What determines direction of rotation?

As Nasty troll pointed out, but yes very common with marine engines, 2 identical engines one will have the cam shaft changed for reverse rotation, and the distrubutor cap to the spark plugs will be wired backwards, thats it. got an old twin screw Chris Craft, oh yea one starter will be reverse rotation, but I would have payed to see the old bike crash, bet that was something to see

Assuming I understand your question correctly, Valve and ignition timing, the engine itself will run in either direction provided the valves open at the correct time and the ignition system follows suit, back in the day before reed valves and port timing 2 stroke engines would run in either direction, kinda scary, my friends dad had an old Bridgestone 175cc 2 stroke street bike back in the day, he was backing out of the driveway which was kinda down hill with the engine not running, and released the clutch to stop while it was in gear, Oh my! that thing started in reverse, he freaked and grabbed a handfull of throttle, hit a parked car and got all beat up,

whether the lavatory flushes in a clockwise or counter clockwise direction relies upon specially on the form of the bowl and the direction the water is permit into the bowl. The coriolis rigidity, created by the rotation of the earth, is lots too at risk of have any effect. an identical is genuine for the drain in a shower bath or bathe. The coriolis rigidity does consequence the instructions of climate lows and hurricanes nonetheless. yet there the small consequence is working on a lots larger section and its cumulative small consequence provides as much as a great sufficient rigidity to regulate the direction of lows to be counter clockwise in the northern hemisphere and clockwise in the southern hemisphere.

its all based on how it was designed. the cam shaft would have to be ground in the reverse format for a reverse rotation. many differences you will find are there through out the vehicle. in the reverse rotation engines, the differential is also set up a bit different.

car engines cc,,,some boat engines ccw ,,,usually twin engines one will be ccw or single Chrysler boat engine,,,has to do with propeller rotation