How do I make this bike as quiet as possible?

Discussion in 'General Questions' started by darkfighter, Jul 23, 2016.

  1. darkfighter

    darkfighter New Member

    Thank you for taking the time to look at my post in advance. I am 15 and just assembled the standard 50cc chinese 2 stroke on a walmart bike, with some cosmetic additions.

    However, since I want to ride around the neighborhood, I will need to make it as quiet as possible and stop noise leaking from the engine chamber, especially between 900-3000 rpm. If there are any parts that I can add to do this and dampen the sound to as minimum as possible, please let me know.

  2. Frankfort MB's

    Frankfort MB's Well-Known Member

    What kind of noise is your motor making? It should sound about the same all the time
  3. darkfighter

    darkfighter New Member

    It does sound the same, except that I want to decrease the sound in GENERAL. About the part of making more noise at 900-3000 rpm as opposed to higher rpms, this is just lower frequencies being able to travel a longer distance and thus being perceived as louder.
  4. jaguar

    jaguar Well-Known Member

    Frankfort MB's likes this.
  5. darkfighter

    darkfighter New Member

    Hmm, don't really have a dremel or any special tools, so I think a better CDI that is tuneable would be great. I have yet to find one that will reduce the noise through timing retardation.
  6. FurryOnTheInside

    FurryOnTheInside Active Member

    I would be (I am) more concerned about the high frequency sound as that is much easier to pinpoint the direction of, and to identify as a two stroke motorbike.
    Have you used the search function (top right ^^^) with words like " sound noise reduction dampening stealth mods " ? You get more answers faster like that. Well, I did when I was reading up about this.
  7. libranskeptic

    libranskeptic Member

    Dunno, but intuitively, i like the idea of shoving those stainless steel pot scrubber pads down the exhaust pipe.

    Lots of baffle & not much restriction.

    Easy to petrol rinse any 2 stroke gunk out periodically.

    i agree u r right to be leery of timing being a solution.

    u r also a wise kid. u have manners toward others. Its right, and it pays in life.

    hope this helps or stimulates a response that does.
  8. jaguar

    jaguar Well-Known Member

    darkfighter, the noise that emanates from the cylinder and head fins is the result of the rapid rise in pressure. The more the timing is advanced the higher the peak pressure which affects the noise level. Admittedly a 5 degrees retardation of spark probably won't make a noticeable difference though.
  9. Ahmad Darwish

    Ahmad Darwish New Member

    Its really not to loud in the first place, it may sound loud while your riding it but if you really need something quieter, the only thing you can do is get good muffler, and if you want more performance, make sure to buy an expansion chamber with an integrated muffler.
  10. darkfighter

    darkfighter New Member

    I know it may not be too loud, but it is getting pretty annoying having to turn the engine off within 50 feet of a pedestrian just to avoid weird suspicion. Perhaps if I pedal at the same time and turn it into an electrically assisted hybrid no one will understand to care enough about how it works.
  11. Wolfshoes

    Wolfshoes Member

    It is possible to shroud the engine to some extent with indoor/outdoor carpeting held on with a velcro strap as a sound deadener.

    Landrider w sound deadner.jpg

    As pictured, the carpet piece is laminated with a commercial remnant adhesive backed plastic and edged with shipping tape. The shroud was used all summer in north Illinois without heating being a issue when using Opti-2 two cycle lubricant which seems to allow the engine to run cooler. The brand label sticker sometimes found on the clutch cover seems to dampen harmonic resonance enough that it's worth having a material stuck to the outside of the cover for no other reason than sound deadening.

    Regarding your question about licensing your motorbike. In general, they are not licensed as a motor driven cycle or moped in most states. Some states would like to make them have insurance but there does not appear to be any cooperation by insurance companies. Usually a motorized bicycle, as a consumer commodity under federal law, can be ridden up to 20 mph and a state or locality could allow a higher speed than that. In some IL state jurisdictions, the 20 mph is a boost after the engine takes over forward motion allowing a speed higher than 20 mph. As true with bicycles, under federal law you have the right to the lane of traffic. In Illinois, a motorized bicycle cannot be considered a motor vehicle if it cannot begin forward motion without pedal assist. Therefore proof of insurance or registration cannot be asked for. I understand it is not all that hard to get the federal legal ability to create VIN's as a builder if properly applied for. You would be expected to have built the frame. My opinion on the engine EPA engine problem is only computer controlled fuel injection will pass for street use as a motor vehicle. Grubee HT two cycle engines pass the EPA on motorized bicycles if the overall weight does not exceed 44 lbs; but after the engine purchase, there is no provision to check the finished bike at this time. Some states such as Indiana, Michigan, Vermont and New York are attempting to impose licensing and or insurance requirements and it is possible New Jersey is as well but I cannot comment on that.
  12. Steve Best

    Steve Best Active Member

    Hey Darkfighter, smart thinking, good question. I'm working from this angle too.
    I bought a few mufflers from my supplier and found this one the quietest:
    I have followed Jag's advice and fastened 10"rubber hose to its exhaust outlet. I used steel mechanic's wire. It works.
    The stock intake was very noisy too, solved with a better filter housing, which the engine needs anyway.
    Jamming 1/2" long rubber hose bits in the cylinder fins got rid of a lot of "PING".
    At this point, I have more noise coming from the gears. Make sure they are greased.
    I haven't made noise dampers up for the gearcase yet. I'm thinking of a rubber coating on the inside.
    Keeping rpm down and off the throttle near people helps, as does pulling clutch and pedaling.
    Very little noise at idle or low rpm and load.

    A tuned pipe would make more power but typically makes more noise.
    Jag has a video that shows the value of having the stinger (outlet) come off the mid-point rather than the end.

    I read an SAE paper about silencing 2 strokes several years ago. It concentrated on exhaust port shape (round is quieter than square or triangular, softer pulse wave) that I remember. The DT200 Yamaha is very quiet, using water cooling, a double wall tuned pipe and efficient muffler.

    Darkfighter, sensible idea, smart guy.
    If we want to keep our rights to ride we need to keep under the radar. Stealth makes sense.

    Last edited: Jul 30, 2016
  13. darkfighter

    darkfighter New Member

    Hmm, I liked the idea of a muffler with the catalytic converter built in, but want to buy from an American seller instead, since the CAD is almost back to normal.

    By the way, does spark plug affect noise? I would imagine it to affect ignition which would affect it.
  14. Steve Best

    Steve Best Active Member

    The same company has an American branch but they do not sell the non-cat chrome muffler to you guys. The black cat muffler is a close second. Cats don't go so well with 2 strokes, they soot and oil up. The American branch is

    Spark plug has no effect on noise at all.

  15. pghewins

    pghewins Member

    i managed to quieten mine quite a bit i bonded 6mm rubber to the outside of all 3 removable covers bought some exhaust wrap and wrapped the outside of stock exhaust cut top off empty butane can make sure its empty first lol and you arent smoking while you do this its the right bore to slide over the stock exhaust then drilled 12 or so 3 mm holes round the base easiest done if you fill with water and freeze it first packed with wire wool and slid over exhaust and held in place with jubilee clip has made quite a difference not such a tinny noise now and no noticeable loss of power swapping to a dellorto copy carb also made a big difference you can get the idle much steadier at lower rpm than with stock nt carb thanks to jaguar for his advice on how to set this carb up
  16. pghewins

    pghewins Member

    a cat will be knackered on a 2 stroke in miles to much oil in exhaust gases and yes swapping to a good ngk or champion or bosch plug makes a hell of a difference to performance and the smooth running of engine from the spark plug provided in the chinese kits i use champion CJ7Y
  17. Purple Haze

    Purple Haze Active Member

    A lot of noise is not coming from the exhaust, but from the chain drive. Pull the left rear cover (the one with the clutch arm) and see if the chain is rubbing the front edge. (they usually do) This alone makes for a noisy ride. Dremel or trim for clearance. A good tensioner (spring loaded) will also reduce noise and lower maintenance. I've found the clutch very noisy on these engines, wish someone would come up with a better idea. Sickbikeparts has a kit that's like Dynomat to fit inside the covers, which helps dampen the clutch noise. The intake (carb) also makes quite a bit of noise. (hissing) Get a good air filter. If you have a muffler that comes apart, you can stuff fiberglass packing (available at motorcycle shops) into the case to mellow the sound. Don't go overboard with it, as it is restrictive.