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Old June 11th, 2005, 13:28
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Rear Main Seal Replacement - All 4.0

Replacing the 4.0 Rear Main Oil Seal

Fairly straightforward, replacing the crankshaft rear main oil seal can be done in about three hours. This will also give you a chance to check on a few other things as well…

You will need a selection of regular hand tools (socket set, end wrenches) to begin with, and a small-diameter (1/8”-5/16”) brass pin punch and a lightweight hammer to remove the upper half of the rear main. You will also need a floor jack and a set of stands tall enough to allow you to suspend the front end of your XJ by the frame, while allowing the axle to hang freely. I have found that regular two-ton stands will hold for an XJ up to 3” lift and 31” tyres.

Parts – you will need a rear main seal, an oil pan gasket set, and you will also want to get a timing cover set. Since you will need to remove your starter motor as well, this might be a good time to take care of those batter cables… I also highly suggest at least one set of Small-Block Chevy valve cover studs, as they can be used in the “rails” of the oil pan during reassembly to simplify handling of the pan and gasket. Using at least four (two toward the front and two toward the rear) will help you keep the gasket and pan in place, serving as “locating pins” to keep everything from sliding about. You will also want some moly-based engine assembly lube.

Start by removing (at least) the positive batter cable. I removed both, but I replaced my battery cables as part of the job – they were due!

Securely block the rear wheels of your XJ/MJ so you can jack up the front end. The trick here is to lift the XJ enough to have a little air beneath the tyres with the axle hanging freely (this will give you enough room to remove the oil sump.)

Once you are blocked and lifted, you can remove the starter motor. Note that there is one bolt that runs thru the starter flange into the bellhousing, and one that runs thru the bellhousing and threads into the starter flange. These bolts are different – one is M10x1.5 and the other is 3/8”-16 (I don’t recall offhand which is which. They are similar, but not exactly the same!) Label one of the bolts, or put the bolt that threads into the starter in the threaded hole so you don’t get them crossed. Unbolt brackets for your transmission cooler lines, if you have an automatic. Do not worry about removing the transmission – it won’t be necessary. Remove the lower inspection plate from the bellhousing, as it would interfere with removal of the oil sump. Pull the transmission cooler lines aside and secure with wire or twine. It is not strictly necessary to remove them completely, unless you are about to replace them as well. Now would also be a good time to remove the oil sump drain plug.
While the oil is draining, get out your ½” and 7/16” sockets – make the 7/16” a deep well version. There are a couple studs in place for various clamps.

Once the oil has finished draining, replace the plug (you don’t want it dripping on your face!) and start removing bolts around the perimeter of the oil sump. Most of the bolts will need the 7/16” socket, you will use the ½” socket for the four larger bolts at the corners of the sump. If you lose any bolts, they are ¼”-20x1” and 5/16”-18x1” – brass or stainless are better and worth the effort to get. If you decide to use anything other than a flange head, make sure to add washers to spread the clamping load on the gasket. This will help everything seal up.

Use a “soft” hammer – rawhide, wood, or rubber – to tap around the sump pan to break the seal. Once you feel the seal start to give, you will be able to get your fingers under the edge and break the rest of the seal. You can then take the now loose pan and work it out toward the rear of the XJ. Set the pan aside once you have it out, you will want to clean it before you put it back in.

Remove the rear main bearing cap. As I recall, it requires use of a ¾” socket to remove the two bolts. You will probably want to keep that soft hammer handy – I have found these to be a bit sticky at times. Set the bearing cap aside for a moment.

Take your small brass punch and press against the end of the upper rear main seal. It may need some “encouragement” with a small hammer, and you will be able to pull it out with a pliers once you see ¾” or so protruding from the channel in the block.

Get the cup of oil your new seal has been soaking in, and take out the upper half. Don’t wipe it dry, leave it dripping. Make sure of the orientation of the seal lip - the narrow “vee” groove should be open toward the bulk of the engine. The oiled seal should slip right into the groove in the block, and you press it into place with the punch with hand pressure only! The seal half should just protrude from the block on both sides, it will be compressed by the lower half.

Take the rear main bearing cap, and remove the lower rear main seal half. Next, clean the cap carefully. Try not to dislocate the bearing shell, and do not scratch it! After you have cleaned the bearing cap, apply assembly lube to the inside of the bearing shell, and don’t be stingy with it! Extra lube will only be dissolved into the oil, and will not cause any trouble.

Once you have the bearing lubricated, install the new lower rear main seal half. With the corner of a clean cloth, wipe the flat surfaces of the rear main bearing cap and the mating surfaces on the engine block. You can now install the rear main bearing cap, and torque the bolts to 80 pound-feet with an accurate torque wrench.

Now that you have the rear main seal done, you may want to think about replacing the front main seal – it is probably getting ready to leak as well. Replacing the front main seal would require removal of the accessory drive belt and the harmonic balancer to access the seal. A stiff screwdriver or a “seal removal tool” will pull the seal from the front cover. Apply a light bead of RTV Black to the outer metal ring on the seal, and pres into place. A block of wood and a light hammer will help drive the seal into place. Lubricate the bearing surface of the harmonic damper and reinstall. (NOTE – you will need a Harmonic Damper Puller Kit to remove the damper, and a ½”-20 bolt and washers - or a dedicated tool with a 1/2-20 thread - to reinstall the damper. Be sure to replace the woodruff key into the crankshaft nose and to not shear the key during installation. Doing so will likely cause your timing marks to be misaligned later.

Get and clean the oil sump pan. Get your tube of RTV Black (you’ll need it!) and your oil sump gasket. I am told that the newer version of the 4.0 oil sump gasket is of one-piece construction, and would be easier than the original four-piece arrangement to handle and keep in place. It will, however, fit all years of 4.0. Whichever gasket you use, apply a light bead of RTV Black to both sides, as this will help hold the gasket in place and make for a seal that is that important little bit better. Also, install at least four of the Small Block Chevy valve cover studs into the oil sump rails – at least two per side. Position the gasket in place over the studs, then press the oil sump against the gasket, using the studs to locate the sump pan.

Put nuts on the studs – finger tight only – and start installing the sump bolts. Using an accurate torque wrench, turn the ¼” bolts to 84 inch-pounds (7 pound-feet) and the 5/16” bolts to 132 inch-pounds (11 pound-feet.) DO NOT OVERTIGHTEN THESE BOLTS – the sump gasket is easily crushed, and crushing the gasket will result in you doing this again!

Once you have the sump in place, reinstall the starter, install the battery cables, and fill the oil sump. Remove the ignition coil wire and crank the engine briefly while monitoring the oil pressure gage. If pressure comes up, reattach the coil lead then start the engine. If it lights and the pressure comes up and stays, you are done!

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