The 0.52 cu in Skychief was a low cost copy of the Dennymite. The crankcase was made of a zinc alloy and did not have a crankshaft bearing. The con rod was also zinc alloy and can fail with catastrophic damage to the crankcase. Early examples had lapped pistons, later ones identifed by the twin exhaust openings (as in picture) had a single ring. They usually run quite well, gaskets can be a problem.