Rear Main Seal Replacement ('85 and earlier)
By Phil Parsons
LATEST VERSION AS OF 3-19-98
NOTE: I am going to assume that you are familiar with basic automotive procedures such as draining oil. I am also assuming that you are reasonably acquainted with your engine bay and have a basic automotive vocabulary. If you have any questions, feel free to email me and I will be happy to make any clarifications. These are procedures that I have used myself, and I know them to be correct. However, I am not responsible for anything that happens in the course of performing these procedures.
For Small Block Chevy up to 1985
Tools List:
Mechanic's hand tools, including a punch and drift set.
Hydraulic jack, jackstands.
Three thick blocks of wood (at least 3" thick), OR an engine hoist (recommended).
Oil pump primer (optional, but highly recommended).
Parts List:
Rear main seal kit.
Exhaust manifold "donut" gasket(s) - some vehicles only use one.
New exhaust manifold studs, since they break about 99% of the time.
Oil pan gasket set.
An anaerobic sealant.
Assembly lube (optional, but recommended).
Engine oil and filter.
Procedures:
1. This job is easier if you have the entire car up on jackstands, but it doesn't have to be. Whichever way you go, make sure that each corner of the car off the ground has a secondary support (i.e. cinderblocks, or something similar), and each corner on the ground is securely chocked. Make sure that the parking brake is set.
2. Disconnect the negative battery cable. Drain the oil. While the oil is draining, remove the air cleaner assembly, remove the distributor cap, and set it aside (you do not necessarily have to disconnect the ignition wires). If your engine uses a fan clutch, remove the upper radiator shroud (if your shroud doesn't come apart, loosen the whole shroud, and just leave it loose over the fan. If your car has an electric radiator fan, you can leave it alone.
NOTE: Since the oil pump will be removed, and the prime lost, I would strongly recommend removal of the distributor at this point so that the engine can be primed before it is restarted. Click HERE for that procedure. If you choose not to do this to save time, you run the risk of possible engine damage from oil starvation upon startup. You should prime the oil pump by hand in a bucket of oil before reinstalling. At the very least, crank the engine with the ignition disabled until the oil pressure comes up before starting the engine.
3. Rotate the engine by hand until the timing mark on the balancer is pointing to the 6 o'clock position. This will position the front crankshaft counterweight upwards, so that you have room to get the shallow end of the pan out.Unbolt both exhaust manifolds from the Y-pipe. Disconnect the catalytic converter air tube, and disconnect the exhaust pipe from the transmission-converter mount. Unbolt the starter (you did remember to disconnect the battery, right?), and set it aside. In some cases, you may have to remove it completely.
4. Remove the engine mount through bolts. They may fight you coming out. Sometimes you can make things easier by positioning the jack under the oil pan (use a block of wood!), and exerting slight upward pressure to ease the weight load on the bolts.
5. Now you're ready to lift the engine. I strongly recommend the use of an engine hoist to do this, but if you don't have access to one, use the following procedure: Position the jack under the oil pan (it may already be there from step 4), and jack the engine up about 3 1/2". Keep a close eye on the oil pan - at the slightest indication of bending the pan, lower the engine and reposition the jack somewhere else. No matter what method you use, go slowly, and watch all of the clearances as the engine is on the way up, particularly the distributor. Once the engine is high enough, place the other two blocks of wood between the cross member and the engine block - make sure that they won't interfere with the removal of the pan. Carefully and slowly lower the engine on to the blocks.
6. Remove all of the oil pan bolts, and remove the oil pan. If the pan gets caught on the crank, try rotating the engine by hand a few degrees either way. If you followed step 2, this shouldn't happen. Unbolt and remove the oil pump/screen assembly. Unbolt and remove the rear main bearing cap.
7. Pry the old seal from the bearing cap using a screwdriver, punch, whatever. Just be careful not to nick the bearing cap surface. Removing the old seal from the block can be tricky, because often it is very brittle. Use a small punch and hammer to drive the seal around far enough so that the other end can be grabbed with pliers and pulled the rest of the way out. Work slowly - if the seal breaks half way, it can be a real pain to get the rest of it out.
8. Clean both the block and main bearing cap thoroughly. Lightly coat the rear main seal halves with assembly lube (use engine oil if you don't have any lube), but leave the seal ends dry (important).
9. Make sure that the lip of the seal is facing the front of the engine. The new seal should have come with a small plastic installation tool. This tool is placed between the new seal and the block to protect the seal from the sharp edges of the block. Keep this tool installed the entire time until the seal half is completely installed.
10. There are two schools of thought regarding the placement of the seal within the block. Conventionally, the seal half is installed so that the ends are flush with the bearing cap mating surface. Many techs like to install it so that one end protrudes from the block, while the other end remains inside the block. In this way, the mating surface of the seal is off-center from the mating surface of block and main bearing cap, ensuring a better seal. If done correctly, both methods will work perfectly well, although the off-center method is indeed more effective, albeit more difficult, because the seal half in the main bearing cap will have no protection from damage from the block during final installation. If you use this method, be extremely careful!
11. Press the other seal half into the bearing cap - you can use your hands, just make sure that the lip of the seal will be facing the front of the engine after the cap is installed. If you are using the off-center method, make sure that you install the seal half so that it will mate correctly with the half in the block.
12. Apply the anaerobic sealant to the mating surfaces of the block and bearing cap. DO NOT GET ANY ON THE SEAL!! Install the bearing cap and torque to about 10 ft lbs. DO NOT FINAL TORQUE YET. Use a pry bar to move the crank forward, then backward. This will align the thrust surfaces of the rear main bearing - this is very important. Once this is done, final torque the bearing cap bolts to 70 ft/lbs.
13. Install the oil pump. It would be a good idea to hand prime it in a bucket of oil first, especially if you do not plan on priming the engine with a primer before startup. Torque the oil pump bolts to 65-70 ft/lbs. (depending on the year - click HERE to check the bolt torque). Making sure the mating surfaces are clean and straight, reinstall the oil pan using the new gaskets. Torque the 5/16" pan bolts to 14 ft/lbs., and the 1/4" bolts to 7 ft/lbs. Lift the engine slightly, and remove the wood blocks, if you used them. Lower the engine into place, and install the engine mount through bolts. Reinstall the starter.
14. Unless you are very lucky, or have had the car apart before, the exhaust studs probably broke when you unbolted the exhaust. Now is the time to fix them (have fun). Install the new "donut" gasket(s) in the manifold(s) (on some cars, the gasket has no flange - in this case, you may have to install the donut in the end of the Y-pipe instead). Reconnect the exhaust pipe to the transmission mount, and tighten up the manifold connections. This step is usually a huge pain in the neck, because all of this stuff very rarely lines up correctly twice. What can I say? Hang in there, be patient, and try not to break things out of anger.
15. Once everything underneath is buttoned up, go topside and reinstall the radiator shroud, and reconnect the battery. Finish your oil change (make sure you remember to put the new filter in =). If you were smart, you removed the distributor previously. Use the priming tool to prime the oiling system. Since you don't have the valve covers off, use the oil pressure gauge as a rough indicator. It can take up to 5-7 minutes, so be patient. Once the engine is primed, reinstall the distributor (refer to the distributor article referenced earlier), the cap, and the wires. If you were lazy and decided not to remove the distributor or prime the pump, disable the ignition, and crank the engine until the oil pressure comes up. Remember, don't crank for more than 15 seconds at a time, or you'll be right under there again changing the starter. If the pressure won't come up, you will have to remove the distributor and prime the engine anyway. You should have listened to me!
16. Once all that is done, start the engine and check for any leaks.
17. Have a celebratory beer(s), and gloat over how good a mechanic you are.
�1998 Phil Parsons (The Best Damn Garage On The Net)
No reproduction allowed without consent of the author.