REMOVAL & INSTALLATION
1977-78 151 Four Cylinder Engines and All 250 Six Cylinder Engines
The rear main bearing oil seal, both halves, can be removed without removal of the crankshaft. Always replace the upper and lower halves together.
- Remove the oil pan.
- Remove the rear main bearing cap.
- Remove the old oil seal from its groove in the cap, carefully prying from the bottom using a small prytool.
- Coat a new seal-half completely with clean engine oil, and insert it into the bearing cap groove. Keep oil off of the parting line surface, as this surface is treated with glue. Gradually push the seal with a hammer handle until the seal is rolled into place.
- To remove the upper half of the old seal, use a small hammer and a soft, blunt punch to tap one end of the oil seal out until it protrudes far enough to be removed with needle-nose pliers. Push the new seal into place with the lip toward the front of the engine.
- On the 250 six engine, install the bearing cap and tighten the bolts to a loose fit- do not final torque. With the cap fitted loosely, move the crankshaft first to the rear and then to the front with a rubber mallet. This will properly position the thrust bearing. Tighten the bearing cap to a final torque of 65 ft. lbs. Install the oil pan.
- Install the bearing cap on the 151 four and torque to 65 ft. lbs. Install the oil pan.
The rear main bearing oil seal in this engine is a one piece unit and is removed and installed without removing the oil pan or crankshaft.
- Remove the transmission, flywheel bellhousing, and flywheel.
- Using a small prybar or a suitable prytool, carefully remove the rear main bearing oil seal- do not scratch the crankshaft!
- Thoroughly lubricate a new oil seal with clean engine oil, making sure both the inside and outside diameters are coated. Install the seal onto the rear crankshaft flange, with the helical lip side of the seal facing the engine. Be sure the seal is fitted squarely in place.
- Install the flywheel, bellhousing and transmission in the reverse order of removal.
The crankshaft need not be removed to replace the rear main bearing upper oil seal. The lower seal is installed in the bearing cap.
- Drain the crankcase oil and remove the oil pan and rear main bearing cap.
- Using a special main seal tool or a tool that can be made from a dowel (see illustration), drive the upper seal into its groove on each side until it is tightly packed. This is usually 1 / 4 - 3 / 4 in.
- Measure the amount the seal was driven up on one side; add 1 / 16 in., then cut this length from the old seal that was removed from the main bearing cap. Use a single-edge razor blade. Measure the amount the seal was driven up on the other side; add 1 / 16 in. and cut another length from the old seal. Use the main bearing cap as a holding fixture when cutting the seal as illustrated. Carefully trim protruding seal.
- Work these two pieces of seal up into the cylinder block on each side with two nailsets or small prytools. Using the packing tool again, pack these pieces into the block, then trim them flush with a razor blade or hobby knife as shown. Do not scratch the bearing surface with the razor.
- Install a new seal in the rear main bearing cap. Run a 1 / 16 in. bead of sealer onto the outer mating surface of the bearing cap. Assemble the cap to the block and torque to specifications.
- Remove the oil pan, baffle, and oil pump.
- Remove the rear main bearing cap.
- Obtain an oil seal tool, or construct one from a dowel as illustrated. Insert the tool against one end of the oil seal in the block and drive the seal gently into the groove about 3 / 4 in. Repeat on the other end of the seal.
- Using the bearing cap as a holder, form a new upper bearing seal in the cap. Cut four 3 / 8 in. long pieces from this seal.
- Work two of the pieces into each of the gaps which have been made at the end of the seal in the cylinder block. Do not cutoff any material to make the pieces fit.
- Press a new seal into the bearing cap.
- Apply a 1 / 16 in. bead of sealer across the outer mating surface of the bearing cap.
- Reassemble the cap and torque to specifications.
On the Buick-built engines, the factory recommends removing the crankshaft to replace the upper seal, but the seal can be replaced using the method below.
- Remove the oil pan and the rear main bearing cap.
- Loosen the rest of the crankshaft main bearings slightly and allow the crankshaft to drop about 1 / 16 in., no more.
- Remove the old upper half of the oil seal.
- Wrap some soft copper wire around the end of the new seal and leave about 12 in. on the end. Lubricate the new seal generously with clean oil.
- Slip the free end of the copper wire into the oil seal groove and around the crankshaft. Pull the wire until the seal protrudes an equal amount on each side. Rotate the crankshaft as the seal is pulled into place.
- Remove the wire. Push any excess seal that may be protruding back into the groove.
- Before tightening the crankshaft bearing caps, visually check the bearings to make sure they are in place. Tighten the bearing cap bolts to specification. Make sure there is no oil on the mating surfaces.
- To replace the seal in the main bearing cap, remove the old seal and place a new seal in the groove with both ends projecting above the mating surface of the cap.
- Force the seal into the cap groove by rubbing down on it with a hammer handle or other smooth round tool, until the seal projects above the groove not more than 1 / 16 in. Using a razor blade, cut the ends off flush with the surface of the cap.
- On the V6s and Buick-built 350 V8, place new neoprene seals in the grooves in the sides of the bearing caps after soaking the seals in kerosene for two minutes.
The neoprene seals will swell up once exposed to the oil and heat. It is normal for the seals to leak for a short time, until they become properly seated. The seals must NOT be cut to fit.
- Reverse the above procedure for installation. Use a small bead of sealer on the outer edge of the bearing cap mating surface.
- Install the oil pan. Run the engine at low rpm for the first few minutes of operation.
The rear main bearing seal on these engines can also be replaced without removing the crankshaft. Extreme care should be exercised when installing the seal to protect the sealing bead (located in the channel on the outside diameter of the seal). Use of a seal installation tool, as described in the above procedures, is recommended.
- Remove the oil pan, oil pump and rear main bearing cap.
- Remove the old oil seal from the cap by carefully prying from the bottom with a small prybar.
- Using a small hammer and brass pin punch, tap on one end of the oil upper seal until it protrudes far enough on the other side to be removed with needle nose pliers.
- Clean all sealant and foreign material from the bearing cap, crankshaft journal and all mating surfaces using a solvent. Inspect the components for nicks, scratches and burrs.
- Coat the lips of the new upper seal with clean engine oil, keeping the oil off of the seal mating ends.
- Position the tip of the oil seal mating tool between the crank journal and the seal seat in the cylinder block. Position the new seal between the crankshaft and the tip of the tool so that the seal bead contacts the tip of the tool.
Make sure the oil seal lip is positioned toward the front of the engine.
- Rotate the seal around the crank journal, using the tool as a "shoehorn" to protect the seal bead from the sharp corner of the seal seat surface in the cylinder block.
Keep the installation tool in position until the seal is properly positioned with both ends flush with the block.
- Remove the tool, being careful not to withdraw the seal.
- Thoroughly lubricate the new lower seal-half (for the bearing cap) with clean engine oil. Install the seal into the cap, feeding the seal in with thumb and finger.
- Install the bearing cap onto the cylinder block, using sealant applied to the cap-to-block mating surfaces. Be careful to keep the sealant off the seal split line.
- Install the bearing cap bolts and torque to 70 ft. lbs. Install the oil pump and oil pan in the reverse order of removal.