Originally Posted by
IO540
There is also the "constant EGT climb" technique which is perfectly OK for the engine, even though technically you are moving the red lever while the power is above 75%.
The doctrine of not touching the red lever anytime above 75% is not based on any engineering principles.
Not in the UK
This method requires the accurate real time EGT and CHT information you can only get from a modern digital engine analyser and the even cylinder to cylinder fuel flow only possible with fuel injection. Since the original poster said he was a new PPL, I took this to mean he would be flying simple rental aircraft, fitted with carbs, and which in general only have the most basic engine monitoring instruments. The prohibition in leaning above 75% power IMO reflects less the posssibilty that it will always be dangerous to the engine and more to the fact that without full real time engine monitoring it is safer to just make a blanket prohibiton not to lean in a regime where damage could occur under some circumstances and would not be detectable in time due to a lack of information available to the pilot. (Ie the first indication of overheating would be a high oil temperature by which time cylinder head damage may allready have occured)