I saw the BSA Victor parked on the street yesterday. Its engine looks very identical to BSA B25/TR25W. My curiosity was popped up!!! What is the major difference between these two model? Gears? Crankcase? etc.? Can BSA B25 Engine be upgraded to B44 specification?
Sorry if the question may sound stupid, but I am new to British bike and have little knownledge.
Besides displacement, the major difference might be bearings. B25 has a shell connecting rod bearing, while B44/B50 has a needle bearing. And B50 I think has a doubled up roller/ball bearing on crank drive end......not sure about B44. A B44 engine will fit in a B25 frame, and maybe a B50 engine will fit in an OIF B25 frame. More or less.
The quickest upgrade is to buy a B44 engine, it will slot straight in as Leon says. The long route to to pull your B25 apart, throw away the barrrel, head, piston and crank. Buy a B44 Crank, barrel, piston & head. Next you have to remove the barrel studs from your B25 and fill in the holes with weld. Then bore out the crankcase to take the bigger B44 barrel and using the barrel as a guide drill and tap 4 new barrel stud holes and install 4 B44 barrel studs. Reassemble engine using all you left over B25 bits but also fit a 28 tooth engine drive sprocket instead of the B25's 23 and a new primary chain.
You gain torque but very little horsepower so acceleration is rapid from low revs but the top speed will be only slightly higher.
Having owned both, the B44 has considerabley more stomp without revving. Additionally with simple minor changes to compression, headflowing, a 32 mm carb and a free exhaust, the B44 is far and away the way to go. And you don't have to worry about the low oil pressure bearing failures that are problematic on the B25. Find you a B44 engine, go thru it, and you'll have a bike that can keep up with modern traffic (not superhighways) without having to keep it revved up all the time.
Loc: Sydney Australia
Goes basically like this C25/B25 + bigger bore = B40 B 40 with longer stroke = B44 B44 with bigger bore = B50
There are 3 frames the early C frame , the Victor frame & the OIF frame. Within these frame groups all engines are interchangeable and between the frame groups they will fit with a bit of jiggery pokery.
You will have more of a chance of finding B50 engine floating around that a spare 441 in OZ as the post classic dirty boys have snavelled most of them and I have a feeling that you have problems with the engine height if you go the B50 route although I have seen B50's shoehorned into Victor frames but I would not like to have to work on one. The others poster have given you good advice. You will find a lot more 441's in the USA at a much more reasonable price than locally but shipping can be a killer. Beware of Enduro's, the frame was designed to be airborn so the seating position is not all that good for street useage and the ET ignition can be a right regular PITA. Having said that I adore them, There are a lot of army B40's floating around . They have a B40GA -????? engine number and they usually go for reasonable prices. You can split these engines and fit a 441 rod & piston which makes a good bike even better. They are 6V ( no problems with mine) but have a funny gearbox ( 3 lower ratio gears with a std top ). This led to the engines being laboured and big end failure so there are quite a few with stuffed big ends around that go really cheaply and a B 44 rod & piston is no more expensive than a B 40 rod & piston and a darn side easier to get.