Ford Mustang/Capri 1979-1988 Repair Guide

Crankshaft and Main Bearings



In-Car Service

See Figures 1 and 2

  1. Main bearings may be replaced while the engine is still in the car by rolling them out and in.
  3. Special roll-out pins are available from automotive parts houses, or can be fabricated from a cotter pin. The roll-out pin fits in the oil hole of the main bearing journal. When the crankshaft is rotated opposite the direction of the bearing lock tab, the pin engages the end of the bearing and rolls out the insert.
  5. Remove the main bearing cap and roll out the upper bearing insert. Remove the insert from the main bearing cap. Clean the inside of the bearing cap and crankshaft journal.
  7. Lubricate and roll the upper insert into position, making sure the lock tab is anchored and the insert is not cocked. Install the lower bearing insert into the cap, lubricate it and install it on the engine. Make sure the main bearing cap is installed facing in the correct direction and torque it to specification.

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Fig. Fig. 1: Remove or install the upper bearing insert using a roll-out pin

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Fig. Fig. 2: Home-made bearing roll-out pin

Out-Of-Car Service

See Figures 3, 4 and 5

  1. Remove the intake manifold, cylinder heads, front cover, timing gears and/or chain, oil pan, oil pump and flywheel.
  3. Remove the piston and rod assemblies. Remove the main bearing caps after marking them for position and direction.
  5. Remove the crankshaft, bearing inserts and rear main oil seal. Clean the engine block and cap bearing saddles. Clean the crankshaft and inspect it for wear. Check the bearing journals with a micrometer for out-of-round condition and to determine what size main bearing inserts to install.
  7. Install the main bearing upper inserts and rear main oil seal half into the engine block.
  9. Lubricate the bearing inserts and the crankshaft journals. Slowly and carefully lower the crankshaft into position.
  11. Install the bearing inserts and rear main seal into the bearing caps. Install the caps working from the middle out. Torque the cap bolts to specification in stages, rotating the crankshaft after each torque stage. Note the illustration for thrust bearing alignment.
  13. Remove the bearing caps, one at a time, and check the oil clearance with a gauging material, such as Plastigage®. install if clearance is within specifications.
  15. Check the crankshaft end-play. (This procedure is described below.) If it is within specifications, install the connecting rod and piston assemblies with new rod bearing inserts. Check the connecting rod bearing oil clearance and side-play. (This procedure is also described below.) If they are correct, assemble the rest of the engine.

If a journal is damaged on the crankshaft, repair is possible by having the crankshaft machined to a standard undersize. In most cases, however, since the engine must be removed from the car and disassembled, some thought should be given to replacing the damaged crankshaft with a reground shaft kit. A reground crankshaft kit contains the necessary main and rod bearings for installation. The shaft has been ground and polished to undersize specifications, and will usually hold up well if installed correctly.

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Fig. Fig. 3: Crankshaft and main bearing installation - 4-140 engine

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Fig. Fig. 4: Crankshaft and main bearing installation - 6-232 engine

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Fig. Fig. 5: Aligning the thrust bearing


Main Bearings

See Figure 6

Remove the cap from the bearing to be checked. Using a clean, dry rag, thoroughly clean all oil from the crankshaft journal and bearing insert.

Plastigage® is soluble in oil, therefore, oil on the journal or bearing could result in erroneous readings.

Place a piece of Plastigage® along the full width of the bearing insert, install the cap, and torque to specification.

Specifications are given in the Engine Specifications Chart, earlier in this section.

Remove the bearing cap, and determine the bearing clearance by comparing the width of the Plastigage® to the scale on the Plastigage® envelope. Journal taper is determined by comparing the width of the bearing insert. Install the cap, and torque it to specification.

Do not rotate the crankshaft with the Plastigage® installed. If the bearing insert and journal appear intact, and are within tolerances, no further main bearing service is required. If the bearing or journal appear defective, the cause of failure should be determined before replacement.

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Fig. Fig. 6: Plastigage® installed on the lower bearing shell

Crankshaft End-Play/Connecting Rod Side-Play

See Figure 7

Place a pry bar between a main bearing cap and crankshaft casting, taking care not to damage any journals. Pry backward and forward, measuring the distance between the thrust bearing and crankshaft with a feeler gauge. Compare the reading with specifications. If too great a clearance is determined, a main bearing with a larger thrust surface or crankshaft machining may be required. Check with an automotive machine shop for their advice.

Connecting rod clearance between the rod and crankthrow casting can be checked with a feeler gauge. Pry the rod carefully to one side as far as possible and measure the distance on the other side of the rod.

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Fig. Fig. 7: Check the connecting rod side clearance with a feeler gauge


Fill the oil pump with oil, to prevent cavitating (sucking air) on initial engine start up. Install the oil pump and the pickup tube on the engine. Coat the oil pan gasket as necessary, and install the gasket and the oil pan. Mount the flywheel and the crankshaft vibration damper or pulley on the crankshaft.

Always use new bolts when installing the flywheel. Inspect the clutch shaft pilot bushing in the crankshaft. If the bushing is excessively worn, remove it with an expanding puller and a slide hammer, and tap a new bushing into place.

Position the engine, cylinder head side up. Lubricate the lifters, and install them into their bores. Install the cylinder head, and torque it as specified. Insert the pushrods (where applicable), and install the rocker shaft(s) or rocker arms.

Install the intake and exhaust manifolds, the carburetor, if applicable, and the distributor and spark plugs. Mount all accessories and install the engine in the car. Fill the radiator with coolant, and the crankcase with high quality engine oil.


Start the engine, and allow it to run at low speed for a few minutes, while checking for leaks. Stop the engine, check the oil level, and fill as necessary. Restart the engine, and fill the cooling system to capacity. Check and adjust the ignition timing. Run the engine at low to medium speed (800-2,500 rpm) for approximately 1 / 2 hour, and retorque the cylinder head bolts. Road test the car, and check again for leaks.

Some gasket manufacturers recommend not retorquing the cylinder head(s) due to the composition of the head gasket. Follow the directions in the gasket set.