I replaced the right (Passenger) engine mount on my M113, CLK 500 model 2005. The left looks to be more difficult as there is even less room. I could not have done the job without a ratcheting 5/8" box wrench. That wrench is usable in replacement for the 16 mm combination wrench you will use to loosen the upper bolt on the mount. Do not waste your time removing the plastic shield inside the wheel well. Removal will not give you a better view or better access to the engine mount. The mount is behind the solid metal of the wheel well. You do not have to drop the exhaust pipe, though doing so would give you a little more room to access the mount and turn your wrench. I spent all of Saturday getting the old mount out and half of Sunday getting the new mount installed and everything else back in its proper place and road worthy.

1) You will be working around the starter, so disconnect the battery so you don't have sparks flying.
2) Jack the front up and get it on solid blocks; remove both of the under engine pans/plastic shields.
3) Loosen both of the sway bar bushing brackets, then remove the sway bar from the right wheel. Then remove the right sway bar bracket. This will give you the room you need to get the engine mount removed and the new one installed.
4) Raise the hood all the way up; remove the air box engine cover and place your lifting chains on the engine.
5) Back under the car loosen both the left and right engine mount bolts from the bottom of the mounts. Do not remove the left bolt just give your self about 3/8" slack so when you lift the engine the left mount can ride up some but not become disengaged from the frame. I did this thinking the realignment on the right mount would be easier if the left mount remained in its place.
6) Now you loosen the top bolt of the right mount. I did not have the physical strength to break that bolt loose. You are working on your back under the car with your hands up between the exhaust and catalytic converter near the starter. It is tight and difficult. I could not find a way to work from above, or from the front end of the car. The design of the metal heat shield around the engine mount forced me to work from the rear in the space near the catalytic converter. Here is where I was lucky to have the ratcheting 5/8" wrench. I got it onto the top bolt and then using a pry bar through the other end of the wrench I was able to leverage with the pry bar against the engine block and got that top bolt broke loose. But that was only half the story. It took at least one hour to get that bolt completely backed out. I could not move it with just my finger tips until it had only two turns left on it. Maybe because the old mount was broke at the top rubber, but I had to use a wrench for damn near the enter removal and you can only get about 15 degrees turn without before removing and resetting the box end of your 16 mm wrench to turn in the confined space. Because the mount sits at an angle I had difficulty using the open end, because it is straight on the wrench, whereas the boxed end is angled and that allowed me to get the wrench on to the top of the bolt and make the 15 degree turn. THIS WAS NOT FUN! Patience required!! NOTE: This top bolt will not come completely out. It is too long to be removed from the arm of the engine mount support. The top of the bolt hits the exhaust manifold, but it will clear the top of the engine mount when you get it raised as high as you can get it. This top bolt also retains the metal heat shield in its place.
7) Now you can completely remove the bottom bolt from the engine mount, raise the engine (carefully) with a hoist. I found it useful to get a second jack under the right side of the engine and with the use of a piece of small wood to spread the load I continued to raise the right side of the engine from the mount of the alternator. NOT THE ALTERNATER! The area where the bolt holds the alternator to the block. There is an area where you can safely raise the engine a bit higher with a jack. That was the trick for me to get the necessary room to remove and install a new engine mount. The limiting factor for how high to move the engine seems to be the lower radiator hose. You will get that hose pretty tight. I was concerned also with the rear of the engine at the firewall, but that seems to be OK.
8) The new engine mount will go in with a new teflon heat shield; Though I think the old one would have been reusable. To get the new mount in place you must be sure that top bolt is raised out of the way. I used a wadded up Scotch Brite pad between the metal heat shield and the support arm to wedge that bolt up and out of the way. There is a pin that sticks up on the top of the engine mount. It positions the teflon heat shield and the mount itself to the engine mounting arm, so be sure you have it aligned properly! Also on the bottom of the mount there are four indents, two will match raised edges on the cars frame. (See the pictures) All these must be aligned. I did this by very slowly, about 1/16 of an inch at a time, lower the jack that was at the alternator attachment and then move the mount by hand to check its placement in relationship to the previous mentioned alignment points.
9) Now you get to start that top bolt into the engine mount. I did this while there was still some play in the engine mount when lowering the engine into position. I was also able to get most of that bolt threaded down into position by hand. Before placing all the weight of the engine on the mount get your lower bolt started as well. Everything should be lined up. Remove the jack from the alternator area and tighten that top bolt.
10) Lower your engine hoist and tighten both the right and left engine mounts bottom bolts.
11) Reinstall the sway bar at the wheel and tighten. You will find it makes it easy to reinstall the sway bar brackets by jacking the right wheel up. It will force the bushing into its proper place and you can position the bracket and tighten it. Also retighten the left sway bar bracket.
12) Reinstall both of the under engine plastic shields: remove the blocks from under the car.
13) Reconnect the battery.

That's how I did it. If you have a better system please let us all know as this was not fun. There is a lot of crawling under from the front then reposition to the rear; then get up and do something from the top. Then down again.

 

Good job and nice write-up! I do think this is much easier with the exhaust removed. That's not really a big job, either. Disconnect the O2 sensor wiring harnesses, remove the bolts to the manifold, the support bracket under the transmission pan, and the union just behind the Y pipe. Just be prepared and have it supported because it is heavy.

 

Is this still a DIY when you need a lifting chain Hahah.. not something I'll be doing.

 

That is funny considering your user name!

 

I am considering changing engine mounts on a '03 SL500 (R230), and my preferred approach is dropping the exhaust. Some say that is an easy job? I do plan to use anti-seize compound when replacing bolts, but are there any gaskets or sealers needed? Thank you everyone for sharing their knowledge.

 

I have not had problems when reusing the large donut gaskets on the exhaust pipe joints, but going new never hurts if you don't mind spending a few dollars and the time to be sure you have the correct size replacements. I think using new bolts and nuts on the exhaust system is a good plan. The engine mounts can use the same bolts as they are not subject to the exposure that the exhaust system gets. On the M113 W209 the upper bolt on the engine mount will not come out as it hits the exhaust manifold. See my write up above for a better explanation.
GOOD LUCK.

 

I sprayed some WD40 on the bolts about 15 minutes before trying to remove them and mine came right out with very little effort. I was going to clean the threads with a wire brush afterward, but they really looked pretty good.

 

Is there a place under the engine to lift the engine with a floor jack instead of using a hoist?

 

You can lift from the oil pan, just pad the pan with a wide board to spread the load. Be gentle.