These forums are really useful for the amateur mechanic! I'm grateful for all the help I've had here, so I am making this contribution in the hope that it will help someone in the future. Disclaimer: I'm a complete novice with limited tools and even more limited knowledge! I plan to have all the parts and tools that I'll need before I start any job, but invariably things do not go as planned. A delay normally ensues while I await new parts or tools, so hopefully someone else can benefit from my mistakes and bad luck!
All work carried out on a 1991 W126 300SE, which has the M103.981 engine (Mileage 92,000)
Inspired by ChrisFix painting a rocker cover -
I decided to give this a go, as my engine bay looks pretty tired.
It was 'ok' but I was not satisfied with the removal of paint by hand, and also that a shiny new rocker cover made everything else look even worse - especially the rusty old manifolds.
I decided that I would take off the battery tray, a known place for corrosion and trapping of leaves & dirt. Well, it is known now that I read Nik Greene's book
. Along with that, I would sandblast and respray the rocker cover, air cleaner cover, and the exhaust manifolds.
The manifolds looked a little daunting, but how hard can it be? I did plenty of research and ordered up the following parts:
Exhaust Manifold Gasket (103 142 14 80) x 5
Exhaust Manifold Gasket (103 142 13 80) x 1
Engine Studs (111 990 04 05) x 13
Hexagon Nut (120 142 00 72) x 13
Manifold to Downpipe Bolts (N304017 008053) x 4
Rivet Nut (000 990 25 52) x 4
Rivet Nut Tool (103 589 01 39 00) x 1
The manifolds sit on 13 studs that go into the head. There are 6 separate gaskets between the head and the manifolds. On each stud sits a hexagon nut with a flange, actually on receiving the new parts, one can see that they are not perfectly round. Turns out that they are called a 'prevailing torque nut'. Not sure on the ins and outs of this, so hopefully someone will chime in, but I expect it is to stop them rattling loose? The other end of the manifolds are bolted to the downpipes, and there is no gasket between the manifolds and downpipes. They are held in place by a long threaded bolt inserted from underneath, through a flange, through the manifold, and then into a rivet nut (a nut that has a square outer edge to prevent it turning against the manifold). A special tool is required to set the rivet nut in place, but more on this later.
I started by undoing the hex nuts holding the manifolds to the head. I believe the manifolds are made of cast iron, and was expecting them to be quite heavy, so my reasoning was that I could get a manifold off the engine while it was supported by its connection with the downpipe, then finally hold onto it with one hand while disconnecting it from the downpipe. I started with the larger manifold, nearest to the front of the car. No problem! It's possible to get a socket (12mm deep or semi-deep) on each of the 6 hex nuts. Because mine were corroded pretty badly, or maybe it is to be expected in all cases, the nut does not loosen off and make it's way back along the threaded stud. Instead, loosening the nut simply unscrews the stud from the head. Not an issue, as long as you have new studs and nuts to replace them with. Incidentally, I did not have plans to turn this into a 'how to' thread until after I encountered problems, so apologies for not having decent step-by-step photos.
Lossening the bolts that connect the downpipe is a real pain. There is not enough space to get a regular tool onto them from the top. I had a go at them with a 13mm crow's foot (actually a 1/2 inch crow's foot was a better fit) and an extension, but once I put the extension on, there was not enough room to get onto the bolt. In other words, my crow's foot was too short - yours may have a slightly bigger gap between the open end and the ratchet hole. I got my hands on a torque converter that I thought would do a better job (it's longer) and might also come in handy later when trying to torque the bolts back on. Incidently, the rivet nuts did not move on me, so it was 'simply' a case of unscrewing those bolts, to free up the manifold. With tiny movements and some patience, I eventually got them out. As it turned out the manifold was strongly wedged into the downpipe, even after the bolts were removed, so a sharp twist freed it up and off it came!
Note: I think the M103 on the W201 has some kind of sensor between, or attached to one of the manifolds, so you may need to look into this if you have a W201.
The rear manifold was another story altogether! Note that this manifold is smaller, but has an additional stud and nut at the rear, and a differently shaped gasket at that end. It is not possible to get a socket onto the nuts that run along the top. Oh dear. Hmmmm, ok I do have box ends! Off I went with a 12mm box end, and managed to free up all but one nut, which instead rounded off.
This was the situation I found myself in.
Oh, I covered up the holes with foil, just to stop anything getting there. And, that's the rocker cover with the dodgy paintwork. You can see tool marks all over the place, where the paint has already been damaged!
So, one nut has not moved, and got rounded by the box end spanner. There is another stud, with nut on, that has come out of the head, but cannot be removed due to a clearance issue. Not a problem, because it is definitely out of the head, and I'll worry about that once I get the manifold off the engine.
In hindsight, all of the fiasco that is about to follow could probably have been avoided if I had used a 6-point box end. In fact, even at this stage, with the nut slightly rounded, I may have been able to get a 6-point box end on there and still turned it. However, I didn't have one (or any patience) and instead asked for advice to remove a rounded off nut. The answers came back as a nut breaker or turbo sockets. Turbo sockets are out because there is no way to get a ratchet in there, but I did find a kind of box end turbo that I believed would do nicely. I also got a nut breaker just in case!
If only we could go back to this, I wonder if a 6-point would have gone on there! Probably.
How can this not be the most perfect tool for this job? Right???
By the time the removal tools showed up I had already tried heat, cold, soaking in penetrating fluid overnight, and lots and lots of swearing. But the damn thing never budged at all.
Yes, it does fit on there, and no I cannot get a box end onto it. But, I can fit an open ended spanner on there, which should be good enough. The problem is, turbo sockets, just like these things, need to be tapped into place to ensure they get a good bite on the offending nut. However, there was NO WAY IN HELL to tap the tool into place. I could press hard, I could hammer from the top (while the bottom slipped off, or vice versa) but I could not get the tool securely onto the nut. So, no matter how hard I pressed it on, once I started turning, it just turned itself right off the nut!!
Continues in chapter 2: The Nutcracker Suite.