Fitting Crankshaft Main Bearings Upper Halves 

Fitting Crankshaft Main Bearings Upper Halves 

( This article is only about Chevrolet Old Model cars ) 

To properly fit crankshaft bearings the motor assembly should be removed from the frame.

Remove the cylinder head, pistons and connecting rods,  push rods and crankshaft gear. Turn the cylinder block upside down either on a bench, on the floor or attach to a fixture.

The upper halves of the crankshaft bearings should be fitted first.

Remove all three bearing caps and the lower halves of the bearings. Lift out the crankshaft.

With the finger rub a thin coat of Prussian Blue on each bearing surface of the crankshaft.

Place the crankshaft in its natural position in the case and rock it back and forth with the hands

Remove crank shaft and scrape the blue spots from the bearing.The blue spots indicate that the bearing and crank shaft rub at these points only, which are known as “high spots.” .

The desired result is to scrape the bearings so that the crankshaft bears evenly at all points.This is an operation requiring much patience, so take your time, as it will pay in the end.

Repeat the operations until the bearing surface is smooth, and touches the crankshaft at all points.

The best results can be obtained by not installing the bearing caps until a perfect bearing is obtained on all three upper halves from the weight of the crankshaft.

The crank shaft can be drawn against the upper halves of the bearing cap, but this will spring the shaft out of line in the event any one of the upper halves are either high or low.

When scraping in the upper halves of new main bearings the crankshaft with the gear attached should be placed in the cylinder block and the crankshaft gear fitted to the crankshaft to determine whether the gears are meshing properly.

In the event the gears are worn to a certain extent it may be necessary to scrape the bearings deeper to get the proper mesh.  There should be only a slight amount of lash after the bearing caps are drawn down tight.

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Fitting Crankshaft Main Bearings Upper Halves article Source – This article courtesy should goes to : Chevrolet Repair Guide of 1923 by Chevrolet Motor Company.