Aircraft Spark Plug Questions & Answers
Connecting the spark plug to the
connector
Terminal sleeves should be handled only with clean, dry hands. Before
installation, wipe off the connector with a clean, lint-free cloth moistened in
methylethylketone (MEK), acetone, wood alcohol, naptha. Make certain that the
inside of the spark plug shielding barrel is clean and dry. Then, without
touching the connector or spring with the fingers, insert the assembly in a
straight line with the spark plug. Screw the connector nut into place finger
tight — then tighten an additional 1/8 turn with the proper wrench. Damaged
threads or cracked shielding barrels may result if the connector nuts are
tightened excessively. Avoid excessive side load while tightening.
By comparing the two spark plugs in this picture, you can see the results of
overtorquing at the distorted end of the left spark plug. Since this distortion
may make the spark plug unusable, great care should be taken to tighten the
connector in accordance with the manufacturer’s instructions.
Torque value for spark plugs
Teledyne Continental engines 25-30 Ft. Lb (300-360 In. Lb)
Lycoming engines 35 Ft. Lb (420 In. Lb)
Pratt & Whitney 25-30 Ft. Lb (300-360 In. Lb)
Wright Aeronautical 35-40 Ft. Lb (420-480 In. Lb)
14 mm spark plugs as used in Franklin engines 20-25 Ft. Lb (240-300 In. Lb)
Information source: Champion Spark Plug Aviation Service Manual AV6-R dated 1993
Note: Information may change - consult the current engine manufacturer's maintenance manual for the latest changes and recommendations.
How do I rotate the spark plugs
The spark plug's firing
polarity causes uneven electrode wear. The magneto sends a positive
voltage down one lead and a negative voltage down the next lead and so
on . Each ignition lead always fires the same voltage (on
horizontal-opposed engines.
 For a six-cylinder engine move plugs 1T to 4B 2B to 3T 1B to 4T 2T to 3B Where T=top and B=bottom and the number is the cylinder position number. |
Difference between the Unison and Autolite spark plug
What happened to the Auburn spark plug
The Auburn plug is no longer in production. The rights to the
Auburn plug were sold to Champion
How do I prevent spark plug lead
fouling
2. Keep idle mixture setting properly adjusted
3. Lean the engine per manufacturer recommendations. Lycoming has an excellent Service Instruction on preventing lead fouling.
4. If applicable for your engine, use the Champion REM37BY spark plug - special plug designed to be more tolerant to lead build-up.
5. Smooth application of power during takeoff.
We believe that the rate of which the power is changed is an important factor. If, after extended idling on the ground, takeoff power is suddenly applied, so that the accumulated deposits are suddenly raised above their melting point instead of being given time to burn off during a more gradual increase of power, we would expect a greater likelihood of fouling.
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Mr. Teasel of Champion Spark Plug Company 1951 Aircraft Spark Plug and
Ignition Conference Report
REM37BY spark plug on the left Continental spark plug Application listing in Acrobat format SIL03-2A
Two types of lead fouling
1. Deposition of metallic lead or lead salts in the spark plug gap causing a direct short.
2. Deposition of metallic lead or lead salts between the insulator and the shell, gradually shortening the flashover path until misfiring occurs. Metallic lead deposits reduce the plug's shunt resistance.
Statistical Analysis of Airline Spark Plug fouling
presented By Shell Oil Company in 1950
The choice of operating variables could exert an appreciable effect on fouling.- The use of abnormally long rich-mixture idle periods
- Extremely lean mixture during cruise which results in poor combustion
- Low mixture temperatures and low cylinder head temperatures
Difference between short reach and
long reach
Spark plugs can be either short reach or long reach.
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Difference between 3/4 "all
weather" and 5/8 spark plugs
3/4 or 5/8 is the size of the nut in the picture
Your engine can use either 3/4 (also known as "all weather" or 5/8 barrel spark plugs.
The number on the spark plug indicates which one you have:
REM = 5/8
RHM = 3/4 "all weather"
For example, REM40E are 5/8 and RHM40E are 3/4 "all weather"
Generally, higher performance engines use 3/4 and smaller engines use 5/8 barrel. 3/4 and 5/8 refers to the size of the ignition lead nut. Before you order spark plugs you must know if the ignition harness lead nut is 3/4 or 5/8. Be sure to double check before screwing the plugs into the engine.
5/8 on the left and larger 3/4 on the right.
5/8 - 24 plug takes a 3/4 wrench on the lead nut. 3/4-20 plug takes a 7/8 wrench on the lead nut.
Generally, if you are replacing the plugs and harness the 3/4 (all weather) is a better setup because the lead end of the spark plug is completely sealed from moisture.
REM designates a 5/8 barrel plug while RHM designates a 3/4 plug
Does the spark plug gasket come
with a new plug
Yes, if you need extra the Champion part number is M-674
Heat rating of spark plugs
A cold plug transfers heat rapidly away from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion chamber or cylinder head temperatures are relatively high. A hot spark plug has a much slower rate of heat transfer and is used to avoid fouling where combustion chamber or cylinder head temperatures are relatively low. The primary means of adjusting heat range are by varying the length of the core nose and the alloy material used in the electrodes. Hot plugs have a relatively long insulator nose with a long heat transfer path. Cold plugs have a much shorter insulator nose and thus, transfer heat more rapidly.
The correct heat rating for the engine design ensures that the plug operates cool enough to prevent preignition but warm enough to resist the accumulation of conductive plug-fouling deposits.
With Champion plugs the higher the number the hotter the plug
Example REM38E is a colder plug than the REM40E plug
Champion Spark Plug Article
Today, the term "hot and cold" is commonplace in general aviation —
especially when related to engine spark plugs.With the introduction of high compression, and high horsepower engines, a need for improved spark plugs was eminent. Spark plugs used in low compression, low horsepower engines were not compatible with the new, more sophisticated powerplants. The non-compatibility factor of existing plugs with new engines resulted in development of spark plugs capable of operating efficiently at high compression ratios and high power settings.
Many aircraft operators have come in direct or indirect contact with the term "hot and cold" during the course of conversation with other pilots or mechanics. Its meaning and relationship to engine operation was sometimes rather vague. What do we mean by "hot and cold" spark plugs? What is the relationship between an engine and spark plugs? How important is it to smooth engine operation? These are but a few questions we will try to answer in this article.
Both spark plug and engine manufacturer working together determine the proper type spark plug suitable for each engine model These plugs can be either fine wire or massive electrode type. Before being released for production, each new type plug is checked in the laboratory and under actual flight conditions. They are tested through a wide range of operating conditions and at different power settings, and only after both engine and spark plug manufacturer are completely satisfied with test data are plugs released for production. To eliminate any possibility of error in spark plug selection, both manufacturers provide spark plug charts as a guide for proper plug selection. Final authority concerning proper plugs for a specific engine is the engine manufacturer. When selecting spark plugs, be sure to also consider the spark plugs’ heat range.
Operating temperature of the spark plug insulator core nose is one factor that governs formation of troublesome combustion deposits. To help overcome this problem, selection of spark plugs with the proper heat range should be made. Spark plugs are susceptible to carbon deposits when the operating temperature of the core nose insulator is at or below 800o F, but an increase of just 100o F is sufficient to eliminate formation of these deposits. Also, lead deposits form because the bromide scavenger contained in tetraethyl lead is nonactive at low temperatures. At 900o F temperature, the bromide scavenger is fully activated, disposing of lead deposits with combustion gases during exhaust cycle. In this case, an increase of just 100o F was sufficient to make the difference between a smooth and rough running engine. To eliminate or keep this problem at a minimum, avoid prolonged idling at low RPM, avoid power-off let downs, and after flooded starts run engine at medium RPM before taxiing.
Deposits formed between 1000o F and 1300o F are low in volume and electrical conductivity and are least apt to cause spark plug fouling. This is the reason for selecting a plug that will operate within the aforementioned temperature range at all power settings.
Now let’s get back to the term "hot and cold" as related to engine spark plugs. Normally, a hot plug is used in a cold engine — low horsepower, and a cold plug in a hot engine — high horsepower. In actuality, these terms refer to the plugs ability to transfer heat from its firing end to the engine cylinder head. To avoid spark plug overheating where combustion chamber or cylinder head temperatures are relatively high, a cold plug is recommended, such as in a high compression engine.
A cold running plug has the ability to transfer heat more readily. A hot running plug has a much slower rate of heat transfer and is used to avoid fouling when combustion chamber and cylinder head temperatures are relatively low.
From our discussion, it is clear to see that there is more to spark plugs than just buying a set and installing them in your engine. Be sure you know what type of spark plugs to use with your engine.
Also, good spark plug service and maintenance is as important as proper plug selection. Take care in selecting and maintaining your plugs, it can result in many additional hours of smooth engine operation. Additional spark plug information is always available from the engine or spark plug manufacturers and other service organizations.
What anti-seize should I use when
installing the spark plug
Per Champion Aviation Service Manual: "Apply anti-seize compound sparingly to the firing end threadsbut never to the first thread to prevent the material from running into the electrodes."
Proper spark plug torque depends upon using the specified anti-seize. Teledyne Continental, for example, specifically states that the their spark plug torque value is for threads lubricated with 2602 anti-seize.
Spark plug electrode gap setting?
and Continental plug application data
016 to .021 for Champion spark plugs. New spark plugs come
pre-gapped.
**Information provided by sacskyranch.com
**Information provided by sacskyranch.com
