Synthetic Oils

SYNTHETIC OILS

Steve Kimball

They Promise a Lot, But Synthetics Aren't for Every Bike

Wanna get more horsepower, increase engine life, get better gas mileage, lower engine temperature, use less oil, and get easier starting? What an elixer that would take. Yet manufacturers of synthetic oils for four-strokes claim their products offer these and other benefits.

Now, why don’t motorcycle manufacturers recommend using synthetics of any kind in their motorcycles?

A number of readers have sent letters to the CW Service department asking about

synthetic lubricants in four-strokes. “If oil pressure drops considerably with thinning out of oil. how can that little pump handle a 5-w synthetic? Don't gears rely on heavy viscosity oils for proper cushioning? What about clutch slippage caused by this super lube? Are there high viscosity synthetic oils readily available which also have rust inhibitors? Which are the good brands and which are the bad brands?”

Asking questions about synthetic oil is like asking questions about motorcycles; other than having two wheels and a motor.

all motorcycles are different and other than providing some kind of lubrication, all synthetic oils are different.

The only similarity of the various synthetic oils is that the base stock forming the oils is made by chemically combining elements refined from good old crude oil. That's right, synthetic oils come from the same mineral oil base that conventional oils come from.

What makes synthetics different from normal mineral oils is the refining process that produces the oil. Normal oils are distilled from crude oil. To produce a synthetic', the refining process continues much further until very basic components of the crude oil are separated. Then the basic substances are combined into new molecular structures to form the base stocks of the synthetic oils. So while both mineral oils and synthetics are derived from petroleum, a lot of extra work goes into making synthetics. And more cost.

Once an oil is called synthetic, it could be an ester or a synthesized hydrocarbon. The esters could be either a diester or a polyol ester and the synthesized hydrocarbons can be either poly-alpha-olefins (PAOs) or alkylated benzenes. These four base stocks are the most common bases for synthetic oils, although other synthetic bases are used for lubricating industrial equipment for a variety of reasons. And these classifications can be broken down into more specific compounds such as ditridecyl adipate, ditridecyl azelate and diethylhexyl sebacate, w hich are all types of diesters.

All this multisyllabic mum boj urn bo really does mean something because the different types of synthetic oil have different properties. (See Table 1.) For instance, an alkylbenzene generally has excellent compatibility with conventional mineral oil but isn't any better at high temperature oxidation resistance, while a polyol ester has excellent high temperature oxidation resistance and onlv fair compatibility with mineral oil.

All of the synthetics share a common benefit: They have excellent low temperature properties. For extreme cold weather use. such as in the arctic, mineral oils must be made with very low viscosity, that is. the ability to pour at eold temperatures. Usually this compromises the lubricating properties of the oil at high temperature ranges. Because of the precise molecular configuration of the synthetics, they are more temperature stable, being able to flow at colder temperatures and retain usefulness at high temperatures, than mineral oils. For this reason the development and marketing of synthetics has been geared toward low temperature use.

For some reason, most motorcyclists aren't concerned about starting their motorcycle when the temperature is 50° below. Generally we're more concerned with high temperature lubrication.

“The motorcyclist has a tendency to believe that his demands on the motor oil exceed passenger car demands from a temperature standpoint." according to T.T. Ordiway of the Witco Chemical Corp. “That's because any of us w ho have spent an\ time on motorcycles have managed to burn ourselves at least once or twice. The facts are that the motorcycle engine oil sump temperatures do not run as hot as the passenger car sump temperatures do in today’s modern automobile."

Hard to believe, isn't it? Look at it this way. An engine runs more efficiently at higher temperatures, but if the temperature is too high the engine will be damaged. With a liquid cooled engine it's easy to keep engine temperature near the desirable maximum without fear of overheating.

With an air cooled motor on a motorcycle there's no thermostat to regulate operating temperatures. The engine has to be designed to provide enough cooling for the harshest operating conditions. That means in normal operation, the temperatures are lower than the normal temperatures of a liquid-cooled automobile engine. Another reason is the difference in power to weight ratio. A 530 lb. motorcycle with a 160 lb. rider and 75 bhp has a power to weight ratio of 9.2 lb./bhp. A 4000 lb. car w ith a 170 bhp motor has a 23.5 lb./bhp power to weight ratio. Both are designed to maintain safe operating temperatures under full throttle use. going up hills or accelerating. But the motorcycle doesn't need to use as much of its potential power as the car does and doesn’t use as much of its cooling capacity as a car under equal conditions. Going up the same hill a modern car will be flat out while a normal bike will be operating at half throttle, only using half its cooling capacity.

Still don't believe it? Checking back to the Cycle World oil cooler comparison test in the December. 1978 issue, a variety of motorcycles operated with normal sump temperatures of 200°. Under racing conditions a GS550 Suzuki hit 212° and a Yamaha TT500 thrashed in a sand wash hit 275°. but for normal street operation most of the bikes ran very close to 200°. Even w hen a Kawasaki KZ 1000 was loaded with fairing, saddlebags, rear trunk, two full grow n men and 50 lb. of cargo and run up a 12-mi. long grade in the Mojave desert the oil temperature only climbed to 234°.

As a comparison, all premium grade motor oils must pass a test simulating a big American car driving up a hill. A 425 cu. in. Oldsmobile engine is run on a dynamometer at 3000 rpm under load. The engine is carefully blueprinted before the test. Every eight hours during the test a sample is taken from the oil and the engine is torn down and analyzed for wear after 64 hours. Oil temperature in the engine is held down to 300° for the test with an oil cooler. Under similar operational conditions a motorcycle engine’s oil wouldn't get that hot.

The Oldsmobile sequence 111C test, as it’s officially called, is perhaps the best indication of how oils work in high temperature conditions. It's one of many tests an oil must pass in order to earn the SE rating from the American Petroleum Institute. That SE rating is really the only way for a consumer to know if he’s buying good or not-so-good oil. The S stands for spark-ignition engines and the E indicates what level of tests the oil has passed. An SA rated oil has passed no tests, an SB rated oil has passed a couple of tests, on up to the SE rated oils which have passed a whole series of tests. There are other tests for diesel engines and many oils will be labeled SE-CC. indicating they've passed the SE classification for spark ignition engines and the CC classification for compression ignition (diesel) engines.

TABLE 1

Oil Characteristics

Because motor oils are designed to pass the series of tests, tests ranging from rust control to sludge buildup, it might seem that as long as an oil has the SE rating it should work fine in any engine. Almost, but not quite. All motorcycle makers specific an SE rated oil for use in their products, but the tests don't include evaluations of use in wet clutches or gear boxes because the tests are designed by automobile makers, not motorcycle makers.

Right now there is a distinct lack of information about synthetic oil use in motorcycles. All motorcycle manufacturers recommend against using synthetics, even synthetics meeting the SE requirements, not because they know the synthetics won't work, but because they don't know if the synthetics do work. Even some of the synthetic oil manufacturers contacted recommended against using their products in motorcycles because there had been a lack of testing w ith motorcycles.

Take Mobil 1 for instance. Mobil w rote. “Mobil 1 was developed to replace conventional mineral oils and we would expect it to perform most satisfactorily in four-cycle motorcycle engines. However, since motorcycles represent a relatively small segment of the market for oil. we have not tested w idely in these engines and cannot make any recommendation for this application. An exception to the above is the BMW motorcycle. This manufacturer does not use valve stem guide seals in its engines. The basic design of the engine and absence of such seals make it possible for a light viscosity oil pass through the valve stem guide clearance space and enter the combustion chamber where it would be consumed . . . We do not recommend Mobil 1 for use in BMW motorcycles.''

Then there are mineral oils w ith friction modifiers such as Arco Graphite or Kendall Synthetic Fortified. Arco wrote. “We are not recommending Arco Graphite in a four-cycle motorcycle engine since a great number of them have the engine, crankcase and transmission clutch assembly with a common oil sump. The clutch facing material used varies considerably from one motorcycle manufacturer to another as well as with various models made by the same manufacturer. Therefore, it has been impractical to test all of these combinations with Arco Graphite . . . Those motorcycles not lubricated in such a fashion, that is. without the common sump, of course would be a different matter, and we would recommend the use of Arco Graphite for this application.”

Certainly some synthetic oil manufacturers do recommend their products for use in motorcycles. Ultrachem, makers of Chemlube synthetic and Chemlube Racing. wrote “These products are suitable for use with multi-plate wet clutches and transmissions as well as engines. They present no seal compatibility problems. Synthetics of the type we use are very well suited to high temperature sporadic use in severe service.”

One person who has experience using synthetics is Kaz Yoshima of Ontario Moto Tech Corp. His 500cc CB400 Four Hondas, running in club road races, were showing signs of inadequate lubrication and breaking before he changed to Ams/Oil. a synthetic. He hasn't had any more trouble with the highly stressed engines. Sinee switching to the synthetic, Yoshima has been running the engines at higher speeds and has noted lower sump temperatures, all without incident.

Running with sump temperatures as high as 280°. Yoshima says oil pressure remains higher with the synthetic than it did with 40w Castrol R bean oil. His race bikes run at speeds up to 13.500 rpm. which makes rod bearing lubrication very sensitive. Yoshima says the bearings showsigns of glazing and gauling w ith the bean oil and failed with normal mineral oil before he switched to the synthetic.

According to literature published on synthetics, they do stand up well to such severe use, which is why the synthetics generally are advertised as providing extended drain intervals. But this. too. is less important for most motorcycles than most automobiles. Because the synthetics don't break down as quickly as mineral oils under high temperature or high load conditions. thev maintain viscosity longer. But any oil gets contaminated with combustion byproducts and must be changed to remove the byproducts. For motorcycles stored during the winter, it’s a good idea to change oil before storage and again at the start of the riding season. At the longest, synthetics must be changed yearly or every 25.000 mi. But how many motorcycles are ridden 25.000 mi. in a season?

Much research is being done by the oil companies into synthetic lubricants, but the major stumbling block to the further development of synthetics is the cost. According to Michael McHenry of Castrol. “We have vet to see a favorable cost/ benefit ratio that justifies fully synthetic products. That is. 100 percent synthetic products cost the consumer four to five times more than mineral oils but do not deliver benefits that are four to five times better in value. There must be more justification than a marketing novelty. This is not an indictment of these materials, but a reflection of the state of the art. We do feel that benefits can be gained through part synthetics, especially in the aircooled fourstroke area and we are working towards that end."

To answer the questions about synthetic oils in motorcycles, there are several points to keep in mind. You may sacrifice the warranty of your new motorcycle by using a synthetic. Oil should be changed at least once a year even with a synthetic w hether it's been run 25.000 mi. or not. Some people have used synthetics with wet clutches without problem, but there is little experience to relv on. A 5w-40 viscosity synthetic will pour as a five weight oil at cold temperatures, but it has the viscosity of a 40 weight oil at normal operating temperatures. In order to display an API SE designation, any oil. mineral or synthetic. must pass the same tests which indicate the oil's stability in heat, rust prevention, sludge prevention, wear resistance and other characteristics.

One question not asked by the readers but perhaps of interest: do the motorcyclists at Cycle World use synthetic oils in four-stroke motorcycles? Generally, no. But some riders here have used synthetic oils in special racing applications when excessive oil temperatures were anticipated. Should you use a synthetic? If you have a special need for it or a particular lubrication problem, a synthetic may öftere help.

Synthetics do offer real advantages to mineral oils when evaluated in the laboratory. Their viscosity changes less with temperature changes. They are generally more stable at high temperature. Their lower volatility can mean lower oil burning in the piston ring area. Reduced ash deposits can minimize preignition.

As T.T. Ordiwav of Witco Chemicals commented. “The only problem is that when you translate this out into the field you are talking about conditions that simply do not exist, and you are talking about advantages that the engines cannot appreciate.”