Only race every 3rd weekend. Just kidding......
Well that is what alum rockers do...There is no way of testing the ultimate fail strength of alum. You have to wait for the 'bang'...Steel does have a fatigue limit that can be tested for. Just beats me why people risk using alum rockers when there are so many stronger steel & S/s rockers available.
I see a number of reasons for these rockers failing, reasons either singly or collectively:
- valve springs too strong
- valve train going solid
- rockers weakened by fitting roller brgs
- less surface area on the exh rockers to carry the load.
- exh valves opens against combustion pressure, so more load on exh rockers, all else bing equal