Rope Seal Help - PeachParts Mercedes-Benz Forum

disarrae · #1 08-12-2013, 06:34 PM

So here's the deal. After an engine rebuild we replaced the rear main rope seal. It has been leaking ever since and it has been replaced several times, with several different brands of seal.
The car is an 82 300SD, converted to a manual.
1. The crankshaft has been tested and balanced, it is not bent.
2. We are using the actual Mercedes seal, from Germany. It has a thicker diameter than the after market seals.
3. It is not crankcase pressure related, we have a vented oil catch can.
4. We are rolling not rubbing the seal in, and the ends are trimmed perfectly. *edit* to the 1mm spec
5. We are using "Right Stuff" gasket material, it is not failing there.
6. It fails from the oil pan side. The top stays dry, there is a clear line of oil on the block when the transmission spacer is removed. When you pull off the upper oil pan, you can clearly see where the oil is coming over the seal.

Any help/feedback would be greatly appreciated. Thanks!

ROLLGUY · #2 08-12-2013, 08:02 PM

Quote:

Originally Posted by disarrae

4. We are rolling not rubbing the seal in, and the ends are trimmed perfectly.

What do you mean by "trimmed perfectly"?
If you are trimming the seal even with the block and/or pan, there is your problem. It needs to be cut proud of the block and pan about 1mm.
Check out:
http://www.peachparts.com/shopforum/diesel-discussion/298852-rear-crankshaft-rope-seal-replacement-without-removing-crank.html

DeliveryValve · #3 08-12-2013, 08:08 PM

^^^^I have to agree if you didn't leave any extra material.

disarrae · #4 08-12-2013, 08:12 PM

True, we are leaving the 1mm. Just no shaggy bits hanging off the edges, using a brand new blade for each end, ect.
I know this isn't rocket science, it seems like there must be something that we're missing. And we've got the manual, read it thoroughly, done lots of research on the forums. Something just isn't right.

DeliveryValve · #5 08-12-2013, 08:31 PM

If can post a picture of the area, that would be helpful.

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ROLLGUY · #6 08-12-2013, 09:13 PM

Is there a possibility the leak is not from the seal but the pan to block joint?

disarrae · #7 08-12-2013, 10:00 PM

Not likely. There was one time when the oil was seeping around the seal ends through a miniscule gap in the gasket material, but the joint itself generally remains dry, and oil was leaking through the seal too. The oil collects on the bottom of the joint on the transmission spacer (we call it the waffle plate). The oil mainly collects in the half circle and then drips down from there.
And we've swapped upper oil pans, just in case that was the issue. The original had a groove worn from wrong sized flywheel bolts being used, we thought that the thinned aluminum might be flexing with heat/stress and leaking. We were wrong.

I'll try to get some pics next time we pull it. We just got back from a test weekend of autoX and the tell tale drip is present. We can get about 20 hours of racing on it before the clutch starts to slip horribly, so we're leaving it in for now. We have a race in 2 weeks and then will tear it apart again.

cooljjay · #8 08-12-2013, 10:14 PM

Really redundant question...probably....but...

Are you using 15w-40 diesel motor oil or are you using 5w-30 synthetic....may not cause a problem, I am not positive as I never dealt with replacing the seal....but stranger things are known to happen...

disarrae · #9 08-12-2013, 11:11 PM

Yeah, we use Rotella Triple 15w-40, made from real dinosaurs. Always have
The Ford 6.0 gets the fake dino

DeliveryValve · #10 08-12-2013, 11:41 PM

So in the upper pan you are using The Right Stuff? You sure it's not leaking? The right stuff might be the wrong stuff.

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cooljjay · #11 08-13-2013, 12:22 AM

Quote:

Originally Posted by disarrae

Yeah, we use Rotella Triple 15w-40, made from real dinosaurs. Always have
The Ford 6.0 gets the fake dino

Well then I suggest you have the same luck I have when it comes to oil leaks, if you try and fix one....some how it just gets worse

ROLLGUY · #12 08-13-2013, 01:25 AM

Quote:

Originally Posted by DeliveryValve

So in the upper pan you are using The Right Stuff? You sure it's not leaking? The right stuff might be the wrong stuff.

.

Agreed. The right stuff is Anaerobic Sealant. It is pricey, but should be used only when the "right stuff" is needed for the job.

fdanielson · #13 08-13-2013, 08:49 AM

Just one man's opinion.

If you are using The Right Stuff between the upper pan and the block I'd bet that is the source of the problem. RTV is too thick and creates a gap between the two parts that is preventing the rear main seal from sealing against the crank. I cross referenced Loctite 574 to Permatex 51813, bought it at my local Napa, and it worked wonderfully. The specs say it is designed to fill gaps up to .015 (Anaerobic Gasket Makers & Flange Sealants : Permatex® Anaerobic Gasket Maker) so you can see it is designed for much tighter assemblies than an elastomeric gasket maker.

disarrae · #14 08-13-2013, 02:54 PM

I like this idea. We'll have to experiment with it after the next pull. I did wonder if that might be an issue, or we weren't torquing the bolts tight enough. But they only go to 9 ft/lbs or something small like that. (I'm too lazy to go get the manual out of the shop and look right now).