Engine Builders/Brains, I need your help...
 

Background:
2013 BRZ
Sprintex 210 w/ 70mm pulley
Flex Fuel
Delicious v9 tune
Full Blown Motorsports Stage 2 heads w/ stock cams
ACT RaceLite flywheel
GFB Lightened pulleys

Last summer I had a rocker go wandering. It punched a hole in the rocker cover and destroyed the head. It wasn't due to a pin failure and the consensus was that the stock valve springs were too weak to keep the rocker in place during hard driving (even though it happened while approaching a stop light.) So I replaced the heads with Full Blown Motorsports Stage 2 heads with dual valve springs. The rebuild was done in december so I drove the car from the shop to my storace space and put it away.

Fast forward a few months and with the warmer weather I pull the car out. Again, it runs fine. I drive it from storage to my house. The next day I drive it a little, but the roads are wet. The most load I put on the engine is some wheel spin. I never get near red line. Following morning the roads are still wet. After the oil is warm, I again play with a little wheel spin, never nearing red line. As I put it into reverse to back into a parking spot, the engine makes a quiet "crunch" and stops and won't restart.

At the shop again, the engine is pulled and inspected. ANOTHER rocker has come loose, It jammed the exhaust cam and broke the timing chain. Cylinder pressures check out, so I don't appear to have damaged the valves. Damage-wise, I got off light and could have the car back on the road in no time.

But why are these rockers coming free?? It's not worth it to throw more parts at the car if it's just going to keep throwing rockers. What is causing this, and what can I do to keep this from ever happening again?

I'm at my wits end, so I'm hoping more experienced minds than mine can figure out a solution. I love this car, but if the engine won't stay together I'm going to have to go back to stock and sell it.

Thanks.

what specs did you shim the valves to? here are the oem specs. they need to be right on. we have never had one fail with upgraded springs and proper clearances

0.10 to 0.16 mm {0.0039 to 0.0063 in} (intake side)
0.21 to 0.27 mm {0.0083 to 0.0106 in} (exhaust side)

Yeah why hasn't anyone made better rockers yet?

They're were built by FBM. I'll have my builder double check them.

damn near every single piece changes the specs when we put them together. definitely keep every rocker organized and position noted. assemble the heads and check the specs. i ended up needing 14 different sized shims when we put my heads together last week. we were able to reuse 2 lol.

So the clearances were checked when the heads were installed and they were all in spec.