Last year I was given 2 vintage helicopters. A Micro-Mold Lark 2 40 and a Graupner Helimax 40.

I refurbished the Lark last year but I'm only getting around to refurbishing the Helimax now.

When I removed the engine from the Helimax i found that it was a British made Irvine 40.  I suspect that this was the original engine from the Lark and that the engine that is in the Lark (a OS Max 45 F) is the original engine for the Helimax.  The reasons I think this are that the Irvine is a British made engine and the Lark is a British made helicopter also the OS Max 45 F is listed in the Helimax manual as one of the recommended engines.

Eventually I will get around to swapping the engines back to their original helicopters.