Hey have a noo ie question

Discussion in 'General Questions' started by wyldman1, May 23, 2010.

  1. wyldman1

    wyldman1 New Member

    Hey I'm sry probably hear it alot but would any mind telling me the difference of 4 or 2 stroke sry don't know

  2. motorpsycho

    motorpsycho Active Member

    for starters...a 2 stroke refers to the # of strokes that the piston makes, to complete the combustion process. A 2 stroke engine's piston makes 2 strokes...down (intake) and then back up (exhaust). there are intake and exhaust ports that are covered by the piston during the process so the engine can make power using only 2 strokes of the piston. a 2 stroke does not have actual valves, but they can use reed valves to make more power. (like the reeds in a woodwind instrument). the majority of 2 stroke engines for bikes do not use reed valves, but they have ports that are covered and uncovered by the piston as it moves up & down (an intake port and an exhaust port.) 2 stroke engines do not have a supply of oil in the crank case to lubricate the bearings and piston rings/ cylinder wall. the oil for lubrication is in the gas (that's why 2 strokes require a mix of gas and 2 stroke oil). a 2 stroke will generally rev a lot higher than a 4 stroke, and in some instances 2 strokes will make a lot more power than a 4 stroke will, especially at higher rpms.
    a 4 stroke is a lot different...the piston makes 4 strokes to complete the combustion process. intake stroke (piston goes down, intake valve opens and fuel/air is sucked into the cylinder...intake valve closes), compression stroke(piston goes back up and compresses the fuel/air mixture. both the intake valve and exhaust valve are closed), power stroke (while the piston almost to the very top of the cylinder during the compression stroke, the spark plug fires and ignites the compressed air/fuel mix. the explosion pushes the piston back down, causing it to make power and turn the crankshaft). exhaust stroke (the piston goes back up, and the exhaust valve opens. the rising piston pushes the exhaust gasses out through the exhaust valve and out of the cylinder). and then the process starts all over again.
    4 strokes use intake and exhaust valves just like a car engine, they have a cam shaft that actuates tappets (or lifters) that open and close the valves at a precise time matched to the position of the piston. a 4 stroke must have a supply of oil in the crankcase (just like a car engine) to lubricate the bearings and the piston rings/ cylinder walls. 4 strokes do not rev as high as 2 strokes do, but a 4 stroke can make a lot more power than a 2 stroke at low rpms. a 4 stroke only uses gasoline..no gas/oil mix.

    think of it this way. think 4 stroke (car engine, lawnmower engine, lawn tractor engine, street motorcycle engine, snowblower engine and now newer dirt bike engines) 2 stroke ( weedeater, chain saw, leaf blower, outboard boat engine, older dirt bike engines, snowmobile engine)
    2 strokes have a very high, raspy exhaust sound, where a 4 stroke has a deeper, thumpier exhaust sound.

    a 2 stroke engine (depending on the build quality) can last a VERY long time if maintained and the correct fuel /oil ratio is used, there are less moving parts in a 2 stroke than in a 4 stroke...less parts that can break or wear out. a 4 stroke engine can last a very long time as well for the same reasons, but there are a lot more parts that could potentially break or fail due to age. run a 4 stroke 1 quart low on oil, and you'll toast the crankshaft bearings.
    on the other hand, run a 2 stroke on just straight gasoline, with no 2 stroke oil added and the engine will lock up from lack of lubrication.
    there is a lot more tinkering and tuning, playing with air fuel ratio's and fuel / oil ratios with a 2 stroke v.s. a 4 stroke, but both types of engines do require some fine tuning at one point or another.
    is one better than the other? it's all a matter of personal preferance i guess. a lot of guys like 2 strokes because of the amazing amount of power that you can get out of a very small engine, by tuning and adding aftermarket exhaust pipes & stuff like that.
    other guys like 4 strokes because they are basically "plug & play" and only require general maintanance. altho you can add aftermarket parts to make a 4 stroke make more power.
    but generally speaking, since 4 strokes operate best at lower rpms, they make plenty of power when it's needed. 2 strokes usually have to rev very high to make big power.
    the thign is, you should really do some research on both engines. if you are going to build a motorized bike, do the research and get as many opinions as you can about both engines before you make a decision on which one you want to buy.
    generally, 2 strokes are cheaper to buy than 4 strokes are...but 2 strokes can be finicky and require mechanical knowledge to get them to run at their top potential (speaking about chinese 2 strokes for motorized bikes that is).
    Last edited: May 23, 2010
  3. wyldman1

    wyldman1 New Member

    Thanks for alll the info man I had no clue about that **** have always wondered for the longest time haha thanks alot.
    What do you think would be better for a first timer
  4. GearNut

    GearNut Active Member

    For a first timer, either type of engine will do you well if it is of good quality, I.E. not a cheap in frame 2-stroke.
    I would recommend a Titan, Robin- Subaru, Honda, HuaSheng, and a few others I can't recall right now.
    Don't get me wrong, a cheap engine will work, but it depends on your level of patience.

    The cheap engine kits all need a bit of fiddling with to get to cooperate nicely, and even then, some last 10 feet, and others last thousands of miles. It depends on the particular engine, how well it was assembled at the factory, how well it was installed, initially broke in, and maintained. A good vendor can be your best asset when you choose one to purchase. Warranty issues are common with the cheap kits.
    The Japanese kits, which cost more, are far easier to get going from a newbie perspective.
    They are generally a friction drive system, which can be installed and running down the road in just a few hours. There are good belt drive kits, both belt to rear wheel and belt primary drive and chain final drive to rear wheel.
    Do your homework, search this site, and get a feel for what folks are saying about their kits.
    You will quickly learn which ones need more work, care and feeding by browsing the technical and help sections.
    Check out the vendor review section too. Learn what other folk's experiences are with the various vendors, a lot of which advertise here on the left side of the screen.
  5. motorpsycho

    motorpsycho Active Member

    It really depends on what motor would be best for a newbie. everyone has different tastes, and different mechanical knowledge.
    i grew up building and working on engines, so from a very early age, i knoew about both 2 and 4 strokes.
    your best bet is to ask tons of questions and then make a determination based on the answers you get...but everyone will be different on their answers because a lot of it is opinion.
    I personally love 2 strokes because of the amout of power you can get from them with a few modifications, they are cheap, and simple.
    on the other hand i like 4 strokes too because they can make a ton of torque in the low rpms.
    for a motorized bike, i just think it's cool to have a 2 stroke because there are so many aftermarket performance parts for 2 strokes, specifically for bicycles (but i'm not sure on the aftermarket speed [arts for 4 strokes....there may be just as many for it).
    2 strokes and 4 strokes will give you different throttle responses, and they feel a lot different from each other when you ride. i personally like high revving engines because they sound so cool with the right exhaust on them. 2 strokes can sometimes be a lot louder than 4 strokes(talking about single cylinder , small displacement engines that is)
  6. wyldman1

    wyldman1 New Member

    Thanks you guys the information has bin helpful I'll get th rest of my info from the info discussions but if I need any more help that I can't find there I'll let the forums knowncant wait to get my bike running with the engine on it two weeks and counting
  7. loquin

    loquin Active Member

    Also, with a two stroke, be very careful when coasting down long hills...

    Since the lubrication is supplied with the fuel, when coasting, you aren't supplying any fuel! For a short time, (slowing down for a light, etc.) this won't matter, but, for long downhill runs, you need to give the motor some gas, just to get oil to the engine...
  8. motorpsycho

    motorpsycho Active Member

    i would have to disagree with you on this.
    what you are saying is that the bearings don't get lubrication while coasting down hill? and that you are not supplying ANY fuel while coasting with the engine running at an idle?
    well, if you are not supplying any fuel, how do you think the engine stays running when it's at an idle? even at idle, fuel is being burned, and oil is getting to the bearings.
    do you think that the oil mysteriously separates itself from the gas only when the engine is idling?
    if you have gas/oil mixed, any time the engine is running, oil is getting to the bearings no matter where the throttle position is.
    if what you are saying is the case, then 2 strokes would never have been made to idle.
    Last edited: May 25, 2010
  9. KCvale

    KCvale Motorized Bicycle Vendor

    If you are going down a long steep hill be worried about you brakes not engine lubricant at idle.
    Let that engine drag help slow you, don't be pulling the clucth and revving it, and if you still can't slow down enough hold the Kill button in, that will stop you even faster.
  10. motorpsycho

    motorpsycho Active Member

    it seems that this post has gotten way off topic, but this is exactly what you don't want to do. This is how the engine can get damaged from lack of lubricant. coasting down a hill, with the kill button pushed in and the motor turning over (not running) trying to make it act as a brake, will severly damage the bearings. this is when there will be no oil getting to the bearings or the piston rings at all...bad idea.
    your best bet (in my opinion anyway) when going down a long hill is to pull in the clutch, let the engine idle and only apply the brake when you feel like you are going too fast. don't ride the brakes because this will overheat them very fast, and you will experience brake fade. the brakes will not work when you want them to when they are too hot.
    if you leave the clutch out and let the engine idle while going down a long hill, you take a chance of the engine over revving without enough fuel /oil to do their job. remember, when coasting down a hill, the rear wheel & sprocket will start to turn faster and faster as you pick up speed from gravity. the rear sprocket will be pushing the chain around the engine sprocket, causing the engine to rev higher and higher. the engine will not act as a brake, the speed of the rear wheel /chain will overpower the engine and cause it to over rev.
    sure, this concept works on diesel engines (an engine or exhaust brake) but diesels make WAY more power and are far more sophistiacted, and the effects of an engine /exhaust brake work a lot different than just letting the engine turn over to slow you down.
  11. wyldman1

    wyldman1 New Member

    Thanks you guys will use the info given very helpful didn't know any of this stuff