Replacing the Rear Main Seal
Joe Angell
I managed to not order the correct quantity of bolts to re-assemble the back of my water pump, so I decided to tackle the rear main seal. I was trying to avoid it, but my friend pointed out that it has probably not been changed in 25 years, so I should really do it. Contrary to all the talk I had seen, this was actually rather straight-forward, especially after replacing the front main seal in the timing cover. Once again I used the guide found on DMCTalk.org.
Getting Access
Since the rear main seal wraps the crankshaft on the back of the engine, you need to disconnect the transmission and somehow shift it out of the way. It's much easier if the engine is already out of the car.
My problem was that my engine was mounted on a stand using the transmission mounting holes, thus blocking access to the rear main seal. The only solution I had was to attach it to the engine hoist and lower it down on some pallets. I was going to wait until it was time to mate the engine and transmission to do this, but now was as good as time as any.
Lifting the engine off the stand to get access to the rear main seal.
The engine resting on its oil pan, the rear main seal exposed for removal.
Removing the Rear Seal Plate
The rear main seal is mounted in a plate that is bolted to the back of the engine. This plate comes off, the seal is removed, a new one installed, and the plate mated back to the block.
The plate is held in place with five 6mm allen-style hex cap screws. Mine were surprisingly easy to remove, like they weren't properly torqued. There are also two bolts along the bottom edge that bolt up through the lower crankcase and through the plate. These are removed with an 11mm socket. It was a good thing I decided to do this -- I'd removed them when doing the lower crankcase swap and had forgotten to put them back in.
With the plate out of the way, the old paper gasket can be removed. Mine didn't stick to either the block or plate, and basically fell out when I removed the plate itself.
The five (5) socket cap screws (blue) and the two (2) hex bolts (green) that hold the plate to the block.
The rear main seal plate removed from the block. The gasket was loose and easily removed.
Removing the Seal from the Plate
Ideally, removing the seal from the plate is done with a press. I don't have one, so I did it the old fashioned way: I used a socket extender and a hammer to bash it out.
First, take a look at how far the seal sits below the surface of the plate. It's only a little below the surface. It's helpful to note this so you know how far in to install the new one.
There is a lip inside the plate, so you need to tap it outward from the inside. I rested the plate on my vice in such a way that the seal was not pressing against the clamps. I then placed my socket extension against the inside rim of the seal and tapped with the hammer, first lightly, and then quite hard, switching from my rubber mallet to a four pound hammer when it wouldn't budge.
After enough hammering, it finally started to tilt out. I tapped on the other side a bit, and eventually removed it from the plate.
A "before" image showing how far the seal is set into the plate. It's really just below the chamfered edge.
Positioning a socket extensions to tap the old seal out with a hammer. You can see the damaged done to the seal from tapping it out on the opposite side.
What is left to the old seal after hammering it out.
The new seal ready for installation into the plate.
Cleaning Up the Mating Surfaces
There are three mating surfaces to clean, with each being present on both the plate and the block:
- Where the plate meets the vertical surface of the block around the crankshaft.
- Where the plate means the horizontal surface of the lower crankcase.
- Where the seal rides against the crankshaft and is pressed into the plate.
I used my bristle disc to clean the block mating surfaces, and a combination of fine grit sand paper and a Brillo-style scrubbing pad clean the crank and the inner surface of the plate.
The crank should be polished clean. Mine was already almost completely clean, so I just needed to remove a few blemishes.
The mating surfaces were quickly cleaned with the bristle disc. Unlike the cylinder head and oil pan surfaces, these required very little pressure to clean up, and it was done in a couple of minutes.
Using a bristle disc on a power drill to clean the horizontal surface of the plate.
The vertical surface after cleaning up with a bristle disc.
The mating surface of the block after cleaning with a bristle disk. I used some light sand paper in some places I couldn't fit the disk, and made sure the crankshaft surface was clean as well.
Installing the New Seal
My new seal was purchased from DeLorean.com, as the same one is used for the 2.8L and 3.0L engines. Following the instructions in the DMCTalk guide, I coated the edge of the new seal with Right Stuff. I had the caulk-style tube, so I just squeezed it a bit while I rolled the seal around it.
Once I had adequate coverage, I rested the seal on top of the outside of the plate and gently tapped it with my rubber mallet, moving around it in a circle, being careful the whole time to make sure that the seal was always as level as it could be. After it was flush with the face of the plate, I shifted the hammer inward a little to tap it in a bit deeper. I wound up seating it further down that the original position, but not by much, as I needed to ensure that it wasn't tilted at all. It does not seat all the way down to the lip, although I imagine that would work fine as well if you did that.
Most of the RTV oozed out, just as the DMCTalk guide said it would. This was easily wiped away with some paper towels.
The new seal partially installed into the plate. Much of the Right Stuff oozed out around it as it was tapped in.
The new seal fully seated into the plate. It's a bit deeper in than the original seal, but that shouldn't matter.
Installing the Plate on the Block
The new gasket is a little bit taller than the plate itself, and the excess has to be cut off. This is pretty easy -- line the two up, and slice it with a razor blade.
With everything cleaned up, I put down a bead of Right Stuff on the plate's rear surface and pressed the gasket onto it, cleaning up the excess. I then applied a bead to the vertical surface of the block as well as the horizontal surface. The DMCTalk guide seems to suggest that you can do them separately, but I don't know how that would work.
I tried to clean up some of the excess Right Stuff with a paper towel, and wound up smearing it around the surface a bit. You probably shouldn't do this, since the idea is to have the sealant be squashed by the plate against the block, and smoothing it out beforehand can lead to gaps if the surfaces aren't even. I still had a lot of sealant in there, though, so I wasn't too worried.
It can take a bit of effort to get the seal over the crank, but it's not overly difficult. It finally popped on after a bit of pushing.
Once it's in place, the five (5) socket cap screws are tightened first. I didn't have an allen adaptor for my torque wrench, so I just made them as tight as I could; the manual says it should be 9 ft lbs.
Before installing the bottom bolts, I applied one more bead of Right Stuff along the bottom edge of the plate, although I don't know if that helped much, since it was all outside the mating surfaces. This time I just didn't have torque numbers for the two bottom bolts, so I just tightened them up enough that they wouldn't come loose and wouldn't strip out the holes in the plate. I used some stainless steel bolts I had lying around, since I couldn't find my originals anymore.
The new gasket is a little bit too long, and had to be trimmed slightly.
The trimmed gasket, ready to be installed.
A liberal coating of Right Stuff applied to the block; the gasket has already been stuck to the plate with more Right Stuff. I used a paper towel to clean up an smear the Right Stuff, which is why it looks so flat -- it's thicker than it looks.
Final installation.
That all there is to it. I hoisted the engine back onto the stand so that I could move on to the future water pump installation.