340 Block Bored to 4.160????? Help

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So again, in what way were the rings 'cooked'?

With this bore size and the right pistons, and this cam, then the DCR may be so high as to lead easily to detonation. Got any pix of the piston tops? Any little speckled pits on the piston tops? Any idea on your ignition advance settings? Did you ever hear any pinging? (And how good is your high frequency hearing?)

Just thinking of what else can cause overheating and 'cook' rings.

This size in KB's? Yeah, that does not make sense for Chrysler slugs.... a few GM and Ford ones show up that have something near to the right compression height and diameter. And we have no idea how much the deck has been milled on this block.
 
Not trying to start any **** here but there is a "Maximum safe overbore" I don't make **** up. I read it years ago in a book by Larry Shepard. This is taken from a website found on a Google search of "Maximum safe overbore of Chrysler 340":
All 273-360 production blocks were cast using
a thinwall process and, as such, a .030" overbore should
be considered a maximum. Some older blocks (cast before 1976)
may tolerate up to a .060" overbore, however, whenever you
plan to machine the cylinders of an "LA" engine more
than .030" over size, it’s advisable to sonic check the cylinders
to ensure that core shift isn’t excessive. You may find, especially
with later blocks, that .020" is the maximum safe over bore.

The website is here:More Power From Your Mopar - Engine Builder Magazine
As someone who is a retired mechanic with some machine shop experience/knowlege, I just had to push this info out. Now, you can defy what the book says, but be wary of the consequences, its like cutting a brake rotor down to the thickness of a sawblade and wondering wny the caliper piston blows out. if you are running the engine 13 seconds at a time, it may last a few passes, if you want it to last in a street car, I'd follow the recommended specs.

 
Dartswinger70 said:
Not trying to start any **** here but there is a "Maximum safe overbore" I don't make **** up. I read it years ago in a book by Larry Shepard. This is taken from a website found on a Google search of "Maximum safe overbore of Chrysler 340":
All 273-360 production blocks were cast using
a thinwall process and, as such, a .030" overbore should
be considered a maximum. Some older blocks (cast before 1976)
may tolerate up to a .060" overbore, however, whenever you
plan to machine the cylinders of an "LA" engine more
than .030" over size, it’s advisable to sonic check the cylinders
to ensure that core shift isn’t excessive. You may find, especially
with later blocks, that .020" is the maximum safe over bore.

The website is here:More Power From Your Mopar - Engine Builder Magazine
As someone who is a retired mechanic with some machine shop experience/knowlege, I just had to push this info out. Now, you can defy what the book says, but be wary of the consequences, its like cutting a brake rotor down to the thickness of a sawblade and wondering wny the caliper piston blows out. if you are running the engine 13 seconds at a time, it may last a few passes, if you want it to last in a street car, I'd follow the recommended specs.
Click to expand...
Obviously. That's why everyone is questioning it.

However.


There were some NASCAR blocks from the 70s that were designed to go .100 over bore. I believe most of those were 360s so if he's got one of them blocks, I could see where someone pushed it to .120
 
Sleeving is ok, my longtime mopar machinist has done it for many years. Problem is you are into 8 holes. Do the math, those 8 holes with 8 new pistons, etc etc. May as well start over with new block.
As mentioned get it sonic checked and go from there.
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...
 
dukeboy_318 said:
Obviously. That's why everyone is questioning it.

However.


There were some NASCAR blocks from the 70s that were designed to go .100 over bore. I believe most of those were 360s so if he's got one of them blocks, I could see where someone pushed it to .120
Click to expand...
How does one identify a NASCAR LA Block?
 
X on front of block is Mopar Performance block. It came before the R blocks.
I had one that was 4.100. It later got bored even a hair more by new owner.
Even those, i have never heard of anything past 4.125
 
B3422w5 said:
X on front of block is Mopar Performance block. It came before the R blocks.
I had one that was 4.100. It later got bored even a hair more by new owner.
Even those, i have never heard of anything past 4.125
Click to expand...
Agreed.

I think the poster above questioning the measuring tool is in to something. I'm a 3D drafting engineer, I've seen even good brand micrometers, especially digital ones be off by as much as .25 of an inch. Especially if they've ever been dropped. We have ours calibrated every month and replaced twice a year for that every reason. But that's because we require a tolerance so tight, most machine shops can't do the work. We get down to .0000008 tolerance. Standard micrometers are certified normally to .0001 or the cheap ones even less
 
Sorry, had To jump ahead

Is it an X block capable of a 4.220?
 
sleeved are about $20-25/pc jobber prices and then you have to machine block to accept them, press them in and have the decks recut. 200 in parts alone.....4.000 360 blocks are cheap and they look just like 340's....
 
dukeboy_318 said:
no. max bore on an X block is 4.140
Click to expand...

There is no " set" max bore on an X block. They came virgin with a 318 bore of 3.90ish.
I have heard of some that were not safe past 4.06 bore. As i said earlier, the largest bore i have heard of is 4.125. Could there be some that have been bigger..... sure. But it would definately be by far the exception to the rule. Generally anything 4.08 to 4.10 with plenty of wall left is being fortunate.
You have to remember most people using this block arent building a 450-500 horse streeter. They are looking to make 600-750 horse. At those power levels, even an X block needs to have plenty of meat left to be up to the task.
 
Robin House said:
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??????
Click to expand...
If you're going to tear it apart anyhow have it Sonic checked then you'll know for sure. Block could be full of crud or something else causing problems. Don't buy anything until you check the block.
 
dukeboy_318 said:
Agreed.

I think the poster above questioning the measuring tool is in to something. I'm a 3D drafting engineer, I've seen even good brand micrometers, especially digital ones be off by as much as .25 of an inch. Especially if they've ever been dropped. We have ours calibrated every month and replaced twice a year for that every reason. But that's because we require a tolerance so tight, most machine shops can't do the work. We get down to .0000008 tolerance. Standard micrometers are certified normally to .0001 or the cheap ones even less
Click to expand...
I am thinking snap bore gauges and a micrometer would be the best way, then you could also measure taper or top and bottom measurements. If someone is opening vernier calipers across the top of the cylinder, it may not be real accurate.
 
dukeboy_318 said:
no. max bore on an X block is 4.140
Click to expand...

Not so;

X blocks are NOT limited to standard production block limitations.

Current-ish, are they even around anymore?!?!?!
LOL! NOT! But the following race block part numbers;

p4876381/789/671/791/673/793 are 4.220 blocks.

All are 48* blocks except the '791/793. There 59*
The 789 is a 48* aluminum block.


So, what block does our OP have? He stated a 4.160 bore all ready.
 
dukeboy_318 said:
Agreed.

I think the poster above questioning the measuring tool is in to something. I'm a 3D drafting engineer, I've seen even good brand micrometers, especially digital ones be off by as much as .25 of an inch. Especially if they've ever been dropped. We have ours calibrated every month and replaced twice a year for that every reason. But that's because we require a tolerance so tight, most machine shops can't do the work. We get down to .0000008 tolerance. Standard micrometers are certified normally to .0001 or the cheap ones even less
Click to expand...

Never ever seen any calliper out by anything like this? You using ones out of Christmas crackers or something?
 
Dartswinger70 said:
I am thinking snap bore gauges and a micrometer would be "a better" way, then you could also measure taper or top and bottom measurements. If someone is opening vernier calipers across the top of the cylinder, it may not be real accurate.
Click to expand...

There, I fixed it. A dial bore gauge is the most accurate method.
 
trigger_andy said:
Never ever seen any calliper out by anything like this? You using ones out of Christmas crackers or something?
Click to expand...
you'd be surprised how badly digital measuring devices can be out of spec. most of the time, its due to crappy programming, or someone has dropped them enough times to throw them off. .025 of an inch is enough to screw a lot of stuff up
 
The OP had 2 threads going at the same time. I merged both to avoid confusion. TMM
 
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