Engine Casting Number??

[70GranCoupe]

I have a 340 block date 5.28.69 it has the conventional 340 casting number 2780930-340 but with an added -6, so it is 2780930-340-6 I know it is not a TA block (3577130TA) but cannot find any reference to what the -6 means in the casting number. All books I have stop at 2780930-340. Anyone know what the added -6 means? Thanks!

[Follicly Challenged]

So the story goes,

Casting Plant core useage indicator, Takes "2" perfect core halves, with 4 cylinder cans in each, to build a V-8. The "halves" are re-used. If a cyl can "busts", rather than scrap that half, they used to just add a new can to it.

Now, if an engine is cast, using 1 "perfect half, and the other half with a "2" "replaced can" the number after the displacement is inserted, as a "3".

 If a core half, during it's lifespan, has had 3 cans replaced, and is then mated to a half that has had 2 cans replaced, remember, it takes 2 halves to cast the block, plus the 3 and the 2, it becomes a 340-7.
So in your mind, if you have a -6 block means, 6 -2 = 4 replaced cylinder cans in the core halves used to cast your block. Always takes 2 halves to cast, so subtract from the number to find how many re-aligned cyl's present in your block.

Racers used to highly prize any casting with a -2 as a perfect core. Mindset was, and still is among many, that each time a can is inserted in a half, it is never "perfectly" aligned and hence a weaker casting.

By following that logic the "higher the number the weaker the block", but that ain't always true either.

Don't ANYBODY FREAK OUT !

I've personally sonic tested(I own one), and found thin cores and shift on "supposed" perfect -2 blocks many times, and conversely, have found good "average" thicknesses present on many lesser desired -8 blocks. No way to tell unless you sonic test.

But GENERALLY, the lower the number, the better the can/cyl wall alignment and thickness.
 
Exceptions, 340-1 means "10", or they may have actually inserted the numeral "10" if not lazy that day.

Hope this helps

FC out.

[firefighter3931]

FC...you're freakin me out ! 

Seriously, thanks for the explanation....excellent info ! 

Ron

[Follicly Challenged]

YABUT ! I Hate starting a post with that, but anyways,

We used to actually go sonic "reading" on blocks to "plot", or, "find" the re-aligned cans using the sonic tester, and the above info.
90% of the time, it was accurate.
We 'd have more 'Gooo" all over the block, thats the GEL stuff to transfer the sonic wave, looked sometimes like something dripping from ALIEN's Yap ! Most of the time we were successful. We could actually "find" the goofy cans accordingly to the casting number.
We were HERO's in our mind, having attained MOPAR NIRVANA ! Yep, we bad ! UH-HUH ! and strutt'in around like "we were there" !
Then Presto, a coupla years later, faster than you could says "you guys dunno squat", along comes buddy with his 1978 440-8 block for us to check for a bracket basher build.

We start spouting off the bible according to us, Blah, Blah, cyl thickness etc., buddy says "just do it "

Darned if the thing wasn't over .300" on all Major thrust walls, and, no less than .250" ANYWHERE else. EXCEPTIONAL !We coulda bored that thing to DEATH and never hit  THIN !
This was either a lesson in "theres exceptions to ever rule", or, the Lord has a sense of humor and turned to St. Peter and said "watch what I do to these ID-YOTS" !

'Nuff said, while the number is nice for Chrysler to have published right there on the side of their blocks, ( all manu's use the 2 half casting system), and, while GENERALLY accurate, it puts in perspective and speaks more to the machining practises to be used when going overbore on a rebuild.

If overboring with a diamond head in your CK/CV, no problem generally(any number), for all mopar blocks to accept .060". It just "follows" and enlarges the existing cyl alignment.

If Boring "perpendicular and correcting perfectly 90 degree" to the decks and mainline, which have already been corrected/squared(race or blueprint), using a boring mill, then it's nice to know info as to where/IF, it may go "thin".
The nice thing about this method is to correct the cam degree variance on cyl running mates, 1 & 6 etc. Ever wonder why that is ? I used to always think it was crappy  NORTON Cam grinders ! You live, you learn ! Hopefully ! Especially KB blocks !

Anyways, as usual, I'm an "almanac of useless information" and better shut-up now.

Long story short, GENERALLY, if you got a high number block, and approaching .060" overbore, get it done with the diamond boring head, not a boring mill. Most "Hotrod" shops have both as standard practise.

FC out.

[70GranCoupe]

Thanks again! At present I am .030" over so I should be safe, but it's nice to know I may have some leeway and the correct way to go about it. Let's hope I don't have to for a while! Sean