How Many Spark Plugs Do I Need?
Unlike the old smart 450 and the Roadster, the 451 smart fortwo only takes 3 spark plugs.
That means it's half the job it used to be and I'm glad of that too.
What Plugs Do I need?
Standard plugs are XU22HDR9 but smart have also been supplying NGK LKR7B9.
Either of these will be supplied if you go to smart with the part number A1321590103.
Site reader Neil S has told us that the NGK plugs seem to give better performance than
the standard factory fitted Denso spark plugs so ask at you dealer to see what they stock.
The only Performance spark plugs available are the Denso Iridium IXUH22. These plugs are
hard to find in Europe but they are available from SmartMods but they only have limited stock.
If you reside in the Americas then head over to SmartMadness for your Denso plugs.
The performance Denso IXUH22 plugs are the plugs being fitted in this guide but
fitting is the same for all other spark plugs mentioned above.
The 451 spark plug specs can be found here.
Fitting The Spark Plugs
These are the plugs being fitted, the IXUH22 supplied by SmartMods.
Remove the engine hatch to reveal the engine. Find the dipstick (yellow in the picture below).
Just below the dipstick are 3 direct coil packs, 1 for each cylinder.
Using a 10mm socket and a ratchet, remove the 3 bolts circled in blue below.
Disconnect the wiring connector to each direct coil pack.
Push the rear of the tab and pull the connector free. Don't pull by the wires.
Pull the direct coil packs out of the engine.
This is what the direct coil pack looks like when removed.
You will need a 10mm spark plug removal socket and an extension bar as close
to the length of the direct coil pack as possible. You need the spark plug tool
specifically and not just a deep 16mm socket because it has a rubber insert that
grips the spark plug so you can remove it from the engine.The plugs are so deep
in the engine that you can't physically get your fingers to them to pull the plugs out.
Place the spark plug remover socket and the extension bar into the hole and
then push the ratchet onto the extension. You simply don't have the room to
position it all if the ratchet is fully assembled with the socket.
Undo the spark plug in an anti (counter) clockwise direction. You may find that
removing the oil cap and the dipstick gives you more room to swing the ratchet.
This is the extension bar, spark plug socket and spark plug removed.
This is where I nearly got caught out. The spark plug socket grips the spark plug
so the plug can be removed from the deep hole in the engine. The problem is that
when you use it to tighten the new spark plugs it doesn't want to let go,
when you pull, the extension comes out but leaves the socket firmly attached
to the top of the spark plug. Because of the depth and access, there is no way to get
the spark plug socket out. Below you can see the rubber insert that grips the spark plug.
So, if you don't have a deep 16mm socket you will have to push the rubber insert out of the
spark plug socket. I used an allen key but a screwdriver will work, mind your hands.
I think the spark plug socket I used was just cheap rubbish which is why it wasn't very good.
I have since used a better quality spark plug socket and it let go of the plug when I wanted.
Floyd has mentioned that you can buy magnetic spark plug sockets which would be better.
The 2nd time I fitted plugs to a 451 I tried a new idea. I wrapped electrical tape into the socket.
This gave the socket a tighter grip on the spark plug after removing the rubber insert.
Here are the 3 plugs, slip off the thread's protective sheath, apply copper grease to the threads if you wish (see more info on this later) and carefully slide one down each hole.
A nice tip for this was to use a short length of garden hose. The plug pushes nicely into the end and you can lower the plug into the hole, twist the hose to screw the plug in and pull the hose out.
Place the modified spark plug socket or deep 16mm socket on the extension bar and tighten.
Tighten the spark plugs down using 1 of the preferred methods (see further down the page).
Slide the direct coil packs back into place, refit and tighten the bolts.
Unlike HT leads, there is no resistance when they connect to the spark plug as they
don't clip around the tip of the spark plug. The direct coil pack makes contact with the
spark plug with a soft spring which creates constant pressure connection.
Plug the connections back into the direct coil packs, refit the oil cap and dipstick (if removed)
Replace the engine cover and you are done. Start the car to make sure it sounds OK.
The torque figure for the 451 spark plugs is 18Nm but this is for a non greased thread.
If you use copper grease on the threads you may want to use a different method.
The 18Nm torque figure is the same for new and reused spark plugs.
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.
10mm Spark Plug Removal Socket
The designated size for the spark plug removal socket is an odd one. The socket will claim
10mm on it but it is actually a 16mm socket. It also doesn't relate to the thread of the
spark plug as in this case they are 12mm (M12). The 10mm actually relates to the diameter
of the ceramic part of the spark plug that the socket grips hold of.
The socket has a rubber insert that holds the plug when the socket is pushed over it, this
allows you to remove spark plugs from deep recesses and lower new plugs in carefully.
Buy Your Denso IXUH22 Plugs
United Kingdom & Europe
United States of America
By printing this document I state I have read and understood this disclaimer