340 Crankshaft balancing.

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tmatador

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I bought a 70 X code engine while back that had been taken apart and have finally gotten around to looking at rebuilding it. My question is I checked the numbers on the crank and it shows to be a 73 model crank so do I need to have this balanced or all the all the same? Or do I need to find a 70 model steel crank to use?

Also this engine had an automatic behind it and it will be going in a 4 speed duster. Any issues with pilot shaft bushing or anything?

Thanks for any reply!
 
73 would be a cast crank, and it would have been externally balanced
 
Thanks! So I assume if I use this crank all I need is to get a fly wheel and Harmonical balancer for a 73 right?

Thanks again!
 
tmatador said:
Thanks! So I assume if I use this crank all I need is to get a fly wheel and Harmonical balancer for a 73 right?

Thanks again!
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What pistons do you have (70) vs (73) will be different weights
cast crank with (70) pistons will take a lot of mallery to balance
 
The crank may be dated 73, but is it a 340 crank? could be a 318 crank. I would find out more about the crank you have first.
 
hi does it have a wide or narrow thin parting line on crank? thin is cast wide is ateel.
 
Blownfish said:
The crank may be dated 73, but is it a 340 crank? could be a 318 crank. I would find out more about the crank you have first.
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According to HP books "How to Rebuild Small Block Mopar Engines" the cast crank 73 340s and some 74-86 318s share the same casting number...only noted difference was that the cast 340 cranks are shot peened. Casting number annotated is 3462387

OP: If you want to use a zero balance flywheel and balancer (if you already have them and don't want to swap) you can try to find a 68-72 steel crank, but there's nothing wrong with the cast crank as long as you're not spinning it to the moon or feeding it ridiculous amounts of nitrous or boost. In case you haven't noticed, even the cast cranks are quite robust.

Regardless, whatever crank you use, just make sure you have the appropriate balancer and flywheel combination...

hi does it have a wide or narrow thin parting line on crank? thin is cast wide is steel.
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Make sure of this...I'm sure if you looked up the casting number, it's probably right, but can't hurt to verify.
 
draginmopars said:
What pistons do you have (70) vs (73) will be different weights
cast crank with (70) pistons will take a lot of mallery to balance
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Hmmm-very good point-what's the weight difference between the two?

Then again, if he's rebuilding the engine and it needs bored, most aftermarket pistons are a good bit lighter...
 
cast cranks were lighter than forged so the same forged rods and pistons used needed more balance on the crank side, hence the strange balancer. Yoll need lots of tungsten to balance it with a neutral balancer and flywheel. Probably cheaper to get a forged crank, really, or use the crazy balancer and drill for a pilot bearing.
 
I agree with pishta.

I would just go find a forged 340 crank and use that. It would make everything much easier.

The cast crank only came in the 340 for 73 only. All other years were forged from 68 - 72. It should be much easier to get parts for the forged ones.
 
well...i would do some math and call machine shop first..

used 340 crank cost?
turning used 340 crank cost? might need it..might not
balancing used 340 crank cost?

even a forged 340 crank will need to be balanced...
 
I tend to agree with Tony-if the engine will be rebuilt anyway, there's nothing wrong with a cast crank as long as the correct balancer and flywheel are used. There's nothing "crazy" about a counterweighted balancer...360s use them with no ill effects. Of course it's preferable by many to use a zero balance setup, and I can't really dispute that, but as mentioned, unless a good 340 steel crank can be bought for the same cost as an appropriate balancer and flywheel (which will need to be bought anyway for his conversion from auto to 4 speed) then buying one would be all but frivolous, no?
 
FWIW...forged 340 crank, fresh regrind...

[ame]http://www.ebay.com/itm/340-Forged-Steel-Reground-crankshaft-Chrsyler-Dodge-Mopar-Plymouth-/121301266731?pt=Motors_Car_Truck_Parts_Accessories&hash=item1c3e1e712b&vxp=mtr[/ame]
 
Not sure what or if you have for pistons and rods, but regardless with all the variations, I would have assembly balanced. Have seen to many people throw engines together and have vibrations. The 273 318 and 340 all came with forged cranks but there bob weights are all different.
 
My 340....72 block, 70 crank and rods...had the rotating assembly balanced....best money spent...she runs so smooth :glasses7:
 
This is a post April 72 340...cast crank, 645 floated rods, KB pistons...balanced with no issues with aftermarket counterweighted balancer, B&M flex plate...runs smooth as silk
 

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I too have built cast crank motors with no vibrations. Nothing wrong with a cast crank. Key is to have assembly balanced with balancer and flex plate as txstang84 did.
 
I built a strong running cast crank 340 twenty years ago and had no problems with it after I got the correct flywheel for it.

Yes, if the engine originally came from an automatic transmission car, you will need to install a pilot bushing in the crankshaft. I made that mistake also...
 
Thanks for all the replies. I am going to take the block as well as the crank and pistons to the machine shop and let them tell me exactly what I got.
 
69MOPE said:
Stroker time! LOL
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was just going to post that

If the block needs bored

stroker kit- lighter pistons, better rods and rod bolts, crank ready to go.

some weights to compare

743.4 (70) piston, no pin
721.5 (73) lighter if cleaned up, remove carbon,no pin
474.5 (2014) stroker, no pin (pin is .924 dia)

005-5.jpg


003-10.jpg


002-7.jpg
 
I'm not sure what you plan to use the motor for but there is one more option for a steel crank, locate a 67-70 318 motor and use the rods from it too. Then add the lighter KB pistons. The other option is a cast 318 crank, they are both neutral balance and will handle some power without any problems.
 
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