Just got hold of a T140 crankshaft to go into my late p/u cases and wondered about what modifications need to be done to make it fit. What balance factor for fast road would be recommended ? Have tried the search functions ( Honest ! ) and had no success, computers ain't my thing.
Spec is Wideline Triton, 60'Thunderbird cases, Morgo barrels and oil pump, new late 650 rods, 69' Bonnie head, Norton g/box and Commando primary cases ( hence T140 crank ).
Any help pointing me in the right direction much appreciated !
Buy the 3-piece 30mm double-lipped timing-side roller bearing,and grind about 0.020" off the O.D. so it fits the pre-unit case.Give it 0.0025"-0.003" interference fit. I always replace the flywheel bolts on these cranks with grade-8 UNF bolts.1-1/2" long bolts,cut down and modified to fit,with thick hard washers.
Pre-unit engines are normally happy in a Triumph frame with 71% (dry) balance factor,and it looks like they should still be happy with that in a featherbed frame.
Norton twins often use a higher percentage,but there are two reasons: *Their different rod/stroke ratio requires about 2.5% more balance factor than a T120. *When you fill a Triumph crank with oil,the balance factor reduces about 2%.When you fill a Norton crank with oil it reduces more than that.Some claim only 4%,but more often they claim 10% or 11%.Still no-one uses more than 84% (dry) on a Norton,and others use less.
This crank has a 30mm metric timing-side bearing ('72 onward). There is no imperial bearing that fits this crank.
I think the bearing you listed fits a 1-1/8" crank to a small-bearing (1") crankcase. These crankcases take the large bearing 1-1/8" x 2-13/16" x 13/16".
I'd rather grind a bearing to get a perfect fit in the housing.The housing could be less than a perfect fit on a standard bearing,because the bearings are always loose at running temperatures even at 0.003" interference cold.
The other alternatives are to grind down the mainshaft to 1-1/8" (more likely to break?),or bore out the crankcase to 72mm.If the crankcase housing wears 0.001" or 0.002" in the future,you can't then just fix it by grinding the next new bearing to fit.