Thank you Sir - duly noted.
340 Piston Selection
- Thread starter NCmtnDWELLER
- Start date
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Loading block up will drop off monday morning to have it decked then get this mess wrapped up !
yellow rose
Overnight Sensation
How do you set the deck height without the Pistons? Are you going to cut the decks until they are square? Or cut them to a random number? You have to take into account variations in rod length, stroke length and even the compression height of the Pistons.
You cut the deck to get what you want. Not to a number. Way too many variables to cut the deck to say 9.560 or any other arbitrary number.
NC Engine Builder
Grumpy Old Man
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I usually just have the deck cut untill it's square, measure and go from there. I like to remove as little as possible from the deck surface.
Block is stock deck height verified
Taking 10ths off for decking process.
yellow rose
Overnight Sensation
That's my question. What is the stock deck height? I've seen them as tall as 9.620 and that was my X block. It was brand new in the box when I bought it. I have a 340 block out there that was 9.565 before I cut it, and another one that is 9.510ish and has never been cut.
When the blocks were machines at the factory, they only cut on them until they had a viable surface. They didn't machine them all down to the factory max spec or the minimum.
That's why you had some engines that ran like a scalded dog off the showroom floor and others needed to be machined first. You had tolerance stack up. You could have a tall deck, short rods and big chambers. Instead of the 10.5:1 you should have had, you'd be lucky to get 9.25:1 with all that stack up.
You have a nominal height, the max they let out the door and a minimum.
Whats the best & easiest way to measure deck height if u dont own any pistons ??
Squaring up the block is among the first things to do once everything else about it checks out. First on my list is basic clean up, sonic check cylinder walls....etc..... if the cylinder walls check good for a boring, then it’s squaring up the block. What ever it takes. It normally doesn’t take much.
I had block baked and blasted its clean and ready for a 4.080 bore its currently 20 over .
yellow rose
Overnight Sensation
I have measured it with a micrometer. I also set the block on the bar on the mill that indicate in and measure off that. All that will tell you is if the block was maybe never machined. The blocks I've measured over the years (many of them never touched) have been all over the board. If you want to do it like people THINK blue printing is, you start with the crank and get it indexed so all the throws are equal. Most aren't. Then, you need a Tobin-Arp machine to equalize the rod lengths. Most are all the same these days but stock rods are usually crapola. The issue I've found is some rods, even rods finished here aren't always exactly 6.123. Which isn't always bad, if they are a bit long and they are the same. Then you do the math, find the deck height you need and machine the deck.
Or, you check all your lengths etc, rough bore the block, slide a piston and rod in all 4 corners and write down where they are relative to the deck. Find the low corner and machine to that, plus what you need to get the deck clearance you want.
Im going to drop 340 block off tomorrow morning at machine shop they are doing all my work plus balancing so I will get um to deck it owner said 10ths should clesn it up but after its decked they can tell me the deck height then will all my other info filled out on sheet sent from Cambell performance I should be able to resolve this issue and have some lite weight quality pistons with about 11.6.1 compression using a 0.40 ths cometic head gaskets.
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