Hoping someone might be able to shed some light on this. Currently rebuilding B40 engine - bottom end done and just on to head. Have a head from a B44 square (bought it from BSA Unit Singles in the States) and would love to use it as the porting's much better. To my surprise though the head I've got has no oil drain holes at all, despite having the correct reference (41-785). Can't fathom this as all the other B44 square heads I've seen have had the drain holes from the valves. Anyone have any idea why they're absent? Thought about simply drilling holes but intake port seems to be in the way to link the hole up with the oil drain hole on the B40 barrel. I also have a B44 round head, which I'll use if I can't make the square head work. The B44 round head has the same oil drain holes as the B40 so this would be almost a straight swap. Some photos are attached of the square and round B44 heads. Any comments/advice would be much appreciated..
As you've found, the repositioned inlet port prevents the oil drain hole from the inlet valve pocket being drilled where it would line up with the hole in the barrel. Easiest solution is to drill the inlet drain hole where it should be on the square head (why your head has no drain holes drilled is anyone's guess but probably just not finished off at bsa?). Then drill the barrel to line up with that and the cutaway in the crankcase mouth to accept a steel tube to convey the oil through the fins. That's the same as BSA did to fit a round B40 head onto late military B40 square fin Ali barrel.
Thanks very much Rupert - much appreciated. I'd come round to thinking that would be the best solution. I have a new alloy barrel for my B40 which conveniently already has 4 drain holes drilled - I just need to drill the nos B44 square head as per the usual locations and then create a new cutaway in the crankcase mouth. Thanks again for your reply. Regards, Andy