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  #1  
Old 09-14-2009, 08:35 PM
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Replacing Exhaust Manifold Bellows in a 1987 300td

The bellows/connector between the two exhaust manifold sections of my 87 300td wagon is leaking. I have another 87 300td and it developed a leak in the same location. I have read all the posts about the possibility of breaking manifold studs during removal.

Does anyone know if it is possible to replace this connector by just removing the shorter front two cylinder portion of the exhaust manifold and the egr/turbo plumbing in the area, or just the larger rear 4 cylinder manifold section? Or do you need to take 12 turns at the manifold stud Russian roulette game and remove both sections of exhaust manifold?

I would love to hear from anyone who has tackled the job or who has a creative way to repair the connector.
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Old 09-14-2009, 09:42 PM
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Decisions! Decisions! To pull it all or try pulling just enough? Either way you go with regard to the exhaust studs and their nuts it usually works a little easier when everthing is hot! So get the all your tools ready and your plan of attack then get the engine and manifold up to temperature before you start trying to turn things!

The entire manifold will require 12 chances for some kind of failure, either stripping a nut or breaking off a stud. If you go the partial route you would have to remove each of the four forward studs or the eight rear studs to get the either manifold to slide forward or backward because you can't pull either manifold straight off the studs with the bellows intact. Now you might be able to get the forward nuts off, then destroy the failed bellows, get the manifold section off the studs, then remove these studs. That way you could install the new bellows, get the manifold section in position, and lastly install some new studs, then the nuts to get everything back into position.

To accomplish this you can use whatever rusting or seizing of the manifold nuts to your advantage. And a second jam nut over the original and then use these stacked jammed nuts to turn the manifold studs out. Again this will be easier with the cylinder head up to temp, use the melted wax trick on the manifold studs at the cylinder head edge not on the ends near the nuts. Another trick that could help is with everthing up to temp and then use a can or two of electronic compressed dust-off gas to spray on and cool, therefore shrink the manifold flanges and studs ever so slightly compared to the warm cylinder head.

If worse comes to worse you can always remove everthing and get it done! I have a very well worth it, $20 set of cobalt left-hand drills and fluted extractors that I've used successfully to remove a couple broken studs that did not have enough meat left to grab with vice grips. If you've got access to welding equiptment using the trick of welding an oversize nut to the remainder of the broken stud is a pretty reliable method also! Good Luck!
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Old 09-15-2009, 12:15 PM
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Replacing Exhaust Manifold Bellows in a 1987 300td

Ahha, brilliant, thanks Professor Billybob! I had not thought to take out the studs to allow for lateral movement of the manifold section, and the bringing everything up to operating temperature is another good trick, although I wouldn't have thought to heat up an exhaust system before getting so intimate with it.

But isn't the danger of breaking something greatly increased by taking the studs out of the head? Do the studs offer more resistance to being screwed out of the head than the nuts do from being removed from the studs?

If I was successful going the partial removal route, the other thing that concerned me was the portion of the original exhaust manifold gasket that would now be left hanging. I wonder if it is reusable if it is not leaking now and I just leave it in place. I was also considering carefully cutting off the exposed gasket and replacing it with an exact portion of a new exhaust gasket. What do you think?

What's the melted wax trick?

I'd like to buy the $20 drills and extractors. I am on Cape Cod too.
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Old 09-15-2009, 01:51 PM
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I have had very good luck removing manifolds from 603 heads (knocking on wood), no broken studs.

There is the occasional stud that comes out with the nut, not a lot you can do about that except re-install it later (or a new stud).

Use penetrating oil for a couple of days pre-removal.
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Old 09-15-2009, 09:52 PM
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Ahha, brilliant, thanks Professor Billybob! I had not thought to take out the studs to allow for lateral movement of the manifold section, and the bringing everything up to operating temperature is another good trick, although I wouldn't have thought to heat up an exhaust system before getting so intimate with it.

I don't like working round the hot manifold but I dislike it less that removing broken studs!

But isn't the danger of breaking something greatly increased by taking the studs out of the head? Do the studs offer more resistance to being screwed out of the head than the nuts do from being removed from the studs?

It's hard to say, when the stud breaks it's usually when your trying to get the nut off! With regard to more or less resistance it would seem pretty much a toss up or close to it, I only say this because as babymog mentions it's not uncommon for a stud to turn out rather than a nut coming off easily. With the cylinder head hot it seems that the studs come out significantly easier than when cold, so that gives that method some advantage.

If I was successful going the partial removal route, the other thing that concerned me was the portion of the original exhaust manifold gasket that would now be left hanging. I wonder if it is reusable if it is not leaking now and I just leave it in place. I was also considering carefully cutting off the exposed gasket and replacing it with an exact portion of a new exhaust gasket. What do you think?

With everything that it takes to get this done I would spend the extra few dollars on a new gasket and just use a section of it as needed. There are spaces between the exhaust runners so using a partial gasket should not present any problem. I would hate to try re-using the original gasket, get everything buttoned up and have it leaking, I doubt it would, but why take the chance!

What's the melted wax trick?

You can do a search and find some discussion of it! Basically it is to use heat to warm a fastener and then apply regular candle type wax to it. The wax melts and because of its properties it will flow into the spaces along the threading and will help to un-seize the bolt/screw/nut allowing it to be removed more easily. As babymog mentions, applying a good penetrant to any fasteners a couple times over a couple days prior to working on fasteners is ALWAYS a good practice and something that you'll never regret! I prefer Kroil but anything is better than nothing!

I'd like to buy the $20 drills and extractors. I am on Cape Cod too.

I got mine off eBay a couple years ago they where about $12 and shipping was $8, they're made in China, but getting one bolt out under most circumstances is well worth it.

Here is a set like I picked up:

http://cgi.ebay.com/NEW-Screw-Extractor-Left-Hand-Drill-Bit-Set-Easy-Out_W0QQitemZ290348450100QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item439a1dc134&_trksid=p4999.c0.m14
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Old 09-23-2009, 02:29 AM
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Smile Success removing the manifold from a 87 300td!

Yea! Got the exhaust manifold off of my 87 300td diesel without breaking a single stud. In fact some seemed barely tightened at all (possible additional source of exhaust fumes I guess). Perhaps the 124s don't break studs as readily as the earlier models as was mentioned above.

Anyone know the torque wrench settings for the 12 exhaust manifold nuts? Professor?

Also the Mercedes parts guys said the nut and washer combination that was on the old exhaust manifold is now replaced with what looks like a copper nut and washer combined in one piece. Anyone have an opinion on which might be better?
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