Connecting Rod Bearing Clearance

Connecting Rod Bearing Clearance


Install the bearings in pairs. Do not use a new bearing half with an old bearing half. Do not file the rods or bearing caps.

The bearing caps are not interchangeable and should be marked during removal to ensure correct reassembly. The bearing shells must be installed with the tangs inserted into the machined grooves in the rods and caps. Install the cap with the tangs on the same side as the rod. Fit all rods on one bank until complete. Connecting rod bearings are available in the standard size and the following undersizes: 0.025 mm (0.001 in) and 0.250 mm (0.010 in).

Measure the connecting rod journal for taper and out of round.

The connecting rod bearing clearances can be determined with the use of plastigage or equivalent. The following is the recommended procedure for the use of the plastigage:

- Rotate the crankshaft until the connecting rod to be checked is at the bottom of its stroke.

- Remove the oil film from the surface to be checked. Plastigage is soluble in oil.

- Place a piece of plastigage across the entire width of the bearing shell in the bearing cap approximately 6.35 mm (1/4 in) off center and away from the oil hole. In addition, suspect areas can be checked by placing plastigage in that area.

- Assemble the rod cap with plastigage in place. Tighten the rod cap. Do not rotate the crankshaft while assembling the cap or the plastigage may be smeared, giving inaccurate results.

- Remove the bearing cap and compare the width of the flattened plastigage with the scale provided on the package. Locate the band closest to the same width. This band indicates the amount of oil clearance. Differences in readings between the ends indicate the amount of taper present. Record all readings taken. plastigage generally is accompanied by two scales. One scale is in inches, the other is a metric scale. If the bearing clearance exceeds wear limit specification, replace the bearing.