Anyone bored a stock 340 block .060 over?

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dibbons

dibbons

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The 340 block I have is dated 8/29/71 or 9/29/71 (but according to the oil pan stamping numbers it was originally built for a 1973 model vehicle). It already has been bored .040" over. I was wondering if all the original factory blocks are the same weight/style/thickness and who may have experience boring their block out to .060" (with or without doing the recommended "sonic" test). Thank you.

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My 70 340 block was bored 60 over when I got it. Had the machine shop check it over and other than honing it for the pistons (which it needed), he said it check good. So one these days I will get around to assembling it!
 
yes ....have or had a 73 blocked bore .060....probably put 2000 passes on it ....still in shed...
 
I have a .060 over 340. It uses TRW forged pistons. It came in my Dart with a 508 hydralic cam, J heads with 2.05 intake valves, yes 2.05 not 2.02, with an 8 in tc and 5.13 gears. It's in pieces at the moment for a freshing.
 
I've built a lot of 340s .060 over, before "sonic testing" was avail (IIRC).

My car in the avatar was bored .060, and I ran it with 12.5 pistons for yrs., and have re-rung it prob all 3 times I trimmed the pistons down.

I know the other engines ran for yrs cuz I maintained them for decades..
 
Yes, some can go .060 but I would definitely sonic test as there is a strong possibilty the block will be thin, and even if it bores to .060 might not have the strength to hold round bores. I would really recommend spending the money for sonic test before spending the money to build an engine that isn't worth it in the first place. I've had 'em go .060 and some that would have been thin for .040.
 
I've done it. I own a certified sonic tester. I wouldn't do it if the power levels are high or the stroke is longer. Every block I've done it with has needed one or two sleeves to get them all where I consider safe.
 
Like Inertia said, i’ve Done a few also with never a problem, lots of ppl said that it will overheat as the walls will be to thin, never happened. Kim
 
I had a .060 over 340 that I sold, guy chiseled me down a hundred because it was 60 over already, but the bores were perfect so it didnt need to go any bigger. That block was O-ringed too.
 
moper said:
I've done it. I own a certified sonic tester. I wouldn't do it if the power levels are high or the stroke is longer. Every block I've done it with has needed one or two sleeves to get them all where I consider safe.
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Hey, Moper.... Do you have an approximate HP level in mind past which more care is needed?
 
I have my own comfort levels and resulting choices, yeah, but it's really up to the builder and customer what direction to proceed. Fact is if the engine lives successfully then you were successful only in staying below the breaking point, regardless of the expected output. Every component has that point of failure and I prefer to "see" as many potential failure points as possible to be better able to guess the breaking point and how to not reach it.
 
dibbons said:
The 340 block I have is dated 8/29/71 or 9/29/71 (but according to the oil pan stamping numbers it was originally built for a 1973 model vehicle). It already has been bored .040" over. I was wondering if all the original factory blocks are the same weight/style/thickness and who may have experience boring their block out to .060" (with or without doing the recommended "sonic" test). Thank you.

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My 340 is bored .60 over and no problems ..... other than it's hard to keep cool and I've heard that it might be of it "being .60 over". Didn't do the sonic test but - mine's not for the track just tearing up the neighborhood ;-)
 
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