Two and Four Stroke Engines

[bear]

So what is the difference between two and four stroke bikes. When I've been telling some old fellas that I got a new bike recently and they all ask if it is two or four stroke.

Were two strokes the only way to go at some stage, and fours a relatively new thing? I thought most road bike nowadays are four strokes.

[Hitcher]

Sigh. I must be getting old.

I shall wear the bottoms of my trousers rolled...

[Motoracer]

A 2-stroke engine doesn't have valves, a 4-stroke engine does.

In combustion engines the inner energy set free by combustion (e.g. of gasoline or Diesel fuel ) is changed partly into mechanical energy. There are several varieties of combustion engine. The most common is the four-stroke Otto Engine, which was invented by the German merchant and engineer Nikolaus August Otto in 1876.

The working mechanism of the four-stroke Otto-Cycle: The engine's cylinder has got two valves, the intake valve and the exhaust valve, which are opened and closed by a camshaft mechanism. A crank moves the piston in the cylinder bymeans of a "connecting rod".

The operation of the engine is divided into 4 parts, which are called strokes:
-1st stroke (Intake): The piston sucks in the fuel-air-mixture from the carburetor into the cylinder.
-2nd stroke (Compression): The piston compresses the mixture.
-3rd stroke (Combustion): The spark from the spark plug inflames the mixture. The following explosion presses the piston to the bottom, the gas is operating on the piston.
-4th stroke (Exhaust): The piston presses the exhaust out of the cylinder.

In a two-stroke engine (e.g. in lawn-mowers or in power saws), the engine is operating every second stroke - there are no valves. It is necessary to use a mix of gasoline and oil (two-stroke oil) as fuel. This is used to lubricate the piston and the crank shaft.

1st stroke
The compressed fuel-air mixture ignites and thereby the piston is pressed down. At the same time the intake port is covered by the piston. Now the new mixture in the crankcase becomes precompressed. Shortly before the piston approaches the lower dead centre, the exhaust port and the overflow conduit are uncovered. Being pressurized in the crankcase the mixture rushes into the cylinder displacing the consumed mixture (exhaust now).

2nd stroke
The piston is moving up. The overflow conduit and the exhaust port are covered, the mixture in the cylinder is compressed. At the same time new fuel-air mixture is sucked into the crankcase

Note: I didn't write the above. I copied and pasted it from a google search. You should try that sometime (searching for info on google that is).

[Coyote]

Easiest way to tell between the two in most cases is a 2 stroke has a whiney sound, and a 4 stroke has a deeper sound. Also, most 2 strokes have the huge pipe to the side of the engine.

2 strokes are damned good fun. My KX is so awesome.

[duckman]

Sigh. I must be getting old.

I shall wear the bottoms of my trousers rolled...
YUP!! - Ya know that rolling your trousers up is very "in" at the moment ... wait wait... it just went "out" again .... :2thumbsup

[bear]

Yeah, good point on the google searching, but were most road bikes two stroke at one stage and then went to predominately four stroke engines?
Was interested as to why the more mature folk were asking the 2/4 stroke question.

[bungbung]

Sigh. I must be getting old.

I shall wear the bottoms of my trousers rolled...

So as to blend in with today's yoof, you will need to make certain one leg is rolled higher than the other depending on your eastside/westside allegiance

[James Deuce]

Yeah, good point on the google searching, but were most road bikes two stroke at one stage and then went to predominately four stroke engines?
Was interested as to why the more mature folk were asking the 2/4 stroke question.
Nope. A lot of cheap and small capacity bikes were two strokes, but mid-90s emissions regulations meant that they couldn't pass various air quality tests, despite such advances as direct injection and the orbital two stroke engine.

The two stroke enjoyed a period of use from about the mid-50s to the late 80s before going away. The big pipe that Alarumba refers to is an expansion chamber, which uses a resonant frequency to help scavenge exhaust gases.

The two stroke was reknowned for being "peaky" and having no torque, but in actual fact puts out a higher specific torque figure by capacity than a similar sized four stroke - it's just that the torque curve follows the horsepower curve, and this helps create the almost mythical "power band" that most of us old two stroke afficianados waffle on about.

There is now a "six" stroke engine in development, which is effectively a two stroke firing cycle with a valved head. Puts out a crap load of power from very small CC ratings.

[James Deuce]

So as to blend in with today's yoof, you will need to make certain one leg is rolled higher than the other depending on your eastside/westside allegiance
Wot abart us old school soufsiders?

[Storm]

Nice to see you sneaking up on your 2 star rating there Jim2 :niceone:

[Hitcher]

So as to blend in with today's yoof, you will need to make certain one leg is rolled higher than the other depending on your eastside/westside allegiance
I should have been a pair of ragged claws
Scuttling across the floors of silent seas.

[NordieBoy]

Yeah, good point on the google searching, but were most road bikes two stroke at one stage and then went to predominately four stroke engines?
Was interested as to why the more mature folk were asking the 2/4 stroke question.

Because it's the more mature folk who know the difference.
2-strokes are a simple engine and get more power per cc than 4-strokes.

A 4-stroke 250 is a nice little bike.
A 2-stroke 250 is an evil little monster.

In motorcross the 125 2-strokes race against 250 4-strokes and the 250 2-strokes race against 450 4-strokes.

[SPORK]

Excuse me! Only the oldies? Come on! As the most junior member here, I demand some respect! Don't think that only the oldies know everything (although I know nothing :))

[aff-man]

easy to tell difference if you hear ring-ning-ning-ning-ning you gots a 2-smoke and if it sounds like your mothers sewing machine you got a 4 stroke (250). plus i don't know of any 2-smokes bigger that 500cc does anyone else?????

[Hitcher]

i don't know of any 2-smokes bigger that 500cc does anyone else?????
Two-stroke diesels are generally a bit bigger than 500cc.

[NordieBoy]

plus i don't know of any 2-smokes bigger that 500cc does anyone else?????

How about the Maico 760 (http://www.off-road.com/dirtbike/nov00rsMaico760.html) from 1981.

Or the ATK Intimidator 700 (http://www.off-road.com/dirtbike/machines/2004/atk/700/)

Older sidechairs were 2-stroke monsters.
Snowmobiles are the main 2-stroke monster industry nowdays.

[Motoracer]

I saw a classic racer at Pukie with 2 X RD350 engines combined. So that'd be a RD700 engine? Looked wicked and the owner reckones he does over 300kmph on it.

[Motu]

I saw a classic racer at Pukie with 2 X RD350 engines combined. So that'd be a RD700 engine? Looked wicked and the owner reckones he does over 300kmph on it.

Bill Buckley used to drive a midget with a 2 stroke V8 in it - made out of 4 RD350 bottom ends andTZ750 top ends,I remember when he used to drive it at Springs.I'm not sure if Buckley was responsable for the motor or not...it was up on display at Haldanes for a few years.

[Motoracer]

Bill Buckley used to drive a midget with a 2 stroke V8 in it - made out of 4 RD350 bottom ends andTZ750 top ends,I remember when he used to drive it at Springs.I'm not sure if Buckley was responsable for the motor or not...it was up on display at Haldanes for a few years.
Holly shit! I would have loved to hear what that sounded like. A 2 stroke V8...

Oh yea, that's right. I forgot about the TZ750... Does anyone know what would be the all time biggect capacity production 2 stroke motor (for motorcycles only)?

[avgas]

yep those old kettles or wot eva were 750's.
Also saw a few RGV750 conversions.
I love 2 strokes - if its not smokin, then its broken

[NordieBoy]

Does anyone know what would be the all time biggect capacity production 2 stroke motor (for motorcycles only)?
Well it's not production but...
48 cylinders is getting large.

http://fran.nelson.geek.nz/motorbikes/wierdness/kwak-48-1.jpg

[Motu]

Holly shit! I would have loved to hear what that sounded like. A 2 stroke V8...


It sounded like you'd just kicked a wasp nest - and as scary!! There was a 3 litre capacity limit around then I think,they were using Holdens and Vauxhalls,a Daimler V8 and an Offy too,they were getting long in the tooth and not many other options,which is why they made the V8,but almost at the same time the VW era came in and within a season the only motor out there was a VW.

Before the 2nd World War 2 strokes were very,very ineffient,apart from the Scott (a 700cc twin,with oil pump lube and water cooling,nothing new under the sun) But a couple of German engineers made huge strides in 2 stroke development,they were responsable for the loop scavange system that is still used today,and exhaust technology leading to the expansion chamber,still often called Kadancy after the guy who invented this.(Google would be better than my poor memory,but will give you lot something to squabble about later)Just looked it up,Walter Kaaden,he worked for MZ in the 50s..The DKW 125 was the result - and after the war was one of the spoils picked up by the Allies.Every small 2 stroke built after the war was a direct copy of the DKW,the BSA Bantam,every Villiers powered small British bike,Harley made a version (grease nipples on the mains!) and the first Yamaha's were a DKW too.There is a legend about a race in Europe where a famous East German 2 stroke engineer crashed in a corner and was wisked away never to be seen again - but we saw his work in the Suzuki's.

The 2 strokes got to working pretty good with power valves and water cooling,they are quite easy to ride now with wide power bands like a 4 stroke - but unfortunatly the are still dirty and won't pass emission tests....the technology is there to get around this,but not economicly viable.

[James Deuce]

There is a legend about a race in Europe where a famous East German 2 stroke engineer crashed in a corner and was wisked away never to be seen again - but we saw his work in the Suzuki's.


Degner - it's true, and he was a racer rather than an engineer, but a knowledgeable racer at that. His defection plan got all messed up though.

[Warren]

Also every 50cc scooter is a 2 stroke.

every = 99%+

[Motu]

Also every 50cc scooter is a 2 stroke.

every = 99%+

Good,I never considered the Honda C50 to be a scooter.And the Ducati was a moped.

[Lou Girardin]

A Commer TS3 diesel has the best sound short of an F1 car and, gee, it's a 2 stroke. But a bit bigger than 500cc or even 50.

[Madmax]

degner! he invented the expansion chamber
(he was a two stroke god!)
I love two strokes, but you have to look after them just right,
Big bore two strokes are such fun
have had a ride on a TZ750
(they never made rubber good enough to hold them
on the road) H2R as well
(would love to ride a KR750)
think i was hansford who said, every time i opened the
gas it wanted to jump the fence back into the pits
(amaroo park)

:love2:
then i am bit insane
:confused:

[merv]

A Commer TS3 diesel has the best sound short of an F1 car and, gee, it's a 2 stroke. But a bit bigger than 500cc or even 50.

You going to talk trucks, how about railway engines? GM made the 710 cubic inch per cylinder V16 2 stroke diesel - that's roughly 11.64 litres per pot or 186 litres total. Now I guess the marine guys will come out of the woodwork and quote their figures.

[2_SL0]

aaaaaaaaaaaaaa, the mighty KX 250. Brings a tear to my eye. (especially as I spent most of my time sitting on the fuel tank to keep the front end down.) Bloody peaky, snappy thing. OOOOOOOOOOOOOH :scooter:

[MOTOXXX]

if you go to something like
www.howstuffworks.com

they have good pics and explinations for this kinda stuff
and pretty much most things as far as ive seen anyways.

[speedpro]

easy to tell difference if you hear ring-ning-ning-ning-ning you gots a 2-smoke and if it sounds like your mothers sewing machine you got a 4 stroke (250). plus i don't know of any 2-smokes bigger that 500cc does anyone else?????
<sigh> :weep: :beer:

[speedpro]

Bill Buckley used to drive a midget with a 2 stroke V8 in it - made out of 4 RD350 bottom ends andTZ750 top ends,I remember when he used to drive it at Springs.I'm not sure if Buckley was responsable for the motor or not...it was up on display at Haldanes for a few years.
And the V4 made from IT490s and an IT250, I think. Bob and Bill did the motors.

[speedpro]

A Commer TS3 diesel has the best sound short of an F1 car and, gee, it's a 2 stroke. But a bit bigger than 500cc or even 50.
Supercharged as well I seem to recall

[speedpro]

I did some work on a ship once. The engine was a 2-stroke, more or less two stories high, 9 cylinders, triple turbo - with exhaust valve in the head. The bore was about 4ft and the stroke at least 6ft. It made max power at 180rpm, red line at 200rpm and idled at 2rpm. Each turbo was about 3ft across. Only the rear three cylinders were used when in harbour. It was started with a key just like a car and even had a huge ring gear and starter motor on one end. It was something like 17,000shaft horsepower, at 180rpm so HUGE torque. I could be wrong on the horsepower figure, it was a long time ago.

[Bonez]

Has the GT750 been mentioned yet?

[Bonez]

Oh and I see rotaries haven't been mentioned ;)

[Motu]

And the V4 made from IT490s and an IT250, I think. Bob and Bill did the motors.

I didn't know about those - what were they in?

I had the TS3 as my avatar for awhile and we had a highjack discusion about it on some thread.The best sounding motor ever made.

[NordieBoy]

Commer TS3 (http://www.oldengine.org/members/diesel/Technical/TS3.htm) Hmmm, an interesting engine.

[vifferman]

Easiest way to tell between the two in most cases is a 2 stroke has a whiney sound.:doh: That must mean that the VifFerrari is a two stroke! I must remember to put oil in the tank.

easy to tell difference if you hear ring-ning-ning-ning-ning you gots a 2-smoke and if it sounds like your mothers sewing machine you got a 4 stroke :blank: So which is it? :confused: The VifFerrari sounds a bit like a sewing machine (it certainly hums). So maybe it's a 3-stroke then ?!? :crazy:

[vifferman]

Oh and I see rotaries haven't been mentioned ;)I was waiting for Motu to mention the Auto Union 2-stroke car. A friend at school had one of those - quite good, but no engine braking.

[Motu]

I was waiting for Motu to mention the Auto Union 2-stroke car. A friend at school had one of those - quite good, but no engine braking.

Shit! - I haven't seen one of those for a hell of a long time...they took a D16 sparkplug and we kept a cleaned set on the shelf for our DKW customer to get a quick swap done.I used to drive around in a Daihatsu Max of my sister in law's,they had a 360cc twin and went bloody well,but it dropped like a stone downhill with drum brakes,no booster and no engine braking,you needed a strong right leg!

[thehollowmen]

Sigh. I must be getting old.

I shall wear the bottoms of my trousers rolled...

You must be if you're quoting something writen before 1917

Guess you can also recognise my handle then? :-P

[cycosis]

2 strokes are beta but cost more :doobey:

[Bonez]

2 strokes are beta but cost more :doobey:
If so does that mean you get more m/c for your dolllar if you buy a 4-stroke :whistle:

[Sniper]

So as to blend in with today's yoof, you will need to make certain one leg is rolled higher than the other depending on your eastside/westside allegiance

Yes and you must wear different coloured socks pulled up as high as they can go :eek: :gob: :buggerd:

[zooter]

check google for some truly gargantuan marine diesel two strokes, pistons bigger than your kitchen. As for bikes there used to be a 750 that was known as "the widowmaker" awesome power without matching handling. I think it was a Kawasaki.

[Sniper]

Message deleted

[Sniper]

<sigh> :weep: :beer:

CR600, mates got one at home. Stupid machine :ar15: :thud: :doh:

[F5 Dave]

The Kawasaki was the H2 750 air-cooled triple. It was truly ahead of it’s time powerwise, but sadly lacking in chassis advancement.

Suzuki, Kawasaki & Yamaha raced in F750 class & has the TR, KR & TZ750 respectively. The TZ was later & a watercooled reed valve 4 cylinder & wiped the floor with the triples.

Suzuki released the GT 750 (water cooled) but decided not to capitalise on its racing successes & launched it as a fat tourer.

The rotary (Suzuki RE5) is not a 2 stroke, but can sound similar. Yamaha had one but it did not go into production, as did DKW I think.

A little later both Yam & Suzuki tried to capture the race replica but followed the 500cc path (the F750 class defunct by now as too powerful) & produced the RZ & RG500 respectively. This time it was Yamaha that was more conservative & weighted the bike down with all sorts of gudubins whereas the Suzuki (disc valve induction) was the raver of the two.

As Jim rightly mentions the reputation for being less ‘torquey’ is mythical. Until recently all trials bikes (well ½ way decent ones) were 2 strokes & produced wide spaced power. The recent change to 4 strokes & both Trials & other Dirt factions is purely legislative. (Will be unable to sell a new 2 stroke in the US soon). Manufacturers are desperately trying to match the weight & power outputs with their new 4 stroke machines & the only way they can compete is by making them bigger capacity, which usually makes them heavier so reliability is now being stretched to achieve weight saving.

All in all poxy tree hugging legislators have killed the 2 stroke despite the fact that such small engines used occasionally are such a tiny drop in the ocean.

[Dr Bob]

and on tother end of the spectrum, the smallest 4 stroke engine.

>Weighing slightly more than 6 lbs. (clutch included), Robin's EH025 is the >world's lightest 4-stroke engine. Meeting all CARB Tier II regulations, the >EH025 is the smallest single-cylinder, 4-stroke, 1.2-hp. engine in its class. >The air-cooled, OHV, gasoline engine uses only half the fuel of a >conventional 2-stroke engine, and its exhaust gas runs cleaner, emitting >less total hydrocarbons. Like a 2-stroke engine, the EH025 is also capable of >multi-position operation

[F5 Dave]

Very useful, wait until those legislators decide 1.2hp is all we realllly need. :eek5:

[Blakamin]

and on tother end of the spectrum, the smallest 4 stroke engine.
>EH025 is the smallest single-cylinder, 4-stroke, 1.2-hp. engine in its class. Like a 2-stroke engine, the EH025 is also capable of >multi-position operation
the 025 is 1.1... the 035 is 1.6
http://www.robinamerica.com/engines/class.lasso?Class=Micro
need to stroke it!

I wonder what they sound like????.... better than the old 2 stroke tools!
might have to put one on a skateboard or something

[F5 Dave]

:whocares:
Wouldn't even make a good lawnmower.

[Motu]

King Kenny said - 'they don't pay me enough to ride this thing.' or words to that effect.Only used the once to clinch his title,took some balls to ride.

[F5 Dave]

For those that don’t understand, they put a TZ750 engine in a dirt tracker as the XS650 based bikes weren’t really making a dent in the Harley dirt trackers.

Apparently they handled real bad but were so fast it didn’t matter.

[AMPS]

Early Saabs were 2 stroke and they cleaned up European rally's for quite a while.
Although that could have been down to crazies like Carlsen driving them.
Lou

[Jantar]

don't know of any 2-smokes bigger that 500cc does anyone else?????

Suzuki and Kawasaki both made 750cc two strokes in the 70s. The Suzuki in particular was very good touring machine in its day, while the Kwaka was a straight out blaster.

[Coyote]

Suzuki and Kawasaki both made 750cc two strokes in the 70s. The Suzuki in particular was very good touring machine in its day, while the Kwaka was a straight out blaster.
Damn, I've just seen one of those KR750s, I want one

[pete376403]

Has anyone mentioned the uniflow diesel yet? Supercharged (some are turbocharged as well), two stroke, 4 valves per cylinder, pressure lubricated crankshaft - eg GM 6V71, in fact every GM diesel, or Nissan UD. Or this: http://home.online.no/~psvhanse/Frames/Eng/Pages/Sulzer/Sulzer.htm

[NordieBoy]

How about the Conley V8?
3.5hp from the non-supercharged version!

http://www.conleyprecision.com/pics/supercharge.jpg

They also have a working Viper V10...

http://www.conleyprecision.com/Dscn1393V-10_closeup.jpg

[NordieBoy]

I've just viewed Conley's VIDEO (http://fran.orcon.net.nz/ConleyV8s.rmm) of a T-Bucket and Cobra and they even sound like V8's :eek: :cool2:

[PeteThePom]

check google for some truly gargantuan marine diesel two strokes, pistons bigger than your kitchen. As for bikes there used to be a 750 that was known as "the widowmaker" awesome power without matching handling. I think it was a Kawasaki.
They did and it was! Called the KH750, kawasaki also made a 250 and a 400 version all sharing similar characteristics of great power and lousy handling/brakes but the 750 was the killer..............

[Motu]

The first triple,the Mach III was ''the killer'' because of it's radical power band,which kicked in with bad results.The 750 had less of a power band and I don't think it made much more hp than the 500.Mind you,Eric Bone who raced both for many years,and still does,reckons he has never been spat off by a Mach III,but has been several times by the 750 - some may have it spit him off at the esses at Paeroa this year.

[Bonez]

We had a border when I was a kid who had a Mach III. Kept fauling plug if used around town. Twas a dailly morning routine to take out the plugs and put the spare set in clean the ones removed. The guy launched himself into a few shop frontages before getting rid of it IIRC.

[betti]

www.dolmette.com

you want two stroke???

this thing is :headbang: mental!

[TwoSeven]

Two strokes are pretty inefficient these days - not because of anything mechanical but because they use poor mans petrol that tends to not do wonders for the environment and all that.

The main difference is that a two stroke has twice as many power pulses as a 4 stroke. It gives a different kind of power delivery to the wheel and can mean a smaller engine design. 4-strokes tend to be more tuneable overall and generally more efficient - although delivering half as many power strokes they tend to require more cylinders or higher revs (which is why inline fours are so good).

[F5 Dave]

Thank you for the thorough & eloquent explanation.

Now I see all & understand.
:pinch: