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Cleaner, Smoke-Free Sleds

Snowmobile manufacturers develop new oil delivery methods to comply with EPA regulations
Yamaha Ski-Doo Polaris snowmobiles EPA regulations
The OEMs were challenged with new EPA regulations to produce cleaner sleds, and oil consumption was a big part of that. Today, each of the four has developed their own method of oil delivery, drastically reducing oil consumption while improving performance.
The no-smoking zone. That’s what you could call the large staging area for the spring snow shoots in West Yellowstone, Mont. It’s amazing to watch 50 snowmobiles idling away, waiting for the snowmobile media test drivers to go for their daily evaluation run. It was not many years ago that 50 snowmobiles all idling in a parking lot would produce a distinct smoke cloud. These days, however, they all run without emitting any distinct smoke cloud or odor.
Polaris 800 H.O. snowmobile engine
Polaris went with an electronic oil pump controlled by the ECU in its 800 H.O. engine for more precise oil delivery under load.
To each their own
Large advances in emission technology (i.e., computer-controlled electric oil pumps) have dramatically reduced oil consumption, almost eliminating the need to carry that extra quart of oil on the trail. For many years, the standard oil pump was mechanical and output was mostly linear, depending on engine RPMs and throttle opening. These mechanical pumps were manufactured by Mikuni, the carburetion people. Back in the 1970s, this was a big improvement – much more convenient than carrying a number of quarts of oil and mixing them with gas every time you filled your tank.

With the introduction of direct or semi-direct injection, there was a problem with oil making it into the crank bearings. Gas was now injected into the cylinder either in the head or in transfer passages, in either case after the air had moved through the crank case. As a result, oil had to be brought directly to the bearings.

In the case of today’s Polaris 800 AXYS engine, the computer-controlled oil pump has six oil lines. Four feed directly to the crank bearings, while two spray on the main rod bearings as they rotate in the crank case. The new Ski-Doo 850 engine has reintroduced an old and proven technology by using “slinger rings.” These rings sit on the crank throws and overlap the crank bearings. Oil first passes through the main crank bearings, and as the oil exits the bearings, the rings catch it. The centrifugal force then pushes the oil into the center of the crank pin and then out through holes to emerge inside the rod bearings. As the oil passes thru the rod bearings, it is then flung out by centrifugal force and sprayed on the cylinder wall. This is old but proven technology that was developed and used in a Peugeot-powered Indy racecar as early as 1914, before good plain bearings were available. At the time, roller bearings were believed to have much less friction than the plain bearings that were available.
Arctic Cat 600cc C-TEC snowmobile engine
Arctic Cat’s 600cc C-TEC engine mixes oil and fuel as it’s delivered, and then gets it to the crank via a slotted piston design.
Ski-Doo 850 E-TEC engine
Ski-Doo’s newest 850 engine uses centrifrugal force to lube the crank bearings, pin, rod bearings and cylinder wall. This method was first used in 1914 Indy race cars.
Arctic Cat has a different philosophy. Cats also have a computer-controlled electric pump, but instead of pumping oil to the bearing, the oil is injected into the fuel flow and then sprayed thru the injection as a fuel/oil mix. In order to get oil to the bearings, Arctic Cat has a clever design with a slot in the piston, which allows the fuel/oil mix to enter the crank case through the piston. The injection is timed so that no mixture enters in low-load conditions, but as soon as the engine starts to produce power, the injection timing is increased to spray the mixture through the piston window.

Latest and greatest

All these different systems have their own advantages, but the biggest improvement is the computer-controlled oil pump itself. The mechanical pumps had a linear output, but power curves and load demands are in the shape of curves and with the computer programs can be made three dimensional in order to better match the fuel injection programs. That means oil flow may be very lean or almost non-existent in low-load conditions (idle or off-throttle). When the engine is under power, oil can then follow the power demands. This has not only led to smoke-free low-load conditions, but also a drastic reduction in overall oil consumption.

Ski-Doo has perhaps raised the bar even further with its new plasma-sprayed steel coating of the cylinders. Steel running surfaces are much more porous than nickel-silica coatings and therefore hold a better oil film on the running surface. This used to be the advantage of steel sleeves, but because of the thickness of the sleeve, heat transfer was reduced. The plasma-sprayed coating is very thin and therefore transfers heat just as well as Nicasil-coated cylinders. With the plasma steel coating and its oil retention properties, Ski-Doo should be able to get away with even lower oil consumption.

Great strides are being made in lubrication management, and the net result has improved reliability and given us cleaner running engines in our sleds.
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