The MGA With An Attitude
Crankshaft Bearing Installation

Crankshaft bearings is in 5 steps spanning 5 web pages.
Click green arrow at bottom to follow pages in sequence.
    A - Bearing Wear and Oil Pressure
    B - Connecting Rod Bearings
    C - Main Bearings
    D - Crankshaft R&R and Regrinding
    E - Bearing Installation - (this page)

When installing the crankshaft bearings (mains or rods) be sure everything is absolutely clean. Clean your hands like a operating room surgeon. The only thing allowed on your hands is clean engine oil. The running oil gap is as small as .0005" to .0015" radial clearance. Something as small as a human hair caught behind the bearing shell can make the bearing bind up on crank journal, or it may reduce the running clearance and starve the bearing of oil flow required for cooling, leading to premature bearing failure. Try to avoid touching the ID of the bearing. If you do touch it, add a dab of clean oil and wipe it out with your finger tip. If you feel anything at all there, clean it and start again.

Clean the bearing cradle, clean your fingers, put a dab of oil on your finger and run your finger through the bearing cradle. It should be clean and smooth. Your finger tip can feel bits of dirt smaller than .001" (as small as .0001"). If you feel anything there, clean it again. Ditto for the back side of the bearing shell. Wipe off as much oil as you can with your finger, but do not use a rag. You do not need any excess oil film behind the bearing shell, and especially leave no bits of fiber from a rag or paper towel.

Install the bearing with the anti-rotation tab positioned in the slot in the cradle. Use a small plastic tool handle to tap on the ends of the bearing shell to seat it fully into the cradle. Rock it back and forth a bit to be sure it is fully seated and flush at the ends. Put main bearing half shells in the block first. Generously oil the bearings and the crank journals. Set the crankshaft into the bearings. Rotate the crank to be sure it turns smoothly and easily.

Install the center journal thrust washers with the white metal side (side with the oil relief slot) facing the rotating surface of the crankshaft. The plain half washers go into the block and can be rotated into place after the crank is in position. The half washers with the anti-rotation tab go on the center main bearing cap before installation, also with the white metal side against the rotating surface of the crank. Oil generously. Tap the center main bearing cap into its seated position. Test rotation of the crank. Install the washers and nuts, torque lightly, and test rotation of the crank. Torque to spec and test rotation of the crank again. If at any time the crankshaft goes tight, disassemble it and start over. You should always be able to turn the crankshaft with your fingers. Repeat for front and rear main bearings.

Installation of new con-rod bearings is similar to the main bearing shells, but a whole lot easier. Put the top half shell in the con-rod and the bottom half shell in the bearing cap. Oil the journal on the crankshaft. Pull the piston down the cylinder to bring the big end of the con-rod into intimate contact with the bearing journal. Install the bearing cap, tightening fasteners, and checking for free rotation of the crankshaft during and after tightening of the bolts.

When the piston is at or very near top dead center or bottom dead center the crankshaft should rotate freely. Even with all pistons installed you may be able to turn the crankshaft a bit with your wrists. As the piston starts to move away from end of stroke the friction of the piston rings on the cylinder wall will cause some drag to increase the torque required to rotate the crankshaft. A well run in engine will have only a small amount of friction for the piston rings. Honed cylinders and new piston rings will have considerably more friction, and each addition piston will add some to the torque load. With honed cylinders and new rings, and all pistons in place, you should still be able to rotate the crankshaft with two fingers hooked over a 10 inch wrench. If you have anything more than 25 Lb-Ft torque required to turn it with a newly rebuilt engine, you likely have a tight bearing problem, which should have been worked out before installation of all the pistons. This is why it is important to keep checking for free rotation of the crankshaft at every step during assembly.

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