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      11-22-2012, 01:33 PM   #16
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Drives: 2007 Z4 Roadster 3.0i
Join Date: Aug 2012
Location: North Carolina

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Originally Posted by 3point0 View Post
I searched for a Z4-specific how-to on replacing spark plugs but couldn't find one, so after reading several threads on various other BMW forums for other engines I decided to give it a go and record the procedure. I'm new to DIY maintenance so please point out any errors or omissions I may have made. This is just a set of directions, you embark on this venture at your own risk and I'm not responsible if something goes wrong on your endeavour.

Tools required, see photo:
# 1 - 6 x new spark plugs. I bought Bosch Platinum +4 (part # 18-3750-6) from Canadian Tire $17 for 2.
# 2 - small flat bladed screwdriver for removing engine cover plugs.
# 3 - ratchet, mine's a 3'8" drive
# 4 - 10mm socket for engine cover nuts (plus adapter for ratchet if needed)
# 5 - 5/8" spark plug socket (not just a regular 5/8" socket, explained later)
# 6 - drive extension
# 7 - finger driver - optional - saves having to remove struts bars
# 8 - anti seize compound - highly recommend you use some
# 9 - calipers - optional - just to check diameters
# 10 - torque wrench - optional - covered later

Step 1: remove the engine cover

Pop the hood and peer in at the wonder of germanic engineering that lies beneath.
Once you've recovered from the resulting emotional upwelling, we start by removing the engine cover.
I have installed a strut bar on my car so I have to remove it first, if you have one do the same, if not skip to the next picture.

We only have to remove the cover on the left side of the engine.
We'll be removing two nuts hidden under little plugs and we'll also have to remove the oil cap temporarily.

There are two small covers that need to be pried off, circled in red above.
Use the small flat blade screwdriver to gently pry the cover off:

Next you'll need the 10mm socket to unscrew the nuts that are behind the previously removed covers. Keep unscrewing these all the way and pull the nuts out of the hole they sit in.

Do this for both of the plugs and nuts.
Next unscrew the oil cap and set it aside.
You can now lift off the engine cover and place it somewhere where it won't get scratched.
There are 4 little rubber pads attached to the edge of the cover, make sure you don't loose them.
Replace the oil cap before moving on.

Step 2 - Remove the Ignition Coils

You'll now be able to see the 6 injection coils.
Each coil needs to be unplugged first.
The plastic cap at the top of each coil swings upwards and ejects the plug from the connector. See this TIS page for more (or less) info.
The coils just pull out but they are quite stiff, so pull hard and don't hit yourself in the face when they come loose.
Start at one end and work your way to the other end.

I layed the coils out on a piece of card numbered from 1 to 6 so I could keep track of any potential issues as I pulled them out, and to be able to put each one back where it came from. It shouldn't make any difference but I always do things that way.

Step 3 - pull the old plugs out

If you look down into the chamber the coils came out of, you'll see the end of the spark plug.

The reason you use a spark plug socket and not a just a regular socket is two-fold. The socket has a little rubber liner at the back which grabs the end of the plug allowing you to pull (or insert) it into a deep chamber such as this. The spark plug socket is also long preventing damage to the spark plug itself.

Use your drive extender to reach the plug with the socket and push it down on the plug. You'll feel it engage. Lefty loosy (counter-clockwise) to take it out.
I won't get into a discussion here about inspecting the end of the old plug and what you can learn from it.

All six plugs and ignition coils laid out in the order they came out.

Before moving on, it's a good idea to verify that the new plugs are indeed the same thread size as the old ones, just in case you bought the wrong ones. This is where you use the calipers to check diameter on both threads.
Old plug on left, new on right.

If they match, I then check the thread pitch by placing one over the other and making sure the threads match fully, which they do.
If either of these, diameter OR pitch don't match, STOP, you've got the wrong plugs. You'll only destroy something very expensive if you try to continue.

Step 4 - Put new plugs in

I use anti seize compound on the threads to prevent problems getting the plugs out next time. The previous plug changer didn't do this on my car and I was lucky to not have anything seized.
Anti-seize compound is available in stick form and in paint-on form. The guys at work call the stuff "cancer" (I know, I know, bad taste), once you get some on you, it spreads everywhere.
The stick style is much more manageable and less likely to make a mess.
Rub (or paint) some on around the thread in several spots.
Go sparingly, it goes a long way, provided you spread it around well enough.

With the stick kind you'll want to wipe it into the threads so you don't have bits falling off everywhere.

You're now ready to start putting the plugs back in. Starting at one end of the block, we'll put the new plugs in.
Use the socket and drive extender, but don't use the ratchet to start with. Do it by hand.
Carefully insert the plug into the socket and lower it down into the engine chamber until it rests on the top thread.
Rotate the plug gently counter-clockwise until you feel a slight step. This helps ensure you don't cross-thread the plug into the block.
Now you can start tightening it clockwise until it is hand tight.

Everyone has different hand strength so this is where the torque wrench comes in. If you're comfortable gauging the torque you apply then continue without the torque wrench. I have a pretty good feel of what the recommended torque of 21 ft.lbs feels like, partly because my ratchet is 12" and I know how much 21 lbs feels like and I do stuff like this at work quite often. There's a widely accepted method of tightening the plug hand-tight and then doing half a turn with the ratchet. Some manufacturers even put these instructions on the packaging apparently. If unsure, use a torque wrench or torque limiting bar.

One note - when you put the plug back in and are ready to pull your ratchet out, it may disconnect at the socket if that connection isn't the locking ball type. At first I was a little worried, thinking I'd have to pull the socket out with needle nose pliers, but you can just pull the whole lot out in one go if you twist the extension slightly as you pull up. Took me a couple tries to figure it out.

Step 5 - Replace the Ignition Coils

In the above picture you can see where I've already replaced the ignition coil on one of the plugs. Just make sure you seat the rubber skirt the right way around and get it all the way down. It kinda clicks into place. Then reconnect the cables. Make sure the connector is flipped all the way up before inserting the cable plug. push it into place and snap the connector shut. We're nearly there...

Step 6 - Put the engine cover back on

This is the exact reverse of the removal. I put anti seize compound on the studs just because. Don't forget to remove the oil cap and to then replace it.

Step 7 - pat yourself on the back and admire your handiwork

Now put the money that you saved on labour into your beer or your mod fund

Let me know if I missed anything
Great job!!!!!!!!!!!