My buddy had a stock Merc 500 efi w/ 150 easy hours and had the same thing happen. It looked identical to your pic.

Tyler, very similar, snap, crackle, pop, to my 558 with a Callies Crank

160 hrs on hp500 with whipple, same thing, ran, horrific noise, when I went through the engine the pistons showed signs of detonation so I figured that was the culprit

She's a strong running 540 now, in my Pantera which needs a good home

Maybe this guy could tell you
http://www.goahead.org/

Tyler:

Lets face it, GM cranks ain't no perfect parts. I suspect with mass manufacturing and the "bean counters" involved its easier to slip a few through.

Sounds like its going to be a nice nrew motor job for you.

Regards,
Ray @ Raylar

I wonder if that crank would have passed a magnaflux or zyglow test prior to the breakage?

GM crank....nuff said.

[QUOTE=mrhorsepower1;2085194]I have seen them break like that in a Drag Race app. The crank had approx. 2000 passes and the engine was making about 875 HP. Broke in the same area. Never seen it in a low horsepower engine though. Ouch! Looks like it's time for a 4.250 stroke !

I Broak One In The Same Spot, Same Motor. Didn't Loose Block. New Bearing Cap And Line Bore And It Was Fine. I Have A 500 Crank If You Need One.
Ron Bender 216-390-1330