rear main seal

nmcm · 11-29-2002, 02:42 PM

I am replacing my rear main seal (Engine to transmission side) and my manual seems to contradict itself in terms of how far in the oil seal is supposed to go. Is it supposed to go as far back as you can push it, even with the crank case or even with the crank shaft itself or some other varient. Please help!

NMCM

marcesq · marcesq's Garage

To the extent that it makes a difference, what engine are we working on.

nmcm · 11-29-2002, 04:56 PM

Yes, sorry about that. It is a 1977 911 2.7L.

yelcab1 · 11-29-2002, 05:01 PM

Until it goes no more.

Superman · 11-29-2002, 05:44 PM

Flush with the case. I'm guessing that is about the same thing as until it goes no more, and I'm not sure it makes much difference. Grease the inner lip certainly, and some folks lightly grease the outer edge as well.

CarreraS2 · 11-29-2002, 07:30 PM

Allow me to relay my rear seal nightmare!

Changed out the rear seal (among other things), put engine back in car - oil leak between engine and tran!

Hmm, can't be the new seal!?!? Its brand new! Try to figure out a different (and hopefully easier) reason. Nothing.

OK, engine back out. Get another new seal. Put it all back together (luckily by this time, it only takes an afternoon).

Leaks AGAIN! Aaarg. Must be something else. Can't be TWO bad seals, can it?

During my research, a shop said to avoid seals that are all black in color. Which mine were. Instead, use the ones that are black on the outside, and brown (Viton) on the inside. So, I buy one of these two-tones from the shop, and try AGAIN.

Yep, that was it. No leaks, and its been many years now.

Just a lesson that I learned. I'm a big fan of the two-tone seals now - and all black rear seals give me nightmares.

dhoward · dhoward's Garage

'til it seats is past flush. Funny you should ask.....

rickeolis · 11-29-2002, 09:56 PM

Having just dropped my engine, I plan on this job soon too, so I wish to thank SoCal and others for their input on this question

cary · 11-30-2002, 10:56 AM

My .02c.
I did mine flush with the case.

Switched to Mobil 1 on a 60k engine at the same time. Doesn't leak a drop.

nmcm · 11-30-2002, 11:46 AM

Thank you all for your swift reply! I am having one of those nightmare stories and want to make sure that I get it right this time. I recently went to a "local area knowledge man" and he told me that I had installed the seal too far in the first time. He said that there is a pressure valve (hole) in the area of the rear main seal. Once the temperatures get on the high side 200-250 this valve (hole) is used to releave the pressure inside the case and if the hole is pluged (by having the seal too far in) the seal will blow. I don't know if this is true or not but it would make sense with my story. I replaced the seal last year and it worked fine for six months until my first hot day. The engine oil temp rose to 220 and suddenly I was smelling oil again!
All of your replies except one stated that the guasket should be flush with the case so it does sound like that is the proper method. Has anyone else heard about this pressure relief valve in the guasket area? Anyway, thanks again for all the replies.

NMCM

RoninLB · 11-30-2002, 12:28 PM

Quote:

Originally posted by nmcm
Has anyone else heard about this pressure relief valve in the guasket area?

NMCM

Never .. and I read Pano, Up-Fixin, Excell , factory workshop man, P-Tech. Bull., BA., Haynes.. would love to learn something new............Ron

RoninLB · 11-30-2002, 12:31 PM

on second thought, there is a weak area in my 2.7 design, behind the engine oil cooler that my crack and leak.. that's all I have for info...........Ron

dhoward · dhoward's Garage

There is NOTHING in the bore where the rear seal fits. (2.0). Any other seal in the entire world is pressed in 'til it stops.That's how you make sure it's square to the bore.

Then again, an expert I know sez that there are magical elves in there, and if you seat it too deep, you'll squash 'em...

nmcm · 11-30-2002, 02:42 PM

Wow,
Lost of responses.
O.K. If that is so true (ie shove it right to the back) Why the special tool form Porsche to install it at the exact spot (just slightly deaper than flush). Now don't say because they want you to buy the tool. There's no special tool for putting on valve cover guaskets!

NMCM

dhoward · dhoward's Garage

If you look at the back of the flywheel, there's a machined ridge around the facing thaht mates to the crank. The seal must be intalled deeper than flush, or the flywheel will rub against the seal, thereby cutting the viton from the metal imbedded in the outer circumference, thus rendering it useless. When you get yours out, take a look. If you like I'll post a picture. Use the right tool to remove the flywheel bolts. I found that by slightly tightening, then reversing, the bolts came out very easily. (of course I was using an impact so easily is a relative term...)
As for the special tool? nearly every manufacturer makes special tools for seating seals, Porsche is no different. You don't have to MASH the seal in, just lightly bottom. (Don't forget the elves...)

BTW, I have mine out right now, Waiting on new flywheel bolts....

Doug Zielke · 11-30-2002, 03:44 PM

Data point from a 3.0.... others may be different.....

I just replaced the seal as part of the overhaul. The *existing* seal was *flush* with the front surface of the case.
Furthermore, 101 Projects (pg.34) details the seal install...flush with the case.

yelcab1 · 11-30-2002, 10:13 PM

If you install the seal flush against the case, the big mass of flywheel is now spinning right next to the seal. Any grit, or irregularity that is caught in between the stationary seal and the spinning flywheel will shred the sealing lip to a zillion bits.

Push it in until it goes no more ! Lesson learned and never forgotten.

Superman · 12-01-2002, 08:54 AM

I already indicated what I think is the correct answer here and I won't be confrontational by restating it. But if the seal can be driven in much further than flush, then I would assert that it does make a difference. Here's an observation: I watched JW replace a seal a few days ago and when he was done, it was flush with the case.

Now, all the clues are there for someone to figure this out. By the way, I have also heard about the superiority of the seal with the brown center. Further, I have now heard from at least two highly, highly experienced Porsche 911 guys that engine rear main seals almost never leak. Leaking from the bellhousing usually is tranny oil getting past the input shaft seal, worming up the shaft and getting flung out by the clutch pieces.

yelcab1 · 12-01-2002, 09:09 AM

I had the rear mai seals leak 3 times, each replaced with brown viton seal and last for 25000 miles. And also the tranny seal leak as well. So I would disagree with the assertion that the rear main seal never leaks (or seldom leaks). It did on my 911, on my wife's Lexus, on my Ferrari, on my friend's toyota, and on a bunch of other 911 on this chat site.

Doug Zielke · 12-01-2002, 09:46 AM

Sheesh!
OK, we don't give a rat's ass how you put in your seal, but....

Factory Manual, Pg E 108-3:
"The sealing ring must be flush with the case."