Quote:
short-coupe wrote:
if your going with the L20, make sure you get the crank from the black top bluebird, series 2, i think, from memory Murray Coote told me you could rev them harder, something to do with the journal between the 3 and 4,
The crankshaft in the series 2 Bluebird engine [Black top] had a rolled fillet where the machined crankshaft journals meet the webs of the crank instead of the radius fillet that was used in everything before it.
This rolled fillet looks like a machined groove at the sides of the journals, but it is in fact rolled in there at the time of manufacture.
Chrysler Corp. Hemi's used this design since 1951 & it was one of the secrets of their crankshafts legendary strength, as this method actually causes the grain of the metal to flow from the journal to the web & this [apparently] seriously reduces the stresses at this point, [compared to the radius fillet] thereby providing improved crankshaft service life, particularly in engines that can see 'severe duty'
Cracking at this point can occur in radius fillet cranks when used at high rpm, hauling heavy loads, over lots of miles, like in some truck applications, passenger models that tow heavy loads, & , ummm, oh yeah, competition use.
So yes, the Black top L20B crank looks to be the one to use.
Well, that's the story as I read it.