2 stroke lubrication

Messages
5,987
Location
Houston, Texas
I couldn't sleep one night and I got to thinking about this somehow. How does 2 stroke lubrication work? You mix the gas and oil together and does the oil separate in the crankcase and lubricate everything? You get gas in the crankcase of a 4 stroke engine and it's not long before it throws a rod.
 
Messages
11,196
Location
NY Capital District
Standard 4 stroke engines use plain bearings. Oil is forced into the bearings via small holes, and it creates a film, a layer between the rod bearing and the crank itself. There is little to no metal-metal contact in most cases. In lawnmowers and other small splash-lubricated engines, the oil being flung into the bearing surface is usually enough to provide a protective layer of oil. 2 stroke engines instead usually use Needle bearings, a type of roller bearing which requires much less lubrication. The oily air/fuel/oil mixture is pulled into the crankcase during the piston uptravel. While it doesn't seem like a lot, the small amount of oil in the mixture is enough to lubricate both the bearings, and the cylinder walls. It's not nearly enough lubrication as in a 4 stroke engine, that is why 2-stroke gasoline engines do not last anywhere near as long as any 4-stroke engine. Hope this helps!
 
Messages
4,262
Location
Port Orange, Florida
Two stroke engines can and do last as long as four stroke engines. I take insult to that statement. Two strokes have many less moving parts and with the proper ratios, can last as long. Two strokes recieve fresh oil everytime, unlike four strokes bathing in dirty oil. They are simply targeted for thier ungreen smoke, or they would be much more popular. Imagine if the technology went into two strokes as four strokes get. Plus the make twice the power as thier four stroke cousins. per size.
 
Messages
10,789
Location
Jupiter, Florida
The gas and oil do separate some. The connecting rod will often have a traveling wet line of oil on it. Believe it or not, properly designed 2 stroke engines have plenty of bearing lubrication. Interestingly enough, the Honda CR500 motocross bike (55 rear wheel HP) can easily outlast the CR450F (50+ RWHP) by a few seasons under serious pro race conditions. The 4 strokes tend to pound the valve seats with pro's at the helm.
 
Messages
2,935
Location
Canada
I have to agree with Panzerman. Two cycle engines can be extremely reliable and long lived if properly lubricated. I have many two cycle engines that are 25 plus years old and some that are over 30 years of age. All still running great. They may not be the best choice for all applications. However, in OPE, they're very hard to beat if light weight and power are desired. Four strokes are relatively tame in OPE applications. Pound for pound they make less power are generally quieter and easier on fuel. If you want lots of power and don't mind the noise, two cycle engines are best. My preference is two cycle wherever possible. Particularly if you have to carry/push the device around (chainsaws, trimmers, leaf blowers, lawnmowers etc.). I can live with four cycle engines on devices like log splitters, water pumps, generators and any other machine that will be running long duration simply for being quieter and easier on fuel. Other than the reliability statement, Nick R's comments are correct regarding needle bearings and lubrication. One thing that should also be noted is the fact that a two cycle engine is much like an air pump and benefits from the additional cooling from intake air moving through virtually every part of the engine from carb to crankcase to cylinder to exhaust. That fresh incoming air entering the crankcase helps keep the internals and bottom of the piston cool.
 
Messages
11,196
Location
NY Capital District
Reliability aside there is also the problem that traditional 2-stroke engines are heavy polluters compared to even the most neglected 4 stroke OPE engine. This is because there are no valves, a portion of the intake charge exits out the exhaust, unburnt gasoline and oil. Also, because there is oil being burnt, that contributes to the pollution. Newer ones seem cleaner burning, but compared to any properly running 4-stroke, they are terrible polluters,which is why we are starting to see a lot more small 4-stroke engines in weed eaters and leaf blowers.
 
Messages
2,935
Location
Canada
"they are terrible polluters" I'd say that's a bit over the top. I agree that they're not as clean as a modern four stroke engine but newer two cycle engines with catalytic converters and digital fuel injection systems are much cleaner burning than engines of the past. What about diesel engines? How often have you seen diesels puking out vast amounts of soot and a number of the other polluting components? Now multiply how many dirty diesels there are on the highways and that should give you somewhat of an idea of a major pollution contributor. Oh, and let's not forget the military and public aviation. Just think of the number of aircraft dumping pollutants into the atmosphere worldwide. And while we're at it, how much pollution do military conflicts contribute to the environment. Think of how much fuel it takes to go to war! Shut down the conflicts in Iraq and Afghanistan for a month and that would likely balance out for the fuel us homeowners use to maintain our yards for an entire year. Yet, here we are, homeowners being punished for running tiny little two cycle engines burning a mere fraction of a percentage point of the fuel being guzzled by the above mentioned contributors. Phasing out two cycle OPE engines in the name of protecting the environment is nothing more than a limp wristed attempt at window dressing to make it appear that something is being done about the pollution problem. We are very small targets that have a large public profile because just about every homeowner has OPE and some of it is two cycle. So when we see two cycle engines being phased out, it is a widely spread action that creates the illusion that something substantial is being done to protect the environment. Where in fact, it's a very minor contribution compared to some of the contributors listed above.
 
Messages
302
Location
New Orleans La
Well maintained two cycle outboard motor can, and will last, 20+ years. Those two cycle Lawn Boy and Toro mowers have an extremely long life span. Back in the day my brother had a Kawasaki Jet Ski. We did't know any better and often used engine oil in the mix didn't seem to have any problems. Certianly I would never do that today.
 
Messages
5,941
Location
Arlington
Originally Posted By: motor_oil_madman
Any quality 2 stroke should last as long as a 4 stroke.
LOL My first real "with a clutch" motorcycle was a Yamaha GT80. It was pretty far from "quality" but it did not seem to break down any more than the 4 stroke Honda Trail 70 down the street.
 
Messages
5,532
Location
Canada
Not all 2 strokes use roller bearings, some use shell bearings and I even have an old Elto outboard that has no bearings (as such) at all! Just steel on steel for the rod bearings. But it's only lasted 62 years! But honestly, how a 2 stroke can survive with just a little oil in a lot of gas, makes me wonder about people that get excited at the thought that, a little solvent in an oil pan of motor oil could do some harm???
 
Last edited:
Top