Ted:

Something you may not be aware of.  When I had my 312 crank ground to 2.100, I did not widen the throws, I narrowed the rods to Y width.  The crank guy said TRW makes a bearing that is narrower than the stock sbc one for use on cranks with larger than stock radii.  I did not use those bearings, I made a fixture from an old sbc rod and chamfered the stock bearings to clear the radius on the crank.  Thinking back, I should have bought the narrower bearings, after I cut the chamfer the bearing surface ended up being narrower anyway.

John

John - "The Hoosier Hurricane"

John.  This is a good topic as there seems to be several different approaches on how to get around the journal width issue when using the aftermarket connecting rods in the Y.  I have been using the narrower than stock bearings but even at that, the bearings come close to kissing the radius or fillet in the crankshaft if leaving the journals at the stock width.  Just getting an additional 0.050” in width at the journal helps in not having to rechamfer the bearings themselves.  At  this point, I’ve got a reasonably good feel for which crankshafts can stand some extra widening of the journals and those that don’t.  For those that don’t, there is just some extra work to be performed on the bearings themselves.  I’m still dealing with a generous radius in the crankshaft fillets at this point as gut feel says that there’s a considerable reduction in strength if the radius at the journal edges are removed.  Haven’t had a broken crankshaft yet and simply just trying to keep it that way.

Lorena, Texas (South of Waco)

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

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

Frank/Rebop

Bristol, In ( by Elkhart) 

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

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    

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) 

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

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    

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