BSA twins used a ball bearing drive-side crank bearing through 1965, then, like Triumph an upgrade to the roller bearing was specified through the end of production in 1972. The roller bearings are available in differing internal clearances, such as a C3 condition, which has greater diametral clearance, but the added clearance does not allow for "flex in the crankshaft". In fact, BSA crankshafts need to be fitted with not only a measured clearance on the timing-side bush, but a lateral end-float of .0015" to .003". I don't know of any advantage to reverting to the early ball bearing on the drive-side of the crankshaft. It is easier to shim the roller bearing on the 1966-later models to achieve the correct end-float.
Really good info! Any thoughts on bearings that work loose in the drive side crankcase? I heard the suggestion that too thick oil will work like a wedge, enlarging the bearing outer race, and thus the bore for the drive side bearing?
I've never heard that oil weight or viscosity has caused distortion to the bore for the roller bearing race on the drive-side crankcase. The crankcases for vintage British motorcycles were cast from relatively porous aluminum, so over many years and miles of service, the bores can become distorted, or a crankshaft can suffer from minor runout and require a larger internal clearance bearing. Observe a cleaned engine case that has been left in an oven for 30 minutes at 350 degrees...you will see oil literally sweating out of the pores in the aluminum.
I have heard suggested that a ball bearing main is a better option in a bsa a65, as it better allows for some flex in the crankshaft?
BSA twins used a ball bearing drive-side crank bearing through 1965, then, like Triumph an upgrade to the roller bearing was specified through the end of production in 1972. The roller bearings are available in differing internal clearances, such as a C3 condition, which has greater diametral clearance, but the added clearance does not allow for "flex in the crankshaft". In fact, BSA crankshafts need to be fitted with not only a measured clearance on the timing-side bush, but a lateral end-float of .0015" to .003". I don't know of any advantage to reverting to the early ball bearing on the drive-side of the crankshaft. It is easier to shim the roller bearing on the 1966-later models to achieve the correct end-float.
Really good info! Any thoughts on bearings that work loose in the drive side crankcase? I heard the suggestion that too thick oil will work like a wedge, enlarging the bearing outer race, and thus the bore for the drive side bearing?
I've never heard that oil weight or viscosity has caused distortion to the bore for the roller bearing race on the drive-side crankcase. The crankcases for vintage British motorcycles were cast from relatively porous aluminum, so over many years and miles of service, the bores can become distorted, or a crankshaft can suffer from minor runout and require a larger internal clearance bearing. Observe a cleaned engine case that has been left in an oven for 30 minutes at 350 degrees...you will see oil literally sweating out of the pores in the aluminum.
Hey guys where can I get that shirt with the triumph on the pocket? Kinda wish you had examples there.
Dave has actually had this one for 20+ years so we're not sure where you can find them anymore.