Hot Spark Plugs Vs Cold Spark Plugs

In modern, computer-controlled cars, ignitions are reliable to the point where you rarely consider that they might fail. You have coil-on plugs, also called stick coils, snapped onto the tops of spark plugs, with not even a plug wire between them. The stick coils and plugs are typically hidden inside the engine under a plastic cover that looks like the top of a Shop-Vac. There’s no distributor, because the functions of advancing the spark with increasing engine rpm and distributing it to each cylinder are performed electronically, with everything controlled by the car’s electronic control unit, or ECU.

This is not the case in classic, antique and brass era cars, unless they have been changed-over to electronic ignitions. If, however, you do have the original ignition, a lot can be learned about the running of your engine.

A hotter plug does what is says, it runs hotter. This will not give any more power and neither will a too cold plug. Because the spark plug resides in the combustion chamber, it’s influenced by what happens there. It serves a dual purpose; not only is it responsible for initiating the combustion event, but it gladly tells the tale of how the chemical to mechanical energy exchange process took place. If all is well, the plug is clean, but if something is not correct, it will leave its mark for the trained eye to diagnose. In many ways, the spark plug could be looked at as one of the first forensic investigators. You can work out whether you need a hotter or colder plug by looking at the current ones. If the current plug is too hot then the tip may be melted or deformed. If the plug is too cold then you may have excessive build up (which can also be caused by burning oil or a rich air-fuel mixture).

If you can be “tuned in” to your plugs, you will be able to read problems in your old car before it leaves you by the road. Cleaning with steel wool is better than nothing. Using a spark plug sand blaster gives the best cleaning although you can damage the porcelain insulation and cause the spark to “go to ground” somewhere besides the end electrode, it’s proper destination.

Encrusted black carbon is a sign of problems. The causes of this condition may be a cold type of plug, which is proper if you are using the car for long road trips. If all you are doing is driving the car off and on a trailer or around the block and back, change to a hot plug.

Excessive oil reaching the combustion chamber, especially at slow or idling speeds, is also a frequent contributor. A hot plug temporarily may solve the problem, but excessive oil is a sign of other problems, as in bad rings or pistons.

If some of the plugs are clean and others have dry sooty lamp black deposits, the sooty plugs are getting too much gasoline, and can be corrected with carburetor adjustments. If a leaner mix is used, and the engine runs irregularly or misfires, go back to original setting and consider a hotter plug.

Incorrect gaps also contribute to fouling, and is attributed to too narrow a gap. Check the gap and published specs on your car and re-gap all plugs.
The spark plug tip temperature must remain between 930°F to 1560°F , regardless of the type of engine the plug is fitted in.

If the tip temperature is lower than 930°F, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling, leading to misfire.

If the tip temperature is higher than 1560°F, the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage.

In identical spark plug types, the difference from one heat range to the next is the ability to remove or add approximately 150°F to 200°F in the combustion chamber.

A Franklin Automobile Enthusiasts

Do you remember the TV series Mash? 

Did you know those helicopters that flew in wounded soldiers were Bell 47s units….and the engines they used were Franklin engines

The Franklin O-335 air-cooled aircraft engines were six-cylinder, horizontally-opposed displacing 335 cu in with a power output of around 225HP. 

When the Franklin auto company went bankrupt in 1933, two of Franklin’s employees purchased the rights to the engine and continued to use the name Franklin. The engines were used in trucks and as stationary units, until WWll began and then went into production for use in over 15 U.S aircraft and helicopters. 

Republic Aviation Inc. purchased the Franklin engine rights in 1945 and produced the Franklin engines for light amphibious aircraft. This company was short-lived with the war ending that year. 

In 1947, the Tucker Car Corporation purchased the engine rights, where the 50 cars that Tucker produced, were powered by Franklin engines. The home of the Tucker Car Club is now at the AACA Museum in Hershey, PA. Tucker reworked the engine from air-cooled to water-cooled and many examples can be seen on the museum floor today. 

In 1961, the Tucker family sold the engine rights to a company called Aero Industries and from there to the “Government of Poland” in 1975. The Polish engine manufacturer is today called “Franklin Aircraft Engines” and are manufactured in Grudziądz city in Poland. 

Saab 900

Absent any questions this month, I will briefly discuss some cars in my shop this month. Both of my sons now have cars. I wanted their first cars to be something durable, safe and inexpensive. Somehow, each of them ended up with a Saab 900 four door. 

When I learned how to drive, people maintained their own cars. Times have changed. Today, people don’t work on cars; they either take it to someone to have it repaired, or they replace it with another car needing less work. 

My older son has a strong interest in cars, and has a nice 900 Turbo. It needed some work when we got it, and while fixing it he was able to learn some basics on how things work and how to maintain a car. My younger son was just looking for basic transportation, and he found it with a base model 900 with an automatic transmission. This car needed a lot of work, and he and I have been working on it for the past year or so. This car was not really worth saving, but was almost too good to scrap. 

These projects are teaching basic auto mechanic skills, like brakes, suspension, electrical and exhaust and also more advanced body work skills with rust and dent repair and painting. They will not only learn skills to maintain a car, but also will have some personal investment in their cars. 

These projects also provide an opportunity to spend time with them. Cars come and go, but quality memories last a lifetime. 

Timing Is Everything!

A co-worker of mine just had an expensive experience with her Volkswagen. 

vw 5v timing

The car has the two liter twin cam engine, with a timing belt. The car had 85,000 miles on it, and had the original belt. This engine has five valves per cylinder, and it is an interference engine, meaning the valves will hit the pistons if the camshafts turn out of sync with the crankshaft. 

Unfortunately, the timing belt broke. When the belt broke, the valves hit the pistons, bending the valves. What should have been a several hundred dollar preventative maintenance repair, just became minimally a $1,200 repair. Minimally, the head needs to be rebuilt with new valves, if it can be saved. The head may well have to be replaced. The pistons could be damaged as well. 

If your car has a timing belt, it is not worth delaying the timing belt replacement, especially if it has an interference engine. A proper repair may involve replacing the water pump, camshaft seals and the front crankshaft seal. 

A Positively Good Idea

Recently I attended a SCCV driving event. Part of their pre-event inspection is verification of a cover for the hot battery terminal. I checked my car a few days before, and realized the positive battery terminal was not covered. I spent a minute thinking of all the possible ways the positive terminal could be accidentally shorted to ground. If nothing else, when working on the car, a wrench or other tool could easily be accidentally dropped, causing a direct short. 

The positive terminal is just a few inches from the aluminum A/C lines, the inner fender, and numerous bare nuts and bolts. I can understand the concern, the battery could easily be accidentally shorted out. 

I went to the local auto parts store and bought a pair of universal battery terminal covers. I had to cut it a little to make it fit my car. Just for good measure, I used a red zip tie to hold it in place. 

I passed the safety check with no issues, they checked to ensure the battery was securely held down, that the hot terminal is covered, the front end was tight, and there was nothing loose on the body of the car. 

I have also decided that the hot terminal of all my cars will be covered, as an extra safety measure. The $5 spent for terminal covers is cheap insurance and piece of mind. These covers can easily and quickly be removed for display on show cars. 

My rear disc brakes with the emergency drum brake

disc brakes with emergency brake
An example of a drum emergency brake with regular disc brakes. 

This was the good news! Something strange happened to me last week. I loaded the garbage and the recycling into the minivan to do the Saturday trip to the transfer station, and the right rear wheel locked up when I backed up. As this happened, the rear axle made unpleasant noises. I thought the parking brake was seized, and was relieved when the wheel moved ok going forward. 

On the way home, the right rear wheel locked up while driving forward, making horrific noises. Again, I thought the noise was originating from the rear axle. I definitely heard the differential banging against the frame cross member it is mounted on. I drove up my driveway, with the wheel seized. I googled the problem, and found many stories of the rear differential failing, causing a rear wheel to lock up. Fortunately, the part is available rebuilt, but they are expensive. 

I planned on removing the differential to verify it was in fact bad before I purchased a used or rebuilt unit. I thought I should check the right rear hub first to rule out any problem there. Fortunately, I found the problem. This vehicle has four wheel disc brakes, with the parking brake on the rear. The parking brake has conventional brake shoes on a drum in the center of a “hat” type rotor. Somehow, something came apart with the parking brake assembly, and the whole assembly broke apart and jammed against the rotor. I have to replace the backing plate, caliper mount, rotor and the whole parking brake assembly. It is bad, but infinitely better than a bad differential. I have never seen anything like this before. 


A few more points about BEARINGS 

Pictured below, and the following is an article from the December, 1960, “Science and Mechanics” magazine. 

Bearing Lubricates Itself 

wheel bearings

Designed to replace ball bearings and have several times their life expectancy, this new Hy-Film bearing never requires relubrication. It utilizes the phenomenon of hydrodynamic oil film. The diagram at left: (1) Oil is drawn from reservoir through bearing window; (2) rota-tion of inner tace under load generates hydrodynamic oil film, supporting race without metal contact; (3) oil forced to bearing ends by film pressure lubricates thrust washer and (4) oil is picked up by slinger and returned to retaining cup, where it is reabsorbed by Permawick in oil return hole. Tann Bearing Company of Detroit, Michigan, designed and developed the bearing. 

What is hydrostatic and hydrodynamic bearing? Hydrostatic bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and the pressurization is done by a pump. Hydrodynamic bearings rely on the high speed of the journal (the part of the shaft resting on the fluid) to pressurize the fluid in a wedge between the faces. 

What are the types of bearings? There are many types of bearings, each used for different purposes. These include ball bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller thrust bearings. 


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I am running out of ideas on what to write about in this column. If you have any ideas, or any questions you want me to answer, please let me know. 

Dave’s Garage…email: dasander@aol.com 

One Thing Leads to…

With no questions to answer this month, I thought I would share an interesting story. 

Have you ever been putting off a big job, expecting it to be difficult, only to be pleasantly surprised at how simple it is? I have had this happen to me. I have also had what should be very simple job turn out to be a nightmare. I recently had what should have been a simple job turn out to be a much bigger job. 

In August I lost the clutch in one of my Saab 900s. This car was from Southern California. It has never seen salt, and rarely saw rain. It is a fun car to work on. Nothing is rusted or frozen. 

saab 900s clutch

Now, on a Saab 900 the engine is bolted on top of the transmission, and the whole assembly is mounted backwards in the car. The clutch is on the back of the engine, which is up front by the radiator. I have done a complete clutch job in about an hour. It is a relatively quick and simple job. 

I realized the problem with the Saab clutch was the master cylinder. I ordered a new one and attempted to install it. It is a traditional master cylinder attached to the firewall with two studs. I was just finishing the installation when one of the studs broke off. I was just tightening the nuts on the studs when the wrench came loose. I had just begun to snug the nut, I hadn’t even begun to apply much tightening force. I removed the part to find that the ear, the stud was threaded into, actually broke off. It was a defective casting. Ok. No big deal. I obtained a replacement and installed it. 

When I drove the car to work the next day I noticed the cruise control no longer worked. Somehow while working under the dash I broke the cruise control. On the way hone, I lost the clutch again. A quick inspection revealed the hydraulic hose between the master and the slave burst. Ok, not a big deal. I replaced the hose. As I was bleeding the clutch, the slave cylinder blew. To replace the slave cylinder the entire clutch assembly needs to be removed. When I removed the clutch assembly, I noticed the rear main seal on the engine, and the pilot shaft seal on the transmission were leaking, the clutch had oil on it, and the pilot bearing was seized. I ordered a complete clutch kit, and new seals. I resurfaced the flywheel while it was apart, and installed the new seals and the new pilot bushing. 

I had a bear of a time installing the new clutch, it just did not fit. I couldn’t align the pressure plate quite right to install the bolts, and the pilot shaft just would not fit in the clutch disk. After wrestling with it for over two hours, and cutting my hands several times, I realized I had the wrong parts. They were boxed wrong. I had ordered the right parts, but the parts supplier gave me the wrong parts. After a conversation with the parts supplier I received the correct parts, and again attempted to install the clutch. I had it almost installed, when I realized one of the dowel pins fell out of the flywheel. I had to take the assembly apart to get the pin out of the bell housing. After reassembly I was installing the slave cylinder bolts when one of them stripped. I could not understand how it stripped, as I never snugged the bolt. Again, the whole assembly had to come apart to fix the stripped threads. I realized someone had installed the wrong bolts at some point, these bolts were too short, and one was cross threaded. 

The project is almost done. Hopefully I just have to bleed the clutch and finish putting it back together. Should be done this weekend, almost four months later… 

Rust Repair

Recently I have had two cars in the garage for rust repair, a Saab 900 and an MGB.

The interesting thing is, on each car the rust was caused by poor body work. Each car had plastic body filler repairing a dent. The body filler was applied to bare metal. At some point, the body filler cracked and moisture seeped in. Body filler does not stop water.

Water can creep down through the filler to the bare metal, and cause rust. On each car the metal behind the body filler had rusted away, leaving rust holes.

After I do the hammering and welding, I coat bare metal with epoxy primer BEFORE I apply any body filler. I also start with aluminum body filler first, then transition to traditional polyester body filler. Aluminum body filler does offer some resistance to moisture.

To fix these rust holes, I used a cut off wheel to cut out the rusted metal. Next, I traced the cut out piece on new sheet metal with a sharpie marker. I carefully cut the piece out, subtracting about 1/16” on each side. The new piece was carefully mig welded in, only welding about 1/4” at a time to prevent heat warpage. After the weld-ing is finished, the welds are ground flush and the metal is hammered flat. Next I apply a layer of epoxy primer, followed by a light skim coat of body filler.

 

Automotive Primers

1018 primer adMy last column discussed the evolution in paint technology. This month, I will talk about what is under the paint and talk about primers.

Automotive primers have come a long way in the last few decades. Primers serve several functions. First, they bond to and protect bare metal. Second, they fill very small imperfections. Third, they provide a stable base foundation for the top coat, or color paint.

Why are there so many types of primer? Not too long ago, primers were lacquer based. If the top coat was lacquer this was simply applied over the primer. If the top coat was an enamel paint, an enamel primer/sealer was applied over the lacquer primer. These primers were often unstable, and did little to protect metal from corrosion. Lacquer primers would shrink months or years after being sprayed, showing sanding marks and causing the top coat of paint to crack. Lacquer base primers do not shed water, they actually absorbed some moisture. This moisture would then find its way down to the bare metal. Of course, lacquer based paint will go back to a liquid when exposed to a solvent, like lacquer thinner.

auto paint sprayAcid etching primers did a good job of adhering to bare metal, but offered little corrosion protection.

Epoxy primers, or “2K” primers bond well to bare metal, and also offer excellent corrosion protection. Epoxy primers are not sandable, and do not work well as a primer surfacer.

Primer-surfacers are used for final body work to give a smooth, flat surface foundation for the top coat or color paint. These primers have filler in them, and are easily sandable. These are the primers that are laboriously block sanded until the surface is smooth and flat.

Once the block sanding is done the primer is sealed with a sealer primer.

Final paint will show color shift if painted over different color primers, and will also show any sanding marks. Color paint is only a pigment, and will not hide anything underneath.

Confused yet? Don’t be. There is a system to priming. You may remember about 20 years or so ago car ads talked about the multi layers of paint. As urethane paints began to dominate the automotive paints, these “multi-layer” paints became standard.

First, an epoxy, or catalyzed primer coats and seals bare metal. There may be a self etching or acid etching primer under the epoxy primer. Epoxy primer has exceptional adhesion and corrosion protection.

Over the epoxy primer is a primer surfacer. This primer is sanded smooth and flat. Over the primer surfacer is a sealer. The purpose of the sealer is to provide a thin, hard, smooth surface over the primers for the color coat. Without the sealer primer, sanding marks and color changes will show in the top coat of paint. Sealers need to be top coated relatively quickly for the color paint to bond well.

If the color coat is a base/clear system, then there are two additional layers of paint on top of the primers.

I am amazed at how well these new primers work. I have had excellent results with using epoxy primer for rust repair. The rust repair actually outlasts the factory corrosion protection. Two part catalyzed primer surfacers are easy to sand, and remain stable forever. No more sanding marks showing up months after a car is painted. I often use epoxy primer thinned with reducer as a sealer. It is a bit more expensive than sealer, but it is one less product to have on hand, and I have been very pleased with the results.

Automotive Paints

This month’s question comes from Wendell Nobel:

Dave, I would love to read a little dissertation on automotive paints. I recall a day when GM cars were all painted with acrylic lacquer and Fords were acrylic enamel. Now we have polyurethane base coat with clear coat, single stage urethane and even some water based stuff. What is an antique car guy to make of it all? Should we use what was on the car when new or get up to date? Will environmental laws make the question moot?

Let me first briefly explain the history of automotive paints. The early autos were painted with the same paint people had been painting carriages with for years. There was no “automotive” paint. Not paint in the traditional sense we think of when we talk about paint today. Early paint was basically linseed oil and a binder, with pigment, or crude shellac. This paint was applied with a brush and took a long time to dry. These paints were not very durable, often literally falling off the metal in a year or two. These finishes offered very little U/V protection and broke down quickly.

The biggest challenge with producing the Model T Ford and other early cars was the time and space needed to paint cars. The parts were laid out on the floor and took days to dry. This bottle neck in the production was a huge problem.

Nitrocellulose Lacquer paint was developed to alleviate the time/space problem. Nitrocellulose Lacquer paint is made from the nitration of cellulose plants (boiling down plant fibers and mixing with nitric acid). This is also how celluloid film was made. The solvents evaporate from the paint, leaving a glossy durable paint finish. These paints need to be “rubbed out” to produce a shine. This paint does not “cure” and will return to a liquid state when solvents are applied. A popular early nitrocellulose lacquer paint was DuPont “Duco” paint.

Nitrocellulose Lacquer dominated the automotive paint market from the early 1920s well in to the 1950’s when it was displaced by Acrylic Lacquer, a synthetic polymer acrylic resin based lacquer. Acrylic Lacquer dried quickly, however, still needed to be buffed to a high gloss.

Enamel paints used enamel resins. This type of paint takes much longer to dry than lacquer and actually dries in two steps. First, the enamel reducer evaporates and the paint becomes solid. Next, the resin oxidizes when it reacts to the air. This is why the new finish cannot be waxed for 30 days after application. The enamel paints dry to a hard, glossy finish and do not need the rubbing out as lacquer needs. The drying of enamel paints could be accelerated by the use of a baking oven.

Enamel paints required the need for clean spray booths. The paint took so much longer to dry than lacquer paints; the finish was much more susceptible to damage from debris before it dried.

Lacquer and enamel paints were much more durable than the paint they replaced, but still offered minimal protection against U/V light and corrosion.

Lacquer and enamel paints are very unstable, and begin a color shift almost immediately. This fact makes them very hard to color match. People go to great lengths to match original colors. Unfortunately, the reality is the “original” color was so unstable there really is no true original color. Two cars painted the same color at the same time would not match each other after a few years time.

Today’s urethane paints offer much more protection than the lacquer and enamel paints they replaced. Urethane paint cures in three steps: evaporation of the reducer, oxidation of the resin and an irreversible chemical reaction between the resin and the isocyanate catalyst. Urethane paints began to be widely used in the late 1980s.

Base/clear paints offer even more protection. The color coat is completely buried under a protective clear coat. The clear coat provides the gloss in the paint.

Modern catalyzed urethane primers and paints offer a finish that can easily last the life of the car. I have found bare metal painted with epoxy primer and top coated with urethane paint offered very effective protection against corrosion.

So, what is an old car person to do?

Nitrocellulose Lacquer is almost impossible to find today. It also cracks easily, and will return to a liquid when exposed to solvents. Lacquer requires sanding and buffing to get a good gloss. Enamel paints are harder to paint, do not have stable color pigments, and oxidize quickly.

An authentic restoration would require the use of the original type of paint. Modern urethane paints do not have the same gloss and color hue; however, they are much more stable. Enamel paints are still available, although somewhat hard to get. Given the time and expense involved in a proper paint job, you have to consider the service life of the paint. Do you want to paint it again in 10 or 15 years?

Modern urethane paints are very forgiving to paint, and last a long time. Modern urethane finishes have a fantastic shine, and require minimal maintenance.

If you want to exactly duplicate an original car, you may want to consider a period correct paint. If you want the best shine, great corrosion protection and minimal maintenance you probably want a modern catalyzed urethane paint. I guess it is ultimately up to the user to decide which way to go.

Just to complicate things, there are new paints being used now which are replacing urethane paints. Waterborne paints are now on the market. Waterborne paints do not have the Volatile Organic Compound exposure of urethane paints. Use of waterborne paint, is being mandated slowly, due to environmental concerns.