2 stroke gas/oil vs. 4-stroke gas/no oil?

[Tom Ludolff]

This is probably a dumb question, but can someone explain why a 4-stroke doesn't need oil mixed in the gas to lubricate cylinder and rings while a 2-stroke does?

 

[rethnal]

That's a good one! :)
4-strokers are lubricated from the bottom vs. the top!

 

[mprest4]

2 stroke has no engine oil in the crankcase - fuel/oil mixture enters the crankcase first and gets pushed into the cylinder.

4 stroke has oil is in crankcase and it gets into the cylinder below rings and lubricates and absorbs heat

 

[Tom Ludolff]

Thanks all. It's starting to make sense now. Tell me if this is right: 2 strokes can't have any oil in the crankcase because the fuel/air has to go through there; but 4 strokes receive the fuel/air through the intake valve on top of the cylinder and, therefore, can have oil in the crankcase to lubricate the cylinder. Is this correct?

 

[weaselcircus]

The following link explains it all pretty well. The very last paragraph on the page answers your question very nicely.

http://www.howstuffworks.com/two-stroke2.htm

 

[Tom Ludolff]

Wow!! That's a cool site!! Great explaination!! Thanks!!

 

[jdbrusch]

I hate to confuse you even more Tom but you might find this fairly interesting.We have a small weedeater motor at work that came out on the market early this year that is a 4-stroke in design but actually burns a 2-stroke mix.This was built for a better power to weight ratio and is made by Shindaiwa.the carb is connected to the crankcase ,and the intake valve draws the gas-oil mix thru the entire crankcase into the combustion chamber,fires on the ignition stroke and than pumps put the exhaust thru a exhaust valve.
Check out Shindaiwa.com and punch up the C4 engine to see what it looks like. :thumb:

 

[Tom Ludolff]

I had to study the animation for a while; but it makes sense. It's basically a 4 stroke, but uses a gas/oil mix instead of a wet sump in order to reduce weight! Pretty clever!! What we need is a clean burning 2-stroke (fuel injected maybe?) to pass EPA requirements. You'd think someone would incorporate some intake and exhaust valves on a 2 stroke to solve the intake / exhaust leakage problem that helps make 2-strokes so environmentally hateful. It would add a couple pounds in valves and cams but it would still fire on every revolution. Would that be impossible??

 

[canyncarvr]

re: howstuffworks.com/two-stroke2.htm

If it explains something to you, that's fine. A bit of a problem with their illustrations. They don't show the underneath side of the piston connected (airflow-wise) to the intake port. The intake charge is colored yellow..under the piston it's white. Makes it look separate. It's not.

The write up makes the connection between the two (intake/crankcase) anyway.

But then, they mention 'explosions' after the sparky sparks, too.

Don't want no explodin' goin' on!

Beside the mentioned rings/piston there's small/large rod bearings that are lubricated via the intake fuel/oil mix, too.

 

[Johnnyboy]

I forget who was working on it... REV, I think with a TM motor. Any way it has direct injection instead of a carb for a 2stroke. Direct injection is a system where they squirt the fuel in the combustion chamber at an exact time instead of other types of injection that feed the fuel through an intake runner. You can imagine it would be incredibly useful with a 2 stroke to prevent unburnt fuel from escaping. I emailed them about it and they said it was clean enought to get it a green sticker in Cali and it improved throttle response. They said there was not really an improvement in power though. REV is a pretty cool company, they are doing the DELL style of sales where you give them all your needs and they send you a bike custom set up for you already. Expensive, I would assume but a good idea none the less.

 

[Tom Ludolff]

That sounds similar to the fuel injected 2-stroke diesel. The only problem is probably cost. But if the EPA really clamps down and you're a die hard 2-stroke fan, you'll pay the price, right??!!