Thanks for sharing your knowledge Frank.

See, even though I'm an old dog I can be taught something. It pays to ask questions.

Once again - this place wins my vote!

       A  L  A  N   F  R  A  K  E  S   ~  Tulsa, OK    

Alan,

       Kinda, but even better. A sharp edge puts all the stess at the corner, the smaller the actual corner, the more concentrated the stresses become.

      Best example I can think of off the top of my head is one sheet of paper is easy to tear from the edge. But if you try to rip it in half from the middle, it's a lot harder. You have spread the force from your hands over a lot more paper.

      You're dealing with tensile strengths in the crank example. Tensile is the amount of force required to pull a material apart. It's expressed in pounds per square inch. The more square inches presented to the force, the stronger the pull required. It's a bit more complicated than that in a crankshaft, but that's the idea.

Frank/Rebop

Bristol, In ( by Elkhart) 

Yes it dose relieve it of stress areas to have a smooth round transition to the bearing surface, It's kinda like when you put a "gusset" on something made of wood or steel. A sharp corner can crack easier than a rounded one.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

thanks Frank,

So, is this a similar principle of relieving surface stress on other parts by grinding and smoothing or even shot-peening like on rods?

       A  L  A  N   F  R  A  K  E  S   ~  Tulsa, OK    

couldn't have explained it beter!

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

Alan,

       At the intersection of the Rod journal to the crank web or throw a radius is ground. This radius is ground into the rod journal to reduce the stress concentrated at the intersection. Sharp edges, particularly on inside corners, are bad news in a casting. By creating a radius you spread the forces out over considerably more area, and reduce the amount at any one point. This actually can apply to main journals as well. A few years back it was all the rage to roll the radius in to the corner, actually deforming the material. This turned out to be a waste of time on cast cranks,but usefull in steel forgings, or billet cranks.    

Frank/Rebop

Bristol, In ( by Elkhart) 

John, Ted,Tim-if you guys wouldn't mind I'd like to learn more about the radius topic. I thought I understood at first but now I guess I'm lost. That explains why I'm no machinist, Anyway can someone simplify for the layman?

       A  L  A  N   F  R  A  K  E  S   ~  Tulsa, OK    

my girlfriend keeps telling me bigger is better

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

Strictly from a stress standpoint, bigger is better, none, as is mentioned is the kiss of death.

Frank/Rebop

Bristol, In ( by Elkhart) 

Ted, that is no joke about the radius. I've been doing crankshafts for 25 years, when I first started I had a young guy train Me and he was all about doing the job fast, you know "Production". Then I started reading about how cranks should be done, I found the tool for radiusing the stone (it was on a shelf in the shop all covered in dust) and I've been grinding with a radius ever since. The worst thing I see a lot of is some guy will bring me a crank out of his "Racecar" usually a SBC steel 350, and want to have it Maged. The crank will be .010"/.010", have no radius, and have a nice big crack in the fillet on the back side of every throw.

A crank that is .040"/.040" is just as good as a Std. (unless it was hardend) but it has to have a radius.

Tim

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias