Basically, don't worry about cylinder head temperatures. It will be normal for the engine to get hot enough to give you a severe burn if you touch it. We've measured cylinder head temperatures on airplane glow engines as high as 375 degrees F! This was using a contact probe at the airflow stagnation point at the rear of the cylinder when the engine was running on our test stand.

If the engine is running on the rich side of peak RPM, and you are using a quality fuel with a high-enough oil content (O.S. states no less than 18%), then you won't have any problems.

bill baxter
Hobby Services Manager