Internally Balance Cast Crank?

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65 Dartman

65 Dartman

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I've got a crank out of a 73 340. It should be and looks like a cast crank from everything I've read. However, it appears to have been internally balanced with extra holes in one of the counterweights. It also rings like a bell when I compared it to a known 70 340 crank. Any way to figure out what I have. There is no casting numbers on said crank where the 69/70 crank has the casting number. I can take some pics if needed.
 
There can/should be holes in the counterweights regardless of being internally or externally balanced.
 
yellow rose said:
Post pics of the rod throws
Click to expand...

This. 318 Cast internal balance cranks have different throw holes than 72-73 cast 340 cranks.

That doesn't mean at some point in its life it wasn't internally balanced.

I wonder if Mopar carried internally balanced cast 340 cranks as a replacement part for 68-71 engines?
 
I've never put all this together. Weren't 318 cranks neutral balance? Could it be a 318 crank?
 
65 Dartman said:
I've got a crank out of a 73 340. It should be and looks like a cast crank from everything I've read. However, it appears to have been internally balanced with extra holes in one of the counterweights. It also rings like a bell when I compared it to a known 70 340 crank. Any way to figure out what I have. There is no casting numbers on said crank where the 69/70 crank has the casting number. I can take some pics if needed.
Click to expand...


mvc-052s-jpg.1714771242


Left: cast ...............................................Right: Forged

When tapping on the cast with a wrench it should sound kinda like a thunk, tapping on the forged will give a nice resounding tiiiing.
 
When it rings it takes maybe 2 seconds to be quiet.
When it thunks, it takes no time at all.It's just dead.
It works best if the crank is standing on it's tail, and not leaning on anything, and no hands . I put the flex plate on backwards with one bolt holding it on;works great.
 
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If it is a 73 340 cast crank...to internally balance it will need some slugs of mallory metal in the front and rear journals...the weight that is offset on the balancer and converter has to be added to the crank...
 
67Dart273 said:
I've never put all this together. Weren't 318 cranks neutral balance? Could it be a 318 crank?
Click to expand...
With no PN, I guess so... but the stroke would be different. Yes, 318 were neutral balanced. 360's should have larger counterweights.
 
I have never internally balanced a cast 340 crank...Have done several 360 cranks...even with scat rods and light weight piston they took a couple slugs of mallory....dont see a 340 being any different
 
There are at least 3 bell-ringers SBM cranks; the 273s,the teeners, and the 340s.
The 340 cranks are the heaviest at around 55#,IIRC
The 273s are skinny little things.You can't mistake them.
The teeners I forget their weight, but they also don't seem to have as many holes as the 340s nor are they drilled as deep. They might be around 50#IDK
 
AJ/FormS said:
Well that kinof depends on what pistons, etc. get installed wouldn't it. I mean Hypers would probably knock off a couple of hundred grams or more
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Right on... with hypers and SCAT rods I would expect it to balance out internally by removing material from the cast 360 crank. Perhaps to include boring out a bit on the inside of the journals. I have been meaning to try to figure this out.....
 
Ummmm, how did we get to 360 cranks, again? lol

IIRC the early 340 pistons were about 742 grams.
And the hypers are about 585?

Since we got to talking about 360s; Mine is a 71, I installed the KB107s which are 502grms. I installed rods from an early teener with the bushed pin holes. These carry the same casting number as the early 340s. I had them evened up and sent everything out to be balanced, including a neutral balance factory teener flywheel,and the 360damper. When I got it back, the damper was untouched, and the flywheel had three small holes drilled into it.
This engine regularly goes 7200, and cruises in O/D at 2200.It is very smooth and revs really quick.I like it!
 
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70aarcuda said:
I have never internally balanced a cast 340 crank...Have done several 360 cranks...even with scat rods and light weight piston they took a couple slugs of mallory....dont see a 340 being any different
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The shorter stroke on the 340's makes a difference.. And the taller 340 stock pistons are a lot heavier than the 360's sp a lot more weight is saved on the 340's.

Thanks on the 360 internal balance....ever consider drilling weight out of the journals, like on the stock 340 steel cranks? (post #6.)
 
nm9stheham said:
Right on... with hypers and SCAT rods I would expect it to balance out internally by removing material from the cast 360 crank. Perhaps to include boring out a bit on the inside of the journals. I have been meaning to try to figure this out.....
Click to expand...

Have done 3 cast cranks...all took mallory metal to balance with light weight rods and pistons...340 will need the same with heavier pistons and especially stock rods..
 
My 72
nm9stheham said:
Right on... with hypers and SCAT rods I would expect it to balance out internally by removing material from the cast 360 crank. Perhaps to include boring out a bit on the inside of the journals. I have been meaning to try to figure this out.....
Click to expand...

My 72 cast 340 crank is internally balanced. I have the pan off, I'll need to look. I have Scat I-beam rods and heavy TRW forged pitsons fly cut to zero deck. The cast 340 has a different balance than the 360 and as I recall is was on the lighter side like 12 oz? My fly wheel for the cast crank had 3 ~3/8" drill points.
 
Take the 340 cast crank in and have it internally balanced...let us know the results...
 
Bad Sport said:
mvc-052s-jpg.1714771242


Left: cast ...............................................Right: Forged

When tapping on the cast with a wrench it should sound kinda like a thunk, tapping on the forged will give a nice resounding tiiiing.
Click to expand...

Both the 70 forged crank and the one out of this 73 block have "a nice resounding tiiing" -- unmistakable! FWIW the pistons are the nice high compression 69/70 pistons, which the PO mentioned prior me buying the short block.
 
nm9stheham said:
With no PN, I guess so... but the stroke would be different. Yes, 318 were neutral balanced. 360's should have larger counterweights.
Click to expand...


I don't think anyone is referring to a 360. 273, 318, 340 cranks will install and run. Whether they are balanced, or "as strong" in a given app, is a different matter. I once put a 273 crank in a 340 because it was all I had and I didn't know any better. Ran just fine LOL. This was a stick, so the converter register was not an issue, and I didn't even know about THAT, then.
 
AJ/FormS said:
When it rings it takes maybe 2 seconds to be quiet.
When it thunks, it takes no time at all.It's just dead.
It works best if the crank is standing on it's tail, and not leaning on anything, and no hands . I put the flex plate on backwards with one bolt holding it on;works great.
Click to expand...
Curious, can you mix and match cast cranks,3.58" throw with forged flat top pistons in a 340 with H rods, and get away without balanceing it? Would it be coincided internal or external balance?
 
Jessearent said:
Curious, can you mix and match cast cranks,3.58" throw with forged flat top pistons in a 340 with H rods, and get away without balanceing it? Would it be coincided internal or external balance?
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No the factory 360 crank does Not fit into a 340, and
if it did, it would punch the pistons up out of the bores by half of the stroke difference.
The rod castings are the same put the 340 has floating pins versus pressed pins for the 360.
And that pretty much makes the balance question moot; but again, the 340 forged cranks were balanced for the factory 745? gram pistons versus IDK 505? grams for the 360 pistons, so no, a rebalance would be required.
I wouldn't put any non-stock engine together without balancing it. I hate doing things twice.

But
many years ago, Chrysler sold 3.58 stroke cranks that dropped right into any 3.315 stroke saddles, 3.79 cranks too.
A 3.79 in a 3.94 bore/318 comes to about 370 cubes, about the perfect size for an A-body. I bet I could suck close to 28 mpgs out of one of those by building it to cruise down at around 65-1800 rpm. It would, of course, need either a manual trans with overdrive, or an A500/518
 
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mygasser said:
if you ask enough times on different old threads are you hoping to get the answer you want to hear? :poke:
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I learned cast crank is lighter than forged, cast aluminum pistons are heavier than forged, mopars 318/340 3.58" throw cast crank "might"require balanceing. And Scats cast 318/340 3.58" is already internally balanced as is. Therefore an economical desicion would be to - go with the Scat cast crank and forged pistons keeping the assemble lite as possible. And H beam rods are roughly 700 grams bushed and Scats are 643 grams. I know you don't believe it, but I would put this lite rotating assemble in my engine and use the neutral balancer on front and not pay for t machine shop...figuring a bob weight ect. Figiting over the last fews grams of unbalanced weight somewhere. Sincerly Jesse
 
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