I Done Me Spark Plugs. #DIY

Last weekend I traveled up north to my hometown in Northland, in the North Island in the Southern Hemisphere. I had my tools up in my parents garage, and my car had been running a bit inefficiently so I figured it was time for some new spark plugs.
I’m not an expert on spark plugs and never planned on writing about how to replace spark plugs or what to look for, but I took too many photos.

First of all, don’t just replace what was in your car, check to make sure you buy the right ones before putting them in - it can ruin your engine.
Telling someone what spark plugs to use is a bit like telling people what oil to use - you can follow a rule of thumb, but ultimately check the owner’s manual for the correct ones to use.

There are 3 important factors that make up a spark plug.

Heat Range:
Different brands use different formats, and NGK’s heat range increases as the spark plug number decreases; for example a 5 range is hotter than a 6 range.
Using too hot plugs can blow your engine, while using too cold ones blows the spark plugs.

Material:
Copper - 20,000km
Iridium - 40,000km
Platinum - 100,000km

Gap:
You have probably heard about gapping spark plugs, or seen a gapping tool on the counter of the local autoparts store.
NGK uses a 1.1mm gap unless stated in the spark plug number.
While the 1.1mm gap will be fine for a factory original engine, as you tune the engine the gap needs to be decreased accordingly. For an RB25DET on 2 bars of boost, a gap of 0.8mm is recommended. Remember that these figures may be specific to Skylines.

Companies like NGK and Bosch offer an online tool to help you find your spark plugs.

An RB25DE NEO uses BCPR5E-11 spark plugs (NGK)
A Honda VT250FG uses CR8EH spark plugs (NGK)

Now that you know your plugs, we can begin
Strip out the parts that get in the way of the spark plugs.
Those of us who own an RB25DE NEO or 1JZ, this is a fun process - and I mean that with sarcasm - look at those pipes. On an R34 like the one above, unplug the AFM and AAC actuator and TPS and intake from the throttle onwards.
Next, undo the six bolts in the V-pipe and disconnect the vacuum hose, oil and coolant hoses along with the smaller hoses near the throttle body, and the two bolts that hold the air intake solenoid.
The V-pipe will lift right out.

Make sure you know which hoses are the coolant lines and clamp or bung them off - coolant can escape them and you don’t want that in your chambers, or burns if they’re hot.
Once you have the intake and hoses out of the way, pull your coilpacks or leads out. Coilpacks are typically bolted in, while ignition leads can usually be pulled straight off.

Fortunately for you guys (and unfortunately for me), my engine was a bit dirty under the coilpacks.
The immediate area around the spark plugs can be vacuumed, however this might not work further down once the spark plugs are removed.
Use the thin suction head, and not the brush since contact with the bristles can push dirt into the engine - you want the area to be as clean as possible before you pull out the spark plugs to make sure nothing falls in when you take out the old plugs.

Sometimes your tools might not be able to reach so far down so often you will need an extension to reach the spark plugs. If your tool set is short like mine, you may need to stack the extenders for the extra length.
At first you will want to loosen the spark plugs using a wrench, or even a breaker bar - after that everything can be done by hand. Mine were a bit corroded and needed to be wiggled out while rotating.

As you can see above, there were bits of dirt and metal sitting at the top of the thread when I removed the spark plugs. While some of this can be burnt up in the engine, some of it might not and can cause damage to the engine’s internal components.

They looked like pieces of meta so I doubt the vacuum would be able to suck them out. The trick I used to get them out is to swab some grease onto a cotton tip and carefully grab them out without letting anything fall into the engine. Afterwards I gave it another quick vacuum with the hope of lifting what’s left out, and then another swab.

The previous owner of my R34 chose the wrong spark plugs, but luckily they were the correct heat range.
Notice the corroded electrodes and thread on the old spark plug.

Before I put the new spark plugs in, I put a small amount of grease on the thread to make sure they go in smoothly and will be easy to remove later on at the next change interval.

First, put them in by hand and make sure they aren’t cross-threaded. Twist them down as far as you can get them.
The service manual supplement for my car stated a torque of 20nm. If you are not sure of your spark plugs recommended tightening, a rule of thumb is as tight as you can by hand, then half a turn with a wrench.

Once you have them in and have torqued them, you can place the coil packs or iginition leads.
The RB25 engine uses a torque around 5nm for the coil packs.
Once in, you can reverse the process to get the hoses and pipes back in place - start with the V-pipe and reconnect the oil, coolant, vacuum and actuator hoses and make sure the v-bands are on properly - I forgot about one and had coolant dripping onto the coil cover (black piece that says Nissan 2500). If I didn’t check it then coolant would have gotten down to the coil packs, my radiator would have run dry, and my engine would have overheated since I went on a short roadtrip right after.

Immediately after replacing my spark plugs, I noticed that my engine no longer sits at 2000rpm hunting for a stable idle on startup, is a lot quieter and uses less petrol - after all, the old plugs were badly worn.
As a good measure, I reset the ECU to let it learn and tune accordingly to the new set-up.