Archive for October, 2010
After reading the two previous blog posts, you’ve probably realized that the piston is the star of the show in the two-stroke engine. It serves three main purposes during the engine cycle. First, it acts as the combustion chamber, pressurizing the mixture of air, gas and Yamaha oil and capturing the power created by the subsequent ignition of that fuel. In addition, the piston also serves as the crankcase when it facilitates the flow of air and fuel into the system via the reed valve.
While all of this is occurring, the piston is also taking the place of the valves as it covers the intake and exhaust ports in the cylinder walls. The multifaceted nature of the piston is what allows for the two-stroke engine’s lightweight and powerful construction. Remember that the piston is under constant tension and doesn’t have a direct source of lubrication, so be sure to be diligent when you’re mixing your gas and oil.
Now that the first of the two strokes is complete, it’s time for the compression stroke. After the first stroke, the momentum created in the crankshaft propels the piston back to the spark plug. When the piston compresses the combination of air, gas and Yamalube 2S oil, it creates a vacuum which opens the reed valve and allow the mixture to be extricated from the carburetor.
Once the piston makes it through the combustion stroke, the cycle simply starts again. This combination of compression and combustion strokes explains the “two-stroke” portion of the engine’s name. Four-stroke engines have separate intake and exhaust cycles in addition to the combustion and compression strokes.
Each cycle of any engine begins at the spark plug. Two-stroke engines derive their power from the fact that the spark plug fires once every rotation, as opposed to every other. When the spark plug fires, the mixture of fuel and air in the cylinder ignites to drive down the piston. As the piston moves downward, it compresses the mixture of air and fuel into the crankcase. The the piston creates pressure in the cylinder, pushing the gases out of the exhaust port.
The intake port is then covered as the piston reaches the bottom of the stroke. Because the mixture is pressurized in the crankcasae, it rushes into the cylinder. This displaces the excess gas and fills the cylinder with a new supply of fuel and Yamaha 2M oil. Now that this phase of the cycle is complete, tomorrow we’ll have the riveting conclusion: the compression stroke!
After reading yesterday’s post, you may be wondering why two-stroke engines aren’t used in more applications; after all, they’re lighter, simpler, cheaper and more powerful than four-strokes. For starters, because two-stroke engines are light and powerful, the system takes more abuse and tends to wear out quickly, which isn’t good for machines like automobiles. In addition, the lubrication system in the two-stroke has been simplified so the gasoline and 2 stroke oil are held together. While this is convenient, it doesn’t provide dedicated lubrication to the engine.
The immense power output from two-stroke motors does come at the expense of efficiency. Not only do two-stroke engines burn through oil rapidly, the oil is also expensive in itself. To compound the issue, two-stroke engines also have poor fuel economy. And the burning of all that gasoline and oil means that two-stroke engines emit a surfeit of pollution. During the cycle, fuel and air leak out the combustion chamber as well, posing a particular threat for marine applications.
Most devices with lower-power applications—such as gardening equipment, ATVs and small outboard motors—use a two-stroke engine, as opposed to a four-stroke. Two-strokes offer some distinct advantages over their four-stroke counterparts. First, a two-stroke engine doesn’t require any valves. This makes the unit much less complex, allowing for a smaller, lightweight construction. Also, two-stroke engines fire on every revolution, creating consistent power; four-strokes only fire every other cycle.
Finally, two-stroke engines will run no matter which way they are oriented. Because the gasoline and bulk oil is mixed in the engine, both fluids will always be in the system. This isn’t the case with four-stroke motors, where the oil is held is a discrete reservoir. Over the next few days, we’ll be covering the basics of two-stroke engines, including the steps in the engine cycle.
Since the machine has been idle for some time, the carburetor should be cleaned as well. You can find specialty carburetor cleaning products that are expressly designed for this purpose. While you’re fiddling around in there, be mindful of the inlet needle, as it tends to get stuck in either the open or closed position. Either way, it will spell trouble for your vehicle.
Inspect the throttle to ensure nothing it’s unobstructed and moves easily. The final thing to do is mix some bulk motor oil with the gasoline and fill up the tank. Once again, you’ll want to refer to your owner’s manual to see the manufacturer’s oil specifications. This will also provide you with the proper ratio to use when combining the oil and gasoline.
Now that we have the hood open, remove, clean and inspect your spark plugs. Personally, I change my spark plugs at the beginning of each year, as they tend to die out quickly. Nothing is worse than trying to start up your snowmobile miles from civilization only to find that one of your spark plugs is dead. You can find specifications for which plugs to use in your owner’s manual.
The starter rope also requires attention, as it has a tendency to fray and wear. Even if the rope looks like it’s in good condition, it’s still a smart idea to bring an extra one along with you on your rides. Replace the battery if you removed it for storage and clean the terminals before making the connection. Tomorrow we’ll go over carburetor maintenance and the proper procedure for mixing your Yamaha 2W oil with gasoline.
While you are conducting the exterior inspection, thoroughly examine the skis and runners for any signs of wear or damage. The runners should be straight and there shouldn’t be any holes, nicks, gouges or scrapes. Now that we’ve examined the outside of the snowmobile, it’s time to bring out the tools and get under the hood.
Begin by greasing all of the fittings and removing any rust or buildup. It’s important to grease all of the fittings each year to ensure their integrity and longevity. Just as your Evinrude oil maintains the inner workings, the grease keeps the fittings in pristine condition. You should have drained any excess gasoline prior to putting the vehicle into storage; if you didn’t, now is the time to.
With a particularly cold winter forecasted here in the Pacific Northwest, it’s time to start thinking about pulling the snowmobile out of storage. Although there may not be any powder on the ground yet, now is the time to go through your preseason maintenance. Hopefully you took the time to clean and tune the vehicle before putting it in storage, as his will make your job infinitely easier.
Start by gathering all of the necessary tools and supplies, including socket wrenches, spark plugs and Yamalube 2M oil. Move the snowmobile to a clear, open space so you have ample room to work. The first step is simply to clean the outside of the vehicle, removing any dirt, grime or debris that may have accumulated while it was idle for a few months. This is also a good time to do a careful visual inspection of the exterior.
Every summer my cousin, Patrick, invites my whole family to his lake house in Portland to stay for an extended weekend of boating, fishing and barbeques. It’s something we all look forward to each August when the weather is warm and the daylight lasts well into the night. And every summer we always return from our visit with stories of adventure, laughter and family togetherness.
Last summer, in particular, delivered one of the craziest stories from that anticipated trip to-date. Patrick, my father, my aunt, my younger sister and I had voyaged out onto the water for an afternoon of margaritas and fishing when, all of the sudden, the boat motor began to shutter and then it stalled out, leaving us stranded hours from home. Fortunately, Patrick has always been the responsible and prepared one of the family. Within seconds he pulled out a backup supply of Evinrude XD 100 Oil to get things oiled up and running again. We were back on shore in no time and arrived just in time for my mom’s famous Sloppy Joes.