Bearings Although bearings (shell-type) are integral to the function of Carrillo connecting rods, we have diligently avoided discussing them. We are not and do not profess to be experts on shell-type bearings. As best as I have attempted to avoid it, I suppose it is time to face up and present some common sense information about connecting rod bearings. In the ideal world the crankshaft should float on a cushion of oil, not on the soft, babbit portions of the bearing shell. In order to attain this desired phenomenon, a constant flow of oil must be supplied to the surface of the shaft that is to be supported. I want emphasize the word "flow". As the term suggests, oil needs to get to the surface of the bearing and exit the support area in a constant flow, allowing fresh, cool oil to continue the desired support between the shaft and the shell. The constant flow is necessitated by the oil's absorption of heat. This heat is generated predominantly by shear and load forces. Any interruption in the flow may lead to the shaft "rubbing" against the shell. Inadequate flow also leads to surface stress or cavitation. Cavitation on the bearing surface is when a vacuum is generated by the speed of the bearing relative to the available oil flow. This vacuum can be severe enough to lift the surface of the bearing, thereby damaging the geometry and oil retention of the bearing surface. Bearing geometry is a factor that affects the flow. Geometry, often referred to as concentricity, is employed to affect the flow and load capabilities of a plain bearing assembly. Generally speaking, the more eccentricity in the bearing the higher the oil flow. In most circumstances, this increase of flow will allow the bearing to operate cooler, however, it also means the contact area is reduced and the loading is higher. The engine builder must decide on which avenue is best for his application. Crush, oh crush, probably the most miss-used term relative to shell type bearings. Crush represents the difference in lineal measurement between the outside perimeter of the two bearing shells and the inside perimeter of the fastened housing bore. This difference, when assembled, is the action that generates the load necessary to secure the bearing shells in the housing bore. Too little crush affects the bearing stability as well as its ability to transfer heat to the connecting rod. Too much crush distresses the shell and upsets the bearing geometry. A couple of less critical, albeit important points are side clearance and fillet interference. Typically, side clearance is only problematic at two extremes. When the side clearance is too tight it will restrict the oil flow; too much leads to the noise generated from the crankshaft and possible interference at the pin boss area. With the advent of larger fillet radii in the crankshaft, the engine builder should routinely check to be assured that the bearing shell does not ride the radius of the crankshaft. If there is interference it is a sure direction for disaster. As a reader of the above, you may note the absence of specific dimensional recommendations. I assure you this is by design. Available to today's engine builder is a variety of the finest ever shell-type bearings that comprise almost sixty years of technology. Refer to manufacturer's directions and suggestions. As always, thanks for your interest. Come visit us again!
Regards,
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