Never seen anything quite like that! Incredible! However, many older MC18 barrels have wear there, but I've never seen any actually worn through!

The most amazing thing is... It actually started. I started it up just before I pulled it apart, and it ran, with a fubar crank with no centre crank seal and this hole in the exhaust port. Even took it for a ride around the neighbourhood.

Fitting 2x MC16 barrels to an MC18 will work, but likely see you with around 50hp. A pair of MC18 barrels is a much wiser choice, and it's worth doing the job properly.

Couldn't agree more, I just have to lay my hands on a decent set of 'B' MC18 barrels somehow, or even a set of MC21 barrels and heads. Are the MC21 barrels also marked with 'A', 'B' and 'C'?

Thanks,

Jacques.