Dar:

The OS twin, four, and five cylinder engines do indeed have steel cylinders, with the cooling fins machined as integral parts. These are all four stroke engines.

The single cylinder OS four stroke engines have a brass sleeve inside the upper part of the aluminum crankcase, the cooling fins are part of the crankcase casting. The pistons are ringed. And unless OS has gone back to chrome plating, the brass cylinder sleeves are nickel plated. Only the multis have steel cylinders.

Bill.