anyone recognise this engine?

Discussion in '2-Stroke Engines' started by zippinaround, Aug 6, 2013.

  1. zippinaround

    zippinaround Active Member

    cant even remember where i got it but i presume its chinese due to the lack of any markings! no idea what size it is either but it looks about 33cc

    Attached Files:

  2. wheelbender6

    wheelbender6 Well-Known Member

    I believe that one came from a pocket rocket. I don't know of a brand name.
  3. HeadSmess

    HeadSmess Well-Known Member

    ^^^with that one.^^^

    standard 49cc pocket rocket kids bike engine.

    cag i think is one brand, possibly. meh. generic chinese.

    make a decent friction drive if you set up ok.

    has no pullstart. forget trying to use the chain/sprocket on a bike with wheels over 16"...
  4. zippinaround

    zippinaround Active Member

    cool looks tiny for a 49cc. i have the pull start for it also. why cant i fit it to a bike with wheels over 16"?
  5. HeadSmess

    HeadSmess Well-Known Member

    cus you will need a sprocket almost as big as the wheel to get worthwhile reduction....

    all about ratios ;)

    oh, yeah, you can USE it on something with big wheels, its just the work involved in gearing if you go with chain. friction drive solves that issue :)

    depends on your mechanical skills ?
  6. zippinaround

    zippinaround Active Member

    I see! so the original spocket would be useless cuz it was designed for like a 4" wheel? friction drive would be easier i think.
    and yeah i'm not the best mechanic in the world but i'm not the worst either still sounds like a lot of work since the drive sprocket is only about 1cm in diameter . i really just want something to help me get up hills because i live at the top of a hill about 2km long and quite steep!
  7. dchevygod

    dchevygod Member

    Put a small spindle directly on the crankshaft and mount it to something it will pull up hill decent if the spindle is small enough.
  8. HeadSmess

    HeadSmess Well-Known Member

    7/8 of an inch is ideal, wheel size doesnt matter on friction drives, you have to think that its the roller circumference speed that governs your speed. the wheel is just a "follower" gear. use 5/8 ID star washers on a 5/8 bolt, with some flange mount bearings ON BOTH ENDS OF THE ROLLER!

    friction drive sux in the wet :(
    get the roller too big and they suck in the dry too!

    for chain redux... a HT say, uses a 44 rear, 10t primary with an internal gear redux of 82:20 or, 44/10x82/20=18.04 :1 which is seemingly ideal for a 26" wheel, but can be pushed to say a 32 or 36 on the rear... roughly 70mm travelled on the ground for every revolution of the engine?

    two strokers will prefer higher ratios so they can spin more easily.
  9. zippinaround

    zippinaround Active Member

    I see that def215 has one of these rack mounted on a full suspension bike with a 100 tooth sprocket and can go 30 mph so surely the standard 68 tooth sprocket would do 15-20? how do i find out the internal gear redux? after thinking about friction drive i don't really want to do that, like you say it sucks in the wet and i live in ireland it rains like 80% of the time also it would most likely chew up your tire pretty quick!
  10. TREEWK

    TREEWK Member

    cag motor

    Have several of that engine, some with the 52cc kit and separate head from cylinder. Most have had trouble with them and have gave up after much effort.

    Mine only ran a little while and would not start again, changed coils, carbs etctera. My thinking that they need a shroud all the way around the cylinder, not just cooling on the fan side.

    They should be a good engine`s if you make a complete cylinder shroud from soda can or some thin aluminum cut off pieces from a sheet metal shop, they may give it to you.

    All the transmissions with the 78mm clutch drum work on those motors. They have the 76mm clutch shoes.

    You can buy a friction drive kit from Dac`s" and a gas tank for gravity feed and you should be good to go.
    If that motor fails, there are many motors that will bolt up to the friction drive kit with just the 4 bell housing bolts. DO NOT RUN IT AT ALL WITH OUT THE FULL SHROD !!!!!!!!!!

    Without shroud fill the tank only half full, doubt it will last that long.

    Good luck , Ron

    After Posting this, I see my Avatar picture is one of my builds with that engine with a CVT and my double right hand freewheel setup. Also have the same setup on another identical bike but with the Titan 49cc 4 stroke. They are still together in my garage, but have not been run in over 4 yrs.

    THE KITS MAY COME WITH 2 ROLLERS OF DIFFERENT DIAM. With 1 1/4" roller mine did 35mph with 180 rider on level blacktop.
  11. TREEWK

    TREEWK Member


    As an after thought, I did do a couple mods with that bell housing. Took the bell housing off the motor , held the dime size sprocket tight with a vice grip and removed the lock nut inside the clutch drum then screwed the clutch drum off. Be careful the drums bend near the spindle = will wobble and tear up inner clutch parts.

    Took the shaft with the sprocket to a lathe and had the sprocket and stem machined off. had it bored on lathe and threaded 5/16" NFT. Bought a 25 tooth cog from "Golden Bicycle Engines" in Michigan. Used 5/16" NFT 1" Allen head set screw to attach golden eagle cog.

    Then decided that 49cc mite be too much for the 16" nylon sheave that snaps onto spokes. When machining the shaft it has to be left long enough so the cog clears the bell housing.

    Then modified another of those bell housings. Took it apart, had a couple of the bell housings bored and threaded 3/8" NCT, bought 6 shoulder bolts with 6" shoulder and 3/8" NCT ends. The original clutch drum threads are 8mm metric. The bell bearing has a larger id than 1/2", found the correct bearing and used that setup in my friction drives with the 1 1/4" rollers with the one way inner bearings.

    A shorter shoulder bolt could be used to attach a v pulley to the bell and use a Whizzer rear wheel 16" bolt on steel v sheave.

    A Friction Drive Kit could be used without the roller, install a small v pulley for 1/2" wide belt, align it with a Whizzer steel sheave
    and lock pulley in place, may need to grind a flat spot on shaft.

    Belt drives are clean, quiet and mostly trouble free.

    My Stretch Cruiser is going to be primary and secondary belt drive!! Trouble free with a 5 hp Briggs flat head for frame clearance.

  12. HeadSmess

    HeadSmess Well-Known Member

    these engines have no internal reduction. that clutch and flywheel is attached directly to the crank. are doing your maths backwards!

    100/6 = 16.666666666666666666666666666666666666666666666666666666666666666666666666666666666666666 ad nauseum.

    68/6= 11.333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333 etc.

    11.3:1 is good if you have, say, a 20" wheel. the 68 toother "theoretically" would let you top out around 120km/h... say the motor does 13000 rpm. at 60km/h, a 26" wheel does roughly 450 rpm.

    13000/11.3 is approximately 1150. that would be the number of revolutions the wheel does a minute. if 450rpm = 60km/h, whats 1150 rpm going to equal? more than double 60km/h.

    once again, wheel diameter AND ratio is critical with direct drives! but is completely irrelevant on friction. all that matters on friction drive is size of roller.

    if you used a 120 toother, while "theoretically" you would go slower, the engine can spin a lot faster, meaning its working in its power band. around 9000rpm on these babies. so you should actually do BETTER than 30mph.

    def125 doesnt say what rpm his motor is actually doing. gear it too high and you just wont ever realise full power as the engine wont ever rev enough, and wont have enough grunt down low to basically even run... use a clutch and youll be replacing shoes faster than you can walk to the shops as it slips and burns itself out...

    if you have a steep hill, the bigger the reduction, the better the power.

    these engines can quite happily move a bike at 100km/h when tweaked. that is, a tuned pipe, a vm19 mikuni, and not much else so far. the "unified head/cylinder" is a right *%^&$ to modify. the seperate heads are good if you wanna play compression ratios etc. the engines wont last long if you try pushing them past 14000 rpm either. thats SCREAMIN!

    thats on a motorbike, with no pedals to assist.

    the reed valves are the main source of running issues. they either bend, warp, break or stick. there are upgraded varieties available...

    heat and shrouding has never been an issue in Australia even with our 44 degree C days... keep the air flowing. that is all.
  13. dchevygod

    dchevygod Member

    Everyone is forgetting the 5:1 reduction easily acquired off a pocket bike, they have a few different sprocket options and are really tough.
  14. HeadSmess

    HeadSmess Well-Known Member

    pulled two apart the other day. closer to a 3:1 redux. one was exactly 3:1, the other was 3.1:1 so you still need a 5:1 on the chain side... 11t sprocket, 55 rear etc.

    i also found it impossible to find primary sprockets sold seperately. i needed that splined shaft!

    so i have two of these gearboxes sitting in pieces, both useless, as i have to order a complete unit for one sprocket? what happens when it wears out? (im hoping youll supply me with a link :jester: )

    this is the chain reduction boxes, i havent seen anything else on a pocket rocket other than these boxes and what is pictured at the beginning here... clutched with a 6t pinion.
  15. zippinaround

    zippinaround Active Member

    yeah i have a plastic cover for the cylinder that attaches to the pull start just have to find it! i like the belt idea but it seems like much more work than just getting a bigger sprocket. If you look on ebay headsmess i found a 6,7,8 front sprocket and an 80 tooth rear sprocket all quite cheap! saying that all this ratio stuff is confusing me :dunce: hahah so if i was to get an 80 tooth thats like 13.33 would that do for a 26" wheel?
  16. zippinaround

    zippinaround Active Member

  17. HeadSmess

    HeadSmess Well-Known Member

    ok. an engine only makes so much power at a certain rpm.

    horsepower is an amount of weight moved a certain distance in a certain time.

    you need to gear an engine so that its output power at that rpm equals or exceeds your desired speed.

    you, bike and engine weigh so much. a lil engine doesnt make that much power. so you cant go too fast.

    simple so far?

    mathematics. yuk.

    a 26" diameter wheel is 81.68 inches round.

    every turn it travels that far.

    i dont do inches or miles, so... times 25.4 for mmmmmmetric.

    2.074 metres a turn.

    a kilometre is 1000 metres, standard 60km speed limit here is 1000 metres a minute.

    so, every minute the wheel will turn 1000/2.074 times. 482 times.

    your engine, say, makes its peak horsepower at 9000 rpm or times a minute.

    output power unknown, lets say 2hp, which, without air resistance, is good for 80km or so with 150kg. drag is a killer. friction. losses. hence you need more power than really calculated...

    60km is a good balance for speed versus power and hills versus dying due to it only being a bicycle!

    so. max power, 9000rpm, to drive a wheel at 482 rpm.

    9000/482=18.6 ish. so, use a 6 tooth sprocket...6X18.6=111.6 tooth rear. i guess you cooooooould use a 112 :jester:

    now... a 20 inch rim will do 60 something inches a turn... remember pi at school? practical application, finally!

    so... 1.595 metres a turn.

    1000/1.595= 626 turns of the wheel a minute at 60km/h!

    now... for an ideal ratio... 9000/626= 14.4:1

    so, on a 20 inch rim, a 6/80 tooth combo would be close to ideal? not perfect, just close.

    its a challenging project. dont be daunted though. theres just a few things to consider if you want something reliable and enjoyable versus cussing it and letting it sit in the back of the yard to rot.

    a bmx or 20" frame is the best candidate for mounting with your given sprockets.

    note what pitch the chain and sprockets are. they do vary. the splined sprockets i mentioned are not the same as the 6,7, or 8 tooth ones you mention. but both come of "pocket bikes". tip. the dirt or offroad ones have the reduction box with splined sprockets ;) also, i think the chain was a more common pitch... just sprockets seemed non existant individually. its always best to use the biggest sprockets available, increases chain life.

    when making a rack or mounts, there is a huge amount of twisting force on the engine. dont under rate it. the more rigid and aligned it is, the longer chains will last. they wont throw so often.

    do it properly and you will be happy :) theyre pretty good engines for the price.
  18. dchevygod

    dchevygod Member

    13.33:1 isn't going to do well with a Cag engine like you have there. They don't revv very high and are all in all lacking. If you want to make it work well get a walbro tunable carb and an expansion exhaust pipe.

    My reduction box is exactly 5:1 headsmess, it has helical cut rotation reversing gears not a chain. 11:44 after the trans and a 460 for power
  19. zippinaround

    zippinaround Active Member

    ok first of all thanks for all the help! yesterday i bought a full suspension bike that has an 18" frame was hoping to mount it on that. I think here in ireland the law is it cant go more than 20 mph on the flat so speed isn't really an issue for me. the biggest sprocket i can find online is the 80 tooth so if i go any bigger i'd have to have it made specifically by an engineering shop. I only have basic tools to work with aswell no power tools what so ever! I may try to get a job in an engineering shop just to have access to some better equipment :evilgrin:
  20. TREEWK

    TREEWK Member

    100_1454.jpg My bad, assumed the shroud was the problem, as Gyro states that is not the case. Would the reed valves be the problem?? Have many engines, quit using the Cags, would be glad to find the cure for the Cag motors.

    The compact 5:1 ratio reverse rotation gear box is a tuff unit, have it on my rear axle build and on my shifter bike. My designed shifter bike is running 8mm chain, there is a fair selection of 6 spline sprockets for the 5:1 gear box and a good selection of 8mm sprockets for the rear wheel using a freewheel adapter or a solid adapter. Have the 12 tooth 1/2" pitch sprocket on the axle drive bike using #41 chain.

    The small CVT is nice , built two bikes with them in 2008, they don`t have 100 miles run time, sitting in my garage. The members on the other forum had "lots" of problems with them after they had more miles on them.

    All my builds will be 3 to 6 hp 4 stroke motors with belt drive from now on, The police don`t bother us here in NW Florida or Northern Wisconsin.

    The shifter bike is very fun to ride, using the rear wheel cassette for a transmission does wonders. Have a 34 tooth on the 7 speed cassette . Have a 5 speed cassette with a 38 tooth cog, it would be nice in mud or woods, am a large person near 300 lbs.

    Zipping, It is confusing in the beginning, what to build. Your 2 mile long hill is a bugger going up. A shifter would be very nice but cost more to build.

    Good luck with it, Ron

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