I think it would run for a lot longer than that without noticeable troubles even if you guessed wrong Ian, but nevertheless what you did makes sense and is probably right. Sometimes the piston skirt is cut away on the intake port side and it is all easy, but if it isn't, it can be difficult to tell. The reason it matters is that the piston pin (gudgeon pin) is usually offset because there is much more pressure on the piston crown when it is on the way down than when it is on the way up. Consequently you offset the pin, or sometimes the cylinder itself, to reduce the connecting rod angle for the downward stroke. This alleviates the bearing pressure on the side of the piston which is being pressed against the cylinder wall on the power stroke. Of course the offset increases the pressure on the opposite side of the piston during the compression stroke, but this is a much smaller load and hence is not a real issue. If you put the piston in backwards, you will be magnifying the load on the piston thrust face during the power stroke, rather than reducing it.
