1946 model 18 rocker box ?

Gents,

During some routine work on 46 model 18, I was kicking it over by hand and my hand was on the rocker box and I felt air leaking between the rocker box and cover When on a compression stroke?? This bike is a recent purchase and runs ok so far. As for the air, is this common to have air in the box area? If not, I would assume that maybe a valve not seating would cause air to leak up past the seat and through the valve guide maybe…I don’t know? I will check the valve clearance too.
Thanks much.

Nate.

At the outset. i have no direct experience with norton singles, having just bought my first basket case. I would think the rocker box would be connected to the timing chest via the pushrod tubes and thus the rather large pulses produced by the long stroke would be felt there. I doubt it is from the valve guides unless the head is badly worn. I would consider what breathing is being employed. I am a rather big fan of valving the breather so it will exhaust but not intake air. This will tend to lower the pressure in the crankcase providing an improvement in both running and oil leaks. I do not have any idea how this is normally done on the OHV nortons but it is always a useful mod. I will be rebuilding a 47 es2 in the next couple of years and so this is a issue of interest to me.

Best.