 Techline-October08-Oil Coolers - Pt I - Adversary is Heat
Why do people debate whether an oil cooler is necessary on air-cooled Big Twins and Sportsters? I just do not get it. There is no reason whatsoever not to run one, or even two, as I do. Moreover, I’m not talking about those cute little chrome ones, although they are better than nothing. We want those big — ugly to some — black coolers with 10 rows of turbulation enhancers, mixing the hot oil in order to obtain maximum heat-exchange dissipation. Heat is the enemy!
Why is there a debate over oil coolers and synthetic oil? It’s like the synthetic oil versus fossil oil debate. Once an engine is broken in with fossil oil, there is no excuse for not switching to synthetic oil! Oh, the naysayers preach their half-truths passed down from the so-called experts. Differing opinions based on mythological mistruths bombard the Harley rider from every quarter. What is he to do? Many times, nothing, as he stays with the status quo for fear of damaging his ride. A well-
chosen oil cooler like Jagg and the use of synthetic oil will help protect against the great engine destroyer, ravaging detonation.
The proper oil cooler and the use of synthetic oil will allow your Twin Cam to run cooler. The use of synthetic oil will allow for an easier, low-temperature weather start-up. More importantly, it will flow faster to starved and drained areas, especially in the cold. Synthetic oil will also adhere to parts longer after shutting the bike down, which benefits you at start-up. Furthermore, synthetics retain higher viscosity while subjected to high-temperature, high-stress conditions. Oil that is more viscous is a superior protector for the engine. Fossil oils break down at a faster rate from the ravaging effects of heat-oxidation than synthetics. Synthetics break down at much higher temperatures than fossil oils.
Finally, to counter a pervasive mistruth propagated by the fear mongers, I know of no case of bearing skid with the use of a synthetic. I have taken the trouble over the years to ask various bearing and oil companies that supply Harley-Davidson, like the respected Timken. This myth derives from the slipperiness characteristic of synthetic over fossil. We want slippery. We also want the superior film strength of oil, which separates moving parts sometimes only molecules thick.
Synthetic is tough; its film’s strength and slippery attributes protect the engine better than fossil oil. The only downside I see is that synthetic oil is more expensive than its fossil counterpart. Of course, the gap in pricing will become less as out-of-the-ground oil prices steadily rise.
Great Engine Destroyer
Detonation is defined as excess heat causing an unwelcome, spontaneous, complete ignition of unburned air/fuel anywhere in the combustion chamber in addition to the normal, planned, timed spark ignition of the air/fuel mixture. Ignition, whether deliberately sparked or unprompted, causes a flame front to travel across the cylinder.
Even though everything I just described happens in a millisecond, there is a principle of physics called combustion lag, meaning it takes time for the fuel molecules to heat up and finally begin to burn. This combustion lag is partially responsible for the need to advance and retard ignition timing. And once the air/fuel mixture is burning, combustion lag continues to delay the ignition of the yet-unburned air/fuel mixture as the flame moves across the combustion chamber. We call this traveling flame a flame front.
Because of combustion lag, the first ignition of the air/fuel mixture must occur before the compression cycle finishes, while the piston is still rising. The flame front must complete its journey across the combustion chamber as the piston is on its way down on the power stroke to ensure that the highest percentage of burn produces the maximum amount of gas expansion to create the maximum amount of usable power.
Octane: Engine Salvation
You do not want explosions in the combustion chamber. Octane is mixed into gasoline to prevent these uninvited and unplanned outbursts of counterproductive activity. Unless, of course, detonation overwhelms the normal burning process. One of the great advances of engine technology in the early 1900s was the discovery of octane. There are many different octane substances or elements. The best early example is lead, which controls the rate of burn. Before octane, haphazard explosions destructively allowed the first engines to hack along with much inefficiency. Octane has the ability to stop chaotic explosions and bring order to the combustion chamber.
My e-mail buddy Mike always sets me straight when I’m wrong or sloppy in my definitions. He once wrote, “Octane is a very specific compound used for comparative testing of detonation resistance of other fuels. The chemical soup we call gasoline does not contain octane, and the additive we put in it does not add octane. We add and delete components to enhance the octane rating. Tetra-ethyl lead was the old and easy way, now it’s a lot more complex. Some are even oxygenates (MTBE and all the alcohols) that also lean the mixture and diminish power unless we compensate for them.” Mike always wrecks my neat and simple explanations, but I appreciate his correctness. Wait until you see how he demolishes my detonation explanation.
Enhanced octane reduces harm inside the engine, but many times produces harm to the environment and to us. Lead, for example, causes mental retardation and learning disabilities in children. It does so to a lesser extent with adults because children will put substances in their mouths that adults will not. Kids will eat things like sweet-tasting lead paint chips or suck on lead pencils. Lead tastes good.
Back in the day, engine exhaust left lead residue everywhere on the ground and in the soil where children play. The government, not as fast as it should have been, quite rightly banned lead after a half century of exploited use. The problem is that lead is a wonderful, albeit dirty, octane enhancer. Successive octanes did not wreak havoc with children’s brains, but they did cause cancer because of all that exhaust permeating the air with silent, debilitating, and, sometimes, carcinogenic fumes. The advantage of the alcohols, like ethanol, is that they burn cleanly. They are a safe octane enhancement. However, Harley-Davidson needs to use ethanol-resistant rubber compounds in manifold seals and other induction components, as ethanol will distort traditionally used rubber composites.
Harley-Davidson warns against high ethanol levels in pump gasoline for this reason. Consult your manual for the acceptable ethanol level for your year and model machine. Gas pump signage usually has percentage levels of contained ethanol near the price-per-gallon notice.
An octane enhancer discourages unwarranted explosions. Octane causes fuel to burn at a predetermined rate. Knowing how long it takes a flame front to travel across a combustion chamber allows the engine designer and tuner alike to advance or retard the ignition timing as needed to get the desired results. The performance tuner can cause the spark plug to ignite the air/fuel mixture at the most auspicious time for maximum fuel burning, known as the percentage of burn, thus creating the maximum amount of heat. Heat expands the gases trapped in the cylinder creating pressure. This pressure drives the piston down, spinning the flywheels, and transferring this energy down the powertrain to the rear tire. Rate of burn, piston speed, and cylinder diameter are some of the main factors determining ignition timing. They also have a part in determining cam timing, which is when the intake and exhaust valves open and close. Thus, the complex blueprint of valves opening and closing and ignition occurring before a compressing piston reaches the top of its stroke, is all about combustion lag, rate of burn, size of cylinders, mechanical parts’ movement lag, piston speed, and the list goes on.
Heat: Savior & Enemy
Modern engine management systems generate a hot spark that jumps across a large gap on the spark plug electrode. Compare the old mechanical points/condenser ignition systems, which have a spark plug gap of around 0.028" with a Twin Cam’s spark plug gap of as much as 0.043". This represents about a 65-percent increase. In order to do this, coil voltage increased from about 18,000 volts to over 40,000 volts.
We need this hot a spark to ignite the lean air/fuel ratios used in modern engines to meet emissions requirements. These lean mixtures burn very hot. Burning some of the generated residual oxides and other pollutants in this high-heat process is the goal from an emissions control point of view.
Heat provides relief from the dictates of the EPA, CARB, and other agencies that monitor the quality of our environment. Manufacturers like H-D use extreme heat in the combustion chamber to burn off noxious pollutants. After all, Harley-Davidson cannot produce vast quantities of motorcycles unless it is able to comply with ongoing, emissions directives.
However, excess heat is the enemy of octane, since it can sometimes produce detonation. Ever increasingly strict EPA regulations dictate that as many emissions as possible are to be incinerated inside the combustion chamber. This necessitates lean burning air/fuel mixtures where the percentage of air is higher relative to fuel than it would be in a power-orientated air/fuel mix. A high percentage of air molecules mixing with a small percentage of gasoline molecules is one cause of excess heat. Lean burning creates excessive heat. Modern ignition systems, more appropriately called engine management systems, have gone a long way to allow lean burning of fuel while attempting to control the ravages of the great engine destroyer, detonation. Detonation, also known as knock, spark knock, and pinging, sounds like there are a bunch of ball bearings bouncing around inside the cylinders. Ongoing detonation, occurring rapidly, is injurious to the engine.
I, like many others, used to think that detonation was the violent collision of two or more flame fronts traveling across the combustion chamber, and have written so many times in the past. I was wrong. Mike let me know this in no uncertain terms, as he asked me rhetorically how I would explain dual-plugging a cylinder head. As soon as he asked this question, it cut right to the bone. Obviously, there would be a collision of flame fronts. Why isn’t this injurious like a fabricated detonation? Time to listen and learn, or relearn, as is my case. After his devastating question, Mike went on to explain: “What actually happens is normal flame propagation generates a pressure wave as it travels across the combustion chamber. If pressure and temperature of the yet unburned mixture exceeds its ability to resist combustion the balance all goes off at once — detonates. There are many causes for detonation. The obvious two, poor-quality fuel or overadvanced ignition timing, are just the beginning. Anything that affects relative cylinder pressure is a part of the equation. Static-compression ratio, valve timing, and the often-neglected rod-to-stroke ratio, are interesting variables to think about. When you increase the stroke with little or no increase in rod length, piston speed relative to degrees of crank rotation over TDC (top dead center) goes ballistic. Now consider that from the perspective of combustion chamber volume, pressures, fuel, and ignition requirements. Colliding flame fronts are an old wives’ tale.” Mike stomped me good, but quite appropriately, on that one, even though I corrected his grammar. That is, everything except the end-of-sentence preposition. (I’m sure that when he reads this, he will also be updating my grammar.)
Anyway, one flame front is as designed while detonation is a rogue, spontaneous, a total explosion out to create trouble. The rogue element disrupts the timing of engine components whose job is to create power. If unwanted detonation ignites before or after the spark plug, it will destructively and simultaneously burn the air/fuel mixture at the wrong time, so there is not enough mixture to burn when the legitimate ignition occurs. If it ignites at the same time elsewhere in the cylinder, it will grossly interfere with the legitimate front, screwing up that particular ignition cycle. Mike was kind enough to take the time to list some causal factors of temperatures reaching into spontaneous ignition ranges, which cause the counterproductive and ravaging detonation. Other assists to detonation are lugging the engine, high-rpm riding, extreme summer temperatures, low-viscosity oil, and other factors. Let’s look at these individually.
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