340 .040 Bore Okay?

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I've done several and like RB, I did find a pattern with the early 360 bocks. More consistent and thicker than the later blocks. Not every one, but most by a good margin. I tested probably 6 or 7, I don't remember. It's been several years ago. I just recently got a sonic tester myself and will be testing all of the blocks I have here. As mentioned above, I've already tested the slant 6 block for my next build and it is ridiculously thick. It is also the "BH" casting block, which is rumored to be thicker....but you know how rumors are.
 
missing linc said:
I have heard of guys going to .080 on a 340, but as mentioned above, the block must be sonic checked by a good, trusted machine shop and you're taking a real risk. I've never gone beyond .040 personally.
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Wouldn't 0.80 be a custom made piston
 
Rover125 said:
I recently purchased a 340 engine that was “completely rebuilt” that the original engine builder said would be a great engine. Engine had sat for a few years / never installed. Thought I would do some checking before putting it into my dart. Fortunately i did. The list of issues I found are too many to list. Tearing the engine completely down. Variations exist with the bore size in each cylinder. Hard to believe! The largest .030 with rust. I know plan on having it bored to .040. Is this too much for a 1971 340 block? Will I run into overheating problems? Thanks in advance for any information.
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I just got off the phone with the machine shop owner who is working on my +.040" 70 340 block. He was roughing in the bores and found a sleeve in the #4 cylinder already. He is going to sonic check the block as he is getting ready to replace that sleeve because he did not like how it was installed 24-25 years ago by another shop. After the sonic check, he is planning on going to +.050" on the bores and purchasing custom pistons.
Sonic check it!
 
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They make .060 over pistons, I've used several sets, I have a set here I will use in the future .

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I saved these pistons to use on a personal motor because of the weight reduction method used by someone we know, that builds killer engines .
Look deep into the piston .

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The factory said you could go .040.. that's the only thing I know there is thats written in stone. LOL
Everyone is right ...only a Sonic test will proove/tell you . Late '70s 360s were pretty bad . .040 over was iffy. Had the entire cylinder go away, no.5...
Roll the dice and risk paying it twice.....or pay now.
 
They didn't have sonic testing avail till mid?70s .
Lotta 340 motors running around .060 over, I got maybe near a dozen out there , still running 40+ yrs later .
 
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I knew I had never, in all the decades seeing a .040 limit on small blocks, so I went to my trusty Engine Manual to check, concerned I may missed it.
If piston manufacturers made .060 pistons, you can be pretty sure they researched it first .
Cheers

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