s50 engine [M roadster] spark plug change, DIY, guide

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Joined: Sun 10 Jun, 2012 09:26
Posts: 393

  M roadster S50

s50 engine [M roadster] spark plug change, DIY, guide

Post by chrisp_1 » Wed 04 Jul, 2012 12:27

1/ Lift bonnet :roll:.

2/ Remove 4 x chrome bolts [Allen-key headed bolts] from the ignition coil cover [the bit that has M-Power written on top of it] and set bolts/allen key aside.
image courtesy of Shantybeater [lifted from his post on identifying s50 / s54 engines]

3/ Working from drivers wing get your finger nails under the bottom lip of the ignition cover and pull it up off the engine and slide out in the general direction of the drivers headlight and set aside.

Mine was a bit tight to wiggle out due to the large rubber grommet on the bottom left of the ignition cover [rear of engine bay] which houses the ignition coil wires. As seen here now the cover is off.

4/You will now be looking at your six coil packs, each with a separate plug with wires running down the engine [in a cable holder] to the aforementioned large rubber grommet at the rear. First 4 seen below.

If your reading this guide to help you do this task I'd suggest you start from the front of the car (coil 1 of 6) as I did, and work toward the back - the basics will thus become familiar and disassembling things to make changing number 6 in particular when you get there will seem less daunting this way.

Firstly, you need to remove the ignition coil starting with the electrical connection [plug]. Using your fingers pull the securing clip for the plug directly upwards like this,

and slide the plug off the coil towards you like this.

5/ Take your 10mm short socket and 1/4" drive wrench and undo the two nuts holding on coil 1 like this.

Mine were very tight to get off but there is no need for them to be fastened on that tight, the nuts are just to secure thing as opposed to structural. TAKE CARE NOT TO DROP A NUT BY USING FINGERS TO REMOVE FROM LAST FEW THREADS.

6/ Using your fingers reach uderneath the black body of the coil and apply gentle upwards pressure to lift out like this.

You should feel a slight pop as it dislocates from the spark plug below but it doesn't take much force - DONT BE TEMPTED TO USE THE ELECTRIC CONNECTOR TO LEVER THE COIL OUT AND IF POSSIBLE AVOID USING TOOLS OTHER THAN SPECIAL BMW ONES [BUT YOU DO NOT NEED ANY].

7/ Take your spark plug socket [16mm I believe] and 1/2" drive with extension piece and insert down the hole and locate onto the spark plug. Turning anti-clockwise on a standard thread remove the plug - it may feel a little stiff at first but shouldn't be too difficult to remove

If its seized don't be too heavy handed and snap the spark plug off or your due a trip to the garage, just squirt a little penetrating spray and give it 5 mins and try again. If the thread feels rough [juddering when unscrewing] there's likely a little corrosion on the threads and in this case a small amount of copper-slip grease on the new spark plug thread can be used to lubricate [I don't use as a matter of course but some do].

8/ Insert your new plug in to the spark plug socket, remove your wrench and insert the plug into the cyclinder head by hand using the extension bar like this.


9/ Now replace your wrench onto the extension bar at 12 O clock like this to act as a reference for tightening the plug.

Check the back of the spark plug box to see how much you need to tighten the plugs from here [assuming you managed to hand thread it right upto the compression washer]. My plugs NGK's indicated 1/2 turn to fully compress so I opted for a third of a turn minimum until resitance was felt - here's the wrench in the tightened position.

10/ Replace your coil by hand and locate it onto the spark plug and the threaded shafts for the securing nuts - you will feel a small 'click' as it locates onto the plug.

11/ Reattach the ignition wire [coil] plug,

and push down on the securing latch.

12/ Re-fit the 10mm securing nuts x2 by hand and then nip up with your 1/4" drive but don't overtighten.

Thats coil/plug [cyclinder] 1 done, SIMPLY REPEAT STEPS 4-14 for plugs 2, 3, 4, 5 before we look at #6 which requires a little extra effort as detailed below.

Now we have changed plugs on cylinders 1-5 it is time to make room to access plug 6.

13/ Remove 2x 10mm nuts securing all of the ignition wire in their plastic housing, 1 by my finger and 1 in bottom right of picture (nuts shown removed)

14/ Remove 2 x phillips screw holding the wiring housing which runs along rear of engine compartment - these screws and the nuts from step 13 are pictures on my windscreen surround.

Also push down the two plastic clips out of the same black bracket pictured [1 just behind each screw] which hold up the pipe running along the back of the housing and let them hang with the pipe. Now place something [such as the box which I used] between the windscreen surround and the housing/pipe - the aim is to bring it forwards in the engine compartment to create some room.

15/ Pull the wiring loom running from the housing toward the brake master cyclinder up out of its locating position, the rubber grommet stays on the loom

16/ Now free the same loom and the one behind it from behind the master cyclinder, you may or may not need to remove a cable tie with some snippers - a new cable tie will be easily installed later.

17/ You can now put your 1/4" drive through the wiring we have free up down onto the 10mm nuts securing the 6th coil.

18/ Unplug the electrical connector for the 6th coil [YOU MAY NEED TO LIFT UP THE IGNITION COIL CABLE HOLDER THAT RUNS ALONG THE ENGINE TO DO THIS HENCE WHY WE REMOVED THE SECURING NUTS EARLIER :wink: pictured again here it's the plastic strip hiding the wires where the coil plugs come out from - it just lifts off and to make it easier I unplugged each coil plug again temporarily.

19/ Pull up on the large grommet securing the ignition wires at the back of the engine and bring forward as shown.

20/ Remove coil as shown.

21/ Attach your 1/2" drive and spark plug socket as shown to the 6th plug and use a wratchet to remove it and replace with a new one as before.

22/ Replace 6th coil.

23/ Replace the large grommet securing the ignition wires at the back of the engine removed in step 19.

24/ Replace the ignition wire plugs onto their respective coils and secure their locking mechanisms.

25/ Replace the ignition coil wires housing if you moved as suggested in step 18.

26/ Replace ignition coil cover whilst everything is loose above it.

27/ Replace cable tie and reinsert wiring loom behind master cylinder and grommet into housing all as pictured.

28/ Remove the box and replace pipe clips and screws as pictured.

Now have a look around and make sure you didn't forget anything - of course not :lol: and make sure your engine still starts ok - mine did :D

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Joined: Mon 19 Jul, 2010 16:08
Posts: 73

  Z3 roadster 3.0i
Location: Whitwick

Re: s50 engine [M roadster] spark plug change, DIY, guide

Post by weedram » Wed 04 Jul, 2012 14:33

Whilst I have no intention of DIY replacing my spark plugs l have to applaud chrisp_1 for a very informative and comprehensive article. Do you work Haynes?

The forum never fails to amaze me with the information that's available. Keep up the good work
One Life - Zed it

Joined: Thu 13 May, 2010 18:14
Posts: 1866

  M roadster S50
Location: Mossley

Re: s50 engine [M roadster] spark plug change, DIY, guide

Post by swamper » Wed 04 Jul, 2012 17:49

that a very good wright up....thanks
the badness makes me do it...!


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Joined: Sun 28 Oct, 2007 19:46
Posts: 422

  M roadster S52
Location: Cheshire

Re: s50 engine [M roadster] spark plug change, DIY, guide

Post by offyourmarks » Wed 04 Jul, 2012 20:22

Great write up :)

Would be an ideal time to do a compression test at this point just to make sure all is well

Joined: Sun 10 Jun, 2012 09:26
Posts: 393

  M roadster S50

Re: s50 engine [M roadster] spark plug change, DIY, guide

Post by chrisp_1 » Wed 04 Jul, 2012 23:08

Thanks for the comments,...

I'd been thinking that I should contribute something and lo and behold I couldn't find a guide on the net for doing this relatively easy task = et voila :pc


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