DIY - Rear Main Seal

This DIY assumes you already have the transmission out for some other reason; transmission swap, clutch replacement, torque converter replacement, etc. I posted this up because I couldn't find one but I saw a few people asking for one.

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The rear main seal is super easy to do. The kit that BMW provides has everything you need; the seal, which is already installed in the frame it goes into, the bolts, the gasket, and a plastic guide cone so that you can easily and without damage install the seal. The ETK refers to the kit as "set of covers" and the part number is 11141438274. The part I referenced covers all E46's from M52's to M54's (Z3's and 5er's too).


^ The first thing you have to do is get the 8 x grade 10.9 bolts out so that you can remove the flywheel. Lock the flywheel in place as shown so that you don't need to buy the special BMW tool that is used for this purpose. I used a breaker bar and a 1/2" drive socket to pull these out as they are tight and difficult to break loose!


^ With the flywheel off you can now get to the rear main seal. The seal before I replaced it.


^ With the cap removed and surface clean. Note the two oil pan bolts that come in to the bottom of the RMS frame.


^ New cap (with seal) ready to go in with white plastic guide cone (included in kit).


^ New RMS installed. Note - I used a thin film of Permatex copper high temp silicone gasket sealant on the bottom of the cap to ensure that no oil leaks from the oil pan gasket as you're not replacing that piece at the same time.

Difficulty level 2 out of 10.

If you are in the process of replacing the clutch you already dropped the tranny and that is definately the hardest part. Now you just need to remove the 8 x grade 10.9 bolts that secure the flywheel to the output shaft of the motor. Then pull the flywheel off and the rear main seal is right there. Remove the 8 bolts that hold it on, six on the front (rear of the motor) and two from the bottom. I removed the six upper bolts first, then I backed off the bottom bolts just a few turns. I tapped them just a bit with a hammer and the cap popped off from the block. Don't use any force here - all you're doing is breaking the cap from the gasket a bit, you don't want to bend the hollow dowels that align everything.

Installation is too easy - the kit comes with the gasket. You line it up with the bolt holes on the block and it just fits over the hollow dowels. Smear a thin film of Permatex copper high-temp gasket sealant (or other appropriate sealant) on the bottom of the cap. Lightly lube the seal with oil. The kit also comes with a plastic guide cone that you place inside the seal - I put a film of oil on this too. Place the assembly up to the outbut shaft of the motor, push evenly and not very hard. It will slip right onto the output shaft and all you have left is to bolt it up.

The bolts all come with thread locking compound on them already. I think you have to reuse the long ones on the bottom so I used a little bit of blue threadlock gel on them. I bolted the bottom up just barely snug first. Then I put the four 10mm upper bolts in first and also just snugged them up. I put the remaining two 13mm bolts in and also just snugged them up - I don't know just a few inch pounds of torque. There are no clear instructions for this anywhere that I found so I went with logic. I tightend the bottom bolts to 6 ft/lbs to bring the cap down to the same level as the rest of the engine on the oil pan (fractions of a mm). I figured the 13mm bolts would pull the cap to the crush gasket with ease even with the bottom bolts installed because I can put 16-18 ft/lbs on them and the cap should sit where it is supposed to. After that I just tightened all the bolts to spec and you're done.

Cheers and GL

great write up. I have 140k on original clutch and ill be placing the clutch soon and will be doing he rear main being it is easy to do.


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Great write up.... This is next on my list of seals and gaskets that need to be replaced!

nice writeup

Well done Mark... now I just need a damn 6 speed tranny hahaha

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Make sure you put silicone on the bottom of the seal housing, especially in the corners where the oilpan/seal housing/engineblock come together. If not, it will leak like crazy and you will have to change the oil pan gasket.

Just ask me how I know all this..............

Just did this , super easy to do if you're doing any clutch work

Though i forgot to oil the gasket :/

sub'd

Torque specs I used according to bolt type and grade according to TIS for oil sump:

Two long bolts going through oil pan to bottom of RMS is 10 Nm. The four short bolts around the top of RMS is 10 Nm. The two 13mm bolts on the sides of RMS are 22 Nm.

The white cap guide cone is used as the seal installer and is used to widen up the inner seal (part that makes constant contact with crank) of the RMS. Use plenty of oil on the seal lip, crank, and also the plenty of it on the white cap. Do not under any circumstance let the inner seal of the RMS bend and watch and ensure that it clears the crank. It is quite an expensive mistake to make. As me how I know. Do not risk a bent seal even slightly. It's not worth it to have a leaking RMS.

If the RMS is stored without the white support cap for more than 6 months, the seal should not be trusted.

TIS how-to: http://tis.spaghetticoder.org/s/view.pl?1/00/32/53

What did you use for torque for the flex plate to crank. I've looked for hours and have not found a definite number. My bentley manual says nothing.

Thanks

What is the 'flex plate'?

Its the flywheel for an automatic trans which on American car its called the flex plate.

Seems to me it is 121 Nm: http://tis.spaghetticoder.org/s/view.pl?1/00/32/56

Originally Posted by Nervous

Seems to me it is 121 Nm: http://tis.spaghetticoder.org/s/view.pl?1/00/32/56

Thanks for the link, I seen that also but do you think that applies to the M54 also?

I think so, yes. M57 is kinda 'diesel version of M54'. At least, flywheel and tranny is the same, so torques should be the same either.

I'm leaking minorly (no spots in driveway) but its from this

Thanks for the DIY, I will be doing my clutch soon and might as well do this while I am there. I have a "ghost" oil leak somewhere an I am hoping this is the culprit...

You can easily see if your RMS is leaking by just getting under the car and looking into the two openings in the tranny bell from underneath. If there are oil drops there then you found it.

^ thanks! Either way, I just added it to my order (and placed the order) for the clutch parts. This might be a dumb question, but do I need to drain the engine oil first? I will be due for an oil change before I get to installing the clutch, but might go ahead and put it off a couple of weeks (the oil change) if I will end up needing to drain it to replace this seal...