>Actually in some situations removing material from a forging helps. Look
...
>surface. This is a good place for cracks to form on connecting rods and
>the polishing lowers the chance. Also forged cranks when prepped at a good
I think the theory says that it removes a "stress riser" -- basically, by
removing extra material, you let the whole part flex at the same rate,
instead of concentrating the flex at the point where the dimension drops,
ie, the end of the flash.
A billet crank would be the ultimate - finely machined over the whole
surface. I'm sure billet costs more due to the machining (much more
expensive to cut away metal than to cast or forge the part so the metal
wasn't there to begin with). I really don't know whether billet are
stronger or weaker than forged. I doubt billet crankshafts are actually
made from a single huge chunk of metal the diameter of the crank throws.
I suspect they are machined from an oversized forged crank. If they were
really from a big chunk of metal, they'd be hideously expensive. You
would have the option though, of using steels that you can't forge --
stronger (but more brittle?) high-alloy steels.
>The manufacturers are going to external balance (Chevy went this route in
>1986) because they can make the crank with much much smaller
>counterweights, and adding mass to the dampner and the rear plate is much
...
>Blocks do not care about internal and external. And forged are better to
Isn't it a lot more demanding of the bearings to have an assembly with
out-of-balance parts strung out along the crank?
I suspect the real reason is that the manufacturing tolerances are closing
up so that the basic balance is much closer to begin with. The powder-
metal con rods in the LT1 (Chebby) engine are forged with carefully
measured amounts of material, and all come out of the factory weighing
within a gram or two of one another. Supposedly, there's no longer any
need to weigh 20 con rods to find eight that match - just put one in
off the shelf! If the crank dimensions can be controlled pretty well,
then the balance internally is pretty close (probably better than the
factories turned out in the 60's) and a final external balancer gets the
customer an engine he can stack champagne glasses on.
Jim
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