I've bought quite a bit from Peak Model and they have always put-right anything that was wrong -- what has their response been to your woes.

As for the piston hitting the head -- does it do it with the sparkplug out?

I had a Chinese motor (not from Peak but one that looks just like theirs) and the piston would hit the sparkplug if you screwed it in without the washer. Turns out they (the manufacturer, not Peak) sent the wrong plug with the engine.

Which engine is it you're having trouble with -- I bet it's a Peak 26, 45 or 65 -- these seem to all come from the same rather poor manufacturer.

If you're having more woes, PM me, I can ring Raymond (the head of Peak) and try to get it sorted for you.