340 bore 4.080 or .040 over

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woody30

woody30

woody30
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Took my block to the machinist and there was pitting in one cylinder after it was bead blasted and magged that didn't quite clean up with an .030 overbore. He said it would be almost negligible after honing but there would be a very minor pencil tip size pit left. An .040 overbore would definitely take care of it. He doesn't have capability to sonic test and neither does anybody else I know anywhere near here, so is an .040 overbore feasable with the 340 block or would it definitely need to be sonic tested? It's a 69 340.
 
I think you should have no trouble at all with .040 over. But. If it does turn out to be too thin, back it off a little
 
I know a lot of guys that bored .030 .040 with no problems. But I would want to sonic check any 340 they are very thin and who knows how much erosion there is in the jacket area, especially if your going to be knocking on the 500HP level.
 
if it were me a would go forty and not worry, just my opinion though
 
I wouldn't' worry about .040 over. Took my '70 block to .060 over no problem.
 
Go .040 over. It was common before sonic testers were affordable to go .060. Assuming you're not going with a 4" stroke you should be fine.
 
how low in the cylinder would the pit be?
is it below the ring pack

if you already have pistons
I would sleeve the one cylinder

if no pistons yet,go .040

We have 3 340- .040 over
0ne is.060 over

no problems
 
i'd just do the .040 over. shouldn't have any probs with it. have fun, mike
 

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It's half way down the cylinder and no I haven't bought the pistons yet. Was waiting to see how the block cleaned up. Been going back and forth on whether to do a 340 build of stroke to 416.
 
woody30 said:
It's half way down the cylinder and no I haven't bought the pistons yet. Was waiting to see how the block cleaned up. Been going back and forth on whether to do a 340 build of stroke to 416.
Click to expand...

since no pistons yet

why stop at 416 :burnout:

4.250 crank @ 446
 
mine is .040 over....no problems.....personally, I wouldn't even have it sonic checked unless going over .060
 
Years ago it was common for folks around here to bore their Fords and Chevys 30 over but for whatever reason it was common to go 40 on a 340 for a first bore. That was before sonic testing was commonplace. I don 't recall anyone having an issue because they bored .040. . A lot of guys even went .060 without sonic testing and rarely had an issue.
 
I've built quite a few .060 motors,, I know 3 of them are still running now,, 3 decades later.. One of them was a 12 1/2 comp motor for a long while..

I also have 2 sets of 060 pistons, 1 set for for an engine I'm about to do..
 
a pencil tip pit? the very tip? if were talking about a pit that is no bigger than say the size of flea, I wouldn't worry about it. The final hone will smooth out any rough edges. I personally would run it and trust my machinist.
 
My 340 is .060" over. No issues so far. :thumbup:
 
71 340 in my panther pink duster is .040 over. Same idea. .030 was just not quite enough to clean it up. Engine is a 10:1 solid roller motor w ported eddys pushing 450 HP, No problems. Engine has been in car for 8+ yrs now
 
ran a 340 to hell an back for 10 years,.sold it,new owner tore it down for milder build an found .40 over pistons,..never a issue and was running fine when tore down...no telling how long it was together when i got it,..bought it off the drag strip....still miss it badly!
 
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