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Sumpology: The Secret World of Four-Stroke Oil
The life blood of a four-stroke engine is motor oil. It breathes it, eats it and oozes it. Most four strokes, save the CRF450 and CRF250, use the same oil to lubricate the valves, cam, piston, crank, clutch, and transmission. This shared oil forces the motor oil to lubricate more than double the moving parts as the independent premix and gearbox of a two-stroke.

In an effort to reduce weight, maximize power and trim the cases, your light-weight four-stroke motocross engine uses just enough oil to get the job done. On a racing machine, it's more important than ever to use the best racing oil made and to change it routinely.

QUESTION:
IS AUTOMOTIVE MOTOR OIL BAD FOR A MOTORCYCLE?

ANSWER: Not bad, but probably not the best. Why not? It is designed in reverse order to a motorcycle oil. The priority hierarchy of automotive oil is:

(1) Maximize fuel economy
(2) Reduce emissions
(3) Offer protection for the moving parts

Today's automotive motor oils do not have the same degree of extreme pressure and anti-wear agents that they did just a decade ago.

QUESTION:
WHEN WAS AUTOMOTIVE OIL AT IT'S BEST?

ANSWER: Oil changed ten years ago when automakers were pressured to clean up the air. Since 1993, the entire automotive industry has worked to reduce exhaust emissions. Automotive motor oil must adhere to the performance categories set by the American Petroleum Institute (API).

These are called the API service categories. The API categories have been around for 50 years, but for the first 35, the categories were upgraded six times to meet the demand for higher engine performance.
The current API designation is SL. The API SL oils are designed to provide better high departure deposit control and lower oil consumption. SL oils are missing important agents that improve extreme use lubrication. In their place are friction modifiers that improve fuel economy.

QUESTION:
WILL AUTOMOTIVE MOTOR OIL HURT MY BIKE?

ANSWER: It could. If you're using and automotive motor oil in your racing four-stroke, you're not buying the best protection. An API SL oil is missing vital anti-wear components:
The most important being Zinc, Phosphorus, and Sulfur. These agents are harmful to the catalyst that is used to diminish the level of pollutants in automobile exhaust.

QUESTION:
WILL AUTOMOTIVE OIL HURT MY CLUTCH?

ANSWER: YES ! The friction modifiers in motor oil improve fuel economy by making it easier for the gears, bearings, pistons and rings to slip, slide and turn inside the engine. Unfortunately, these friction-minimizing agents also make it easier for the clutch in a motorcycle to slip. If you are using automotive motor oil in your bike, apart from CRF's, you are losing hook-up and acceleration, as well as reducing the life of the clutch.

QUESTION:
WHY SHOULD I MEMORIZE THE ACRONYM " JASO"?

ANSWER: As soon as it became apparent the the American Government was mandating economy over protection, the Japanese Automotive Standard Organization (JASO) developed a standard specifically for performance four-stroke motorcycles. JASO designates two different four-stroke oil classifications:
MA and MB. The MB oil is low friction and the MA is without the friction enhancers (ie. Honda synthetic silver and gold)

QUESTION:
WHY ARE MOTORCYCLE-SPECIFIC OILS BETTER?

ANSWER: Motorcycle specific oils are pumped up with five times the anti-wear, anti-scuff and extreme pressure additives of regular motor oil. As an added plus, motorcycle oil does not include (except for MB rated Honda Silver), molybdenum disulfide and other friction modifiers that wreak havoc on clutch performance.
Maxima, a popular motorcycle oil supplier, starts with a API SG Service Category base oil, the last formulation that wasn't regulated as to the amount of Zincdialkyldithiophosphate (zinc, phosphorus, and sulfur) it could contain. Maxima then boosts protection through a proprietary mix of performance additives. The end result is a motorcycle oil that doesn't break down under extreme heat and is tough enough to cushion meshing gears.

QUESTION:
WHICH FOUR-STROKE RACING OIL SHOULD I USE?

ANSWER: If the bottle of oil doesn't list that it is an API SG Service Category or JASO MA spec, it's not good enough for your motocross bike. Although a bottle of oil might say "motorcycle specific" or "safe in wet clutches," the best endorsement is the API SG or JASO MA designation. It's better to be safe than sorry. There is a caveat that applies to CRF owners, however -- which we will clear up in a few paragraphs.

QUESTION:
WHAT VISCOSITY SHOULD I USE?

ANSWER: The most popular viscosity is 10W40. It's thin enough not to bog down the crank and offers ultimate protection under an extreme lad. Every owner's manual lists the recommended oils, brands and viscosities.

QUESTION:
HOW IS A CRF LIKE A CAR?

ANSWER: The Honda CRF oil system separates the combustion side of the engine from the transmission. The CRF separates the engine sump to keep the metal shavings from the transmission from floating around in the same oil that is use to lubricate the piston, rings, and rod and crank bearings.
The upside of this design is that the CRF can use a slipperier JASO MB - spec oil in the top-end, while using a JASO MA-spec oil in the transmission.

QUESTION:
WHAT ABOUT THE CRF TRANSMISSION?

ANSWER: Do not use automotive motor or gear oil in the CRF transmission. It the gear oil doesn't have the word "two-stroke gear oil," safe to use in wet clutches, Or the API SG or JASO MA designation, don't use it.

QUESTION:
IS IT BETTER TO SEPARATE THE ENGINE AND TRANSMISSION OIL?

ANSWER: Yes and no. Honda uses separate oil for the CRF's top-end and transmission. This is not a new idea. BSA did it decades ago. Yamaha, Kawasaki, KTM, and Suzuki use the same oil in the top-end and transmission.

QUESTION:
WHICH IS BETTER?

ANSWER:
Separate oil:
The benefit of separating the oil, like Honda does, is that the top-end is not contaminated by clutch debris or broken teeth. Additionally, the heat of the combustion side doesn't thin out the transmission and clutch oil. The CRF can use an MA-series oil in the transmission and slippery MB-series oil in the top-end.

The downside is that the oil quantity in each chamber is reduced (to approx. 650cc),
increasing the need for more frequent oil changes. Any oil loss, no matter how small, becomes critical when you have a small pool to draw from.

Shared oil:
The benefits of using the same oil throughout the engine, like the RM-Z, KX-F, KTM, and YZ-F, are that the lare supply is less likely to reach critical levels, overall engine temperatures are reduced and oil changes aren't demanded as frequently. On the downside, shared oil engines must use an MA-series oil for the clutch (which means that the top-end doesn't get the benefits of the slippery MB friction modifiers).

QUESTION:
WET SUMP, DRY SUMP OR SEMI-DRY SUMP?

ANSWER: Don't get to confused by these terms. by definition they are different, but in action they all work about the same.
A wet sump engine has a pool of oil in the crankcase. A dry sump engine doesn't store oil in the crankcase, but instead in a remote tank and oil lines. A semi-dry sump engine is, in reality, just a marketing term for a wet sump engine that tries to elevate the crankshaft out of the pool of oil.

The Yamaha YZ-F is a dry sump design. All other four-strokes use wet sumps, although they go to great lengths to avoid the negatives of an old-school oil pan under the engine. Suzuki and Kawasaki coined the semi-dry sump terminology, but the KX-F and RM-Z are at the very least semi-wet sump engines.


QUESTION:
CAN OIL MAKE MORE HORSEPOWER?

ANSWER: YES. Special blends of low viscosity ESTER SYNTHETICS can protect like a 30W under extreme use, but let the crank spin like it has a 0W. Zero weight is the same viscosity as water. But, the real secret to getting horsepower out of four-stroke oil is to use less of it. Most modern four-stroke engine designers try to keep the crank (and even the transmission gears) from being submerged in an oil bath. It takes horsepower to slog these parts though heavy oil. Thus, lessening the amount of oil that pools at the bottom of the crankcase or gearbox increases horsepower.

QUESTION:
HOW OFTEN SHOULD I CHANGE MY OIL?

ANSWER: Yamaha recommends changing the oil and oil filter every five rides. Honda's Eric Crippa advises changing the engine oil as frequently as possible and changing the oil filter every fifth time. one for the problems with a frequent service regimen is that it provokes people to use CHEAPER oil.

QUESTION:
CAN I LEARN ANYTHING FROM MY OLD OIL?

ANSWER: YES. Pay careful attention to the condition of the spent oil. If it looks and smells dirty, you need to service it more often. Extend the time between service intervals if the oil appears and smells clean.

High-end race teams, Formula 1 and Reno Air Racers send their used oil out to have it analyzed. Laboratory tests can use a spectrograph to determine what metal particles are in the oil - and whether that particle evidence could be pointing towards a potential failure.

This is too expensive and extreme for a local racer, but you should always sift used oil for broken clutch plates, teeth from gears, or any other unusual conditions.