340 / 318 Crank question

Thank you Mr P you are a Gentleman, appreciate your input as always.

Bud.

I don't agree.
It's a forged crank.
Cast cranks have sharp edges and squarish counterweights. This crank has rounded "kidney shaped" counterweights that to my eye look forged.

R.

1ST thing I thought too..... Balance job would be a mess with the heavier 340/360 rods. Lots of Mallory..$$

I know several drag racers of SB motors that looked for the forged steel crankshafts out of the 318-3 truck motors to use in there short stock stroke 340 motors, they had to have thin steel plates welded onto the counter weights to get them to balance correctly. This was before Mallory metal was used in balancing IHTHs

Would a set of H-beams and a light forged piston/pin get you into the 318 balance ballpark?

Kevin

The big rod weighs 758 grams, the small rod weighs 726.
318s used the big rods from like 1973-on, and piston weight didn't change if one really weighs the items. The 318 cranks before and after this change point were the same old castings, no changes there.

The 318 piston weighs 591 grams plus the pin. My 30 over replacement piston comes in at 600 grams exactly, no pin.
Total weight is over 1500 grams with pin and rings..

It's mind-bogglingly heavy. The 340 piston adds another 130 grams. Small-block size with bigblock weight. No wonder taxi 318s ran forever.

You can get a decent rod that weighs around 650 grams and a decent 340 lightweight forging should come in at 500 grams plus pin.
There's no earthly reason to have to add weight to a 318 crankshaft to balance a modern rotating assembly. Well, I guess if you are building a 100% replica.

Back to the crank, the absence of a parting line doesn't tell me as much as the shape of the counterweights.

To the OP: Could you find the casting or forging number on the crankshaft and take a picture and post it? Let's put this issue to bed.

R.

Fix the crank you have if possible. Its steel. Check to see if the crankpins are drilled, if they are, its not a steel truck crank.

The stocker guys actually use the cast crank because it is lighter. Using stock 318(lighter) rods and NHRA approved pistons of stock weight, they are not adding metal back to these cranks, which would defeat the purpose of using lighter cranks. These engines are buzzing 7500 or more all day. My buddy's 74 g- stock Duster low comp 340 with cast intake and J heads runs 7.0 eigth and 10.9 quarter with a cast crank. You will never hurt a cast crank on the street imo if you indeed have one.

I picked up this crank today for $125.00 bucks, it's a 340 "cast" crank. Turns out the crank in the block is a Steel crank according to the machinist. Going to send it out for repair. The local machine shop has had this crank on the rack since 1985.

Are you going to try to use the cast crank? I had cast crank 360 internally balanced it took 2-3 slugs of Mallory as I recall and cost me over 350$ 15 years ago. I won't do that again. Just my

First - on the forged crank, I told you so way back there.

Second, disregard any scare stories about 360 cranks because they don't apply. In your case, the crank would neutral balance if built as a 318, so any replacement piston that weighs 591 grams or less will balance up fine with no additional weight in the crank.

Look at the Number 1 and Number 4 crank throws. Are they bored out with a hole around 1" in diameter? 340 crank. Are they not bored out or a little hole like 3/8"? 318 crank.
The 318 and 340 used the same casting, so they will have the same casting number.

R.

Post deleted by Budsworth