Why does a 2-stroke gas need to have a gas-oil mixture and a 2-stroke deisel doesnt?

I was thinking of this for a little bit and My thought was well because the diesel is an oil so it lubricates itself so I asked my dad and he said 2-stroke diesels have oil in the bottom of the crankcase so they use that oil to lubricate so then I thought why can't a gas 2stroke use the idea like the diesel 2-stroke( or a 4stroke engine) and just have oil in the bottom of the crankcase, the only reason I thought of was because the engine wouldn't have enough torque at low RPMs to make it through the oil but the oil shouldn't be that thick... I know someone would be able to tell me and Id be like "I feel like im an idiot right now".

Okay, to start with some of this is an educated guess. Two stroke gas has oil in the gas to lubricate the bottom end of the motor. Now this is the guessing part, they have the fuel mixture go through the bottom part of the motor because the pistons going up and down in the base acts like a small turbo to force more air into the cylander, I believe the 2 stroke deisel has a turbo on it.

Just my educated guess

yes but what about the 2stroke weedeaters, the Fuel Mixture doesn't enter the bottom end of the motor nor does it have reed valves, it enters the sidewall of the cylinder like the exhaust exits the sidewall of the cylinder. So If you put a turbo on a gas 2 stroke(like a large weedeater style 2stroke which the intake port enters the sidewall) then you would be able to run oil in the crankcase and have an oil control ring? Seems like something you would have to test out to actually get the answer because its nothing thats been looked into recently(it must of been looked into when 2strokes were being made)

2 stroke engines require pre mix or injection to lubricate the cylinder walls and bearing.

2 stroke diesels don't require this because diesel is an oil already,

Now I understand a little more, do the two stroke diesels have oil in the crank case then?

Chopperhed wrote:

2 stroke engines require pre mix or injection to lubricate the cylinder walls and bearing.

2 stroke diesels don't require this because diesel is an oil already,

Agreed.

W1ldyOvvnZ wrote:

Now I understand a little more, do the two stroke diesels have oil in the crank case then?

Some do but normally you don't need to add oil because diesel is an oil so the fuel will lubricate everything.

Petrol is technically an oil but its almost useless at lubricating so you need to add 2 stroke oil.

Now I get it, so its not necessary to run oil in a 2 stroke diesel, it keeps it lubricated better though?

Currect one example of this would be diesel engines (including car/truck engines) can run on cooking oil.

Weather diesel is better at lubricating than 2 stroke oil, I have no idea.

Ok now I understand, do you know why they dont put oil in the bottom end of two strokes though?

W1ldyOvvnZ wrote:

Ok now I understand, do you know why they dont put oil in the bottom end of two strokes though?

When the piston is at the top on the cylinder, it past the intake port in the wall of the cylinder, which allow the fuel and air the enter the bottom half of the cylinder. As the piston goes back down, it forces the fuel/air down around the crank shaft to lubricate it. The fuel/air then goes though a passage to enter the top half of the cylinder. Piston then goes up and spark plug fires and boom.

This is a 2 stroke.

The example shown above is caqlled a piston ported engine, as the piston opens and closes the transfer, intake and exhaust ports.,

Some engines use a rotary valve attached to the crankshaft to open and close the ports (Seadoo engines for example)

I know what you mean but what if you were to take a weedeater engine where the fuel/air mixture enters the top end of the engine only and put oil in the bottom end would it work better? I know it probably wouldn't work if you were to do it with something like a snowmobile etc.

Chopperhed wrote:

The example shown above is caqlled a piston ported engine, as the piston opens and closes the transfer, intake and exhaust ports.,

Some engines use a rotary valve attached to the crankshaft to open and close the ports (Seadoo engines for example)

Indeed, but as far as i know the principle of lubrication is the same isn't it?

W1ldyOvvnZ wrote:

I know what you mean but what if you were to take a weedeater engine where the fuel/air mixture enters the top end of the engine only and put oil in the bottom end would it work better? I know it probably wouldn't work if you were to do it with something like a snowmobile etc.

No, you cant run a petrol engine on oil, it has to be vapor

And that is what the crank case is for on the 2-stroke motors is to make the fuel a vapor.

Not entirely, it's mainly for lubrication, But it does help.

2 stroke diesels have a sealed crankcase and pressurized oiling just like a 4 stroke. Diesel fuel lubricates the lift pump, injector pump & injectors but it does not lubricate the lower end.
Even though your weed eater doesn't use reed or rotary valves, the crankcase is still pressurized with fuel mix when running. That's why they will be hard starting or won't run at all if there's an air leak at the crankcase gaskets.

Ok i think I get it all now, it only took five people:P

AcreFarm wrote:

That's why they will be hard starting or won't run at all if there's an air leak at the crankcase gaskets.

Bad crankshaft seals will do it as well.

Running a 2 stroke with a crankcase leak will generally result in a burned/holed piston