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Pelican Technical Article:

Engine Mount Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$100 to $300

Talent:

***

Tools:

16mm wrench, 13mm socket, extension, engine hoist, floor jack, jack stands, wheel chocks, safety glasses, torque wrench

Applicable Models:

Mercedes-Benz C350 (2008-14)
Mercedes-Benz GLK350 (2010-14)

Parts Required:

Engine mounts

Hot Tip:

Work on a cold engine

Performance Gain:

More power to the road

The engine mounts on a car are the direct mechanical connection holding the engine to the chassis. Almost all engine mounts have a rubber portion that allows a small amount of flex to reduce vibrations. If the engine was just directly bolted to the chassis, you would feel every vibration from the engine.

The rubber portion of the engine mount is particularly susceptible to failure due to the conditions of the engine bay. Heat and oil can take its toll on the mount, causing the rubber portion to crack and separate. When this happens, the mount collapses and no longer supports the engine correctly. Replacement is tough due to the very limited space on the C350. You should be prepared to spend more time than you think it is going to take. Sometimes the 16mm bolt on the top of the mount will line right up and screw straight in and other times you will find yourself raising and lowering the engine trying to get everything to line up. It will line up eventually. Just be prepared to spend the time on it. If you get frustrated walk away and come back later. Don't plan on doing this if you need to use the car in the next hour.

A simple way to test if the mounts are failing is to have a friend sit in your car while it is running. Place the car in drive, and with their foot firmly on the brake pedal apply a small amount of throttle. Then place the vehicle in reverse and do the same procedure. If you notice the engine having any large movements your mounts are in need of replacement.

You need to replace engine mounts in pairs, even if only one side is bad.

Begin by removing the front engine cover (red arrow) and two air ducts (yellow arrows).
Figure 1

Begin by removing the front engine cover (red arrow) and two air ducts (yellow arrows). While you do not technically need to remove the rear engine cover (yellow arrow) pull it off as well to give you more room. Please see our article on engine cover removal for additional assistance. You will also need to remove the under body engine trays to access the compressor; please see our article on under tray removal for further instructions.

Remove the drive belt by placing a 17mm socket on the tensioner and turning it counter clockwise until you can slip the belt off of the motor (red arrow).
Figure 2

Remove the drive belt by placing a 17mm socket on the tensioner and turning it counter clockwise until you can slip the belt off of the motor (red arrow). Use care not to pinch your fingers between the belt and tensioner.

This photo can be used to install the belt after the job; you can see where the belt travels around the alternator (red arrow), power steering pump (green arrow) and the A/C compressor (yellow arrow).
Figure 3

This photo can be used to install the belt after the job; you can see where the belt travels around the alternator (red arrow), power steering pump (green arrow) and the A/C compressor (yellow arrow).

Both engine mounts will be loosened from above and removed from below.
Figure 4

Both engine mounts will be loosened from above and removed from below. There is not a lot of room to access the 16mm bolt on the top of the mount. You cannot even see it directly and will need to work by feel (red arrows).

You can see some of the right side mount (red arrow) and how you can get a 16mm wrench on it (yellow arrow).
Figure 5

You can see some of the right side mount (red arrow) and how you can get a 16mm wrench on it (yellow arrow). Do yourself a huge favor and use a boxed end-ratcheting wrench. Getting onto the bolt is difficult enough. You have very little room to loosen so a boxed end-ratcheting wrench is the only way to go. There was not enough room for me to access the top of the mount on the left side so I had to move the A/C compressor out of the way while keeping the lines attached.

There are three bolts that hold the compressor to the engine and its mounts.
Figure 6

There are three bolts that hold the compressor to the engine and its mounts. The two front bolts go into the mount at an upward angle (red and yellow arrows). You will need to decide whether it is easier for you to remove the bolts working from above or below the compressor. Note: a lot of components have been removed for photographic purpose only; you do NOT need to remove anything other than what is described in the article.

The lower mounting bolt can be accessed from below (red arrow).
Figure 7

The lower mounting bolt can be accessed from below (red arrow). There is not a lot of room between it and the sway bar so you will have to take your time.

You can access the rear A/C compressor-mounting bolt by using an E12 socket with a wobbler or universal.
Figure 8

You can access the rear A/C compressor-mounting bolt by using an E12 socket with a wobbler or universal. Slip it between the tie rod boot and power steering lines (red arrow). You can now move the compressor and lines out of the way. Remove the bolt on the top of the left side mount.

Attach a chain to the center engine mount eye hole and lift the engine.
Figure 9

Attach a chain to the center engine mount eye hole and lift the engine. If you place a flat piece of wood between a jack and the oil pan you can also lift the motor that way. You are going to want to lift the engine as high as you can to give enough room to get the old mounts out but more importantly to install the new mounts. The new mounts will be taller than the old worn out mounts.

Make sure to check for clearance on all the lines while raising the motor.
Figure 10

Make sure to check for clearance on all the lines while raising the motor. You may need to disconnect some lines, like the hydraulic line bracket on the alternator (red arrow).

The mounts are attached to the sub-frame by two 16mm bolts that pass through openings in the sub-frame (red arrows).
Figure 11

The mounts are attached to the sub-frame by two 16mm bolts that pass through openings in the sub-frame (red arrows).

Use a 16mm socket with an extension (yellow arrow).
Figure 12

Use a 16mm socket with an extension (yellow arrow). Remove both bolts from the mount (red arrow). It's a tight fit but you can now remove the mounts from the sub-frame from underneath.

The new mounts will be taller than the old tired out mounts so you may need to raise the motor a little more when installing.
Figure 13

The new mounts will be taller than the old tired out mounts so you may need to raise the motor a little more when installing.

The anti-twist locks (red arrow) must sit in the cut outs in the engine mounts.
Figure 14

The anti-twist locks (red arrow) must sit in the cut outs in the engine mounts. Be prepared to raise and lower the engine to help get the top bolts started. It can be a bit of a pain to get things lined up and started while basically working by feel so take your time. Installation is the reverse of removal.


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