Join Date: Jan 2012
Vehicle: R171 SLK 55AMG 2005
Other Toys: RUF SCR 1985; 930 Turbo 1985; MB 170V 1951; MB E500 W124 Ltd 1995; VW GTI 16V 1989; 928s 1982
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I have just conducted the spark plug change and found it relatively straight forward by comparison to many other vehicles.
Some of my learning's that may assist others contemplating this for the first time:
1. Pulled the original plugs after 61,000km and 15 years. No issues whatsoever with plugs being siezed - Mr Petricca who assembled the engine used a seating paste and it appears to have ensured no sticking issues. The electrodes were eroded and had about 30% life left in them with a discoloration of the insulator in the center of the plug - I replace with new as I doubt we will cover too much mileage over the next decade;
2. I found it simplest to unbolt the ignition boxes first and then lever the plug leads off each plug using the trusty 17mm open ring spanner. Exercise firm pressure and go slowly to avoid damage. Once the lead has been removed, flip the ignition box over onto a rag on the center manifold - prevents mixing up the reinstallation;
3. I used a simple plug socket onto a short extension bar. It takes a little time. I found that the rear-most plug on the right side as you face the engine was the biggest challenge due to the priximity of the heat-shield. Replacing the extension with universal joint knuckle from your socket set was the simplest way to extract the plug attached to the plug socket without running out of space;
4. I systematically replaced each plug complete and then torqued upto 20Nm which I found to perhaps be too much. I would not advocate any more torque than this, especially being an alloy block;
5. I did not apply any anti-sieze past as the NGK Iridium Plug is already coated with a plated lubricant to prevents galling of the plug threads....I will tell you in 5 years when the next change occurs but I am confident that the plugs are well hidden from direct moisture that would expose them to seizure from corrosion....I used to liberally wash engines and with greater informed wisdom, I have resorted to dry-cleaning engines to avert damage over the past years. The old plugs had no signs of moisture on top of them....note that this has been a dry-mileage weekend vehicle in temperate parts of Australia with no icing and road salt;
6. Once the plugs had been installed, I was sure to tidy up the tappet covers and general area and then clean the leads, ignition boxes and plug caps with CRC Electrical Cleaner. Once cleaned, I applied 303 Protectant which will provide high temperature detailing that will endure for a while whilst strapped to the engine;
7. I did not remove any of the plug leads from the ignition boxes as I have done with other German Vehicles (Porsche/VW), especially with Beru leads that it is very easy to damage the lead from attempting to remove the connector at the box...I found no problems with keeping the unit whole and flipping it over to remove and install the plugs. This saved time and provided consistent re-installation without having to refer to photos. Always take a picture of the work area prior to starting in case you need a reference...brain fade occurs so easily when mixing fatigue with OCD tendencies;
8. I did apply anti-seize to the bolts holding the ignition boxes to the tappet covers - this made reinstallation far simpler. I only torqued to less than 10Nm to avoid damaging the epoxy assembly;
9. Go carefully...if you drop any of your sockets, then the ramps have to come out and undercovers off to recover these tools. Consider doing it with an oil change to simplify recovery of dropped items...I dropped them three times and I have worked on many engines myself;
10. I found the a trick to locating and removing and reinstalling to save back strain. Once loosened to finger tight, face the engine from the front and reach in to remove or install. I found it was much simpler and saved loads of time and strain - one can balance your weight on the metal inlet manifold whilst working the plug with the other arm - easy and comfortable. Approaching from the side is best left for the work of the wrench and torque wrench.
Total time, doing it slowly was around two hours and this included cleaning stained tappet covers with the secret sauce...Autosol mixed with penetrating oil applied by scouring pad and removed with Brakleen soaked cloth and then coated with 303. The covers looked brand new again and really pop.
I would rate the task as being a satisfying/rewarding challenge for novice to build confidence and rather simple for those familiar with basic oil services. I found it a wonderful way to explore the engine and seating of elements....really well engineered power plant for simple servicing. Remember the better the tools, the easier the task.
Finally reward yourself with a good Shiraz after the test drive.