I've been quoted $350 to change my plugs and wires (labor only). I already bought the plugs and wires.

From looking at videos and reading, this job could be a bear. I am nervous about removing the motor mount to gain more access as some recommend.

Is this job really that hard and worth the $350?

Thanks

 

It's a pretty easy DIY, the wrench to pull plug wires is an absolute necessity. No need to mess with motor mounts.

 

The mercedessource video is a great one to watch. Not on a clk, but m113 motor.

 

you can do it and save the 350 just take your time

 

Thanks for the advice. Ordered the wrench. Will attempt this weekend.

 

A qualified MB mechanic (not a chain store mechanic) can change the spark plugs in one hour.

With the right tools and mindset, it's no more than a medium difficulty DIY level job.

You do not have to lift the engine, one side at a time, by removing the associated motor mount bolt. Additionally, the M112 engine in our CLK320, has a bit more more wiggle room.

You'll find some good tips in this video.


Some additional suggestions are:

-Raise the hood up the full service position (e.g. to full vertical) for improved access to the rear plugs.

-You'll need a T30 Torx bit to unfasten the coils. The pair of plugs per cylinder fire in a prescribed sequence. To reinstall the wires in the right order, for each cylinder, you'll find various letters on the coil packs and boots with the proper inter-connections coded on the value cover. Before removing the spark plug boots, it's a lot less confusing and faster to just mark the wire for each forward plug, for each cylinder, with a piece of tape, dab of paint etc.

-The special 17mm offset boot removal is key. In addition to quickly and safely removing the boots, the boots have a strong seal and it can also be used, if additional leverage is needed, to fully install the boots on the new plugs. Before removing the plugs, I used a can of compressed air to blow out any debris in the area.

-You'll need a 3/8" ratchet and a good assortment of extensions to access the plugs. The MB recommended spark plug replacement interval is 5 years or 100,000 miles, whichever comes first. If this has been exceeded, you might find it difficult to get a plug to break free. In this case, a 1/2" ratchet with extensions and/or 1/2" to 3/8" adapter might be helpful.

-It's very easy to cross thread a plug into aluminum heads. The above video describes an excellent method to avoid the resulting heartache and $$$$$. I used various pieces of gas line hose to make sure the plugs start and turn smoothly. To simulate finger force, the hose should only fit onto the plugs metal tip.

-Likewise, it's also easy to strip the threads in an aluminum head by over tightening. The new plugs must be properly torqued to 28 NM or 21 ft.lbs. If you don't have a torque wrench, just turn the plugs until snug and then continue turning an additional 90 degrees. The procedure is as suggested by Bosch, for tightening plugs with flat seals, which are the type used in our M112 and M113 engines. Other engines you might encounter may specify plugs with conical seals, in which case, they should only be tightened an additional 30 degrees.

-Use caution when working around any can crankcase breather piping. With age, they become fragile and easy break.

As others have suggested, take you time. Pick a day when you're of the right frame of mind and not rushed for time. You should be able to complete the task in 2 - 3 hours.

Did I mention having a 6 pack of beer on hand too (but only to celebrate a job well done)?

 

Did the job this afternoon. 2-3 hours max. Thanks for the all the advice. Wasn't close to my hardest DIY. No removing motor mounts. No lifting the engine for more room. Was able to access plugs and wires by removing air-box and washer fluid reservoir. Mercedes tool is a must. Got one for sale if anyone wants to try this DIY. I do not plan to ever change the plugs again.

 

did you check the gap on the plugs?

 

I did not. Read that they come pre-gapped. Please tell me that it is so. I DO NOT want to go back in there.

Car is running fine.

Gap on old plugs looked similar to new ones.

 

They'll be fine.

 

Good job, 33!

 

The only time its not a fun DIY is if you pull threads out of the holes. Not sure if Mercedes uses inserts from the factory or not?