Hi all
Greetings. My first post and first British bike for 40 years.
I recently started a rebuild of an early (distributor) B40. Provinance a bit of a mystery as it came back from the States but as far as I can see has never been registered and has a B44 (competition) frame. I think it's circa 1963 given a low frame number and engine No B40D 1036 and distributor ignition.
I have two queries that I hope you might be able to help with.
Firstly, the head is secured by 6 studs - four around the bore and two additional smaller dia studs outboard of the pushrod tunnel through the barrel. This seems to be at odds with my BSA parts book and Rupert Ratio's book which suggest the six studs were adopted after 1966. Is it possible this barrel and head have been retro fitted to the older bottom end.
Secondly, on reassembly with new barrel gasket, head gasket, when I refit the rocker box there is a lot of slack in the pushrods/tappets. It's as if the pushrods are too short. I have to wind the tappet adjusters a long way down to take up the slack to the point I can't really get the lock nut on securely. I can't find out if there are any variations in pushrod lengths but given that the stroke remains constant across the range this seemed unikely.
I'd really appreciate any pointers on the above two points.
Cheers
John
6 head studs came in mid 1961. See bulletin below.
Thanks.
The parts book isn't dated but I suppose it must predate the bulletin.
I have just found a paragraph in the unit single manual about different heads fitted, showing standard B40 61-63 with 4 stud head and 64-65 are 6 stud.
I have a 1 1/8 choke which lists theb6 stud head with big valves SS90. So I guess that answers the rocker question. It needs the SS90 bigger valves.
Further investigation needed.
Cheers
John
Hi
Got the head off my SS90 at the moment and I've measured the pushrods as being 7.625"total length. I think that a C15 has different pushrods (according to Draganfly) so may be slightly shorter. The B40 exhaust port sits about 15mm higher than a C15 as I found out when a C15 front pipe didn't fit which may explain slightly longer pushrods. Someone may have some C15 pushrods that they could measure to confirm. B25/C25 pushrods are a lot shorter due to different valve clearance adjustment method.
B40 and SS90 use the same pushrods and exhaust valve, the inlet valve is a larger diameter on the SS90 but the valve is the same length so this shouldn't affect tappet adjustment.
Hope this helps, Colin
Hi
Found some C15 pushrods for sale on an auction site and they are listed as 7 5/16" long, my SS90 (same as B40) ones are 7 5/8" long, making a difference of 5/16" in length. This may explain your need to screw the adjusters in so far.
Cheers Colin