ORIGINAL: Pull Up Now!
Very timely, your post on the lost pushrods. I just took delivery last night of my 77cc Evolution. My RC'er son noticed the pushrods seemed to be a little looser than we're used to seeing on a typical Saito 150, for example. So, I made a mental note to check the valve lash before the first run. And then I saw your post about your missing pushrod. So, here's a question, after you did the FIRST recommended valve clearance adjustment, was there too much lash? If so, I'd expect the pushrod loosening to continue for a whle but at a much less agressive rate. But, 20 flights might be quite enough time, even at a reduced rate, for enough loosening to have occured. Check your head bolts, too.
I hope I'm right about this, but since aluminum expands at a faster rate than steel, the crankcase and cylinders, at temperatuare, are going to grow (expand) more than the pushrods. So whatever the valve clearance (lash) is cold, seems like it would get worse at running temperature.
Again, anyone seen an exploded parts list and diagram of this engine (Evolution 77cc)?
Here are some more pictures of my home-made exhaust ring project. You'll recall I found a ''copper'' ornamental sprinkler whose inner hoop seemed about right to construct an exhaust ring. I think it will work, here are some progress pictures. I was surprised to find out the hoop is not copper, but copper plated stainless steel. It's non-magnetic. It's ok though, I know I can braze stainless steel. I'm just glad it didn't turn out to be aluminum!