Quoting George Braly:
I once asked this same question about shock cooling to the former (20+years) head of engineering at TCM.
How cool is too cool for the CHTs? He thought a moment and said: “239F.”
Q.) Carl, where the heck did that number come from?"
A.) (grin) That is the temperature at which the thermostat is set on the liquid cooled TCM engines. They use the same pistons, rings, valves, etc as the air cooled engines.
Maybe if the CHT is that low you don’t get the problem, but 240F is unachievable on aircooled engines. You would need a PT6 powered fan 
Also, could it be that the number of those engines they have sold can be counted on one’s fingers, with a corresponding lack of feedback from the field?
CHT can be acceptable in a reasonable range as long as the cylinder is evenly cooled top, bottom, front and rear. The problematic cylinder on IO520/550 engines is #6, front left.
By putting 12 thermocouples on the circumference, the problem was identified, a fix was developed. The uneven cooling resulted in the aluminium cylinder becoming egg-shaped while the steel piston remained round.
How would even cooling impact the exhaust valve guide temperature?
Peter wrote:
The detailed description is here.
Everyone has to decide himself if advertisement for an oil additive is a good source for understanding what and what not to do with your engine.
Is there a claim that Camguard reduces valve sticking?
Yes they do: They first explain that it is deposits on the shafts that cause the problems to them claim:
“I will mention that the oil additive, Camguard, contains unique deposit control additives. These additives
work in conjunction with the ashless
dispersant to keep engines deposit and
sludge free and it is the only product to offer this technology.”
So the entire story is their sales story …
It might keep the engine clean and I don’t doubt that, but I am not aware Camguard does anything for valve guides. I have been using it for ever and still got the problem.
On #2 which has a much lower CHT than the rest.
I will mod the baffle on the #2 cylinder to bring up its CHT about 15-20F. It’s an easy job…
1 333
2 307
3 340
4 326
5 344
6 348
