Rear Main Seal Service and Replacement author and copyright: Paul Regish (AKA: Paul)

Are you noticing a puddle of oil on your driveway underneath your CJ? Does motor oil leak out from the bell housing area right behind the oil pan when the motor is running? Chances are your Rear Main Seal is worn and needs to be replaced. This article will guide you through the process of removing the oil pan, replacing the seal and putting everything back together again. Although before we begin anything, a common misdiagnosis of a rear main seal leak is actually a valve cover leak. Oil can drip down the back of the motor and out of the bell housing and create the exact same symptom as a rear main seal (RMS) leak. It is always best to check your valve cover as closely as possible for leaks and fix them before doing the RMS.

DISCLAIMER

The reader assumes all responsibility in performing the operations outlined herein. This document is meant to serve only as a guideline, and cannot be guaranteed to provide complete information in every circumstance. As every 4x4 project is different, it is up to the reader to determine if the project, and any unforeseen complications that may arise, are within his or her ability to deal with, and improvise solutions to. It is also strongly recommended that you read this article in its entirety before beginning, to familiarize yourself with the procedures and tools involved. I did this conversion myself with no outside help, only my wits, so if you’re mechanically inclined this shouldn’t be too hard. However, you just never know, so if you screw something up, I don’t want to hear about it. To summarize: Proceed at your own risk.

This article is meant for the AMC Jeep 4.2 Liter Straight 6 cylinder motor made from 1980 to 1986. It may be useful with earlier and later models, but I will leave that up to the reader to decide.

Skill level: beginner to Intermediate

Time: 5 Hours (but let the RTV dry overnight)

Tools: standard sockets and wrenches, various socket extensions, torque wrench, floor jack, jack stands, couple feet of a 2x4 piece of wood, standard screwdriver, rubber mallet, small punch, pliers (preferably needle nose)

Parts: Oil Pan gasket, oil, filter, rear main seal, Ultra black RTV, spray tac adhesive spray.

Disassembly Procedure:

1. Disconnect the battery.
2. Disconnect the cable at the starter.
3. Remove the two starter bolts and the starter. be careful it's a little heavy coming out.
4. Drain the motor oil and remove the oil filter.
5. In order to remove the oil pan, the passenger side motor mount must be removed. At this time you need to support the motor in such a way so it will not move once the motor mount is removed, this will make installation of the mount much easier. Myself being a little leary about being directly under a motor with only one mount holding it, I usually elect to supprt the motor in TWO places, from the front underneath the crank pully (see front motor support picture) and the rear at the flat spot of the bell housing. Use a 2x4 piece of wood cut to length and wedge it up to the crank pully in-between the steering arm and drag link. (see picture). You can also support the motor from the back with a jack stand or floor jack at the flat spot of the bell housing.
6. Remove the cross bar under the oil pan that runs from one motor mount to the other. Make a note or mark which way the bar goes as it can be a little confusing when reinstalling. This bar is held on to the frame by one of the four motor mount bolts on either side of the frame.
7. Remove the clip on the top of the passenger motor mount that holds the fuel line down.
8. Remove the three remaining motor mount-to-frame bolts on the passenger side. If you have supported the motor properly it should barely move.
9. Remove the three motor mount-to-motor bolts. There may be a ground wire attatched to one of these. The motor mount should then fall to the ground. (see motor mount picture)
10. Remove all of the oil pan bolts. make a note of the four bolts at the corners of the pan that are slightly larger than all of the rest of the bolts.
11. Use a screwdriver to gently pry all around the pan until it comes off the block. Be careful not to bend the pan.
12. Clean the pan, block mating surface. I used mineral spirits. Just be sure it is all dry before you reinstall. the front rubber portion of the pan gasket is most likely to be stuck to the front of the motor.
13. What you will now be looking at under the motor is seven main bearing caps. Each has two big bolts holding the caps on the crank. The very last one towards the back is the rear main bearing cap. I have a picture of it in this article,
14. I happened to take it after I reinstalled the cap as you can see the fresh RTV. (see rear main installed picture) I used Blue RTV but I was later told that black RTV is even better. Remove the rear main bearing cap using the appropriate socket. Once the bolts are off it may take a tap from a rubber mallet to jar the cap loose.
15. You wil notice that the rear main bearing cap holds the oil pan gasket on one side and the bottom half of the RMS on the other side. Take them off and clean the cap really good. (see rear main picture)
16. Loosen all the other remaining main bearing bolts.
17. Look up into where you took off the rear main cap and you will see the other half (circle) of the RMS. Use a small punch to tap on either side of the seal to dislodge it. You should now be able to move to the other side, see the seal coming out and grab it with a pair of pliers.

**This should complete the disassembly process. Take a beer break. One more tip though, now that you are in there it is a good time to check the slack on your timing chain. You should be able to reach up from the passenger side and poke it with your finger. If its got a good 3/4 of an inch of play, it may be time to replace that as well.

author and copyright: Paul Regish (AKA: Paul)