Pistons are one of the most important components in an engine, and because of that importance, they have to work correctly or you may as well just get a bicycle and pedal yourself wherever you want to go. Pistons suck in the air-fuel mixture and helps compress it within the cylinders. Then that fuel gets ignited by the spark plug and rotates the crank which then gives power to the wheels. Pistons also takes the sudden increase of heat from the ignition and when that’s all said and done expels the exhaust gases.
The movement of the piston up and down is called a stroke and piston engines are categorized by the number of strokes needed to complete one power cycle. A two-stroke engine, like the one found on a Yamaha Banshee 350, has a 2-stroke, 2-step engine, whereas most other ATVs and UTVs have 4-stroke, 4-step engines.
Now since we’re done talking about what a piston does and why it’s important let’s discuss what can cause your pistons to fail. While there are a number of ways to damage your pistons, there are three really easy ways we'll be discussing:
First, damaging your piston is extraordinarily easy when using the wrong kind of fuel. Shocking we know, apparently our parents were right. We’re not talking regular vs. diesel gas, we’re talking about the octane in fuel. The octane rating of gas is important because when the temperatures and pressures from the combustion process exceed the octane of the gas, it causes the fuel to ignite spontaneously. This spontaneous ignition causes high pressure quakes to pulverize the piston and after a while will cause the pistons to fail. It’s for this reason race cars and ATVs for example, can’t just use the cruddy 87 octane some of us use in our less spectacular cars, instead they use racing fuel to curtail the potential piston damage and for the increased compression ratios it can handle.
Secondly, by having a very lean air/fuel mixture your pistons will be forced out of commission along with a ton of other problems. We’ve talked about this before in more depth in our Carburetor Vs. Electronic Fuel Injection post. This for the most part only applies to carbureted vehicles because EFIs are computerized and keep a close watch on the air/fuel mixture. A very lean mixture can create a hot spot in the combustion chamber which can lead to premature ignition, causing the piston to burn because it was subjected over and over again to high combustion temperatures.
Third and lastly, your piston’s skirt can be shattered because the cylinder has too much clearance. This clearance allows it to rattle inside the cylinder. Pistons swell up a little when the engine heats up decreasing the clearance between the piston and the cylinder which leads to it cracking and then eventually shattering. Clearance is very important so when you’re boring your cylinders or buying new pistons make sure to take account of measurements. Even if the clearance doesn’t cause a catastrophic mess like shattering the pistons, it will still result in a loss of compression, power and the piston scuffing. Some aftermarket pistons, like Niche Industries’ Blaster 200 piston kit come Moly-coated to allow for tighter clearances, somewhat alleviating this problem, though coatings still can only do so much.
Those are three of the easiest ways to damage your piston; there are tons of other ways, some which we’ve probably never even heard of. That’s why this is industry is fun to be in and watch. If you have any question about pistons or have any weird or wonderful stories of piston failures please share them in the comments.
Sources:
1.Back to Basics Preventing Piston Problems:http://www.enginebuildermag.com/2001/08/back-to-ba...
2.Getting a Fix on Piston Diagnosis and Inspection:http://www.underhoodservice.com/getting-a-fix-on-p...