2 Stroke Mechanical Word Glossary By J-nitro

Discussion in 'The Workshop' started by J-Nitro, Aug 22, 2007.

  1. J-Nitro

    J-Nitro Active Member

    2 Stroke Mechanical Word Glossary By J-Nitro

    Following a very important suggestion by Our well known Moderator - Wobbly-51, I wanted to make a glossary of 2 stroke terminology I will start by The most common parts mention here on Scooter Shack, It will probably need alot of editing :(:

    A Barrel

    The Barrel is usually made from a hard-wearing cast iron or an alloy compound. The barrel is the main part of the cylinder; it is a crucial and very precise part of a 2-stroke engine, which houses the piston and conrod movement inside. it's main job is to contain the air tight mixture of fuel/oil and air before the mixture is combusted

    After ignition from the spark plug, the mixture drawn in gains massive amounts of energy and expands forcing the piston down the barrel, precise ports on the barrel let the burnt toxic mixture travel out of the barrel into the exhaust

    Here is a typical picture of a 2 stroke barrel:


    You can straight away see the exhaust hole or the proper name is "tract" for the burnt hot fuel + air to escape away into the exhaust

    This barrel has lots of very broad flat shaped "fins" coming of it. The reason the barrel has these "fins" is because it can get rid of heat quicker because there is more surface area for the air to get to.

    Without these the barrel would heat up much quicker and have less area for air to get to it and cool it down.

    Usually Air cooled engine has these "fins" attached to them because liquid cooled barrels have a built in water passage around them to cool it down

    The Crankshaft (aka Crank)

    The crank is also a very, very crucial part of any engine which is usually the most expensive part to fix if it goes wrong. Cranks have to be very strong, resist extremely high-wearing temperatures therefore lots of processes are involved in the making of these, to ensure they are fit for the Job.

    The Job of the Crankshaft is to translate the movement of the conrod which gets forced down by the expanding air pushing on the piston. So when the conrod pushes down the circular bit on the crankshaft rod moves around

    Once the piston has gone all the way down the barrel, the circle bit on the crank moves back up again and so does the piston, and so the cycle starts again, it moves back up because of the cranks clever design

    So because we know that the piston is constantly being moved up + down, up + down etc etc... We know that at the same time the crank's rod is being spun around again, again and again etc...

    Now we have a constantly spinning spindle - Great!, all we have to do is attach a belt or a chain and put a wheel on the other end of a wheel driving shaft, that way every time the crankshaft turns around - you guessed it! The wheel will spin around too.

    That is why when the engine is switched off, the crank doesn't spin and so the wheels don't move do they? using this theory we can say when you rip the throttle back your making the piston go up and down faster, turning the crank faster, making the wheels go faster too!


    The crank is measured by how many turns it does every minute we call this measurement RPM e.g. if the engine is doing 7,000 RPM the crank is turning around 7,000 times a minute! pheww!


    The crankshaft above is a standard half circle one, which is connected to a flat shaped connecting rod aka "con rod"

    Notice how the conrod has a circle hole at the end? this is where the con rod meets the piston and it is locked into place by a pin threaded through

    The Piston

    If you've ever took the lid of your barrel before (cylinder head - where the spark plug screws in) you will notice a heavy cylinder shaped object with one or two rings around it, we call this the piston.

    The job of the piston is to push the conrod down to turn the crankshaft around (above). The piston is usually made of cast iron or a more expensive alloy. The piston has 1 or 2 rings with splits in it for a reason (see piston rings section).

    Another job of a piston is to suck in air and petrol/oil so it is ready to be ignited by the spark plug, when ignited the piston is forced downwards, down the barrel, forcing movement on the crank. Due to the connection between the conrod and the crank, the piston automatically moves up the barrel to begin the cycle again. You could also say that the piston controls the flow of gases coming in/out of the cylinder.

    This is a piston head, connected to a con-rod, coming out of the crankcase the barrel has been removed because the 4 long tubes (studs) hold the barrel in place


    Piston Rings

    This is probably the bit in the engine that is subjected to the most friction and wear other than the tyres + crank. The main Job of the piston ring(s) is to seal off anything that tries to get past the piston along the barrel e.g. burnt fuel + air going down the sides of the barrel and into the crank case with clean air + fuel mix.

    You can either get a piston with 2 piston rings or 1 piston ring, 2 piston rings last longer and don't need as much attention, but create more friction as they slide down the walls of the barrel, where as a single ring piston will have 1 ring around it creating less friction and therefore produces more power output at the wheel.

    Usually racing bikes and "crossers" have this type of structure. This is because less power is used to push 2 rings down, so less power is wasted. However a 2 piston ring system is more reliable and wears 3 x less than a single ringed piston, meaning you don't have to change them so often.

    These two circular shaped pieces of metal are called piston rings they fit into the grooves on the piston head, they both have a single split to they are easy to get on/off and change they close up, so there is no split when they are pushed together and slid inside the cylinder barrel.


    The cylinder Head

    A dead easy part that is easy to understand!

    The piston head acts as a lid on a tupperware container, it seals the gases in during combustion on top of the barrel, it is simply bolted on top of the barrel and through this "lid" we can use it for more than just a seal.

    We can implant sensors in the cylinder head which records the temperature inside and also most importantly we can implant a programmed device that generates a spark automatically called the "spark plug".

    We must be careful though when sensors, spark plugs and so on are screwed into the top as the piston will be almost tapping the top and could crush a spark plug that is too long easily and smash goes your new piston head!


    Notice how the cylinder head has these cooling "fins" as well? it is so the whole cylinder (barrel+head+piston) can achieve maximum efficiency when trying to cool itself down using fresh air.

    Reed Valves (aka Reeds)

    You hear all the time in 2-stroke conversations people mentioning "reeds", again an absolutely critical part of a 2 stroke engine as they rely solely on the changing pressure inside the crank case (the bit where fuel/oil and air is stored under the piston ready to be burnt).

    So the weight and dimensions of this block have to be perfectly balanced otherwise the engine won’t run at all. This is because the special job they do to make the engine run.

    When the piston is forced down by an explosion of fuel/oil it causes huge pressure down on the crankcase, when you compress air the pressure builds up and the fuel/oil/air mix wants to escape!, so they pressure causes this to be forced into the barrel (or combustion chamber) ready for explosion.

    Now - nothing is left in the crank case, a vacuum!, so when it rises up again automatically, it's huge vacuum forces pulls the reed petals open letting in a fresh new fuel/oil/air mix into the crank case again and the cycle begins from scratch again!

    The reed petals are made from very delicate thin pieces of steel or an aftermarket carbon fibre - why so thin and possibly so strong you ask?

    Well they have to be thin enough to be pulled against the block due to the vacuum pressure sucking the reeds back, think the heavier the reeds the more energy is wasted trying to suck the reeds back to let air/fuel/oil in again

    And they have to be strong because the vacuum is very powerful in the crankcase

    Using this information now you can see why carbon fibre reed petals are better, because they are lighter than metal so less energy is wasted to pull them back!

    here is a diagram of how reed petals, which fit in a reedblock, works:

  2. wobbly_trials

    wobbly_trials Active Member

    RD350, SR125, ICE125
    looking good, copy into a word document and i'm sure with a bit of proof reading mr.terro will be able to use it on the main site, with your consent ofcoaurse.
  3. The General

    The General Member

    nice this is and the jet guide should be in the guides section

  4. Leeroy

    Leeroy Member

    nice! alot of effort put in well done!
  5. neosman

    neosman Member

    good work.
  6. MiNoR cOnFuSiOn

    MiNoR cOnFuSiOn Administrator Staff Member

    et2 monster
    jet guide shouldent as its a basic idiots guide to installs. not an acutal instruction guide on how to WORK out jeting. swift said it himself. will be put into guide form once weve all added bits and bobs as we want it complete (needs some correcting and adding again as its a little more complicated and there are 5-6 names for single named parts like the exhaust port (ie its a tract, the port is the internal part) but anybody with anything worth adding should do so and myself and terro can sit down and take the relevent gear out and throw it together as a full indepth guide once EVERYTHING is there. the jetting guide on the site by myself will be re written as soon as i have some free time as i want to cover a few more things. im going to add alot to the transmission/roller setup aswell to explain springs belts and pulleys.

    but ye as i said anybody who thinks they can add to the guide post it in here and we will compile thew guide once ALL the infos at hand. other than that please dont post in this section as conversations will make for 30 pages of posts for 20 posts worth of info.

    cheers anyway j-nitro. brill start and we can use alot of the info here.
  7. xenovia

    xenovia New Member

    excellent information, you must have worked hard on this. Well done!
  8. kishan

    kishan New Member

    nice info there,will come useful for me now.
  9. Haresign

    Haresign New Member

    GPR50 + Peugeot 307
    now i know how it all works lol
  10. Major Rel14b1lty

    Major Rel14b1lty New Member

  11. alex_1966

    alex_1966 New Member

    nice 1 j-nitro , well helpfull for beginers
  12. Oakley

    Oakley New Member

    Exellent info :D

    Atleast i have an idea how it works now ;)
  13. dylanbws100

    dylanbws100 New Member

    gee...excellent! well detailed. Mind if i put this on stumbleUpon?
  14. NRG_JON_92

    NRG_JON_92 New Member


    I spell checked all of this for you there where a few/little mistakes well done :tup: i also found this very useful :tup: :tup: :tup:
  15. j3rd4n2k9

    j3rd4n2k9 Member

    well done pal good work, im sure this will help in the near future :cheers: :good:
  16. grantmc3

    grantmc3 Member

    piaggio nrg mc3
    very good topic i will remember this when someone with few brain cells asks me what a piston is
  17. Smiithy

    Smiithy Member

    Thanks :D
  18. J4CK

    J4CK Member

    Piaggio NRG 172
    Schweet thanks :)
  19. donlon

    donlon New Member

    Good stuff, you should think about making the content read in alphabetical order as it grows. Excellent effort and so useful ( to me already). Thanks a bundle.

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