a65 and c90 engines and unleaded mogas

[phil brookman]

would like to hear ur stories with using unleaded mogas and operating these engines ....
i have used unleaded mogas in vw for hundreds of hours without any real issues ...but not all engines are the same ...

[Brian Hope]

Hi Phil, my experience with mogas in a C90 is that it runs no differently than when it is on avgas as far as day to day use goes. It does however burn cleaner and there are less carbon deposits at top overhaul time.
Some say the valve guides and seats need the lead in avgas as a lubricant, I am not wholly convinced but as you are likely to be running a mix because mogas is generally only available at your base airfield via jerry-cans, that is a non-issue.
Some also say they have more carb icing problems, again not something I have experienced over many hundreds of hours.
Vapour-locking is a potential issue but, dare I say it, not something I have ever experienced either. As you rightly say, not all engines are the same, and that goes for those of the same type as well.

Bear in mind that your aircraft has to be approved by LAA Engineering to run on mogas (the A65 and C90 engines are cleared but LAA also has to be satisfied that your aircraft's fuel system is satisfactory too), and as an SEP/SSEA you are only permitted to run on ethanol-free mogas.

[phil brookman]

thanks brian ...wonder if u would be covered in the event of a crash if u had mogas with ethanhol in it .
quite an escape clause that would be for an insurance company ...
trying to find a jodel at moment a65 or c 90 powered ...should u hear of anyone

[Ian Melville]

Providing you test the fuel for ethanol before use, and comply with the law, why would there be ethanol in it?

[MikeM]

Should small Continentals (the engines, I mean...) be timed differently if predominantly using mogas rather than avgas? Thoughts?

[howell]

An interesting debate, we cannot purchase Mogas West of Exeter that is with at least 5% Ethanol.
We await the deliberations from the LAA as with the price drop on Mogas recently down to 1.10 a litre in our local Texaco Garage and the ready supply it would be very helpful to at least use a mix of both Avgas and Mogas with Ethanol.
Chris Howell.

[Jim Alex]

I've had sticking valve probs in two 0-200s and a C90 the common thread being recent head overhaul with valve guides reamed to min clearance. Use mogas and after a few hours, problems. Back to avgas and prob goes.

[G.Dawes]

When it is said that valves are lubricated by the lead in fuel, it actually means the valve faces and seats, the actual rubbing surfaces of the guides and valve stems are lubricated by oil seepage from the heads.
I would imagine that the valves are too tight , as you say minimum clearances, then that changes when the temperatures change in use. The valves do get spalled and the guide material has been changed several time since I have been working on these engines, Bronze, phosphor bronze, cast iron , plated and no plated ready sized and needing reamed. you name it and it has been done, The main reason for valve trouble is high head temperatures, Make sure that you have all the gaps sealed around the baffles and the small intercylinder baffles are there and effective, Head temperature gauges might be a good idea.