How a two stroke works!

[Reckless]

I came across this page by accident but I thought it might be interesting to some of you. Because alot of the time 2smoker descriptions stop short of how the expansion chamber works in the proceess. This one doesn't, so I thought I'd post it for all those that might be interested in understanding their 2smokers better!

If your interested click here (http://www.southernskies.net/page_info/runningtwostrokeengine.html)

Nice gif at the end someone made! Shit I even managed to attach it to the post!! LOL!!!

[merv]

I came across this page by accident but I thought it might be interesting to some of you. Because alot of the time 2smoker descriptions stop short of how the expansion chamber works in the proceess. This one doesn't, so I thought I'd post it for all those that might be interested in understanding their 2smokers better!

If your interested click here (http://www.southernskies.net/page_info/runningtwostrokeengine.html)

Nice gif at the end someone made! Shit I even managed to attach it to the post!! LOL!!!

Yeah smart fellah that invented the expansion chamber and figured out how to stuff more charge into the cylinder.

Wasn't that Kaaden from East Germany and MZ and Degner defected with his secrets to Suzuki? http://en.wikipedia.org/wiki/Ernst_Degner

[YellowDog]

Did this at school in the late 1960s.

Thanks for the recap :)

[oldskool]

Thanks for that, the animation of the expansion chamber in action gives me a clearer understanding of why I have so much oil dripping out of my muffler.
I must go and reseat mine back into the barrel with a new gasket so it doesn't leak as it does.

[camchain]

I love these things. Haven't seen this particular ani before. I reckon it's being a bit optimistic re efficiency of expansion chamber negative pressure wave controlling how much of the fresh charge is wasted out the exhaust. Grubby ol' 2 strokes!

When I see an ani like this I always wonder if a 2t exhaust valve of some sort could work. Reed valves were certainly a big improvement on the intake side.

I have a question re 2 stroke lubrication that someone here will probably know. I read an interesting tech article a while ago which I'm sure described a pool of oil in the crank which is constantly being replaced/replenished. I've never pulled a 2t down that far so I don't know if this is true.

[Reckless]

I would guess not true it'd run like a pig if at all. There is way enough oil in the Petrol to lube the big end which is being replaced/replenished constantly anyway. Unless your running really high compression how often do you do a big end "very seldom" no need for a pool of oil in there as well I reckon.

[camchain]

I would guess not true it'd run like a pig if at all. There is way enough oil in the Petrol to lube the big end which is being replaced/replenished constantly anyway. Unless your running really high compression how often do you do a big end "very seldom" no need for a pool of oil in there as well I reckon.

Hmm Seems like you would have seen this 'pool of oil' if it was there - when disassembling an engine. I don't think I saved the article but was pretty in depth and (from memory) the author noted what he described as a 'common misconception' re 2t lubrication. i.e. he reckoned main lubrication comes from some oil remaining after combustion and this is where main lubrication comes from, not when oil is supended in charge of fresh fuel. I also think Ive heard somewhere that not everything on the Net is true though...

Just quietly - I'm still dicking around with my jetting.

[Reckless]

If the pool of oil was deep enough for the crank to be dipped in it wouldn't it be smashed about so much it'd be dragged up the ports and into the combustion chamber. I still can't see it working at all! Its not like a four stroke. I would also guess not every drop of Fuel/oil mix is shoved up the transfers ports so there is always some oil in the bottom end area at all times anyway.
s
Now I've gotta sign off and do some bloody work myself!! LOL!!!

[secondfield]

Supercharged via sonic energy huh .... quite bloody amazing really.

[IIIRII]

I always thought Bill Wisenewski invented the tuned pipe

http://www.modelaircraft.org/files/museum/bio/Wisniewski.pdf

Areomodelling guys were light years ahead of other 2 stroke people

And still are

[clmintie]

Don't know if Bill really was first, but look at the performance these guys are getting out of modern motors... Very cool, they sound amazing. I have a mate who's just s a bout to go to the world champs, his dedication and metallurgy knowledge is bordering on the insane.... :blink:

Specification: F2A 15.Top 2007

* RPM 42000
* BHP 2.27
* volume 2.48 cc
* bore 15 mm
* stroke 14 mm
* piston / liner - DISPAL 226 (30%Si)

[Reckless]

F***ck me!! 42,000 revs thats huge!

[camchain]

If the pool of oil was deep enough for the crank to be dipped in it wouldn't it be smashed about so much it'd be dragged up the ports and into the combustion chamber.

Yeah reckless, as much as I quite liked the pool of oil idea, I thought the same thing as you, hard to imagine oil that deep where it didn't just get splashed outta the way.

Expansion chamber probably really only does the business at higher revs where port timing and chamber resonance hits a sweet spot - hence the term "getting on the pipe." Trials bikes don't have the big exhaust power bulge but produce plenty of low end/mid range grunt.
One of the best things about 2 strokes is that sexy expansion chamber - it's purty.

[camchain]

Crazy little engines. 42,000 revs is wicked. Would like to see the dainty wee dyno that measured the power output! Tiny carb must be a difficult thing to make and tune.

[Motu]

The expansion chamber is using the same sonic impulses as used in 4 stroke tuning - but because the 2 stroke exhaust signal is so weak,it needs to be amplified.Before the loud speaker,people amplified their voices with a megaphone....and at the other of the scale,people hard of hearing amplified sound with a hearing trumpet...the megaphone in reverse. So you have the two main components of an expansion chamber.

[clmintie]

Crazy little engines. 42,000 revs is wicked. Would like to see the dainty wee dyno that measured the power output! Tiny carb must be a difficult thing to make and tune.

The HP figure is pretty impressive too............

Motors are very easy to tune, because there is no need to 'throttle' them, it's just a straight through venturi with a spray bar and needle.....

The control line speed glow plug motors run on 80% methanol/20%de-gummed castor (some use synthetic, or syn/castor blend)

Here's a link to 'model' dynos

http://www.rctek.com/engines/dyno/engine_dyno.html

[camchain]

The expansion chamber is using the same sonic impulses as used in 4 stroke tuning - but because the 2 stroke exhaust signal is so weak,it needs to be amplified.Before the loud speaker,people amplified their voices with a megaphone....and at the other of the scale,people hard of hearing amplified sound with a hearing trumpet...the megaphone in reverse. So you have the two main components of an expansion chamber.

Sounds right to me - good description. Weaker 2t sonic pulse due to lower compression ratio?

With simple straight through 4 stroke exhaust, the talk used to be about 'tuned length' for right amount of back pressure.

[camchain]

The HP figure is pretty impressive too............

Motors are very easy to tune, because there is no need to 'throttle' them, it's just a straight through venturi with a spray bar and needle.....

The control line speed glow plug motors run on 80% methanol/20%de-gummed castor (some use synthetic, or syn/castor blend)

Here's a link to 'model' dynos

http://www.rctek.com/engines/dyno/engine_dyno.html

Interesting. Engine life must be pretty limited, poor little beasties.
(Only thing I ever had to with model planes is when I got interested in Richard Pearse and built a scale (near as I could from book drawings) model of his plane. It didn't glide at all untill I added fabric to wing underside. I bet it would've gone OK with 40k rpm engine dragging it along though!)

[clmintie]

Slightly off topic...........but.....

Ken Buckley flew this one indoors at the North shore event centre, goes OK......


Back to 2T stuff................:done:

[barty5]

Talkin bout 2Ts cant rememver where i read it but the reakon it takes about 20min running form when the oil that come through from the carb enters or passes through the carb, Which due the the presure is seperatred out hence you get your lubrication is burnt and passes out the exhaust. interesting little fact i thought.

[noobi]

Talkin bout 2Ts cant rememver where i read it but the reakon it takes about 20min running form when the oil that come through from the carb enters or passes through the carb, Which due the the presure is seperatred out hence you get your lubrication is burnt and passes out the exhaust. interesting little fact i thought.

yea i read somewhere that the fuel/oil mix is seperated out in the crankcases and the fuel moves up the ports and combusts, and the seperated oil in left to lubricate the crank etc. and it takes 20minutes or so before any significant amount of oil is available to lubricate the bottom end?
but this doesnt make sense to me.
given the rate in which oil and fuel bond on a chemical level. it would take a fairly strong catayst to seperate the fuel/oil mix out into the parts again.
i assumed that the atmospheric difference from the piston causes fuel and air to be sucked into the cases. and this lubes the bottom end and the fuel/mix is sucked up the ports to the piston?

thats just my interpretation of it

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

[barty5]

Not sure on the whole tech side of it but assume the persure formed by the piston stoke is enough. A lot of the 2Ts ive worked on do have a resonable amount of oil in the bottom of the casing when split open. Cause the fuel oil mix isnt going to lube as well the would fuel tend to want to wash the bearings. Try it sometime on a some bit of metal with mixed fuel works but not as well.

[noobi]

Not sure on the whole tech side of it but assume the persure formed by the piston stoke is enough. A lot of the 2Ts ive worked on do have a resonable amount of oil in the bottom of the casing when split open. Cause the fuel oil mix isnt going to lube as well the would fuel tend to want to wash the bearings. Try it sometime on a some bit of metal with mixed fuel works but not as well.

yea and that suggests that fuel/oil seperation is occuring. i still want to know why the fuel and oil would want to seperate. seeing bond together so fast.
why does the fuel vaporise? i understand that it seperates out but WHY???

[barty5]

yea and that suggests that fuel/oil seperation is occuring. i still want to know why the fuel and oil would want to seperate. seeing bond together so fast.
why does the fuel vaporise? i understand that it seperates out but WHY???

only thought on that is cause under presure the oil is heavyer and force it to seperate the fuel vaporises due to the air flow through the carb and the smal amount of fuel being sucked through. Due to the volume of air fuel mix ans air speed it turn to vapour.

[Motu]

i still want to know why the fuel and oil would want to seperate. seeing bond together so fast.
why does the fuel vaporise? i understand that it seperates out but WHY???

It's because of pressure - but negative pressure...what we call vacuum.Lower the pressure and gasoline will vaporise...but the oil won't.

[camchain]

As I understand it, 2 stroke engine is like a pump. I thought the fuel charge moving through engine was a mix of suck & push. Suck (from carb/intake) when piston moves up - and push (up the transfer ports/into combustion chamber) when it moves down?

I'm wondering how much the charge changes as it passes through a hot engine before the big bang. Being a vapour heat must change it to some extent?

Petrol is much more combustable than oil, so not all the oil in the charge will be getting cleanly burnt during combustion, especially as much (trail) riding not at high revs or at whatever the sweet spot for max engine efficiency is. That's gotta be a good thing for good lubrication. (Bit of crossover info happening on the spark plug thread re different premix ratios depending on intended use)

Barty, how much oil did you see in those crankcases? Spoonful, or half a cup, enough to dip the big end?

[camchain]

Hey climintie, Ken Buckley any relation to Bill Buckley the genius designer of that Buckley 2 stroke GP bike? (he says in a vain attempt to avoid the issue of being off topic)

That's a nice model (I notice the sneaky rudder at rear of the top aerofoil on), a lot prettier than mine. I hung some weight off it where pilot & engine would sit - it didn't even get close to flying properly.

[B0000M]

Barty, how much oil did you see in those crankcases? Spoonful, or half a cup, enough to dip the big end?

i know im not barty but - when i pulled mine apart there was about probably a teaspoon full, plus a nice thin even coating on everything

[crazyhorse]

B.O.R.I.N.G [yawn!!!]:dodge:

[one fast tl1ooo]

B.O.R.I.N.G [yawn!!!]:dodge:

well a chick would say that!!:laugh:

[merv]

B.O.R.I.N.G [yawn!!!]:dodge:

Why, what strokes do you like?

[IIIRII]

Your've never heard anything come on the pipe untill you have heard one of these

http://www.youtube.com/watch?v=JGBHips72TA

Or

For something even more cool sounding

http://www.youtube.com/watch?v=UtiEC1grF_Q

Crappy vhs converted etc: ....

[kezzafish]

ha talk about another thread takeover but i'm in on this one lol! 1/2A conbat used to be me and my dad's thing... great fun. we had a flying wing factory in the back of our shed cos we kept crashing into each other! I've still a few 1/2A flying wings and a 1.5cc diesel at home. goes fukken hard... who'd of thought a 2.5cc diesel motor can do 160 kph like in this vid. they're mighty spectacular when they collide too

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[barty5]

[QUOTE=kezzafish;1129285583] I've still a few 1/2A flying wings and a 1.5cc diesel at home. goes fukken hard...

QUOTE]

So when the ktm motor finally packs a sad you have a half decent replacement for it then sweet probly go better. Wont cast as much ro maintain.:Pokey:

[Sammikins]

B.O.R.I.N.G [yawn!!!]:dodge:

Obviously a little too technical for some to comprehend... :weird:

[barty5]

i know im not barty but - when i pulled mine apart there was about probably a teaspoon full, plus a nice thin even coating on everything

Booms about righht that bout all ive seen your not talkin bout huge amounts enough to coat and bit of resadue much more than that i would be lookin at seals closely.

[B0000M]

Booms about righht that bout all ive seen your not talkin bout huge amounts enough to coat and bit of resadue much more than that i would be lookin at seals closely.

haha, if its trans oil its red, if its 2t oil its green. simple!

[camchain]

haha, if its trans oil its red, if its 2t oil its green. simple!

Uh-oh motul 800 is red, i'm too colour coordinated.

OK, little oil in crankcase so no *dipping the big end then (*kezza - your slacking, Freudian door was ajar on that one)

Been reading up a bit more, apparently an important function of 2t lubrication is rust prevention during engine down time, and there's a bit of a trade off with lubrication. Never knew that but obvious now I think about it with air/moisture in mix.

Here's something worth a quick squiz - It's a 2 stroke Jim but not as we know it. NZ design, groovy pivot piston.
http://www.greencarcongress.com/2006/03/pivotal_piston_.html

[B0000M]

Uh-oh motul 800 is red, i'm too colour coordinated.




lol, i use TTS, always have (since mid 90s), never had an engine fail.

[camchain]

TTS is likely good stuff, and that's a good history. but you know red is fast (the next best thing to orange).

Regarding puddles of oil again, I get a little bit that sits in bottom of my intake boot behind carb. Wondering if reeds are a little worn and getting some blowback? This is just a guess, it's definitely (red) 2t oil, definitely not drool from over-oiled filter. Anyone else get this?

[tommorth]

haha planes on a wire we used to make those at school electic ones though flew them in the gym never went that fast though balsa biplanes etc

[flyingcr250]

TTS is likely good stuff, and that's a good history. but you know red is fast (the next best thing to orange).

Regarding puddles of oil again, I get a little bit that sits in bottom of my intake boot behind carb. Wondering if reeds are a little worn and getting some blowback? This is just a guess, it's definitely (red) 2t oil, definitely not drool from over-oiled filter. Anyone else get this?

yea my old 300exc used to do the same thing, i thought it was just fuel mist evaporating and leaving the oil behind

[Reckless]

Regarding puddles of oil again, I get a little bit that sits in bottom of my intake boot behind carb. Wondering if reeds are a little worn and getting some blowback? This is just a guess, it's definitely (red) 2t oil, definitely not drool from over-oiled filter. Anyone else get this?


yea my old 300exc used to do the same thing, i thought it was just fuel mist evaporating and leaving the oil behind

Look at Carb front in the GIF attached to my first post you'll see why?

[xen]

Look at Carb front in the GIF attached to my first post you'll see why?

Ah cool, makes sense now thanks. Mine does that..

[camchain]

mmm I seeee. Bit of blowback pressure going down to BDC. Thought reeds would seal better.