Leading
Hi John, nice talking the other night. Hope to see you in Page.
I thought I might jump in here a little.
Leading isn't a big problem with low hours it is more of a long term high hour problem. It's an accumulation problem. Rotax SB's no longer recommend 100LL because of the long term deposits and associated problems. Decalin and TCP are the two widely used lead scavengers. Decalin is less corrosive than TCP so it makes it easier to transport or carry with you. Many have switched to Decalin. It is 1/2 oz. per 10 gals. Running a higher rpm (5300-5500) can help keep some of the leading down. Neither of these two items keep all lead away it just helps some.
The Rotax engine can easily handle 91 oct with or without ethanol. Most fuel lines today can handle the ethanol since most of our autos use it and in several countries at twice the concentration than here in the US. So the deciding factor for many aircraft becomes the fuel tank material and construction.
The 600 hr. mark (pre mid 2006 engines or use of 100LL more than 30% of the time) for a gearbox inspection should not show any large deposits of lead during the inspection. The slipper clutch is supposed to be disassembled and cleaned of lead because right around 800 hours with no maint. any solid 100LL use and the clutch is trashed with lead and most likely isn't functional any more. Using unleaded auto fuel allows the inspection time to be a 1000 hrs. on the engines that qualify for that time period. Older engine's approximately Mid 2006 and before still have a 600 hr. inspection with or without leaded fuel. Lead also coats the tops of pistons, valves and sometimes causes valve guide issues, it settles in the oil tank and needs to be cleaned and can cause acid etching on the valves. The lead coating will combine with moisture like you may have in really humid climates and it gets drawn in as an engine sits and cools. I have seen several sets of valves with acid etching from this, but you'll never see it unless you dismantle your engine. I have seen other examples of this in Rotax classes that were taken out of other engines. Owners that use a steady diet of 100LL have had to have their valve guides reamed as early as 1000 hrs. It may or may not happen to you, but it does happen.
So 100LL leading is not a short term problem and not one the user may see until things get inspected or becomes an issue down the road.
Using 100LL also ups the maint. times like oil changes, gearbox inspections, ect... which increase ownership cost.
Your right that 91 oct. isn't at most airports and we all get stuck using 100LL when we travel, but the more you can stay away from it on a daily basis the better off your engine will be. It's like smoking cigarettes, it won't kill you or disease you today or after a pack or two, but long term use carries consequences and they will eventually show up.
If you're stuck using 100LL just make sure you keep up a good maintenance program to help cut down on its affects and build up. It can save you money in the long run.
I use 91oct. with ethanol because that's all I can get and only use 100LL with Decalin when I travel.
Your engine is like your body. It usually works good when it's young, but starts to have aches, pains and break down when it gets older so good maint. along the way can help greatly.
