I had the same thing happen to mine! After the 5th flight, I noticed the compression was leaking out the exh. valve. I went to adj. the lash and when I loosened the nut, the adj. screw w/nut fell off! It fractured right at the juncture w/ the rocker arm. Hmmm...

I checked the lash when new (before I ran it ), and it was o.k. so I left it as was. I figured a bad batch of screws, or a problem during assembly?
TT/Ace sent me a couple extra screws N/C...

I haven't run it since, and that was a year and a half (approx. ) ago...
I just put that engine in my new H9 P-40, and figured all was o.k. but now I'm wondering again!