Lycoming O540 J1A5D

[tazin river]

I know there is no mogas stc for this engine but does anyone know if in a bind, premium gas can be burned in that engine?

Thanks

[Strega]

not the best idea but if you got stuck?

[tedcuthbert]

That engine has an 8.5:1 comression ratio so should be ok on 91 or higher auto fuel. Other 0-540's were approved, not sure why that one wasn't. Perhaps because there were not enough engine & airframe combinations out there to justify the cost. Or is is there a fuel pump? that's usually a no go for auto fuel. Give Petersen a call, they should be able to tell you. Though, even if there is no technical reason, it's not legal.

[akholland]

You are correct, the O540 j1a5d has a booster pump that provides about 3psi "during takeoff and landing" as kind of a safety feature I guess to make sure you dont starve that fuel thirsty gravity fed engine's fuel system. I have read on other sites where people experienced issues with regular gasoline vaporlocking the pump at 100 plus degrees in texas. Here in alaska at zero to 70 degrees its probably not that big of an issue. I would be more worried about making sure I had the right style float in my carb and proper seals throughout the system that wont be eaten out by pump gas. Some people also said they wouldn't have a problem trying it out at 65% cruise and swapping tanks for the flight duration with a 5 degree timing retard from factory setting. problem is if you retarded your timing the thing would lose power for takeoff, decrease burn efficiency, etc.. and who wants that. 8.5:1 pistons are fairly high compression when you compare it to like a 6.5:1 or 7 in a smaller 4cylinder lycoming that has an autogas stc. Im curious what the compressions are for the approved A and B series engines and what the differences are that could effect it. For now I suppose we stick with the spendy 100ll that's going slowly out of production until someone figures it out.

[Colonel Sanders]

http://www.tc.gc.ca/media/documents/ca- ... /mogas.pdf

[akholland]

Thanks that's good info i'll read through that. I also found another link for the differences between the B/A and J motors. Seems mostly to be the combined vs. seperate mag's and the crank counterweights.. Did I miss anything important?

Type Certificate Data Sheet for the o-540, see link below and page 5 for the list of differences.

http://www.tvbf.org/docs/lycoming-o-540.pdf

[Bulawrench]

I had a case recently that mo gas was used and the valve seat went to mush.
The document has the level of lead to be very low. 5 parts compaired to 1127 parts avgas.
Not to mention the ethenol content that mo fuels contains.
Yes, it has been used but safer to use the right fuel. It becomes more of a problem at altitude.

[akholland]

I could def see it eating a valve if It was run on ethanol added fuels. I did more research and I think the j1a5d was a 7.2:1 piston? Luckily in alaska we dont have to deal with that ethanol garbage so a guy could get away with it, for now till the EPA gets ahold of our fuel. They do make test kits though to make sure it doesn't contain that crap before you put it in. Just talked to a buddy who told me he knows several people who have ran it in their j1a5d for years with no issues.

[akholland]

N.m. its 8.5:1 compression. O540 j1a5d just looked it up in right place this time. I think there was a lower HP model with lower compression though that ran 80 octane