Quote:
Originally Posted by mgarblik
Interesting that you bring up Billet source. Tom V always makes a big deal out of material for crankshafts being real "Timken ball bearing steel" There is something to that for sure. The mention of the Crower Billet crankshaft breaking may have some tie in there. For a couple years, Crower broke with tradition and bought a quantity of Chinese billets. They made a good size run of Pontiac billet Pontiac cranks from this stock. To their credit, they sold these cranks for about half the price of their domestic sourced billet cranks. We bought 3 of them and had no issues in the nitro engine with them. But you just never know. Of the 100's of things to worry about in an engine that can fail, a broken crankshaft would still be pretty low on the worry list. A good harmonic balancer with a press fit to the crank nose, a premium bolt with 200 ft. Lbs + torque is a must on a performance engine. My balancer of choice for a serious engine build is ATI.
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The reason why I make a big deal about the "Timkin Ball Bearing Steel" cranks, Mike, has to do with HOW CLEAN the STEEL IS before you start the machine work carving the cranks out of the Billet Material.
The "dirt" in the material creates "Voids" in the steel which are potential
locations for the crank to crack and fail. Even if it is a Billet material.
The "Timkin Ball Bearing Steel" billets that Moldex Crankshaft has always used to make billet cranks is a "very clean" steel.
When Bob & Frank and the BOP guys wanted to bring in the chinese cranks for the Pontiac Market,
I said we need to see how clean the steel is vs the Timkin Ball Bearing steel material.
So I had the Ball Bearing material tested. As advertised very, very clean steel.
Maybe one or two specs of dirt in a 2" x 2" section of material.
I had material from the off shore "Scat Cranks" tested. Of the batch of offshore material I had: the steel probably had less than 50 specs of dirt in a 2" x 2" section of forged material. A pleasant surprise.
I checked a couple of other brand steel billet cranks at the time and there was one other crank custom manufacturer (using the same material - "Timkin Ball Bearing Steel") that also had the very clean results.
Now all of that said, if the billet crank failed in a high stress location due to that one spec of dirt, then that is
the luck of the draw. Impossible to get perfectly clean steel. But the odds are like a Russian Roulette with a firearm.
If you have a revolver with 6 bullets in the weapon there is a high probability that you are going to die unless there
is no firing pin to fire the round. So there always are exceptions.
Same deal with quality Moldex or Bryant Crankshafts made with Ball Bearing "Clean Steel".
You may still have a failure but the odds of a failure are much much lower. You get what you pay for.
You may have a crank made with dirty steel that at a given HP level never fails.
You may have a Ball Bearing Steel crank that fails at 3500 hp due to the crank design and specific
engine crank support structure (block) where any crank would fail.
But IF you are buying better material cranks then the "odds" of success are in your favor.
500 mile NASCAR crank sees a lot different stress over time vs a 6 second drag engine.
Tom V.