Hello all...
Well I just finish building my sbc. First day I ran it for 15 minutes and everything was great. Next day, started it up and ran great for about 10 minutes. Then all of a sudden I hear a small rattling sound and then a abrupt engine stop. At this point I start sweating a lot and thinking WTF. Coolant is now running from the header. So I tear it down and to my disbelief a exhaust valve had broke off, bounced around cracked the cylinder wall. Screwed up a new piston and then jammed itself up into the head. Definitely a bad day! So here's my question. I can't seam to figure out why the exhaust valve broke to begin with.
Engine info;
350 bored 40 over.
Forged flat top Pistons.
6 inch forged rods.
Scat stroker crank.
Dart pro 1 215 heads. 2.055/1.60 valves.
Lunati 630 lift roller cam.
1.6 roller rockers

There was no evidence that the exhaust valve hit the piston to start this problem. So if anybody can help me out by letting me know what might have caused this please let me know so this doesn't happen again I would be great full. Thanks