Over the course of the Holidays and various forms of tiered forms of lock down that nobody really adhered to, I took my Mustang out. Now to be within to rules I took the car out to place where I could exercise after parking the car up. It just so happens that the car was parked in a pretty good place to take some photos while I was out exercising. There was nobody about, the odd car now and again going past, that was about it.
The garage was opened and the dust cover removed and placed on top of my tool chests. Excited to see the car after a number of weeks I got in and started the car, well tried to start it. The car was turning over fine but it didn’t fire up. I opened the hood and had a general look round under there. Fuel filter, yep fuel in there. I took the air filter off and checked the carb was squirting fuel, yep it was. After putting the bits back on I jumped in the car thinking it was just standing time issues. Turning the key the car started to turn over again, still but no fire up. Now I could smell fuel quite strongly, so I decided to leave it for a few minutes with the hood up to evaporate the fuel a bit. As it was getting late in the afternoon it was worth one more try before I give up and look at it properly another day. Third time lucky? She again spun over the crank slowed down and “BANG”. The backfire sounded like a grenade going off in my garage which made my ears ring, timing was obviously out to ignite at the wrong time. The car was running now a few seconds of really rough idle then it settled down to a smoother choke running. I backed the car out OK and drove of fine. However, there is a lot more to this story a little later…
I parked up and took some pictures before my little walk somewhere different. It just so happened where I was parked up would make a good backdrop. I took over 200 pics that afternoon, but this little selection are my favourites so far. I even done a black and white variation on a few of them. The pictures are variations on angles and lighting etc.
The next couple of photos I tried to start of with colour on the right and gradually fade it to black and white on the left. I played with the contrast to make the bottom one more antique and faded too. It sort of works I think, let me know if I hashed it or smashed it! I may even do some sepia variables as well.
The Journey Home.
I got back into the care and started the car, eventually after a few seconds it did start, but it was unusual to take that long. The drive back was about ten minutes and were not right. I got a few hiccups under mild acceleration from a standstill and the odd flat spot on a 40mph straight. I can’t deny that I was a bit worried. The car was parked up in the garage and covered her up with a nagging feeling in the back of my mind.
Next day I went out to the garage to just start her up. Turn of the key and the car spun over, then over and over. I tried to start her a number of times and smell of fuel was quite strong. I had a problem that was evident.
I sent Adam a text at Mustang Maniac to ask for a little advice when he had a moment. Adam being the kind soul that he is told me to get to my tools and he would call me back in a few minutes when I was ready. To his word he called me and talked me through some tests to look at with him over the phone. We swapped out the new coil with an older one that I had with the same result of spinning over with no fire up. We swapped over the coil HT lead to the distributor after testing with my multi-meter Ohm settings. Nothing. We then earthed out the coil HT to the engine to see if a spark jumped over to the engine. How did I manage that? Simple I talked sweetly to my wife who came out for a couple of minutes to turn the car over for me.
The diagnosis was narrowed down to the Pertronix ignition sensor which has gone to the great scrap yard in the sky! I needed a new one, it was a simple as that. Adam said he would get one out to me via mail ASAP as their location was in a high tier restriction for Covid reasons.
The next day my courier turned up with the part. I took a drink along with the part into the garage, unlocked the tool chests and settled down for a few hours. The distributor cap was removed and the single screw was removed the Pertronix sensor. The downside was the wiring loom had to be cut open to expose the wires for the sensor. The fitting of the Pertronix sensor can be found here.
I done a rough fit without the neatness of wiring loom and connected up ready for the start up. I got in the car and turned the key. The car fired almost instantly and run smoothly all the way to the choke coming off. I let the car cool down and got back to routing the wires back into the loom and neaten it all back up again. A couple of hours later the work was finished and up to my own self imposed high standards. The aftermarket part is now looking like part of the stock loom again and I’m happy. I need to take the car out for trip to make sure everything is still as it was. But, as we are in a current national lockdown that is out of the question right now.
All that remains is for me to thank Adam at Mustang Maniac for his time, even though he was officially “Closed” over the holiday season. I needed the part and I paid for the next day courier service from his WebShop. I was offered the multiple choices of delivery and the costs options. Normally I would drive and pick it up, and it’s also a good excuse to catch up for a chat with some friends. There is a an advantage of being a loyal customer and personal friend with a Mustang parts supplier, who will help go out of their way for you when you need the help.
Since I refitted the new part, I have been on a number of forums about the Pertronix Ignitor series. It seems that I was a lucky boy after all in the fact I got home at all. Most of the time these units are absolutely fine and last forever and a day. But, if you get a bad unit they just stop dead. You could go down the road, pull out of a junction and it stops dead in the middle of the road as one person reported and that’s it. The same symptoms I had – no restart. I had issues where I had a cut out which progressively got worse to the point it didn’t start again. Now I intend to get an old school set of points and condenser to carry with me as an emergency get me home kit. If the points burn out after a few miles due to the hot coil 45,000 volts with 0.6ohms I won’t mind. As long as I get home they are cheap enough to replace again.
My 2021 didn’t start very well, in more ways than one. It could have been much worse of course, I’m just lucky it was a simple problem to replace. Onwards and upwards I guess.
On my last post (rather a large post), I explained the critical settings of the spark plug and the benefits of quality ignition leads. That’s all well and good, but if you don’t have the correct pulses or power going down those leads at the right time then you will have problems. While I was checking and replacing spark plugs, I decided to strip down and rebuild the top end of the distributor.
Firstly what is a distributor?
A distributor consists of a rotating arm or rotor arm inside the distributor cap, which sits on top of the distributor shaft. This shaft has an insulated body to the vehicle’s ground or earth. The distributor shaft is driven by a gear on the camshaft on most overhead valve engines, and attached directly to the camshaft on most overhead cam engines. The distributor shaft usually also drives the oil pump. The metal part of the rotor contacts the high voltage cable from the ignition coil via a spring loaded carbon brush on the underside of the distributor cap. The metal part of the rotor arm passes close to (but does not touch) the output contacts of the distributor cap which connect via high tension (ignition) leads to the spark plug of each cylinder. As the rotor spins within the distributor, electric current is able to jump the small gaps created between the rotor arm and the contacts due to the high voltage created by the ignition coil. The voltage then travels down the HT leads to the spark plug where it again jumps a predetermined gap to ignite the air fuel mixture in the cylinders providing drive to the crank and thus power to the wheels via a transmission. (In a nut shell description.)
The principles are the same for a 4 cylinder, i6, v6, v8, v10, v12 etc. The rotors may travel in a different direction (clockwise or counter-clockwise), the number of leads on the distributor cap may be more, the firing orders will be different etc.
To show those principles of the spark, here is a simple 4 cylinder diagram with points. A v8 just more of plugs, more cap points, more cam lobes to open and shut the points etc. but you can see the idea on a less cluttered diagram.
Modern cars tend not to have points, but have electronic sensors to replace them. Latest technology has a sensor on the cam shaft which fires the spark plugs without the need for a distributor or even a coil, as the power for the spark is handled by ‘coil’ packs which are mounted on top of the spark plug lead fittings.
This post is a going to be a very cut down version of the whole process I have documented. The full rebuild with all the photos, explanation step by step can be found here. I will only be covering the Pertronix ignition process on this post, but I do cover the points process or refitting and setting as well on the full walkthrough.
* Disclaimer (just in case): If you are in any doubt on your ability to try this – DON’T. Get it wrong you and could damage the insides of the distributor, the car wont start or run properly. This is a guide on how I done it, I can’t held be responsible for your actions.
First thing is to make a note of where the HT (spark) leads go and to what cylinder. Take a few photo’s if you’re not sure, label the leads up with a marker or sticky label of some sort. If you look closely the top of the Mustang distributor caps it has the number ‘1’ on the top, this is where you plug the lead for cylinder one. The diagram below right is for the firing order of 260/289/302 with a standard cam. Check your manual if you’re unsure.
Take the leads off and unclip the front and rear retaining clips to release the cap. The rotor arm can now be removed and the small usually oil soaked felt pad under it can be removed. Both my rotor and felt pad needed to be replaced.
Depending on your set up there will either be a set of points and condenser picture below left, the points gap is covered on the full process here.
An upgraded set of electronic points as mine (below right) will be set to the manufacturers recommended gap, more on that later once the rebuild is completed.
I removed the electronic set up, but once the condenser and points are removed (above left), the principle is exactly the same for dismantling and re-assembly up to the fitting of the Pertronix or points and condenser.
My Pertronix is held in place by a single screw at the bottom of the shoe which also pivots at the top where the original points screw would have held the top part of the points. Then remove the black sensor collar.
Disconnect the vacuum pipe to the front of the vacuum canister which goes to the carb. Check for any leaks or cracks on the pipe if you find some replace the pipe.
Next there is a metal lever that goes into the distributor (which will now be known as “dizzy” from now on). There is a tiny clip that holds the bar onto the pin. Remove the clip very carefully and make sure you don’t loose it. Remove the vacuum can from the dizzy.
Check for signs of perishing on the diaphragm on the inside. To check the function of the vacuum you can suck the can from the front and you should see the arm move towards the inside of the can, repeat a few times. If all is good you can clean it up and keep it safe, if not replace. Next remove the screw that holds the earth strap to the lower dizzy plate.
Next to the cam lobes there is another e-clip at the top of a pin. This holds a washer and under that a fairly strong sprung washer. Slip a small flat ended screw driver and gently tease it away. If you’re not careful it will ping up and be lost in the depth of the engine bay. Remove the washer, sprung washer and keep safe with the e-clip.
With the washer and spring washer out the way, you should now be able to lift the plate up and lift it up over the lobes of the cam.
The lower plate is now only held in place with a single screw the opposite side to where the cables come into the dizzy. Undo the screw and remove the lower plate.
Removing the lower plate there should be three raised points which separates the upper plate and should be smooth. I noticed one of mine was loose so I removed it then re-stuck it back on later.
With the lower plate removed you can now see the advancing weights and springs.
NOTE: The springs are different tensions. The one has less tension and and allows the weights to swing out under rotation to advancing the timing. The other spring is stiffer and at certain centrifugal force this spring takes over slowing down the advance. The larger and stronger spring is a loose fit to the anchor points and is normal.
On top of each weight there is again a an e-clip. Remove with a small flat ended screw driver and make sure it does not ping off. Make a note of which weight goes where and repeat for the other side.
Keep them separate or mark up a piece of paper and lay them on the paper so you know which pair go together and if they are the 13deg weight side or the 18deg weight side. Without taking the whole dizzy out this is about as far as you need to go.
You could possibly remove the springs, the two springs making careful notes on what one goes where. I decided against that just in case I stretched a spring putting it back on. This would have a detrimental effect on the timing and advance. My springs weren’t to bad so I decided not to chance it.
Now you need to clean the inside and remove any old dried grease and debris. Don’t go mad in here with the fluids, use just enough to clean. I found carb cleaner is good, and also sprayed onto a cotton bud to clean the springs and surrounding area.
You can move the move the weight plate with your fingers to clean parts that are partially covered. Don’t go mad with forcing open of the springs, you don’t want to stretch them. Make sure there is no bits of debris in the bowl or trapped anywhere.
The bowl should now be clean of all debris and old grease.
I started with the weights. take each weight and either clean with a degreaser or similar, or take some ‘000’ grade super fine wire wool to take the roughness of the weights.
Make sure that NO wire strands are left on the weights or fall into the dizzy bowl.
I used a small punch to wrap a little wire wool around and then clean the inside of the holes. You are lightly cleaning – not reboring the hole. Also clean the clip, any rough edges or rust could impede the movement of the weights.
With the weights and clips cleaned it was time to fit them back to the dizzy. You will need some proper lubrication. I researched a fair bit and the general recommendation is an engine assembly grease. Light smears not huge blobs!
If you examine the weights it easy to see where the wear marks are, apply a little grease to the weight. wear points and into the holes. Note that the whole weight doesn’t need greasing, just the hole, outside edges, the top where the clip holds it in place and the underside where it rests on the pin base.
Place the weight over the pin and lower it into position. There may be some excess grease, but that can be removed later. Make sure the weight is free to move and rests within the cradle. Apply a film of grease to the clip and place onto the weight.
You need to press the clip onto the post into the recess. I found again a small flat headed screw driver would do the trick. It can take a few goes to get right. Just make sure it doesn’t ping away. With both weights and clips in place it should look something like this.
Lower plate needed some love in respect that the plastic/nylon stop had worked a bit loose. Both the front and the back of the lower plate was cleaned with fine wire wool. You can see the slide pads are just hot pressed into the holes of the plate from the factory. With the plate now repaired I cleaned the yellowish and two red pads of the old grease and debris. I took some 5000grit and then 8000grit to remove any rough parts. Not sand it down, but more of a polish. Check the vacuum post has no wear and burrs.
Again make sure NO wire wool or cleaning material is on the plate before refitting. Place the plate back into the bowl area to cover the plate with the post side facing upwards. Align the hole and screw into place.
Take your assembly grease on a cotton bud and apply a film over the plastic pad areas and the post.
The upper plate may need a clean with wire wool or degreaser depending on the state of it. Pay attention to the brass bush which sits on the post of the lower plate. Brass is a soft metal and you don’t want to create a problem so be careful not to damage it with the small punch, degreaser with fine wool. Remove any burrs on the top side of the bush to allow the sprung washer to move without snagging.
On the underside of the upper plate you can see where the plate has moved across the slide pads over the years. Apply a film of the grease on these areas and into the brass bush and the vacuum post.
Place the upper plate onto the lower plate, locating it via the brass bushing. make sure it’s free to move all the way. Clean the components that hold the top plate to the bottom plate. Top washer, sprung washer and the e-clip all need to be clean and smooth in order to not snag the movement.
To refit a further film of grease over both sides of the of the sprung washer on top of the top plate brass bush with the curled edges facing up. Top washer with grease applied on the top and bottom, place the washer on top of the sprung washer.
Next refit the cleaned up earth strap for the top and bottom plates.
On the Pertronix setup, wipe over the plastic collar and slip it over the cam lobes with the recess facing upwards.
With the vacuum advance module clean the arm at the back and apply a film of grease on both sides near the hole and in the locating hole. The vacuum module can only fit on in one way following the curve on the outside of the dizzy.
With the arm located take the e-clip clip with some grease and again fit into place so that the arm is held down. Secure back in place with the two screws.
Setting up the Pertronix or points, don’t use grease here as you want the srews to hold in place. Place the Pertronix on the plate, and the other end of the earth strap that is attached to the bottom plate on top of the Pertronix while aligning the top pin to the other locating hole.
With the sensor and the collar in place you need to set the correct gap. A ‘tool’ is supplied with Pertronix which is a plastic strip to set the gap which is 0.80mm. Left pic shows the gap is to small. The right pic shows the correct way to gap the sensor. Keep the plastic gap tool flat to the sensor face and slide the the unit until there is a slight drag between the collar and the sensor. Tighten the screw fully.
In the centre of the dizzy where the rotor arm sits is a recess. This has a felt pad to oil which is to keep the cam lubricated lower down. I would recommend this is replaced with a new one and filled with fresh oil, or reuse the old one with the old oil it’s up to you. Most people use a drip of the engine’s dipstick at oil change. But my research leads to me to say that this should be a very light engine oil to allow the oil to run through the felt. It’s debated if this is still required. However, Ford wouldn’t have milled out the centre shaft and put a felt pad in there for no reason!
Place the rotor arm on top of the dizzy shaft and locate into place. These can only fit in orientation as there is a keyway on the inside of the rotor to match with the shaft cut out.
Now take your marked up HT leads or follow the chart and fit back onto the dizzy cap. Job done.
If you made it this far thank you. Another long post but still cut down a bit from the original page here.
I’m looking forward to using up some holiday and time off over the Christmas break, hopefully I will be posting some more, hopefully less technical or intense.
The ignition systems on modern cars is highly complex. Even on classic cars that technology has moved on, but you probably don’t realise it. The humble spark plug is a highly complex part of the engine and the plug leads that supply the power are no exception.
What started out as me showing you how I remade a broken lead and setting my spark plug gaps, turned into a bit of a monster research project. I didn’t realise that there was quite as much involved for a throw away part that only costs a few quid (bucks). From what I have learnt I will try to explain; cause of bad plugs, incorrect gap setting, how spark plugs and their leads are made, how they work and how you can make your own custom plug leads!
HT ignition cable sets can vary from £15 to £150 (or more depending requirements).
Spark Plugs can very from £2 each to easily over £20 each
Crimping tool £5 to £25
Spark plug gap tool or feeler gauges £2 to £30
What is an Ignition, Spark Plug or HT lead?
It’s a simple, but critical cable which transfers the power from the distributor cap to the spark plug, where it then provides the energy to create a spark at the plug electrodes, which in turn ignites the air/fuel mixture to give you the power to turn a crank which will eventually drive the wheels.
The ignition lead is comprised of a conductive material surrounded by a silicone jacket. The primary purpose of the silicone surround is protection and looks to a degree. Ignition leads sit in close proximity to the engine itself and so are subject to dramatic changes in temperature, caustic chemicals and frequent abrasion. A silicone outer layer helps to protect the conductive core from external damage, extending its lifespan.
The core itself, which carries the current, will either be made of copper or carbon, depending on the age of the vehicle. Older vehicles used copper, modern ones carbon. Now days older cars can use the modern carbon style for better reliability and consistency and still look stock.
It’s a common myth that bigger and more elaborate HT leads will give you more horse power. What they will do is provide the optimum efficiency and stability that may have been lacking on older worn leads. They should last longer and keep performance at a constant level.
How do you know if the HT leads have gone bad?
1. Decrease in power, acceleration, and fuel efficiency
One of the most common symptoms of an issue with the ignition cables is engine performance problems. The ignition cables carry the spark from the coil and distributor to the spark plugs so that engine combustion can occur. If there is any issue with the spark plug wires the engine spark can be disturbed, which can result in engine performance issues such as misfires, a reduction in power and acceleration, as well as a reduction in fuel efficiency. In severe cases bad cables may even result in engine stalling.
2. Visible wear or damage to cables
Visible wear or damage are symptoms of issues with the ignition cables. Old cables may dry out or perish, which may lead to cracks in the insulation. There are also instances where the cables may rub up against a hot manifold or engine components, which may cause them to melt and burn up. Both of these issues may compromise the cable’s ability to transport the spark to the spark. This can lead to misfires and other performance issues, and in more serious cases may even lead to the cables shorting against the engine.
3. Check Engine Light comes on (modern cars)
Faulty cables can lead to engine misfires as well as excessively rich air fuel ratios, both of which can set off the Check Engine Light if detected by the computer. Many modern vehicles are now being manufactured without the good old fashioned ignition cables, however they are still found on a very large majority of older cars.
Process To Make Your Own:
Regardless of the vehicle, making the wire is the same in principle. Most of the time the ‘generic’ HT leads tend to have the spark plug boot already connected. Most kits will give you an option of metal crimp ends and rubber boots depending on application.
These can be straight, 90deg or 115deg angles (as below) etc. depending on the manufacturer, engine fitting, style, age and type of engine etc.
These HT leads can be single colours, multi coloured, cloth wrapped, silicon covered or custom variations of anything in between.
The spark plug boot fittings can be pretty much anything on top of the spark plug terminal, to nothing with just the thread or a simple screw down for the clamped earlier designs.
Or any of the following styles; stud, clip, screw, solder or crimp etc.
My Mustang leads are set to the 115deg from the plug with an open end which allows you to cut the wire and route where you want it. Or you could buy prefabricated leads without the hassle or making them of course. But you may be limited to the routing of the wires that you wanted.
Process to attach the fittings.
Making your cable connection will require a plug crimping tool, usually around £10 to £25 for a ratchet set. They have the main crimping section at the bottom of the jaws, outer layer cutting jaw and then the inner cable crimp at the top, if needed.
Measure the length of the cable you need and trim approx 1″ longer than you need, this will allow for trimming and crimping the core. Better to be a fraction to long than too short and put stress on the cable.
Depending on the connection you have you may need to trim to the inner core and crimp twice.
If there are no boot(s) on the cable you will need to put these on first. Make sure they are the correct way round. This is so often forgotten and will lead to a wasted crimp and an even shorter cable when you have to redo them. To make life easier to slide the cable through the boot is apply a little dielectric grease. this protects the rubber and also allows electrical current through it just in case it gets on the centre core.
My cables needed to expose the inner core only. Trim of the outer silicon and the inner layer to leave an exposed amount of core.
Fold the core cable over back on itself. making sure that the core is on the back of the fitting.
Place the fitting and cable into the crimps with the open side on the fold part of the jaws.
Slip the boot over the fitting and make sure it seats correctly. With both ends crimped and ready to fit test the integrity of the lead via a multimeter ‘ohms’ setting with a tester prong at each end of the cable. With everything in place you can fit the cable.
Note; the distributer cap boot fittings (male fit) tend to extend past the rubber as it has to sit deeper into the distributor cap as in this pictures here to make a contact.
Repeat for each lead you need.
This is probably the least thought about part of the engine and least understood. Yet these relatively cheap disposable parts can make a huge difference to the running of the engine, and the designs behind them can get highly technical. i will try to break it down into smaller sections.
What is the Spark Plug?
This is the part of the engine that detonates the air fuel mixture in the engine’s cylinders to make the explosion to force the piston down to rotate a crank, which in turn drives a shaft to the gearbox.
Design of the plug will dictated by the engine manufacturer, such as where it will be located how far from the chamber etc. things like centre mounted plugs on an over head cam tend to be thinner and longer to reach the top of the cylinder. Traditional side mounted mounted plugs can be shorter or fatter depending on where it needs to sit in the cylinder head.
A good rule of thumb for the correct depth is something like this, all the information will be in the manufacturers guides.
To shallow a plug and the spark will not ignite the fuel/air in the cylinders correctly. To long a plug and there is a danger that the top of the piston could hit the plugs. The incorrect depths could also play a part in heat dissipation, fuel economy, power and even the overall drivability of the car.
A selection of various designs from short to long, to thin to fat and marine application.
The firing end has a number of different ways to create the spark, single, double and even quadruple toe electrodes, angled etc. Each design will give a specific spark for a particular engine. Here is a description of the more common ones.
Standard spark plugs typically feature a traditional ground electrode.
Double fine wire electrode (DFE) spark plugs apply a fine wire pin to the ground electrode in addition to a fine wire center electrode. A smaller electrode requires less voltage to jump the gap, resulting in fewer misfires, which translates to increased fuel economy and horsepower. A smaller electrode also reduces flame quenching. Reducing the electrode size on a standard nickel plug would result in a drastically shortened life span, so smaller electrodes require exotic metals such as platinum or iridium to maintain (and at times surpass), the longevity of a traditional spark plug.
A flat ground electrode is shorter and closer to the metal shell and center electrode, providing a faster path to transfer heat away from the ground electrode. Its low profile design is resistant to vibration.
Developed for engines that tend towards increased carbon depositing as a result of their design, hybrid spark plugs have a standard ground electrode as well as two smaller ground electrodes on each side. When the insulator becomes clogged with carbon, the ignition voltage jumps over to the side electrodes, enabling the plug to operate even under severe conditions. Once the plug has reach operation temperature and the deposits are removed, it returns to “normal” operation, with the spark jumping between the center and main ground electrode.
A low angled ground electrode is shorter and closer to the metal shell and center electrode, providing a faster path to transfer heat away from the ground electrode. Its low profile design is resistant to vibration. A smaller electrode requires less voltage to jump the gap, resulting in fewer misfires, which translates to increased fuel economy and horsepower. A smaller electrode also reduces flame quenching. Reducing the electrode size on a standard nickel plug would result in a drastically shortened life span, so smaller electrodes require exotic metals such as platinum or iridium to maintain (and at times surpass), the longevity of a traditional spark plug.
Some engine designs require the spark plugs have the ground electrode placed to the side of the center electrode rather than below as on a traditional plug. This may be for combustion chamber design as in the case of a rotary engine, or a surface gap design as used in leaner air/fuel ratio’s on industrial engines. The side electrode design tends to wear faster than a traditional plug. Erosion at these points creates a larger gap between the center and ground electrodes, causing plug misfire. Thus, if the engine design requires a side discharge plug, more ground electrodes extend plug life.
Multi-Ground plugs are offered in 2, 3 and 4 ground electrode designs. It is important to note that multi-ground does not mean multi-spark, there will still only be one spark at a time. Caution should be made in selecting a “high performance” plug.
If your car came OE with a multi-ground plug, your engine will likely wear through single electrode plugs, especially fine wire plugs, at a rapid rate.
Projected square platinum electrode (PSPE) spark plugs apply a square shaped tip of platinum to the end of a shortened ground electrode.This ground electrode shape allows the spark to be focused between the fine-wire center electrode and projecting platinum ground electrode. A smaller electrode requires less voltage to jump the gap, resulting in fewer misfires, which translates to increased fuel economy and horsepower. A smaller electrode also reduces flame quenching.
In a semi-surface discharge design, the voltage path skims across the surface of the insulator. When the spark discharges, it burns off any carbon build-up. The wide gap improves ignition capability and is less sensitive to gap growth. Additionally the concave cut in the ground electrode promotes even gap growth.
A slant ground electrode is shorter and closer to the metal shell and center electrode, providing a faster path to transfer heat away from the ground electrode. Its low profile design is resistant to vibration.
A thin square pad of platinum is welded to some ground electrodes to ensure durability.
True surface discharge or surface gap spark plugs have no side electrode, instead utilizing the entire face of the plug shell as a ground to ignite. Thus the gap remains constant through the plugs entire life. They have no given heat range as the electrode design prevents the firing tip from overheating, and the insulator is flush with the metal shell to dissipate heat quickly. Therefore, these plugs are susceptible to fouling in cold applications.
Surface discharge plugs may be required in high compression applications or with high energy ignition systems. They are also used in rotary engines as they present a flush face to the combustion chamber, eliminating interference with an electrode tip and exposing the spark to the entire air/fuel mixture for improved combustion.
Many variations of the surface discharge plug exist, including the semi-surface discharge, intermittent gap, supplementary gap, and surface air gap plug. All designs create a spark along the insulator nose to remove carbon build-up.
A taper cut ground electrode serves a similar function to a cut back ground, fine wire ground and angled ground electrode. Also known as an inverted v-tip, tapered v-profile, trimmed side, v-trimmed or wedge shaped ground electrode, all trimmed designs have the same purpose: to reduce quenching and shadowing by reducing the surface area between the electrodes which could hinder the growth of the flame nucleus.
A trapezoid cut ground electrode is a variation of a taper cut ground, which serves a similar function to a cut back ground, fine wire ground and angled ground electrode. All trimmed designs have the same purpose: to reduce quenching and shadowing by reducing the surface area between the electrodes which could hinder the growth of the flame nucleus.
When the air temperature is high, as in the summer, the inlet air temperature becomes higher, increasing the load on the engine. In times like this, it’s better to choose a plug with a higher heat range.
Various circumstances such as engine conditions and driving conditions are rough measures for choosing a plug. If you are doing lots of strenuous driving for a considerable time using normal plugs, the plug will overheat. This is why the idea of a Standard plug fits all for all car’s doesn’t work.
The heat is controlled by the design of the inside of the spark plug head More material that can be in contact with the cylinder the greater the cooling. (The dark grey shading represents a hollowed out area between the insulator and the thread.)
Each manufacturer has their own coding for heat ranges, this is a comparison of some popular plugs.
If the horsepower has been increased through tuning, the increase in explosive power leads to an increase in combustion chamber temperature, making pre-ignition more likely; in such cases it is necessary to choose a plug with a higher heat range and a higher level of heat resistance provided by Denso. The same with other plugs of course just different numbering approach.
Types of Spark Plug Cores:
Sparks like to jump from the sharpest point on the center electrode to the sharpest point on the side electrode. Ideally you want a plug that retains its sharp edge for the most amount of miles covered. Precious metals like platinum and iridium are harder metals and have higher melting temperatures than the nickel alloy electrodes found in traditional copper spark plugs. The smaller the diameter of the center electrode, the lower the voltage needed to start the spark.
These plugs have a solid copper core, but the business end of the center electrode is actually a 2.5mm-diameter nickel alloy. That’s the largest diameter electrode of all the spark plug types. Remember, the smaller the diameter, the less voltage required to initiate the spark. Nickel alloy is also softer than either platinum or iridium, so the sharp firing edge you get right out of the box tends to wear out quickly. Despite those shortcomings, copper spark plugs are still a good choice for certain applications. Copper spark plugs are best for older (pre-‘80s) vehicles with low voltage distributor-based ignition systems. Don’t use copper spark plugs in high-energy distributor-less ignition systems (DIS) or coil-on-plug (COP) ignition systems. They’ll wear out too quickly.
There’s one exception to that advice. Some late-model high-performance engines were designed specifically for copper spark plugs. In those cases, copper spark plugs are considered to be high performance spark plugs. If your owner’s manual calls for copper spark plugs, don’t upgrade to platinum spark plugs or iridium spark plugs.
A single platinum spark plug is basically styled after a copper spark plug with a platinum disc welded to the tip of the center electrode. Since platinum is harder than nickel alloy, it holds its sharp edge for as long as 100,000 miles. Platinum spark plugs also run a bit hotter, preventing spark plug deposit build up and fouling.
Platinum spark plugs are usually the best spark plugs for newer vehicles with electronic ‘distributor-based ignition systems’ (DIS). If your owner’s manual recommends platinum spark plugs, don’t downgrade to copper spark plugs to save money. However, you can upgrade to either double platinum spark plugs or iridium spark plugs.
Double platinum spark plugs were designed for “waste spark” DIS. In a waste spark system, the spark jumps from the center electrode to the side electrode for the cylinder that’s on the compression stroke. To return the electrical pulse back to the ignition coil pack, the spark jumps backwards (side-to-center) on the partner cylinder. Since the partner cylinder is on its exhaust stroke, nothing ignites and the spark is “wasted.”
You can’t use single platinum spark plugs or traditional copper spark plugs in these systems because the side electrodes aren’t designed to handle the reverse spark. But double platinum spark plugs, with a platinum disc welded to their side electrode, work exceptionally well. Both the center and side platinum discs remain sharp, allowing sparks to fly easily in both directions without causing rapid electrode wear.
If your owner’s manual recommends double platinum spark plugs, then those are the best spark plugs to use. You should never downgrade to single platinum spark plugs or copper spark plugs. However, you can upgrade to an iridium/platinum combination plug (an iridium center electrode with a platinum-tipped side electrode).
Iridium is harder than platinum, and in most cases, iridium spark plugs last approx 25 percent longer than comparable platinum spark plugs. Because iridium is costly, iridium spark plug manufacturers reduce the diameter of the center electrode to as little as .4mm. In addition to saving money, the “fine wire” center electrode on iridium spark plugs increases firing efficiency.
Many carmakers require iridium spark plugs or iridium/platinum combination spark plugs for coil-on-plug (COP) ignition systems. If your owner’s manual specifies iridium spark plugs, don’t downgrade to platinum spark plugs, or double platinum spark plugs, or even copper spark plugs. They won’t perform as well as the iridium spark plugs and cause some potential problems with running.
As the spark ignites the air/fuel mixture, the colder side electrode tends to “quench” the flame. To combat quenching, some spark plug manufacturers cut a “U” or “V” shaped channel into the “spark receiving” surface of the side electrode. The larger channeled area reduces quenching and allows the flame to grow more quickly. Other manufacturers split the end of the side electrode to reduce the flame’s contact with the side electrode and allow the flame to shoot straight down into the cylinder.
Are these type of plugs better? There’s no general consensus or conclusive evidence on whether these designs work better or not. However they will perform at least as well as a non-channelled plug, if not better.
Condition of the Spark Plugs:
These little pieces of technology can tell you an awful lot about the condition of your engine, at each service you could take them out and check, but you don’t have to. Many years ago when spark plugs were a standard core, they used to be replaced with every car service along with points. With modern computer controlled injection, you should be running ‘normal’ most of the time.
On carburettor cars the tuning and air/fuel mixtures are much easier to spot.
A visual inspection of the spark plugs could like the following;
If the firing end of the spark plug is brown or light grey, the engine condition can be judged to be good and the spark plug is functioning correctly.
The gathering of different deposits on the firing end is influenced by oil leakage, fuel quality and engine operating period. The deposits can come from Carbon, Lead, Bromine, Calcium, Sulphur, Barium and Zinc.
Dry and Wet Fouling
Dry and Wet Fouling is another way the firing end can be damaged. If the insulation resistance between the centre electrode and the “shell” is over 10M ohms the engine can start up normally, however if the insulation resistance drops to 0 the firing end is fouled by either wet or dry carbon.
If your spark plug firing end looks yellowish brown on the insulator nose, this is found on spark plugs that have been damaged by lead. Also, this particular type of damage cannot be detected by a resistance tester at room temperature. Lead compounds combines at different temperatures; those formed at 370-420 degrees Celsius have the biggest influence on the resistance.
If your spark plug has overheated, the insulator tip is glazed or glossy. Deposits which have gathered on the insulator tip have melted, and there is a chance that the insulator will have blistered.
Breakage is normally caused by a thermal shock due to sudden heating or cooling – replace immediately!
A worn spark Plug not only wastes fuel but also strains the whole ignition, this is because is requires a higher voltage. A worn spark plug can reduce the engine efficiency by reducing the fuel economy and increases the exhaust emissions. For your reference, The normal rate of gap growth is about 0.01 0.02mm/1,000 Km for four stroke engines and about 0.02 0.04mm/1,000 Km for two stroke engines.
Erosion, Corrosion, Oxidation
The electrodes have oxidized, and when the oxidation is heavy there will be green on the surface. The surfaces of the electrodes are also fretted and rough.
An Abnormal Erosion is caused by corrosion, oxidation, or reaction with the lead. This results in abnormal gap Growth.
Lead Erosion is caused by the lead compounds in the gasoline which react chemically with the material of the electrodes (nickel alloy) at high temperatures. Crystals of nickel alloy fall off because of the lead compounds permeating and separating the grain boundary of the nickel alloy. Typical lead erosion causes the surface of the electrode to become thinner and the tip of the electrode looks like it has been chipped.
If the firing end is melted, this means it has over heated. Mostly, this will result in the electrode surface being rather lustrous and uneven. As note, the melting point of nickel alloy is 1,200 – 1,300 degrees Celsius.
What’s important is to inspect the condition of your current plugs, and then choose a plug accordingly.
Fitting the wrong plugs could damage your engine.
A chart for comparing different makes and designs of spark plugs.
Some cars run on better brands than others. In my past experience NGK were a great plug, but didn’t last long. Bosch platinum were great when warm on lots of motorway miles, but a little lumpy when cold. Trial and error depending on your driving style and engine will get the best results for economy and power.
Spark plugs are designed to last and give optimum performance for as long as possible. Racing plugs in racing engines tend to be designed to give the max for shorter periods of time. They wouldn’t necessarily make big performance gains in road cars, unless you intend to drive it like you stole it!
Copper cored plugs you can expect between 10,000 to 20,000 miles.
Platinum or Iridium tipped plugs can be expected to last 60,000 miles.
Some top quality branded plugs are expected to last 120,000 miles before changing.
You pay your money and take your chances. Buying cheap plugs where bits can break of in the cylinder could possibly destroy a good engine.
Setting the Spark Plug’s Gap:
The gap sizes are pre determined by the manufacturer to get the correct combustion in the engine’s cylinder or combustion chamber. These should be adhered to unless specialist tuning requires the changes.
Such an instance to increase the gaps could be changing from old school standard points ignition to a Pertronix electronic ignition. The sensor in the distributor cap does not have metal contacts to take the voltage. The sensor sends a signal to the ignition coil which can produce more voltage and power as a result. This in turn can allow a small increase in the spark plug gap to give a stronger more powerful spark. The theory is that the better spark gives better combustion of more fuel air mixture and could give you more horse power with the correct carb settings.
* Narrow Gap
When the spark plug gap is too narrow, or under specifications, the amount of room needed for the air-fuel mixture between the hot tip and the ground strap is decreased. The duration of the spark has less travel distance, thus not remaining hot enough with sufficient charge to ignite the air-fuel mixture. The symptoms of narrow gap include a noticeable (continuous) cylinder miss, hard starting if all the plugs have narrow gaps, rough idle and engine hesitation. A spark plug that does not fire, resulting from a narrow gap, will appear black or wet when inspected. The black or wet appearance indicates unburned fuel.
* Excessive Spark Plug Gap
Excessive spark plug gap results when the voltage has too far to travel. The increased length of the spark travel weakens it, robbing it of the hot, strong ignition charge it needs to fire the plug. Excessive plug gap also results in cylinder misfiring, a possible no-start condition, wet, black or fouled plugs, engine hesitation and rough idle. Excessive spark plug gap also happens as result of normal electrode wear and age.
Incorrect spark plug gaps as above can cause the following symptoms;
* Rough Engine Idle
An engine that has a rough, irregular engine idle is often due to spark plugs that are incorrectly gapped. Spark plugs that are gapped incorrectly it will upset the air/fuel mixture, which in turn affects engine combustion and idle.
* Engine Hesitation
If spark plugs are gapped too wide, the ignition spark loses some of its strength as it crosses the spark plug gaps. This can result in engine hesitation.
* Engine Missing
Spark plugs gapped incorrectly can cause an engine to miss, or run erratically, especially during idle. The incorrect spark plug gaps can cause uneven firing of individual spark plugs and delay engine combustion; both of which can cause an engine to miss or idle erratically.
* Poor Engine Performance
For an engine to run at optimal levels, its spark plugs have to be gapped according to factory specifications. Any spark plugs that are gapped incorrectly can result in poor engine performance by altering engine combustion, weakening the ignition spark, and delaying the arcing of the ignition spark as it crosses each spark plug diode.
* Engine Knocking
Engine knocking, or engine pinging, is a classic sign of an engine that has incorrectly gapped spark plugs. Engine knocking is the result of incomplete or delayed engine combustion, especially under acceleration.
To set the gaps.
Remove the spark plugs and inspect them for damage. Inspect the firing end for condition and to see how the engine is running.
Remove any loose fowling or oil on the plug first. Take a small brass wire brush and remove the deposits until the metal surfaces are clean. Brass is a softer metal than the spark plug and will not damage it, but should be strong enough to remove any build ups.
If your spark plug has a terminal cap, check that it is fully done up. Use a pair of pliers to pinch it tight. If the cap is loose this will cause issues for connection and will give you erratic sparks.
Use you spark plug gap tool of choice to set the gap if you need too. There are the disc styles, feeler gauges and open loop styles. I like feeler gauges or the hoop wire design. These can be metric or imperial measurements depending on your choice.
Once I know the current gap by placing the correct gap setting tool into the gap, I can either open or close the gap as required. To close you can gently tap the electrode on a solid metal surface, or use T-shaped part of a special plug gap tool to close it. In order to open use the tool again and lever it upwards. If you don’t have the tool, be careful not to damage the electrodes at the bottom when trying to open the gaps.
Two different ways to gap spark plugs. Remember that when tapping the electrode at the bottom, the weight of the plug itself is enough to close the gap.
DON’T over tap it when closing the gap, little and often. Check, repeat.
The gauge or setting tool that you use, should have a slight drag on it when you pull it through the gap.
When refitting the spark plugs back into the engine always tighten the first few turns by hand first to avoid cross threading. Don’t knock the spark plug when inserting it. This could alter the spark plug gap and give you problems as described above.
If in doubt – recheck it.
Replace the spark plug boot with a very thin smear of dielectric grease to stop the rubber boot sticking to the top of the plug.
I hope that helps with an understanding of a forgotten and abused part of the engine. If not please read if you are having trouble sleeping. 🙂
The last official car of the ‘Season’ if you can call it, for me was back at Stonham Barns. This was to be the American Car Show on the 27th September 2020. I woke up to a grey sky completely devoid of any colour at all, but no rain was forecast all day, well not on any apps anyway. The wife did tell me that it would rain, woman’s intuition I believe it’s called. I was having none of that and set off with high hopes.
I got there just after nine and there wasn’t a lot there, maybe fifty cars or so. I got told to park up with a two meter distance between the cars. No argument from me there.