HOW TO POUR CRANKSHAFT MAIN BEARINGS
November/December 1981
Bud Motry
20201 Arthur Road, Big Rapids, Michigan 49307
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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.
Main 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.
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.
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