2 Stroke Oil Function

oh wow. 2 of these in one week.

Since the tranny is seperated from the crankcase in a 2 stroke, there is no lubrication in the cases for the lower end. So you mix the gas that goes to the lower end, up the ports to the top end and is burned.

You can read more here with more specific details:

http://www.howstuffworks.com/two-stroke.htm

Here is another link:

http://www.eric-gorr.com/twostktech/twostroketech.html

Matt I don't want to be critical but it seems that he already knew about the crankcase lubrication from what he posted.

Originally posted by NX650
I understand that the oil/fuel mix sucked into the crankcase lubricates the crank, various bearings, piston walls etc... My question is whether the oil (or any unburned oil) has any function inside the cylinder.

Click to expand...

Anyway, NX650, I belive that your question is very interresting because I have often wondered this my self. I think you are correct in you assumption that the ideal oil would be one that burns completly. The oil should not even be needed in the combustion chamber, the gas cools the piston when it enters the combustion chamber. So I have to ask, if you had a fuel injected two-stroke, why couldn't you change the intake ports so they come from the injector and not the case and just fill the case with oil?

Inside of the cylinder it will still lubricate. The piston, rings and cylinder wall need lubrication. Out of the combustion chamber it will lubricate the power valves before leaving. Once combustion has happened, then the oil has no purpose once is hits the expansion chamber.

The excess unburned oil that a 2 stroke puts out is why the government regulators do not like them. The oil injected 2 stroke has many advantages for a street bike. You are always using the proper amount of oil needed by the motor and when you chop the throttle, you dont have excess like you would in a non-injected motor. These are much cleaner, but you have the remember you need a seperate oil tank, pump and injectors which add weight and bulk to a bike. not something you really want to deal with in the woods.

Duh! I forgot about the power valves. Good point.

cweingartz, I was thinking the same thing!!! You should be able to inject the air/fuel mixture just as the piston covers the exhaust. This would allow you to fill the low end with oil, like a 4-stroke, and burn cleanly without any unburnt mixture leaking to the exhaust!!! Only problem is you need an injection system, which adds weight and cost. But I'd pay, wouldn't you??!!! At least it would fire on every revolution!!

Yeah and you could have the oil in the case come up and lubricate the power valves, that way there would be no need for any oil in the fuel. How much more do you think that fuel injection would weigh than a carb?

What a great way to spend the day after Christmas - enjoying mind twisters about 2 strokers!!! OK Woodsy lets see if you can confuse matters a little more then they already are.....
The crankcase on a 2 stroke serves as a fuel/air mixture resivour to assist in flow metering as well as atomization. On a fourstroke this metering takes place at the valves and then the full depth of the cylinder is used as a resivour. The 2 stroke uses the crankcase area for this and then moves the fuel/air mix from this area to the combustion area thru the transfer ports.
This is one of the reasons that "flow benching" is necessary when porting - the assurance that ample amounts of air/fuel mix is present and coming from the ports in the same amounts/time. If you simply "injected" fuel into the combustion chamber during compression you would possibly have some sort of combustion but the effeicency of it (the fuel burning process) would be extremely poor due to the lack of proper mixture!
Maybe a precylinder resivour that fuel would be injected into and then a "blower/turbo" used to force the fuel air mix into the combustion chamber after the piston passes the exhaust opening (this would be during compression so the blower force would have to be extreme)? Of course, as already stated, this would add an additional 100 pounds - not good!
In answer to the original question - the remaining unburned oil after combustion serves no use (even the powervalves could live without carbon/spooge buildup) but it does pollute! This ineffecieny is what has been plaquing the 2 stroke producers for years. If we could find a way to mix air/fuel (2 stroke oil included) with such extreme accuracy throughout the engine RPM range that it would burn as cleanly as fourstrokers we could save the 2 strokes from extinction!!
Hey that was fun :))))))
Woodsy

There's gotta be a way to save 'em!!!!

the bimota v-due used a system suggested several threads back where the bottom end is like a four stroke with the fuel & oil injected into the combustion chamber thus giving a more precise mix & therefore cleaner emissions .

Bimsb6 you REALLY had me going for second! I was so exciteddddd that I started stuttering :))) The fact is that the Bimota Due uses standard 2 stroke crankcase technology (crankcase flow thru tranfers).

Here is a quote about them taken from the following webpage: the exact configuration of the fuel injection system is not yet known for the Bimota, but it seems that they have chosen to scavenge the exhaust gases by pumping fresh air through the crankcase and the conventional two-stroke transfer ports. Reed valves are still used to regulate the flow of air into the cylinder, each cylinder being supplied through a separate reed block. There are six transfer ports and three exhaust ports, a common configuration for contemporary two-strokes. The fuel injection system will be linked into an engine management system that checks many of the factors that influence the amount of fuel to be injected, including air temperature, water temperature, exhaust gas temperature and airbox pressure.

It seems that they tried to clean the gases out of the jug prior to fuel/air transfer with some success though! COOL CONCEPT!!

There is print of the motor on here: www.motorcycle.com/mo/mcbimota/bimota500.html
that is very revealing for anyone interested! Very interesting stuff but still basic 2 stroke as I explaned earlier!
Keep the thread going!
Woodsy

For those intersted here is another one on the Bimota: http://www.motorcycle.com/mo/shows/00bologna.html
Kinda a sad ending!!!!
Thanks again for the challenge about the Bimota - I didnt even know they existed until I read it here - REALLY INTERESTING :))))
Woodsy