Can a 2 stroke run on pure gas without damage?

Question by Andrew T: Can a 2 stroke run on pure gas without damage?
I tried it cause I can out of oil to mix. Did I wreck my engine?
I know everything about 4 stroke engines but next to nothing about 2 stroke. Educate me please
It still works. Thanks much for the info guys

Best answer:

Answer by james r
Since 2 stroke doesn’t have an oil system, it is a must to mix the oil in the gas for lub purpose.

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12 Comments
  1. Reply
    -R May 31, 2013 at 11:51 am

    Kiss that baby goodbye.

    You probably ground out the cylinders and the rings will be sloppy, therefore allowing gas and oil to slip past and burn in the exhaust. not good keemosobbie.

  2. Reply
    VB.NET Guru May 31, 2013 at 12:41 pm

    No .. The Oil you add to the gas is extremely beneficial to the engine. Without the oil, you will burn out the engine.

  3. Reply
    Joe P May 31, 2013 at 1:15 pm

    The only lubrication a 2 stroke has is the oil mixed in the gas. The gas oil mixture goes thru the crankcase before it goes into the cylinders. Running gas with no oil in a 2 stroke is the same as running a 4 stroke without any oil in the crankcase

  4. Reply
    Jim J May 31, 2013 at 1:21 pm

    Not for long. There no oil system to reduce the friction. That comes from the oil mixed with the gas. Its like running a 4 stroke with no oil in the crankcase.

    j

  5. Reply
    forhirepen May 31, 2013 at 2:13 pm

    You can’t run it for long without oil in the mix. If you know about 4-stroke engines then this is similar to draining all your oil in 4 stroke and running it. You caused excess wear.

    If the engine still runs you did not wreck it.

  6. Reply
    tin2mik May 31, 2013 at 3:04 pm

    im lost

    if you are wanting to know if a 2 stroke engine can run on just gas the answer is no
    two stroke engines work on the same principle as the four stroke AIR and fuel comes in and spark plug provides spark and explosion pushes the piston down

    without air it will not explode it wont even flame

  7. Reply
    albertgiles46 May 31, 2013 at 3:58 pm

    A 2-stroke shouldn’t last very long on straight gasoline. The internals of the 2-stroke are lubricated by the oil/gas mixture. You may have a ‘extraordinary’ machine, if it still runs. Or you still had some amount of oil in the jug you used, that kept it from wrecking.

  8. Reply
    Ralfcoder May 31, 2013 at 4:50 pm

    It can for a short time, but the oil in the fuel mix provides lubrication for the engine. Running it for a long period with straight gasoline is similar to running a 4 cycle engine without oil. Do it long enough, and the engine parts will overheat and seize up, or weld themselves together into an engine-shaped lump.

    If you can still turn the engine over, you may not have damaged it severely. But you’ll never know for sure without opening it up. If you’re familiar with 4-stroke engines, maybe you can try this – pull the head, and look at the cylinder. Is is scored? I’m no expert or small engine mechanic, but that’s where I would expect to see the first sign of damage. This quick inspection will cost you nothing more than a head gasket and some time.

  9. Reply
    Helper May 31, 2013 at 5:16 pm

    The down stroke of the piston creates the fuel/air mixture pressure that gets pumped into the cylinders. If you have no oil then only the gasoline comes in contact with the moving parts.

    No you haven’t wrech your engine (if the engine work fine now). But eventually it will fail – and fail much sooner than it normally would.

    Good Luck.

  10. Reply
    Stevo C May 31, 2013 at 5:28 pm

    Well, since you know just about everything about 4 strokes, think about it this way: You decide to run your 4 stroke engine for an hour without any oil… what happens? Rings break, piston and cylinder become scarred, even the crankcase itself will be damaged. The reason is because the oil in the gas mixture is the only oil the engine gets, so you need to have it to reduce damaging friction. If your 2 stroke still runs, get some mix in their, maybe even with a little extra oil ratio and run it, and you might come out being ok. Hopefully you haven’t wrecked it, although you certainly could have.

  11. Reply
    cpttango30 May 31, 2013 at 5:54 pm

    The reason you add oil the the two stroke gas is because that oil is what lubricates the connecting rod and crankshaft. If you do not lubricate then it will damage it.

    The gas and oil mix goes in threw the carb threw the Reed valves into the crankcase from the crankcase it goes in to the ports around the cylinder now due to the combustion of the gas you have pressure in combustion chamber this forces the piston down and the exhaust port is cleared by the piston before the intake ports are so the gas starts to escape out the exhaust port this causes a negative pressure to build drawing in the gas and oil mix form the crankcase. This is a very inefficient method of supplying and exhausting combustion byproducts from the cylinder that is why many motorcycle manufactures are going away from it.

  12. Reply
    Country Boy May 31, 2013 at 5:57 pm

    Wow, I hope you shut the motor off immediately. A two stroke motor operates on a different principal than a four stroke. Instead of intake and exhaust valves 2 strokes have an intake port, transfer ports and an exhaust port. The gas oil mix lubricates the roller bearings on both ends of the crankshaft and needle bearings on both ends of the big end of the connecting rod and pistion wrist pin as well as the piston skirt and ring or rings. There’s no crankcase oil inside a two stroke motor. Special two stroke oil must be used mixed with gas or stored inside an independant oil tank where it’s metered with the gasoline as the motor runs.

    Operation af a two cycle motor goes like this: When the piston is at top dead center the very tight crankcase is full of air / fuel / oil mix. The spark plug fires pushing the piston down the allowing the exhaust gasses to escape from the cylinder through the exhaust port. As the piston and rod travels all the way down to the bottom of the stroke the fuel, the air, fuel and oil is forced up beside the piston through the transfer ports on top of the piston. As the piston travels back up a vacuum is created inside the lower half of the motor called the crankcase. The skirt of the piston uncovers a lower intake port beneath the piston and fuel and oil mix is sucked in the crankcase through the carburetor. The whole process starts all over again. The biggest difference between a 2 and 4 stroke is a 2 stroke every time the piston reaches top dead center the sparklug fires the compressed fuel and oil. This system is called a piston ported 2 stroke.
    Some two strokes depend upon reed valves to sence vacuum inside the crankcase and fuel is allowed to be sucked in past the reed valves, The reed valves slam closed as soon as there is no more vacuum inside the crankcase. Fuel still travels through transfer ports parallel to the piston then inside the combustion chamber. As the piston covers the exhaust port fuel, air and oil is mixed and compressed untill it reaches a few degrees before top dead center when the spark plug fires.

    Modern 2 strokes have capacitive dicharge ignition with spark advance and retard, just like a car or truck 4 stroke. The spark advances as rpm’s go up and retards as they decrease to prevent spark knock and pre-ignition.

    Keep in mind, that small bit of oil mix ratio oil is all that makes the 2 stroke live.

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