This is one of those fascinating whodunnit threads… and I feel lucky that I didn’t have this happen when I R&R’d the rocker boxes to install new gaskets on my Unit 650—which I’d never worked on before.
I do, however, remember it took me a while to be satisfied that I had the pushrods properly seated. Pretty fiddly process but once in place, they’ve stayed put—and I do not baby this engine.
I think what I did—after it felt like the pushrods were seated properly—was simply rotate the engine and check to see if the valves were opening and closing as they should, then set the clearances. But is there any other test one should or can run to ensure they’re copasetic and won’t jump out…?