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hi...what is the difference from a "small"-'medium"-"large" journal cranks..were there actually different size cranks made or is this in reference to how much the journals have been ground/polished in rebuilding?...thanks kent
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Re: 327 cranckshaft
SB cranks up to 1966 all had 2.3" main journals and 2.0" (nominal size) rod journals.
Beginning in 1967 the 350 cranks/blocks (and ONLY 350 cranks/blocks) were designed with 2.45"/2.1" journals, and these journal sizes were extended to SBs of ALL displacements in 1968.
The 400, which I think was introduced in 1970 has 2.65" mains, and IIRC the same 2.1" rod journals as the other contemporaneus SBs.
The reason for the larger journals has nothing to do with the bearing sizes being inadequate. It was done to maintain crankshaft journal overlap with the longer strokes, which is a big factor in crankshaft torsional stiffness.
Back in the early seventies, some F5000 engine builders realized that small journals made more power in those 8000 rev engines, and with only a 3" stroke, crankshaft stiffness was adequate with the small journals, but they offered less friction because at a given speed the surface velocity is less than with large journals, which resulted in a small, but measureable power improvement.
Duke -
Re: 327 cranckshaft
duke,,thanks alot for the info....kentComment
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