Were OS SF series engines offered in both ringed and non-ringed versions? I have a chance to pick up what the seller says is a NIB SF ABC engine but I thought these were ringed engines.

Thanks for the input, folks.

I'm pretty sure you could buy both versions from OS back in the day.

Yes, I do believe they offered both options. I used to have a .40 SF that was ABC.

I know the .40, .46, and .61 were all offered in both ringed and ABN versions, I have had them all. These are all good running, well behaved sport engines that put out good power, not great.

The SF ABN engines were where the first liner peeling was noticed, as I recall. I have a .46SF that ran great until its liner peeled the plating.

I also had two .61SFs, one ABN and one ringed. I sold the ABN version and the ringed engine is still flying on one of my planes today.

I've seen some nice running SF's some years ago

The first time that I encountered a .61SF engine was when I test flew a fellows kit built Super Kaos in 91 or 92. He had a humongous looking prop on it for an 11x7 user like me. I asked him about it and he said that it was the size that the manual recommended. He had bench ran the engine until it was sweet, so no further attention had to be paid to break-in. I had been away from the hobby for a few years and had missed some of the OS long stroke info that had circulated.

The Super Kaos was built beautifully, but had been painted, so it wasn't as light as it could have been had plastic film been used to cover it.

A few laps around the flying field and I had it trimmed out to where it was comfortable to me. It was time to play.

I pulled back on the elevator in order to go straight up for a couple of hundred feet, fully expecting this over propped sixty to fade out, causing me to terminate the climb. Wrong. The model just kept going up and up and up and up with nary a sign of fading out (overheating). I was astounded. This was a stock muffled engine without a pipe/pump/or over sized carb. While it didn't rev up all that high, it didn't slow down when going vertical. That was when I fell in love with the OS .61 SF/RF engines. I now have half a dozen of them.


Ed Cregger

Hi, a pic from my 46 SF "ABC"

My SF .40 ABC P. I wish it was ringed.

David

If anyone has a .46SF with a peeled cylinder, you can use a Mecoa .46 ABC cylinder & piston for a drop in replacement.

I have not tried this on mine, since I have been flying a couple os .55AXs, but I did e-mail Mecoa and asked about it and they replied that it was a drop in fit. Apparently, the Mecoa .46 is an exact copy of the OS .46SF.