You should have somewhere between 0.0015" and 0.003" interference at room temperature,say 20C.
Aluminiuum expands roughly twice as much as steel. The difference is about 0.001" per inch diameter for 100 C. temperature rise.With 50 degree rise on 2-13/16 diameter bearing,you lose 0.0014" of your interference fit.Crankcases can,and do occassionally,reach 100 C.
Even if you had 0.002" inteference at room temperature,you could have less than no interference when the engine is hot.
Pete, If you are correct these bearings would not stay in the case very long but most do. I for one would have like to see an additional retainer of some sort but the BSA system seems to have worked but requires very accurate machining to hold tolerance for an interference fit. HOWEVER, once that outer race move relative to the case, the case is junk.
From that Norton post: "Just to re-confirm what I had found in the past I pulled an old virgin 750 bottom end off the shelf and checked the end play. It had a tight .002 IN.- about right for a ball bearing. I stuck it in the oven at 220 F. for one hour. The end play was then .034 and I could move it back and forth by hand."
I assume that this increase also happens to our BSA engines once they get up to temp?
David, I suspected the same thing and measured endplay on a roller motor. I then heated the whole assembled bottom end up in an oven. The endplay increased measurably with a dial indicator. Coefficient of expanison of Alum is approximately 2x that of steel. Based on that I would set the endplay at the bottom end of the limit, but, I have often wondered what gets hotter under normal operation the crank or the cases Mr Mike
im not sure im buying this, when you run the bike its air and oil cooled,i cant see the cases getting much hotter than the oil, and if its growing that much whats happening at the cylinder base,timing gears ,primary chain? not to mention piston and rod alighnment.if it expanded that much every time it cooled all the bolts would be loose.
BSA CYCLONE BSA METISSE TRIUMPH TR6C BSA BUSHMAN INDIAN WOODSMAN
My bike was running 018" of end float when cold, never checked it hot. The crank was perfectly fine when it was pulled apart. It probly didn't do the primary chain too many favours but if anything it probably worked in harmony with the wobble in the clutch basket
I'm with wak though. If you just heat the whole engine then yes the cases will expand a bit, not at any great expanse though otherwise the cases would crack at its mounting points. When your running the motor, the moving components generating heat are made of steel, the oil flow is removing heat, some is transferring to the cases which is being cooled by air flow. The overall rate of expansion is probably fairly even. Run the engine for 20 miles and check it then!
I think as long as you have enough clearence so nothing nips up tight and not too much so that the engine throws its self apart there is little to worry about.
So, on a 1966 A65 roller type bearing, the crankshaft can still float with the spacer, gear, and rotor all tightened up? It doesn't feel like it. Or should I measure end float with out the spacer, gear, and rotor torqued up.?