Rotax loss of compression due to lead??

[gossend]

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.

 

[KeithO]

Dick, lead seems to be one of the contributors to the demise of the Jabiru engine, on the ring side by lead deposits together with oil residue getting coked into the ring grooves, ultimately immobilizing the rings. But that is a factor that seems to impact the Jabiru more than any other engine because they simply run so hot.

Since the automotive conversions are usually well cooled and stabilized its entirely possible that valve stems may be the victim. Although anyone running an auto conversion ought to be running rec gas to get away from lead and using decalin whennone is forced to use 100LL on cross country flights. Plenty people running Rotax and Jabiru powerplants and not using any additives. Like usual airport managers moving at a glacial pace to offer pilots unleaded fuel of any variety.

 

[Lufthans]

I'm running my third Subaru EJ-25 conversion on my Jodel.

Prior to taking off the first one, I had run 100LL for five hours. Upon taking the engine apart, the engine rebuilder looked at me in horror: "What the beep did you do with this engine?". The inside was covered with a grey blanked of lead.

That's the last time I've run 100LL in one of my engines.....

 

[lr172]

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.

Because there is no evidence to prove this is actually happening. This is mike's hyposthesis for stuck valves and it is completely unsubstantiated. The fact that it never happens on Rotax engines kind of disproves his theory. As do the 10's of millions of auto engines that ran leaded fuel with CHTs of 200* and never had stuck valves. There are several theories for why this happens and IMHO Mike's is the most "out there" in terms of being a likely fit. If the lead oxy bromide could magically stick to everything, there would be all sorts of other problems, most notably stuck rings. Also, the cyl head woulld be literally covered with it and it isn't. The coating there is just the typical soft, fuel additive deposits seen on most every engine.

Sorry, but no one is going to convince me that the build up in the lycoming exh guides is anything but good old fashion coked oil. That oil, before it coked, was holding lead deposits in suspension, so no surprise that lead will be found inside the coked oil when analyzed.

Larry

 

[rv6ejguy]

Leaded fuel in Subaru and many other auto conversions engines seriously reduces valve and seat life. Been known for a long time.