Dm, I just lock the throttle on ringed engines at about 4,000 to 4,500 rpm and just let it run and in about 1/2 hour to 45 minutes it will start to speed up slowly. Then you'll know that the compression is improving. After one hours it can be flown, I just let flying take care of the heating and cooling cycles. It works every time.
Spiff, I pushed my Webra .50 too soon and had the same result as you, but it came back very quickly. It's hard to resist reving an engine that is so willing.