Floating bearings
Floating bearings
(OP)
What was (were) the perceived advantage(s) of full-floating insert-type plain bearings in connecting rods of high performance engines? I ask this past-tense because the last time I saw them advertised (by Potvin, Moon, Fobert, and maybe others) was about 1957. They were available for then-popularly-raced OHV V8 engines (Olds, Cad, and Chrysler hemi as a minimum). They were similar in design to the stock '32-48 Ford bearings- each insert pair was as wide as the crank journal and served a pair of rods.
I have no experience with them, and want to understand any possible inherent advantage. All input is welcome.
I have no experience with them, and want to understand any possible inherent advantage. All input is welcome.





RE: Floating bearings
Regards
Pat
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RE: Floating bearings
Tangless bearing shells make me nervous.
Brian,
RE: Floating bearings
The heavily loaded roller tappets in our in-line injection pumps had a similar construction at one time, but the pin, intermediate bush, and the roller were all hardened and ground steel.
PJGD
RE: Floating bearings
The reduced surface speed may have been the key attribute; just thought I might be overlooking some other advantage.
RE: Floating bearings
I may be a little dim - but just what are these plain bearings you are writing about?
Do you have a picture or drawing etc.?
RE: Floating bearings
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RE: Floating bearings
I thought flatheads were weird, even before I learned about full floating bearings.
Okay, not weird, but different.
Mike Halloran
Pembroke Pines, FL, USA
RE: Floating bearings
RE: Floating bearings
RE: Floating bearings
A long time ago I assembled a few JAP V-Twins as used in Morgan trike "cars' and as best as I recall they had curious arrangements of shared/inner/outer inserts among the fork/blade rods. I think the insert for the blade rod was captive in the forked rod ???
RE: Floating bearings
Dicer- Oil leakage from rod journal/bearing is determined solely by the end clearance of the rod(s) to the journal's cheeks.
Rod big-end bore "finish" for a floating bearing is only slightly more critical than for a "normal" rod.
Locating-precision requirement of the rod caps is identical.
I'd say that the 1932-1948 period constituted "used for years" (Ford V8 engines with floating bearings).
RE: Floating bearings
Regards
Pat
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RE: Floating bearings
RE: Floating bearings
I have never done any tests, but at the time, after thinking about the bearings' oil clearance (~0.003" diametral ) vs the normal side clearance ( ~0.007" each/ 0.014" per pair) the logic/cause-and-effect seemed "wrong" to me.
RE: Floating bearings
The perceived advantage of floating rod bearings was probably equalized fatigue/wear at the bearing surface. But that was only an advantage when the bearing ID was cylindrical as manufactured, and the shell had a constant wall thickness. This is no longer true with modern engine journal bearing shells. They now have a variable wall thickness. The idea is to give the optimum bearing bore shape under operating loads and temperatures.