A (forged) 340 Crank is Not a (forged) 273/318 Crank?

-
dibbons

dibbons

Well-Known Member
Joined
Nov 6, 2009
Messages
5,849
Reaction score
3,915
Location
La Paz, B.C.S., Mexico
Just read on another forum that a 340 forged crank has "lightening" holes drilled in the #1 and #4 rod pin areas, the 273/318 forged crank does not. Never heard that before. I wonder if that is universally true for identifying the Mopar factory forged crankshafts?
 
The 340 had lightening holes to compensate for the heavier rods it used. you can make a 273 forged or a 318-3 forged truck crank (even a 318 poly!) 340 spec by balancing to heavy rod specs. The 340 forged cranks PAW sold were poly cranks drilled to 340 specs.
 
I wonder how many have switched cranks between 340 and 273/318 without taking into consideration those holes? What is the worst that could happen?
 
Heavier reciprocating weight equals slower revs so it won't be as fast, doubt it would be very detrimental to the engine...
 
I think the forged cranks all use the same casting number but are balanced differant.
 
I have the original 318, from my 69 B-Cuda. It ran real good on points, when pulled. Will this engine have a forged or cast crank,??. It has a casting date on block of 6*6*68.
Dave
 
barracudadave67 said:
I have the original 318, from my 69 B-Cuda. It ran real good on points, when pulled. Will this engine have a forged or cast crank,??. It has a casting date on block of 6*6*68.
Dave
Click to expand...


Mama says that motor is the debil.
(a little waterboy there)
But I would think it has a forged crank.
 
dibbons said:
I wonder how many have switched cranks between 340 and 273/318 without taking into consideration those holes? What is the worst that could happen?
Click to expand...

I've used 273 cranks (great with aluminum rods...less balance work), 318, 318 poly and 340 cranks. I always drilled the 1 and 4 rod throws. Once balanced, they don't know from whence they came.
 
They both weigh the same, but the mass is located differently, Left= 340, right is 318
100_1405-jpg.jpg
 
Max1196 said:
They both weigh the same, but the mass is located differently, Left= 340, right is 318
View attachment 1715166470
Click to expand...


The left crankshaft is a forged crankshaft the right crankshaft is a cast.
My bad I didn't blow the picture up good enough to see if that is grinding on that throw, both cranks are forged.

A cast crankshaft should be lighter than the forged.
 
Last edited:
I did it once when I was a kid and it had a vibration and it pounded out the rod bearings, f#@%ed up the good crank.
 
Jadaharabi said:
The left crankshaft is a forged crankshaft the right crankshaft is a cast. Identified by that little line of casting on that throw.

The cast crankshaft should be lighter than the forged.
Click to expand...

There both forged if you look close you can see the lines
 
My understanding is the forged is 1 solid piece that is pressed and hammered into shape. An the cast is poured into a mold.
 
And to complicate the issue a little more, let me offer two fotos of the crank pulled from a 340 core motor: no holes in the #1 nor #4 rod pin areas, but TWO balancing holes drilled in both the upper and lower counterweights. I wonder ...

DSC04756.JPG


DSC04757.JPG
 
You can have two identical cranks, that weigh the same and they will take different balance corrections. With the same bobweight.

A few degrees difference in where the counterweights are makes a big difference in balance correction.
 
You must log in or register to reply here.
-

Back
Top