Mod Filter


for all your modding needs, recommended by Evilution

Roadster Spark Plug Change

Mod Description
The Roadster engine is almost identical to the Fortwo engine so the sparkplug changing guide is the same. What does differ is the access. Here is a quick way.
Mod Details
PremiumNo Difficulty Mod ID475 CreditFerrina Cost£ï¿½5 For452 Roadster Link Copy to Clipboard

Removing the rear panels of a Fortwo is easy, removing the rear panels of a Roadster is a bit more of a pain so here is a far easier way of doing it. Thanks to Ferrina for the information.

What Spark Plugs Do I Need?

For the Roadster there are 2 options for standard plugs
6x NGK R LKR8A (OEM fitted).
6x NGK R LKR8AP (Platinum) – thanks Neil.

Upper Plugs

You’ll need an HT lead remover. The one you can buy from smart is cheap but alright. They sometimes take a bit of bending and reshaping to make them perfect though.

Smart part number A 638 581 02 67

If you want a better quality tool, go and buy a Hazet 1849-9, Hazet 1849-6 or the budget Sealey.

Remove the top spark plug HT leads. Don’t pull them by the wires. Use the proper tool.

Here you can see how the HT lead remover works. It has tabs that fit under a ridge in the sparkplug connector.

With all 3 plugs pulled off of the sparkplugs, fold them back out of the way.

Use a spark plug socket on a ratchet to remove them from the engine. (anti-clockwise).

Lower Plugs – Hidden Access

The lower set are the same as before but we are going to cheat on the access.

Run a pencil line around the outside edge of the number plate on the right side as you look at it.

Then remove rear number plate.

Using an electric drill and a 50mm hole cutter (I used one which is used for making stair banister post holes), carefully cut out three holes 10mm inside the pencil line as shown below.

If you want to be more accurate and you are using a 50mm hole cutter, measure up 35mm from the pencil line.
The hole centres from the right hand line are, 50mm, 110mm, 170mm.

You will see from the next picture that the tolerances aren’t particularly tight so don’t be too worried about getting this spot on.

With a very long HT lead remover, a long extension piece, rachet and a universal joint, the spark plugs can be removed with very little hassle and replaced with the panel still in situ.

The smart’s own HT lead remover is rubbish. The better the quality HT lead remover and spark plug socket with a universal joint, the easier this job will be. However, you will find that normal HT lead remover tools are too short.

If you are handy with a welder, you can lengthen the tool. Or you can make the tool from a metal tube. I’ll add that info soon.

To remove the spark plugs, you’ll need a 16mm spark plug socket and at least 45cm of socket extensions. (thanks Harry H).

You don’t have to be that precise though. As long as there’s enough plastic to screw the number plate to, you could do this. Then you’ll have room to reach in with the HT lead tool.

If you space the numberplate a little, it’ll increase air flow through the engine bay.

Spark Plug Replacement

If you wish, apply a small amount of copper grease to the thread (read more at the end).

Change the plugs and torque to:
For 698cc cars, NGK R LKR8A (New & Used) 22.5 Nm

Do not over-tighten!

Replace the caps. After sliding them on, a gentle tap may be needed to fully seat them. I used a long screwdriver and placed the tip on top of the plug lead ears. A light tap with the hand is all that’s needed to settle the cap onto the plug properly.

All tight? Plug leads on? Press the leads into the slots on the engine to secure them. Replace engine cover. These were my plugs.

The middle lower plug threads were covered in oily rubbish. This was caused by the last service not being done properly and the plug being loose and leaking slightly. (Full Mercedes history when the car was bought)!

Copper Grease, Yes Or No?

This topic came to my attention during a conversation with a mechanic. Personally I have always added a dab of copper grease to my spark plug threads ever since shearing a plug in half trying to remove a plug from a fiesta. Fixing that sort of mess takes time and money.

The argument put forward was that lubricating the thread reduced the thread friction when fitting meaning that the plug will turn further before reaching the correct torque figure. Using the correct values when torquing (quite low figures) means it’s unlikely to seize in place so in theory you would not require any copper grease on the thread.

An extension to the argument was to use copper grease but to forget the torquing. Instead, the idea is to finger tighten as tight as you can then use the ratchet to give half a turn. This is enough to squash the fire seal ring and is often recommended by manufacturers.

There is no right or wrong answer to this, go with what you’d prefer. An additional idea is to loosen the spark plugs and retighten every service where you don’t change the spark plugs. It just reduces the chance of the threads seizing.

Extra Bonuses

Apart from the obvious time it saves, doing this mod has a few extra bonuses. You can:

  • inspect the turbo studs
  • view the upstream lambda sensor
  • inspect the TIK pipe
  • check the turbo
  • view the back section of the engine

Additional Modification

Ferrina rightly points out that if the 50mm holes continued all the way along, top and bottom, the number plate could be slightly spaced out from holed panel. This would act as a vent and would allow hot air from the engine and the exhaust to escape the engine bay.