Everyone knows that running 100LL in your Rotax 912 is not advised. Doing so requires more frequent oil changes, and lead buildup in the gearbox can foul the clutch. What about loss of compression due to lead deposits on the valve seats? Has anyone seen much of this?
Here's the skinny according to Mike Busch:
Combustion of 100LL produces a series of fast chemical reactions that end up creating lead-oxy-bromide, which is a gas. Like all gases, this one has a condensation temperature below which it will precipitate into a solid. That solid, mixed with carbon and whatever other junk is in the fuel shows up on valve stems. This causes morning sickness and eventually stuck valves, especially if the engine routinely operates at CHTs below about 350 degrees. If the engine runs far colder, as in water-cooled heads, the condensation is even more concentrated on the valve seats, which are the coldest surface in the combustion chamber. This will quickly lead to loss of compression due to leakage past the valves...and eventually burnt valves as well.
Evidence of this is beginning to appear in the automotive conversion community, where water-cooled heads are common. Recently Viking Aircraft Engines published a safety bulletin precisely to this effect.
My question is, Why are we not seeing this with the rotax engines? or maybe we are.
Here's the skinny according to Mike Busch:
Combustion of 100LL produces a series of fast chemical reactions that end up creating lead-oxy-bromide, which is a gas. Like all gases, this one has a condensation temperature below which it will precipitate into a solid. That solid, mixed with carbon and whatever other junk is in the fuel shows up on valve stems. This causes morning sickness and eventually stuck valves, especially if the engine routinely operates at CHTs below about 350 degrees. If the engine runs far colder, as in water-cooled heads, the condensation is even more concentrated on the valve seats, which are the coldest surface in the combustion chamber. This will quickly lead to loss of compression due to leakage past the valves...and eventually burnt valves as well.
Evidence of this is beginning to appear in the automotive conversion community, where water-cooled heads are common. Recently Viking Aircraft Engines published a safety bulletin precisely to this effect.
My question is, Why are we not seeing this with the rotax engines? or maybe we are.