Triumph (TWN) BD250W Video

Video of my 1941 Triumph (Triumph Werke Nürberg) model BD250W (W=Wehrmacht). It is a 250 cc 'eins cylinder doppelkolben' (one cylinder with 2 pistons) 2 stroke engine. One piston controls the exhaust port, the other one the intake. The carburettor has a rotating valve for access of the mixture to the crank case. Lube oil is administered by a small lubricating oil pump which supplies 1 microliter oil every rev. The function of the 2 pistons results in asymmetric timing: the exhaust port opens before the intake port but, contrary to engines with 'symmetric timing' closes before the intake port. The crank of the exhaust piston runs 18 degrees ahead of the one for the intake. Cylinder is of the 'stachelschwein' (porcupine) type for enhanced cooling.