of the deck and spent some time checking with precision machinist bar & close visual inspection. I also used ARP head studs. No issues so far 🤞. Bottom line is MLS not as forgiving to any discrepancies. But to get my CR and quench where I wanted this was my best option to avoid piston change.

 

What bore size? 4.100 4.060 ?
I may do a permatorque gasket due to forgiving. Heads freshly machined. Block decent

 

If you are thinking composite gaskets like Felpro, try the thinner and better sealing GM ones.

I had my current 350 bored .030 and the stock bore gasket worked very nicely.

 

If it’s a 4.00 bore gasket would it work on a bored .040 motor?

 

Or this one?

 

My MLS are Fel-Pro 1142-026 ×4.100 bore. .026 thick not .027 sorry.

 

The 10105117 is .028 and composite.

I used it to seal my aluminum heads onto a fresh decked block, but it really shines on a used block. No clearance issues with my .030 bore.

This shot is the results from claying the valves with the head on.

The thicker Felpro stuff works, but you lose compression. MLS needs a fresh deck.

GM also makes the same gasket (different number), but with a 4.100 bore.

 

If it’s a 4.00 bore gasket would it work on a bored .040 motor?

You realize how small

What’s the best bore head gasket for a .040 over 302.
i see em from 4.060 and up. Stock steel heads.
Hows the ones in pic.
Heads have been surface cleaned. Block has not. Machibst says he can cut .006 off block and leave stamping numbers if I want to.

If it’s a 4.00 bore gasket would it work on a bored .040 motor?

you do realize just how small 4 hundreths of an inch actually is ?

 

You realize how small


you do realize just how small 4 hundreths of an inch actually is ?

Yeah but wasn’t sure what size. I know some increments were basically same but wasn’t sure if I needed 4.100 versus 4.040

 

.040 = 1/25"

 

Melmount I am fine with 4.100 on a + .030 bore. It is more important to get your quench and dynamic CR optimal. Select the gasket that does that & move forward. .
It is good to be selective, informed & particular but at some point the drive for perfection sucks the joy out of a hobby. Trust me I know, 4 decades in aviation programmed me to only accept perfection. Which isn't obtainable. Don't over think this. Don't second guess your choices. The longer you do the further away the joy of driving your pride and joy becomes. Keep moving forward, everyone has an opinion, ask, but in the end trust yours. Don't end up where I am.

 

I agree but I rebuilt the motor to find out shop cracked both heads installing seats. Then rebuilt it again due to cylinder discoloration cause heads leaked into cylinders and it sat. Rebuilt with new pistons and fresh bore. This time grit or lack of oiling due to missing Welch plug, ate the bearings. I am now doing it a third time. This engine been kryptonite to me. But both shop and friend feel terrible about it, none the less it sucked.
I guess it got me gun shy. The heads that cracked cut for the seats went ok but were too thin. When installing the new ones it cracked em.

 

Sorry its been such a battle. I can relate. I rebuilt my first Chevy motor at 18. My 74Z28 spun a rod bearing because I was being stupid. Only 26,000 miles on the car, 2nd owner. The machine shop rebuilt it and before I got through break in at around 400 miles it spun the same rod bearing. They didn't trust me due to my age, but they did the machine work again on short block and I tore down the heads and went through them using the How to rebuild SBCs book, which I still have. I worked at a small Fied Base Operator at local airport and I tore dow the engines and helped assemble, usually changing jugs, pistons, props. So I had access to all the good tools.

I have always thought bout cylinder head gaskets this way. I would rather have the gasket bore a little large than the same size as the bore. When you squeeze soft metal to compress it it has to expand width wise even if its minimal. This is really only an issue if zero decking a block I would think. Hit a lead sinker with a hammer or put it in a vise as it compresses it gains width. Not quite the same thing, but you get the point. The cylinder sealing ring to effectively seal would have to be mallable enough to seal very minor imperfections. So torquing to seal it seems it has to deform even slightly towards cylinder. I may be wrong here, but I have always selected the gasket that will give me the CR & quench I am looking for and slightly larger than the cylinder bore. Maybe its not necessary. I would like to compare the sealing ring thickness and bore after having been torqued compared to new. Just to see if its altered at all.

Would like to hear from others on this, maybe I am over thinking it myself?

 

Makes good sense to me. A 4” bore head gasket on a bored block I would think potentially could have metal from gasket into the cylinder.

 

I used a GM LS9 gaskets-4.100" for my 4.030" bore and didn't care about the difference in compression.

Hanging Out — Discussing Head Gasket Bore Sizing With Cometic Gasket

Sizing your head gasket properly is more than just the compressed thickness. The bore size can have an effect on the whole build.

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