I know there are folks who are not a fan of Mike Busch on this forum. The dude admits he is more of a data analyst. Points of random data exists. If we can organize the data, then we have information. If we read the information, we can gain knowledge and which leads to wisdom....or maybe leads to improved reliability of Lycoming engines. It seems to me like Engine Data analysis is Mikes strong suite. The facts below are his, not mine. Below is a synopsis of the data Mike shares in that video link in post 28 and this AOPA article
https://www.aopa.org/news-and-media/all-news/2020/july/pilot/savvy-maintance-valves
-Cool running engines have more sticky valves than warmer running engines.
-Valves stick due to buildup of deposits on the valve stem inside of the valve guide.
-Laboratory chemical analysis by a petrochemist from Exxon has been performed on valve stems.
-TEL is used as an octane booster in 100LL fuel requires a scavenging agent.
-This lead scavenging agent that is added to help avoid fouled spark plugs.
-A chemical reaction during the combustion event produces a byproduct of the scavenging agent called Lead OxiBromide.
-The Lab analysis showed that Lead OxiBromide is primarily the source of the buildup on the stems of stuck valves.
-Engine Monitor will show a rough running engine from a sticking valve to produce an EGT value that is not normal. As the engine warms and the stuck valve loosens, the EGT will indicate normal.
-Lead Oxibromide that remains as a gas above temps of 1100F.
-After the combustion event we want the Lead OxiBromide to remain gaseous (above 1100F) to pass harmlessly out the exhaust.
-The hotter the temp, the faster the lead is scavenged.
-A cooler surface will condense these gases and over time form hard deposits on surfaces they contact, like a valve stem of an open exhaust valve.
-Sodium filled Lycoming valve stems run cooler than Continental valves and the chances of a stuck valve is more likely with them.
--Mike thinks that the conventional wisdom that the carbon deposits on the valve stem inside the valve guide from oil contacting the hot stem and carbonizing the oil is wrong.
What Mike says to do....
-Since CHT is the best indicator for Valve stem temperature, keep the CHT's between 350F - 400F to avoid Lead Bromide buildup on your valve stems.
-Lean aggressively on the ground and low power operations to keep combustion temps as high as possible.
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