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100LL in RV-12

edward7048

Well Known Member
for those using 100LL in a RV-12 with Rotax 912 ULS and decalin
what ratio are you using? I have only been using 92 octane without
ethanol or 93 octane with ethanol. I am planning a couple of
cross country trips this summer and will have to use 100LL only.
 
for those using 100LL in a RV-12 with Rotax 912 ULS and decalin
what ratio are you using? I have only been using 92 octane without
ethanol or 93 octane with ethanol. I am planning a couple of
cross country trips this summer and will have to use 100LL only.
1/2 oz per 10 gals:D
 
for those using 100LL in a RV-12 with Rotax 912 ULS and decalin
what ratio are you using? I have only been using 92 octane without
ethanol or 93 octane with ethanol. I am planning a couple of
cross country trips this summer and will have to use 100LL only.

I think it tells you on the bottle of Decalin, but yes it's ? oz per 10 gals. The bottle I have has a little graduated cup next to the regular bottle cap. If you loosen the bottle a little you can gently squeeze the required amount into the measuring cup. Then simply unscrew the cap and pour into the tank.

Pour in before or after fueling, makes no difference. You might notice a little white color on the end of the exhaust pipe after you've burned 100LL a while it's the lead.

Depending on how much you use, you'd need to adjust your oil change interval and if you remove the tank to clean the lead sludge out you'll need to make sure the oil lines are purged/pressurized afterwards. Your Rotax mechanic can help you with this if you don't already know.

Check around your route there are some airfields with 93 non-ethanol on the pump but they're not always well advertised. I have one near me in SC and know of 2 in VA and one in TN. Might as well use it if you reach it?

Have a great trip!:)
 
Have friend that runs 100LL exclusively in his 912 ULS. 400 hours on the engine to date without a single problem. Just has to change the oil every 30 hours or so. He doesn't want to lug Mogas to the airport and he's a big believer in supporting his local FBO.
 
I read on this BLOG that 1 oz/10 gallons was OK. Have you seen that? I think there is a guy on the East coast who runs his RV12 that way with really good results. I think he was/is a Van's RV12 demonstrator there.

EBB
 
100LL is 100LL even with Decalin.
Decalin only helps reduce some of the leading and should be used when using 100LL, but the lead is still there. If you can stay away from it you are far better off. It's like a person smoking. You can smoke for years and look like nothing is wrong, but eventually it catches up. The occasional use like when traveling is minor use compared to a steady diet. Lead will still build up over time in the engine. You are still relegated to do 600 gearbox inspections and do oil changes at 25 hrs. The lead can still cause valve sticking later on and lead can get under valve seats and then it has to be removed. The gearbox clutch at about 800 hrs. will cease to function properly due to lead build up. If you over use Decalin it won't hurt the engine, but it just becomes a waist and doesn't do any good after a certain amount.
 
In the UK, we were limited in the use of MOGAS in certified aircraft (certified Rotax powered) due to the abundance of Ethanol.

Having maintained a number of certified 912S engines that were operated on 100LL, we never saw any issues. Same goes with many 912 powered Eurostars.

Inside a Lycoming or TCM you'll find grey sludge, so no surprise if there is some in a Rotax but - what physical damage or problems does it actually cause?

How does it actually stop the clutch from functioning? Does it slip or not slip?
 
I've run 100LL exclusively in 912VA using Decalin at 1/2 oz per 10 gallons. Engine has 825 hours on it. No problems with the lead. Even with the gearbox inspection, no excessive lead was found in it. We just clean the tank at every oil change, 33 hours. Even with the frequent oil changes, I found that the plugs would start to load up at about 100 hours. At $2.50 each, I just change them instead of cleaning and gapping.
 
Lead deposits build up over time. 800 hrs. on this engine is nothing. Lead deposits will eventually build up on piston heads, in the crank case, on and in the piston rings, in the valve guides, under the valve seats. At some point usually during the life of the engine some parts may need dis-assembly and cleaning where someone using 91 oct. won't need it. The gearbox overload clutch is made up of 16 plates encased it their housing. The lead infiltrates this housing and fouls or clogs these plates. This prevents the clutch from working in a prop strike situation and transmits all the energy to the crank shaft which usually causes it to twist instead of the clutch doing its work. Time to replace the crank then. During the gearbox inspection (at 600 hrs regardless if you have a 1500 hr. or a 2000 hr. TBO) if you use 100LL the clutch gets torn down and all the lead deposits get cleaned out. You can't do this in the field and must go to a distributor.
All the guys I know toss the plugs at 75 hrs. We were taught that in Rotax school. Like you said at 100 hrs. they start to suffer.
You could run this engine on the original 3 liters of oil for many many years, but who wants to do this, eventually at some point something will happen. Same with lead eventually you will have some extra cleaning and there is no way around it.


Mlock,
Did you have the clutch torn down and cleaned or just the guy who opened the box up just look at the exterior of the clutch housing?
 
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The gearbox was completely torn down and rebuilt by Lockwood Aviation while at the Sebring Expo in 2014. They showed me the complete inner workings and remarked to me how low the lead deposits appeared especially since 100LL was used exclusively.
 
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