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360 Rear Main Seal Replacement

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DMack View Drop Down
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Joined: Mar/27/2019
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    Posted: Jan/19/2021 at 10:35pm
Hey my AMC Brothers & Sisters,

I have a 1973 Javelin with a 360 and 727 automatic.  Had the motor professionally rebuilt, balanced and assembled in 2018.  It sat on an engine stand for almost 2 years, before I finally got the car back together and installed it.  Now that I have 500 miles on it...it has developed a rear main seal leak.  

After a bunch of input and discussion with AMC owners across the U.S., I decided to leave the motor in the car, hang the motor and drop the cross member in order to change it.  

I thought I'd offer up some instruction/advice if anyone opts to go this route.  Maybe you've never done this before, or maybe you've always pulled the motor.  My goal here is to just offer some possible options to consider. 

Total time to get the point where I could pull the pan off was approximately 1.5 hours.  I get that pulling the motor out and getting it on an engine stand certainly makes it easier to replace the pan...but... there is plenty to unhook, drain and remove in order to pull the motor out.

Soooo....

I started by removing the air cleaner and taping up the airhorn on the carb.  Moved on and fabricated a cradle to support the motor from above, so I could remove the cross member below. I used a 3/4" x 1-1/4" x 48" solid steel bar with a hole drilled in both ends, so I could mount a piece of 2"x 2" wood on each end to set on the inner fender edges.  Then, I used 2 ratcheting straps from the cradle bar, down and around the exhaust manifolds.





When the motor is supported by the cradle.
  1. Disconnect the battery
  2. Jack it up and place 2 jack stands right in front of the sway bar mounts (at the frame).
  3. Pull the wheels.
  4. Remove the starter
  5. Unbolt the four nuts on the bottom side of the motor mounts

  1. Remove the drag link (4 points, Idler arm, Steering arm, 2 inner tie rods)
  2. Remove the end-link hardware for the sway bar and swing the sway bar down
  3. Remove the 2 nuts (on studs) and 2 bolts that hold on the cross member
  4. Mark the orientation of the adjustment bolt, then remove that bolt that secures the passenger lower control arm to the cross member.
  5. Pry the lower control arm out of the cross member.
  6. Swing the cross member down on the passenger side and out of the way.

At this point you have full access to the oil pan
  1. Drain the oil
  2. Remove all (20) bolts that are holding the pan on.  
  3. Pry slightly on the edge of the pan in order to get it to release
  4. Pull the pan straight down to get it off.
  5. Check the pan to see if the small button that mounts on the underside of the oil pickup has fallen off.
At this point the entire bottom end of the motor is exposed.  This is the point where you need to clean all the mating surfaces on the block and remove the end seals, one is on the lower side of the front cover and the other that mounts into the rear main cap.

Loosen the rear main bearing cap and remove the cap (make sure you note the direction). Check the cap to see if the lower half of the crank bearing came off with the cap or if it is still stuck to the crankshaft.  On the crankshaft side of the rear main cap you will find the bottom half of the rear main seal.  It will normally just lift out unless some adhesive/sealant has been used to secure it in place.  Once the cap is off, take a small screwdriver or punch and push one end of the upper seal towards the top of the block. This will force the seal out of the other side of the block.  When it is exposed enough, grab the end of it gently with a pair of needle nosed pliers and rotate it further until it comes completely out.

Now is the time to "spotlessly" clean every thing!!







I'll post again as soon as the new seal arrives, and I can document the re-assembly!!

JUST AN UPDATE....CALLED SCE AND THEY ARE NO LONGER PRODUCING A REAR MAIN SEAL FOR THIS APPLICATION.  SCE NUMBER 12905 OR RS 085-5 ARE BOTH DISCONTINUED!!

A little bit more update on this posting.

I ended up using the Fel-Pro rear main seal, as there were limited options.  The SCE seal is no longer produced. There are a few other manufacturers but I already had a new Fel-Pro seal.

To install this while in the car is a little bit trickier than when the engine is out and upside down.

Install the upper rear main seal half by lubricating the top half of the seal with motor oil on the seal side, then place the end of the seal into the upper groove of the channel in the block. Then rotate the seal into place.  this takes a steady pressure up on the seal. Make sure you don't distort the seal as you are pushing/rotating it in.

Now the lower seal. Put a dab of RTV under each wing of the lower part of the seal and push it into the rear main cap.  Put another small dab on top of the seal wings at the joint where the upper and lower seals meet.  Also put a very thin smear on the outside edge of the rear main cap, that faces the transmission.  Make sure your crankshaft bearing is properly mounted in the cap.  Put the cap back on and finger tighten the two cap bolts.  Gradually increase the torque on the bolts and finish with a torque wrench at 100-105 ft. lbs.

You need to install the pan rail gaskets first, then the two curved pan gasket ends last. The reason for this is that there is a notch in the two rubber seals that go on each end of the pan, and they match up with two tabs that protrude from the pan rail gaskets.  You can use a very thin layer of RTV, to hold the gaskets in place, but I would actually recommend using 3M black trim adhesive instead.  The goal is to hold the gaskets in place not seal them them with RTV.  Once the pan rail gaskets are in place, put a bead of RTV on each end seal and push the seal up into the end cap channels.  Make sure to put a good bead of sealant at the corners of the seal where the pan rail gaskets meet the rubber main cap seals.  Make sure you remove any excess RTV that may be inside the oil pan/block.  If a chunk of this dries and falls off it can wedge inside your oil pickup and block oil flow.  At worst it can get wedged inside you oil pump and cause oil pressure drops.  Place a medium bead of RTV on the end cap seals where the seal will contact the oil pan.

Now comes the time to put the pan back on. One thing I discovered...REMOVE THE ENTIRE SWAY BAR.  When you are trying to get the pan back on, the front sway bar makes it difficult to position it properly.  Much easier to do with it out of the way. 

My particular application has a 727 automatic and the cooler lines are the one thing you have to push out of the way in order to get the pan to go straight up.  Just a little leveraging on the cooler lines, nothing too aggressive.

Once the pan is in place and all the bolts are started in to the block, gradually start tightening it down.  DON'T OVER TORQUE THE GASKET!!!!!  You'll be replacing it again, if you over torque the gasket and split it.  Follow the manufacturers torque specs.... and fight the urge to go "just a little bit more!!!"

Now that the seal is on and the pan is re-installed... reverse the order that you took it apart and put it back together.  

Make sure, in your JOY of being done, that you don't forget to put motor oil back in the motor!  

For my application, I went and test drove it for about 20 miles and brought back in to check it.  There was some residual oil that was still dripping out from inside the transmission bell.  I cleaned that up with some brake clean and drove it again.. 

Finally there is no more leak!

Hope this helps someone if they need to do this wretched job... Many Thanks...


Edited by DMack - Jan/28/2021 at 2:12pm
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Joelfanti View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joelfanti Quote  Post ReplyReply Direct Link To This Post Posted: Jan/20/2021 at 4:59pm
Weird it leaked after being rebuilt. Installled backwards mabey ?
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DMack View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMack Quote  Post ReplyReply Direct Link To This Post Posted: Jan/20/2021 at 5:08pm
Originally posted by Joelfanti Joelfanti wrote:

Weird it leaked after being rebuilt. Installled backwards mabey ?

No installed in the proper direction, but the seal itself is the problem.  

There are several threads on the Forum that discuss this issue.  The Fel-Pro and Mahle seals appear to be "undersized" by about 40/1000 of an inch compared to the factory seals or the SCE replacement seals.  Also, because it sat on an engine stand for almost 2 years, all of the original lubrication may have dissipated to the point where the seal may have been essentially dry and scored on start up. 
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