How To Pour Crankshaft Main Babbitt Bearings
November/December 1981
By Bud Motry
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This photo shows all the bearings that have been poured. The bearing cap on the left has been filed and scraped to fit. The lube hole has been drilled. The bearing cap on the right has just been poured showing the very little babbitt seepage on one end. This bearing has not been touched since pouring. The lower right side of the bearing casting shows the asbestos shims that are used to prevent the molten metal to be poured in the cap from fusing with the lower half.
Photo by Bud Motry
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Main babbitt bearings may be poured in much the same manner as connecting rod bearings. However, there is a slight difference. Main bearings are a little more complicated. I have found it easier to pour main bearings in halves rather than one piece. The lower halves should be poured first.
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The set-up requires four sheet metal washers approximately 4' x 4', with a center hole drilled to exact size of the crankshaft journal. These pieces will close off both ends of the bearings. An accompanying photo will illustrate the use of the washers. As the bearings will require a flange on one side of the bearing, it will be necessary to fabricate a 'U' shaped piece of scrap metal approximately 1' x 5' that can easily be bent to fit around the casting. The metal strip can be held in place by pounding the ends over the engine casting.
The crankshaft must be positioned in the center of the bearing casting. By using the connecting rod attached to the piston, in place, it will support the crankshaft when the connecting rod cap is tightened. The cap is tightened when the crankshaft rod journal bearing is at its lowest arc. This also assures clearance between the rod bearing cap and the base of the engine block. The crankshaft gear is in place against the cam shaft gear, with a shim between the gear teeth to provide clearance. This assists in supporting the crankshaft in place. To check horizontal alignment of the shaft, I use the main bearing casting surface as a reference point.
With the bearing cap studs in place, I use them for a steady rest, and with a straight edge over the top of the shaft, measure the distance from the casting surface to the straight edge. Now make four spacers of this dimension, cut a piece of pipe, or use washers as spacers over the studs. It is easy to check the horizontal position of the shaft with these spacers as a guide. The rod bearing cap may be loosened to effect a change in alignment. The inside washers are held in place by use of a wood wedge between the washer and the crankshaft web. The outer left washer is held in place by the crankshaft gear. The outer right end washer is held in place with a hose clamp around the shaft. Any gaps may be sealed with furnace cement or asbestos packing. Slight leakage, however, is not objectionable because it seals very quickly. Check the alignment again, before heating the casting and the shaft with a torch. If the casting is cold it will not permit the metal to flow freely and will leave gaps in the bearing. With the molten metal hot enough to cause a pine stick to smoke when submerged and then removed from the metal, it is hot enough to pour. It only takes a moment to pour the bearing.