Rear main seal DIY

[Cubieman]

I don't like these 'new style' seals that BMW has switched to, also retroactively for older cars it seems.

Over time the front and rear main seals create a low spot on the crankshaft, you can feel this spot with your finger, it's quite pronounced.
If you install one of those new style tensionless seals, and your low spot it quite large, they will never seal, they leak.

I prefer to stick to the 'old style' seals with a spring inside them, they provide more tension and are more forgiving if the crank surface they are riding on isn't absolutely brand new.
A generic 110x90x12mm seal with the right properties and a spring is suprisingly easy to source.

Now I am thinking about whether or not to use the new style seal (sans spring) R.M.S on my S85, doing a flywheel and it's right there and leaking slightly.
I did notice that the seal does not have a spring, not wanting to fuck around with a seal that may leak. Don't know if there are any alternatives to the the new seal.

Also have to deal with the bed plate parting lines, you have to buy a special tool for a syringe, and use two different compounds to do it "right", almost like an epoxy type substance. I used Toyota FIPG on the front main seal bed plate parting lines and no leak so far, and I do believe the new seal did have a spring.

[BL92]

I am doing the job on floor on stands

with these suffice for engine support and gearbox removal

[dukeofchen]

I am doing the job on floor on stands

with these suffice for engine support and gearbox removal

Yes that will suffice for engine support, for the transmission jack you'll want one that's as low as possible given the limited clearance on jack stands. I know HF makes one too so you can compare the height on that unit vs the pictured one. Get the car jacked as high as the stands can safely go because you'll want every inch of clearance possible.

As for steps the FCP video posted above is what I used to perform the whole job, my first time doing just about all of it. Not sure exactly where SMG specific steps come in as I did it on an MT.

Other tips would be to remove the fan/fan shroud, so you can let the transmission sag down as much as possible without worrying about contact up front. Laying on the ground you're going in almost blind going for the bolts securing the top of the transmission, so every bit of visibility helps.

For those bolts also crucial to have a bunch of extensions / wobbles / swivels that you can chain together to get the socket on the bolt. I'd say those bolts and mating the transmission back up are the hardest part on jack stands.

It's a hell of a job to do this way but just be patient and give yourself time.

[BL92]

Thanks for that

This jack is a lot lower to clear



I have Quickjacks to be able to get more height over the jack stands, its just Quickjacks have no side access


What are thoughts on part list

I need a spring and ball pin along with the seal
Need exhaust gaskets and bolts

i wonder if i can get away with reusing the release bearing? i am not sure if a new release bearing and an old clutch are compatible

[dukeofchen]

Thanks for that

This jack is a lot lower to clear



I have Quickjacks to be able to get more height over the jack stands, its just Quickjacks have no side access


What are thoughts on part list

I need a spring and ball pin along with the seal
Need exhaust gaskets and bolts

i wonder if i can get away with reusing the release bearing? i am not sure if a new release bearing and an old clutch are compatible

Exhaust bolts would depend on condition, I've reused mine plenty of times but I don't live in an area where underside corrosion is a concern. Exhaust gaskets from the headers to section 1 you will want to replace as they are crush gaskets.

Don't personally have an opinion on the throwout bearing and pivot fork, certainly wouldn't hurt to replace as they are wear items but depends on condition / age.

One easy part I would absolutely replace if it hasn't been done is the pivot pin (#6 in this diagram), they become brittle with age and if it snaps you'll be pulling the transmission again as it's integral to the clutch release mechanism. New OE plastic, steel, and brass replacements are among your options there - I went with this one. Also re-lube the appropriate contact points with the appropriate moly grease when putting back together. While you're in there would also be a good time to refresh all the shifter bushings if you haven't yet, it's a PITA with the transmission installed.

[BL92]

Thank you so much Duke

[George Hill]

What are thoughts on part list

I need a spring and ball pin along with the seal
Need exhaust gaskets and bolts

i wonder if i can get away with reusing the release bearing? i am not sure if a new release bearing and an old clutch are compatible

If I was just replacing a rear main seal the only thing I would for sure replace is the pivot pin.

But if the clutch had a decent amount of miles on it I would consider replacing it. When I replace a clutch kit I always replace the fork and guide tube as well.

LuK clutch kits are cheap enough that if you are going to replace the TOB I would just replace the kit since it comes with a TOB anyways.

Inspect the pilot bearing, generally they can reused in a RMS replacement, but I replace them with clutches no matter what.

I always replace the exhaust to header nuts and bolts if they are rusty, gaskets usually can be reused if they've been replaced recently but if original I would plan on replacing them.

*Personally if I had the trans out, I would replace the pilot bearing, clutch kit, guide tube, fork and pivot pin. Inspect the flywheel and input shaft seal and replace as necessary.