Dar:

There are still several ringed engines with steel sleeves. K&B for example has chromed steel sleeves in all their ringed engines, but granted, these are two stroke engines. All the little Coxes are steel sleeve with iron pistons, I think Fox still has some made that way also. Two stroke engines as well.

Actually, I can't think of any 4s engines still using steel sleeves except the OS multis. Saito has some ABCs, most of the newer Saitos are AAC. And YS, as you have mentioned, is Nikasil. And the Magnum/ASP engines are ABC.

The OS 50SX I'm not sure about, but I'd make a bet it's ABN. There was a big flap a few months ago about the OS 91FX, It was advertised as ABC. But when nobody could make one run they started getting taken apart and checked, OS and Horizon had to backtrack quickly when everybody saw the nickel plating in the cylinder. On brass, yes, but it was definitely ABN rather than ABC. And some did peel. Nowhere as many 91s peeled as 46FXs, but there were failures.

Just remembered another ABN 4s engine - the Thunder Tiger line.

Bill.