Dumb Question? Why don't 4-strokes need oil mixed into the gas?

[Tom Ludolff]

How is it that 4-strokes don't need oil mixed in the gas while 2-strokes do?

 

[SCHLAVA]

The oil that you put in your fourstrokes transmission also is pumped to the cyclinder and valvetrain for lubrication. A two stroke crank and topend are separated from the trans on a two stroke. That is why you need to add oil so that it lubricates the topend.

 

[Hogwylde]

Originally posted by SCHLAVA
The oil that you put in your fourstrokes transmission also is pumped to the cyclinder and valvetrain for lubrication. A two stroke crank and topend are separated from the trans on a two stroke. That is why you need to add oil so that it lubricates the topend.

HUH???????

First of all, you need to understand how a four stroke engine and a two stroke engine works......which obviously neither of you do. A simple search on the internet should give you detailed descriptions and probably drawings too. Once you understand the differences, then you will understand why/how the oil in two stroke fuel lubricates the crankcase and why/how the oil in a fourstroke crankcase does it's job.

 

[JBTX]

www.howstuffworks.com

It's not working for me right now or I would link you directly. On the left, there is a link to engines.

 

[Layton]

Try http://www.howstuffworks.com/ as JBTX says.

Go to the engine section. You will find "How car engines work" which is basicly the same as a four stroke bike. Then down near the bottom of the page you will find "How 2-stroke engines work"

You will find that the 4-stroke engine gets it's lubrication from the oil in the crankcase where the 2-stroke gets its lube from the oil in the gas.
The 2-stroke's gas/air mixture from the carb passes through the crankshaft area before it gets into the cylinder where on a 4-stroke it goes directly into the cylinder.

A simplified explination but maybe it will help. :)

 

[Jasle]

Originally posted by Hogwylde


HUH???????

First of all, you need to understand how a four stroke engine and a two stroke engine works......which obviously neither of you do. A simple search on the internet should give you detailed descriptions and probably drawings too. Once you understand the differences, then you will understand why/how the oil in two stroke fuel lubricates the crankcase and why/how the oil in a fourstroke crankcase does it's job.

 

Hogwyld,  actually he is right on target.  A 2-stroke not only needs oil for the topend but the wristpin and crank bearings.  This is what he is trying to get at.    Try not putting oil in the gas.  The first thing to go is usually the bearings.  ON a four stroke oil is pumped in the rod bearings and crank bearings.  Some even spray the underside of the piston.  as well as the valvetrain.  So schlava is on the right track. 

 

[Hogwylde]

There is no bike out there that pumps oil to the piston. And, only a handful that share there engine oil as gearcase lube. ALL pistons are lubricated by either splash or flinging off the crank/conrod. Those engines with oil supplies in the crankcase PUMP there oil to bearings and it's flung off from there. Two strokes, having NO oil supplies or pumps, rely ONLY on splash or flinging of the oil suspended in the fuel supply that circulated through the crankcase.

I knew what he was trying to say because I know how they work, BUT....he said it in such a confusing way that someone that doesn't know how/why two strokes VS four strokes work (as the original author)

 

[Layton]

Originally posted by Hogwylde
And, only a handful that share there engine oil as gearcase lube.

If we are talking about dirt bikes I thought only the new Honda four stroke had the trans oil seperated from the crankcase. :confused:
I know the older XR's and KTM's use the same. What about the Yamahas?

And it wasn't really a dumb question if you don't understand how engines work. ;) When you go to "how things work" you will see that there are many different types of engines and not just 2 and 4 stroke ones.

 

[WoodsRider]

Originally posted by Hogwylde
Two strokes, having NO oil supplies or pumps, rely ONLY on splash or flinging of the oil suspended in the fuel supply that circulated through the crankcase.

Actually two-cycle gasoline engines rely on crankcase vacuum, port geometry and cylinder scavenging to lubricate the bearing and cylinder walls. Nothing is "splashed" around.

I believe this thread would be better off in another forum since it has absolutely nothing to do with enduros, hare scrambles or trail riding. ;)

 

[Jasle]

Originally posted by Hogwylde
There is no bike out there that pumps oil to the piston. And, only a handful that share there engine oil as gearcase lube. ALL pistons are lubricated by either splash or flinging off the crank/conrod. Those engines with oil supplies in the crankcase PUMP there oil to bearings and it's flung off from there. Two strokes, having NO oil supplies or pumps, rely ONLY on splash or flinging of the oil suspended in the fuel supply that circulated through the crankcase.

I knew what he was trying to say because I know how they work, BUT....he said it in such a confusing way that someone that doesn't know how/why two strokes VS four strokes work (as the original author)

 

I guess if you changed you statement to say that there is no dirtbike out there that pumps oil to the piston I would agree.  However the statement was just made that some four stroke engines do.  The GSXR had backside piston jets for cooling. As does the hayabusa. Definetley a fourstroke!  Here is the quote from the hayabusa literature "High efficiency liquid cooling system for optimum engine operating temperature- including compact air-cooled oil cooler, plus oil-jet piston cooling. "

 

 

[SCHLAVA]

Thankyou Jasle. And Hogwyled if I'm not mistaken older husabergs and huskys used to pump oil on to the piston and cylinder sleeve. But then again I've only been on bike for about 25 years I probably have no idea in hell how engines work!

 

[NVR FNSH]

Hmm, my '88 XR600, '99WR400, '88 Katana 1100 - GSXR derivative engine with oil piston jets for cooling, wife's '92 XR250R ALL share oil for engine & gearbox lubrication. My '90 KX500 on the other hand has a separate transmission sump and relies on pre-mix to lubricate the engine.

Make sure you are 100% correct before you blast someone for a dumb question.....

Brian

 

[Tom Ludolff]

Thanks everybody!! I went to www.howstuffworks.com. It all makes sense now. That's a very interesting site. I've spent hours on there already!!