Nominally 50 degrees. Therefore rear cylinder, (Number one) should be timed at about 35° BTDC on compression then 410° after that, front cylinder should fire. I recall that at some stage in the distant past slight errors were found in the cylinder angle on some machines. As far as I know, herring bone hoses and uncrimped ferrules were the most common fitment; anyway, that is what is illustrated in my series "B" Parts List.