It has a hemi-head and, unusually, the spark is fired after top dead centre because of the very high flame speed in a compact engine with this head design.
Dead centre is rarely a problem for internal combustion engines, as these usually require cranking over to provide cylinder compression and so do not attempt to self-start from stationary.
Positioning of the propeller relative to the crankshaft is arranged such that the engine pistons pass through top dead centre during the swinging stroke.