Are you the type to service your spark plugs at annual? Proper aircraft spark-plug servicing should be completed more often than just during your major aircraft maintenance.
Think of it this way, if you serviced your spark plugs only once, would the wear and tear just stop?
The more hours you fly, the more deterioration your aircraft’s spark plugs can incur. Sadly, the annual inspection is usually the only time of year these spark plugs get pulled.
In this article, we hope to answer the following for you about your spark plugs:
- How does a spark plug work
- When to change aircraft spark plugs
- How to change your aircraft’s spark plugs
- How to clean your aircraft’s spark plugs
- How to gap your aircraft’s spark plugs
- How to reinstall your aircraft’s spark plugs
Let’s dive in first with how exactly a spark plug works…
There are two different types of spark plugs: the massive electrode spark plug and the fine wire (iridium) spark plug. The massive electrode spark plug makes up roughly 90% of all aviation spark plug sales. The electrode spark plugs have a typical life span of 300 to 500 hours.
Fine wire spark plugs are more expensive, but that extra money comes with added benefits. With thin lengths of iridium welded to the electrode tips, these spark plugs erode three times slower than electrode spark plugs. The reason for this durability is due to iridium being the hardest wire available.
The spark plug has one job: to send sparks across a gap to ignite the fuel within the engine cylinder.
The major thing here, which we will discuss later, is the gap distance. The gap distance is what regulates the voltage build up. If the gap is too narrow, it will not have built up enough charge. If located too far apart, it will have too much built up to overcome resistance and jump the gap. This exceeding voltage can damage your ignition system.
Every time this spark occurs, your spark plug electrode metal becomes ionized. This consumption of metal leads to a widening gap each time the spark plug fires, causing a need for replacement.
It is suggested by Champion Aerospace to service your spark plugs every 100 hours.
When to Change Your Aircraft’s Spark Plugs
Now that we know exactly how a spark plug works, let’s get into when to change your aircraft’s spark plugs.
The biggest indicator of wear on spark plugs is the electrodes. An easy way to tell if your spark plug needs changing is to see what the center electrode looks like.
Do you have a football shaped electrode, or is the ground electrode worn 50%?
Yes? Time for a change…
When considering changing a spark plug, you must look for other “red flags” as well:
- Bent electrodes
- Carbon deposits
- Damaged ceramic insulators
- Oil fouling
- Lead buildup on electrodes
How to Change Your Aircraft’s Spark Plugs
Before we begin, here is a list of suggested tools:
- Torque wrench (that measures out 360” pds)
- Open end wrench set (the size of the lead nut)
- Spark plug socket and driver
- Spark plug cleaner
- Spark plug tray
- Spark plug gapper and gap gauge
- Spark plug anti-seize
- New spark plug gaskets
Now that you are well equipped for this job, let’s get started.
Begin by going through each cylinder. Before doing this, however, check to make sure the magnetos are off.
Starting with the No. 1 cylinder, remove the ignition lead connectors. Do not twist wires when removing the connectors. This can be easily avoided by utilizing two wrenches.
Now, inspect your wire terminal’s ends and clean the springs. If needed, now is the time to replace any damaged springs. After this is done, carefully remove your spark plug and place in the correct spot of your spark plug tray. Continue this process until all spark plugs are removed. Make sure to keep this tray organized and in the correct order!
Once you have completed this step, it is time to clean your spark plugs.
Cleaning the Aircraft’s Spark Plugs
At this point, if you notice any lead fouling, you should consider switching to fine wire plugs. Often, switching to these can clear up that issue. See the previous infographic on the advantages of fine wire spark plugs.
The next item to get out is your aircraft spark plug cleaner. This item will provide the easiest way to clean your aircraft’s spark plugs being that it can lightly sandblast the plugs. If you don’t have one, borrow it from a mechanic or simply purchase one that’s inexpensive.
If you have not checked which plug cleaners are specifically designed for your aircraft plugs, you need to do this. If you choose the wrong plug cleaner you can ruin your plugs. DO NOT use glass-bead media; it can become embedded in the insulator gap and cause arcing in the plug.
If you have large amounts of lead deposits on your electrode plug, consider using a vibrating cleaner and/or dental pick to carefully remove this build up.
For fine-wires, all you need is a dental pick to carefully remove the lead without damaging the insulator or the iridium electrode. Blow out the debris with an air compressor.
Now that you’ve cleaned the spark plugs, check the outside of each plug for any build up. Specifically, pay attention to the plug threads where the plug goes into the engine. Make sure the plug threads and the lead threads are clean and free of any moisture or debris.
After you’ve finished cleaning your spark plugs, examine them very carefully. Do they have any chipped areas? Any cracks? If yes, then they need to be replaced.
Gapping the Aircraft’s Spark Plugs
Now that you have properly cleaned your aircraft’s spark plug, it is time to set the gap.
First, we do not recommend you try and adjust the gap on a fine wire plug yourself. Leave it to a professional.
Required tools for this:
Begin by checking your gap with the gauge. It is common for the gap to have grown during service. So, if you have massive electrode spark plugs, set the spark plug gap with a spark plug gapper. Typically, you’ll be looking for a setting somewhere between .016 and .021. If you do not know for sure what they should be set at, consult your aircraft’s maintenance manual.
After you have finished setting the gap, you will need to run a test on the spark plugs using a spark plug tester. Check each electrode’s resistance making sure they aren’t reading more than 5,000 Ohms. If they are reading 5,000 Ohms or above, they need replaced.
- Using a cheap automotive gapping tool
- Using needle-nose pliers to close the gap
Reinstalling the Aircraft’s Spark Plugs
We are on the finishing steps! Almost back in the air, stay with us…
First thing you’ll want to do is an easy step: rotate your spark plugs.
This is easily accomplished by taking the plugs from cylinders one and four and then switching them from top to bottom. Repeat this with cylinders two and three, as well. If you have a six-cylinder engine, check your manual for the correct rotation pattern.
By rotating the spark plugs, you’ll help to prevent problems such as lead or oil buildup. Also, by swapping the location of spark plugs, you change the polarity of each spark plug. This change will help with the overall wear of the electrodes.
Now that you’ve rotated the spark plugs, it is time to place them back in their proper positions in your engine.
Before putting the spark plugs back, put a light coating of aircraft spark plug anti-seize on the threads. Do not put any anti-seize on the first two threads, you may accidentally get anti-seize on the electrode.
Begin by putting the spark plug in its proper position (keep your tray in order!) and tightening with your fingers. After you have tightened down each spark plug with your fingers, get out your torque wrench and finish tightening the spark plugs.
TIP: always be sure to use the proper torque wrench specified by your engine’s manufacturer.
Lastly, reattach the ignition wires properly and make sure to consult your maintenance manual again for the proper torque. Remember to use two wrenches, one to tighten the nut and the other to hold the wire.
So, there you have it. Now you know how, and when, to change your spark plugs! Learning this skill can save you time and money.
Remember, less time spent on the ground means more time where we all want to be… in the air!
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