340 Block Bored to 4.160????? Help

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Robin House

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Hi guys, been on the site for a while now but this is my first post.
I picked up a 73 Dart Sport last year with a 340 in it. I opened it up and just did a top end refresh and tossed on a set of x-heads. I had over heating issues all summer, tossed in a new 3 core rad, new fans and multiple thermostats. Still had issues. I just pulled this engine apart and found that the rings were cooked. before ordering new rings I wanted to double check the piston size and found that they were at 4.160..... IS THIS MY OVER HEATING ISSUES???? CAN THS ENGINE OPPERATE AS A DRIVER BORED THIS MUCH??????
to top it all off there is a little pitting in one cylinder. I don't think its enough to cause problems but with the size of the bore I'm guess they could not go any farther to get the pitting out.

340 block cylinder.jpg
 
How did you come upon the 4.160" number? Is that an actual measurement you took, or are you going on something stamped on the piston?

A .060" over 340 has a bore of 4.1". If the piston is 4.160", that means your engine is bored like .120" over.
 
Hi guys, I picked up a 73 Dart Sport last year with a 340 in it. I opened it up and just did a top end refresh and tossed on set of x-heads. I had over heating issues all summer, tossed in a new 3 core rad, new fans and multiple thermostats. Still had issues. I just pulled this engine apart and found that he rings were cooked. before ordering new rings I wanted to double check the piston size and found that they were at 4.160..... IS THIS MY OVER HEATING ISSUES???? CAN THS ENGINE OPPERATE AS A DRIVER BORED THIS MUCH??????
 
I beleive the max overbore is .040 so the stock bore is 4.04 (or 4.040) so you can bore it to 4.08 max. so I am thinking that is pushing it on the bore. You can double check my numbers, It has been a while since I was in the books on this, but I remember not being able to go to .060 on these engines, I may be wrong. As for the overheat, i dont know if it is because of the overbore.
 
Looks like it's time to sleeve every cylinder or look for another block.
The walls must be paper thin and not stable at all.
The cooked rings reflect this.
120 thou over? What was somebody thinking?
The pistons must have been expensive!
Yes, it is the cause of your overheating issue...........
 
Dartnut said:
Looks like it's time to sleeve every cylinder or look for another block.
The walls must be paper thin and not stable at all.
The cooked rings reflect this.
120 thou over? What was somebody thinking?
The pistons must have been expensive!
Yes, it is the cause of your overheating issue...........
Click to expand...
I was thinking the same on the pistons, along the lines of "Where did they find .120 over 340 pistons" Maybe they used 383 pistons or something?
 
in my opinion there is no such thing as "max. overbore". I know there are 318´s around that were bored to 4" after sonic check - could be that the previous engine builder found pretty thick cylinder walls. Ok, going to 4.160" is pretty big for sure, but i would not call it impossible. Pistons must be custom made or adapted from another application. Check the casting no. - is it a stock block? Could be a race block with thicker walls / siamese bore....

I doubt someone would search for Pistons in this size without checking the block - but of course i could be totally wrong ;-)

Michael
 
Mopar Performance race block... did come in several flavors.
Hard to come buy these days, can be bored to 4.220 IIRC.
 
I think I would first pressure test it to see if the boring has resulted in some hairline cracks or tiny pores into the water jacket from the bores. Coolant leaks could be causing the pitting' the pitting pattern in the pix is sloped, almost as if there was liquid in that bore.

I dunno see why the bore is an issue per se, unless the walls are paper thin and flexing. It do seem like a ton! OP, what do mean by the "rings are cooked"? Are they broken?

What pistons and cam are you running?
 
nm9stheham said:
I think I would first pressure test it to see if the boring has resulted in some hairline cracks or tiny pores into the water jacket from the bores. Coolant leaks could be causing the pitting' the pitting pattern in the pix is sloped, almost as if there was liquid in that bore.

I dunno see why the bore is an issue per se, unless the walls are paper thin and flexing. It do seem like a ton! OP, what do mean by the "rings are cooked"? Are they broken?

What pistons and cam are you running?
Click to expand...
Running 4.160 KB Pistons
cam is Comp Cam x-treme Energy .462 intake/.470 exhaust lift. 262 intake/270 exhaust duration.
 
Only one way to find out. Tear it down. Have the block sonic tested.
 
Rusty is right on. Have it sonic checked. My 72 340 block is .060 over and there is a fair amount of meat in the thrust areas, but, that is that block. You need to measure yours.
 
Find another block I wouldn't put 2 cents into one bored that far over...
 
As previously stated have it sonic checked and magnaflexed before making your next move if it is that far over I wouldn't use it..
 
stroked340 said:
Find another block I wouldn't put 2 cents into one bored that far over...
Click to expand...
What your thoughts on sleeving? Only thinking this way because I know this block, if I go pick up another block I'm starting over hoping there's no surprises
 
Doesn't sound right to me.
It would have to be custom pistons not just set of KB's and a guy over bores that much and slaps in a 262 cam ?
 
Robin House said:
What your thoughts on sleeving? Only thinking this way because I know this block, if I go pick up another block I'm starting over hoping there's no surprises
Click to expand...
Post some pics up of this thing
 
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