i need a little 340 help. Lets Talk head gaskets

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roscoes-garage

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Hello All,

I have a 340 I purchased several years ago as a short block. I was told it was 12.5:1 pistons they are .040 over. I've cleaned it and am ready to complete for my duster.
the issue is I purchased a set of the 340 Edelbrock Heads (60179) with the 65cc combustion chamber i am using .040 MLS head gaskets and the top of the piston are hitting the heads.

The combustion changer depth is 0.050 I also had a set of J heads sitting around (they need to be reworked) they are at 0.100

I know there are a lot of thickness options i have on the MLS head gaskets. Has anyone else run into this issue? the block has never been decked. (I know the full history) is there a combination that worked?

Thanks
Chad
 
The chamber on the edelbrock and stock J-heads should be pretty similar shape and would take a 340 piston above deck height, but who knows what the dome on those pistons was designed for. I think I would get a couple of 1/8" spacers and raise the head above the deck and loosely put a couple bolts in. Use some modeling clay in the cylinder to see where, and how much the interference is at TDC. Most of those dome pistons can be shaved down to get clearance and you are probably going to want to do that or change them because you will proably be above that 12.5:1 compression if they are like the old TRW domes. Unless you like running race gas.
 
Measure your stroke (stock should be 3.31) and how far above the deck the flat on the piston is above deck at tdc with a bridge depth mic. If you need to check clearance front to rear with clay, you can also use a pair of FelPro 518SD gaskets on one side to come up with a .120-.125 inch spacer.
 
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In my experience, those old 340 pistons do not fit in edelbrock heads, or the new ones like Ross, they are for the old iron heads, Icon does make a 360 piston that does fit Edelbrock heads. Good luck
 
That part number head is designed to be used with a factory high comp 340 piston. They take a standard rpm head and machine it 060 to get there. I bet a standard rpm head 60779 would be just fine. You can get new heads or new pistons, pick one.
 
Here’s a picture of the Pistons.

IMG_3012.jpeg


IMG_3014.jpeg
 
TT5.9mag said:
That part number head is designed to be used with a factory high comp 340 piston. They take a standard rpm head and machine it 060 to get there. I bet a standard rpm head 60779 would be just fine. You can get new heads or new pistons, pick one.
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thanks but the heads you refer to have less clearance then the ones i have see the attached pics. i have both sets of heads.

60179.jpg


60779.jpg
 
gzig5 said:
The chamber on the edelbrock and stock J-heads should be pretty similar shape and would take a 340 piston above deck height, but who knows what the dome on those pistons was designed for. I think I would get a couple of 1/8" spacers and raise the head above the deck and loosely put a couple bolts in. Use some modeling clay in the cylinder to see where, and how much the interference is at TDC. Most of those dome pistons can be shaved down to get clearance and you are probably going to want to do that or change them because you will proably be above that 12.5:1 compression if they are like the old TRW domes. Unless you like running race gas.
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i dont mind the race fuel due to the memories this motor has to me.
 
Garrett Ellison said:
Measure your stroke (stock should be 3.31) and how far above the deck the flat on the piston is above deck at tdc with a bridge depth mic. If you need to check clearance front to rear with clay, you can also use a pair of FelPro 518SD gaskets on one side to come up with a .120-.125 inch spacer.
Click to expand...
yes its the stock stroke. that just seams like a huge head gasket but looks like i need a t least .080
 
James Clews said:
That edelbrock head has closed chambers!
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He has the 340 style Edelbrock head with .060 removed from the chamber for stock 340 pistons above deck.

Designed for non-emission 1968-73 340 C.I.D. Chrysler engines. RPM Chrysler 340 heads have chambers machined .060" for clearance with early high-compression engines. The special valvetrain in the 1970 340 T/A is not compatible with these heads. Head comes with springs for hydraulic flat tappet cams.
 
That’s Big Ole flat dome (reminds me of what you would see in a two stroke motorcycle engine) sticking out of the hole. Can you get a physical measurement of how far above deck the piston is on the valley side and the outside of the block? That combination is almost begging for a set of properly worked 974 (E58 hi po and some industrial 360s) heads with 11/32 2.02/1.60 valves.
 
I know this not what you want to hear but here goes. The block deck looks terrible. I would believe a composite gaskets would have a hard time sealing . I couldn't see a multi layer sealing.

What you need to do is take the pistons out and get new pistons and have the block square decked. You will have to get it balanced also. What you are working with is a breed of many parts that don't go together. And those pistons look to be from the stone age,

A block when the machining is done right should look like this for a multi-layer gasket.

100_0458.JPG
 
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It definitely wouldn’t hurt it to go through a thorough disassembly and cleaning that would be part of all that.
 
Looks like old school pistons designed for old school big open chamber heads.
 
Garrett Ellison said:
It definitely wouldn’t hurt it to go through a thorough disassembly and cleaning that would be part of all that.
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It’s a balanced assembly. I had a shop check it. They also checked the block before punching it out to fit the .040 pistons. Yes, it looks worse in the pic than it is. Mostly discoloration. It’s clean and true. This was a promise to my dad kind of a tribute. The parts are matched. I just wanted to use the aluminum heads.
Normally I would just stroke kit and use new parts.
 
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I'd just have the pistons fly cut to fit the heads to get good quench. Yes it means re-balancing but throwing thicker headgaskets on can cause other issues as well.

Does your build require 12.5:1 static compression?
 
dano said:
I'd just have the pistons fly cut to fit the heads to get good quench. Yes it means re-balancing but throwing thicker headgaskets on can cause other issues as well.

Does your build require 12.5:1 static compression?
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i don't require 12.5:1 compression just want to use the setup since my dad ran this combo a long time ago. Yeah Little worried about the intake gaskets with the thicker head gaskets. I'll see if i can put the J heads on to see if they fit with the .040 head gaskets then make the decision.
 
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