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FCP Euro Service Kits

FCP Euro Kits

I was recently asked if I would write an article on spark plugs and wires. Like tires, additives, cleaners, batteries, etc., we have so many choices and each with a claim to be the “best.” So just where do we begin to get the right product for our classic Mercedes?

The best place to start is at the beginning. What did Mercedes recommend when the 1975 450SL was on the road? The plug that was called for initially and would have been installed as original equipment with a points system, would have been a Bosch or Beru plug and wires.

From 1969 through 1975 the Mercedes 450SL’s with the D-Jetronic fuel system, would have come with a transistorized system or “TI” and referred to by Mercedes as the “Switch Gear” an early version of electronic ignition by Bosch.

Through the 1975 D-Jet era, the transistorized system or switch gear, was comprised of: ballast resistor, condenser, coil, non- resistor spark plugs, distributor cap, points, rotor and copper core wires and the switch gear box. This box is located on the left front fender (right if you are facing the car) near the headlamp assembly.

Should you be experiencing issues with performance, idle, etc., several things must be considered when checking things out. First and easiest thing to do, is to pull a few plugs on both sides. Here are the various conditions of plugs and what they tell you about the engine. The spark plug images were adopted from NGK.

If your plugs show anything other than normal (pre end of life), it is time to move on to whether or not you have the correct plugs for your system. Mercedes-Benz strongly disagrees with using a platinum tip plug and resistor type plug for the OEM setup. A great well priced plug for the D- Jetronic era “TI” system, are NON-resistor type plugs - NGK BP6ES. Be certain there is no “R” in the number. The “R” indicates it is a resistor type plug. The Mercedes-Benz owners manual states under “Spark Plugs” and I paraphrase, If you need information on spark plugs, contact your Mercedes-Benz dealer so it will not provide any further assistance.

If however you have or will install a 21st century electronic ignition, such as the Pertronix Ignitor No. 1885, you WILL use a resistor type plug. I use NGK BPR6ES. I am also using the standard Bosch coil, not the Flamethrower from Pertronix. This set up was relatively simple other than the modifications necessary to the unit fitment. It is NOT a plug and play process due to how the distributor and Pertronix are made. Again, this pertains specifically to the 1975 450SL. I am not certain when Bosch changed the distributor design for this not to be an issue. Pertronix does not “recommend” any of its units for a 1975 Mercedes 450SL as they can not warranty a modified product and they do not have and electronic ignition that is specifically designed for this car. I did inquire with Pertronix as to whether or not they would release a model specifically for the 450SL and was told, “most likely not, as the demand is not great enough.” Makes reasonable business sense.

MERCEDES 450SL WITH PERTRONIX IGNITION

In a later article I will address the installation process of a Pertronix Ignitor and some of the minor challenges you will face when converting the system, such as getting your tachometer to work and fitting the unit in the distributor. This conversion should last a life time.

MERCEDES 450SL SPARK PLUG WIRES

With regard to wires, Bosch is the way to go whether you have the OEM system or a new electronic ignition. Wires “wear out” becoming dry and the insolation degrades within the wire casing causing a “leaking” of the electricity. This “leaking” will cause erratic engine running and poor gas milage. I was told by a Mercedes technician that it is recommended for the wires to be changed out every 40,000 miles on average. If you are using your car as a weekend car, that replacement date would most likely be a couple of decades from now. The wires chosen for my 450SL, are the Bosch 09027, push on OEM style connectors. You may also opt for the screw on terminal type. Also check the wire holder that is on top of each valve cover to be sure wires are securely held in the proper place. TIP: Wires should be changed every 40,000 miles for optimal performance.

MERCEDES 450SL COIL

If your coil is more than 8 years old, it is recommend that it be changed out. While it will still carry enough charge to give you a nice jolt, it may not be enough and consistent enough to deliver the proper spark for excellent combustion. I chose a Bosch Ignition coil, No. 00027.

MERCEDES 450SL DISTRIBUTOR CAP & ROTOR

Two rather simple parts to replace are the cap and rotor. If however they are worn out, they will have a significant impact on the performance of your engine and fuel economy, as will all of the parts covered in this article. Quality replacement parts for this servicing are the Bosch 03120 distributor cap and the Bosch 04018, rotor. TIP: Cap and rotor should be replaced every 40,000 miles.

IN THE END

When doing any work on your electrical system or any system for that matter, it is always important to evaluate all components of the system. Be sure all wiring is intact, not cracked, brittle etc. Check your ballast resistors for cracking and replace with exact and proper part number. Should the Switch Gear be disconnected, never leave lose wires hanging. Properly cap and secure. Don’t ignore lose or broken wires. The risk of fire is too great!

The image shows many of the items that may be needed, or should be checked for wear or damage.

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Written by :
West Kenyon

West Kenyon is a Multi-Media Design Consultant and automotive enthusiast. Cars in his collection include a 1956 Austin FX3-D, better known as a London Taxi, a 1965 Rolls-Royce Phantom V, and a 1975 450SL and 1981 240D by none other than Mercedes-Benz. West said, “owning one or a number of vintage cars is often an expensive proposition", which is why he does the majority of mechanical and interior work/restoration himself. West added, “not only does it save a significant amount of money to do the work yourself, it also provides full opportunity to know the job is being done with excellence and allows for an unprecedented appreciation and knowledge of the car.” For FCPEuro, West will focus on providing in-depth information on both the Mercedes-Benz R107, 450SL, D-Jetronic version and the W123, 240D. Glücklich Autofahren! (Happy Motoring)


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