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HIGH CHT'SFrom CP52, Page 5 (July, 1987)
Recently we have had two
separate cases where builder/flyers had been battling with really high cylinder head
temperatures. Talking to them on the phone, we discussed baffling, cowling inlet and
outlet sizes, carburetion, and spark plug heat range. Frankly, we, and they, were running
out of ideas. Amazingly, both of these EZ flyers had obtained their engines in the same
way, removed from a factory airplane with relatively low time and running fine when
removed. As a result, both of these engines were installed in the EZs and flown as
they were received.
The cause of the high CHT's was finally traced to one or both
magnetos being timed too far advanced. In one case, one was timed 15°
ahead of normal. In the other case, both mags were 25° too far
advanced!! Beware, guys, some of the supposed FAA approved mechanics, A&P's and even
AI 's may not be any smarter than you are when it comes to timing magnetos.
In both cases, once the mag timing was adjusted to the normal
position, CHT's were immediately reduced to normal. There is a lesson here. No matter
where you obtain your engine, whether it is a factory new one, a rebuilt one, or a
"used one running well when removed.' check the timing before you go flying. If you
don't know how to do this, get help from an experienced person who does. Assuming that the
timing is correct could be a very expensive mistake.