Rear Main Seal

[n/a]

Hi,

My 66 230sl is now running great, however it is leaking from the rear main seal very badly.  Every time I stop there is a puddle of oil under the car.  I was told this is a very costly thing to repair (over $1500), since the crank has to come out to replace the seal.  Can anyone enlighten me from your experience?  The car is setting at the shop awaiting the go-ahead from me.  Thanks

Doug Goins

[ja17]

Hello Doug,

Clean everything up just to make sure a leaky valve cover gasket or such is not causing a leak down around the pan and rear seal.

Yes these seals are not meant to be changed during the usual life of the engine. The top "rope" seal is pinned in place so the crankshaft must be removed to replace it.
The lower half of this seal can be replaced by  removing the oil pan.

How is your oil pressure? When your rear main bearings begin to wear this can also cause the rear seal leak to become worse. Sorry it sounds like no easy fix.

Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Rear seal replacement is usually done during engine rebuild. Maybe yours is ready for more work. You will have to pull the engine and take most of it apart. $1,500.00 just to change a $10.00 seal seems like money poorly spent so I'd have a look at the crank and see if the whole engine needs a rebuild. The 1500 would go a long ways toward your project should you need it.

 Rear seals must be installed properly or they will leak forever. I've made special installation tools that work really well. I think the book tells you how to make one. Don't ever install the rear seal by cutting the rope flush with the parting surface of the block or pan. It needs to stick up about .6mm or .025'' on both the pan and the block. Sealing all this up is also a challenge due to the block and pan expanding at different rates when hot.

Question for this week:
Why do they use an aluminum oil pan?

Question after that one has the right answer:

Roto caps. What are they and how do they work? More importantly, how do you test them?



Daniel G Caron

[Mike Hughes]

I'd say that they use an aluminum oil pan because it adds stiffness to the block and can be cast in shapes that would be difficult to make in one-piece steel stampings.



- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[Benz Dr.]

Hummm...... the block is probably strong enough. Metal pans are actually quite common on domestic
 ( NA ) cars so I think the manufacturing process would be well established. If anything, the aluminum pan would require more costs to make and then machine all the surfaces. Remember, there's no gasket between the pan and the block so it needs to be made right.
So, I'm going to say '' no cigar '' Try again.

Dan Caron
SL Barn

[Cees Klumper]

Rotocaps are installed underneath each valve spring and they serve to rotate the valve continually (for better sealing?), How to check them I'm not sure, but I imagine they should turn freely.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[rwmastel]

quote:I'm going to say "no cigar" Try again.

Here's some guesses.  How about:
 - lighter weight
 - no rust
 - no electrical conduction


Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[knirk]

Can the rotocaps be checked by running the engine with the starter, and observe that each valve rotates?

Per G. Birkeland
69 280 sl aut 834
Norway

[Benz Dr.]

Oil pan..... nope.

 roto caps... Case knows what they are and how they work but - how to check them.....??

 You can remove the oil fill cap with the engine running and actually see the one directly below turn very slowly at idle. No cheating - which way does it turn - and they all turn in the same direction. But how do you know if they ALL work?

Dan C

[Benz Dr.]

You could use the starter but it would be very hard to see each one move. They don't move very quickly and then you'd have oil all over making a mess. ( The valve cover needs to be removed, right?)

Daniel G Caron

[bjudd]

While seeking info about replacing my rear transmission seal I stumbled on this discussion with Dr. Benz's questions and riddles.  I don't believe the answers were ever given.  How about it Dr.?

bjudd
1969 280 SL 5 sp

[Kenneth Gear]

How about the front main seal, is that a less involved job?

Ken G
1971 280 SL
Silver/red

[Benz Dr.]

Roto caps? I think they turn clock wise.

 I test them with a hammer.

 Alloy oil pans are all about cooling the oil. Alloy is a better heat exchanger than other metals. Ever pick up something made of alloy and notice how much colder it feels to the touch? It pulls heat away from your hand.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Vince Canepa]

To check the rotation of the roto-caps on the main engines of the ships I manage we painted a stripe on the valve retainers with metal marking paint.

Dan is correct about the heat dissipation.  However, I do think the aluminum pan contributes to the strength of the block and the stiffness of the main bearing area.  That is why many manufacturers have been going that route on modern engines, even the US domestics.  And less vibration in this area makes a quieter engine (although the valve train/IP drive on the M127/129/130 seems to cancel any advantage there).

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

[JPMOSE]

Heat dissipation would have been my guess, as I have read many articles referencing the importance of keeping an engine clean for this reason (along with the transmission).

Best Regards,

J. P. Mose
1968 250SL