Here's the written version:
https://resources.savvyaviation.com...ticles_aopa/AOPA_2020-07_why-valves-stick.pdf
It's a rehash of Ed Kollin's work, although Kollin likes slightly lower CHT.
https://aslcamguard.com/wp-content/uploads/2019/08/Camguard-Parts-1-to-3.pdf
Kollin borrowed the valve illustration from TRW, then relabeled it. Here's the original:
Take a good look at the illustrations. Busch/Kollin argue that the valve stem must be kept above the condensation temperature of lead oxy-bromide, which Kollin identifies as being about 1300F. However, none of the illustrations show anything near that high at the part of the stem which peeks in and out of the valve guide.
Not that it really matters,
because the original TRW illustration is generic. There is no evidence that the illustrated temperatures are actually those found in a Lycoming or Continental. They simply re-labeled the generic values in Fahrenheit, and placed "Lycoming" and "Continental" at the bottom. Frankly,
that is made-up data.
Although Busch/Kollin claim the Lycoming sodium filled valve is more prone to deposit formation because the stem is cooler, the illustrations actually show a higher stem temperature at the location of interest. For example, note the location of the yellow 600C zone for the sodium filled valve in the TRW illustration, vs the 600C location for the solid valve. It's no surprise. The whole point of the sodium filled valve is to move heat from the head of the valve to the stem.
Neither writer offers any sort of concrete connection between actual valve stem temperature and their favorite CHT range.
Kollin does stress maintaining higher combustion temperatures, and I agree. A lot of owners are pouring fuel into hot cylinders, or trying to run way LOP, in order to maintain a reasonable CHT. For a moment, forget about what to call reasonable. Instead, consider this. Very rich and very lean both lower combustion temperature. Put another way, they put less heat
into the cylinder head. It works, but one is costly and the other makes less power, while neither expedite the chemical reactions Kollin described. Instead, work on taking more heat
out of the head, i.e. a better cooling system. It allows cruise at peak EGT, which is precisely what Lycoming has recommended for decades....as does Kollin, if you think about it.
This afternoon, somewhere over southern Indiana. Peak EGT, with low CHT and low cooling drag. Results not worth the time?
So, why am I poking holes in the referenced Busch opinion? (Yes, it's an
opinion column.) Because it illustrates a point.
We live in a society full of misinformation, often generated by good people. Followers spread the misinformation without giving it critical thought, or making an effort to find the underlying data. It's just human nature, and top to bottom their belief is often quite sincere.
It doesn't matter
who says it...vendor, bystander, or industry expert. Nor does it matter
where you heard it...Oshkosh, a magazine, an aviation forum, or God forbid, Facebook. Ask for the underlying "why", and think about it before passing it along. If someone presents a contrary opinion,
and brings good data to the debate, be happy!