Im missing something

Discussion in '2-Stroke Engines' started by built_not_bought, Sep 5, 2016.

  1. built_not_bought

    built_not_bought New Member

    Ok, was riding the other day. Exhaust decides to rattle loose and fall off. Had no tools and no choice but to continue the ride. Had to go about 15miles to fix. At first everything was fine. The last 3 miles I had alot of bogging. It literally stopped in my driveway.... Ok now time to fix. Only now it seems my clutch wont engage. Loosened the flower nut. Released the clutch cable. Redid bith as if a fresh setup and nothing. When I pull in the clutch it rolls freely. When I dont pull in the clutch it rolls very rough as if trying to start but wont start. I have compression, I have spark, gas is on and Im lost.....

  2. KCvale

    KCvale Motorized Bicycle Vendor

    Chance are it's the woodroof key on your right front drive gear.
    That goofy looking tool you got with your kit is how you pull the gear to look.
  3. built_not_bought

    built_not_bought New Member

    Im lacking that tool... Im going to order another... I think this time Im going to fix it and sell it. I want to go 4 stroke. Seems a little better as a daily rider to me. Thanks for the idea to check.
  4. crassius

    crassius Well-Known Member

    if muffler was completely off with no part of pipe still there, you might have seized the piston a bit - pop the head off and look at cylinder wall - if it doesn't have any large scrapes in it smear a lot of oil in there and with head still off roll bike to see how piston runs up and down - if it feels a bit stiff at first, then gets easier you may be OK then
  5. built_not_bought

    built_not_bought New Member

    Took head off, walls look great, piston goes up and down smoothly. Walls still look brand new. Plug end looks normal as far as temp goes.. I might be to close to the project. Might need to step back and think before another approach. Sometimes it helps.
  6. crassius

    crassius Well-Known Member

    if it moves well with head off and not with head on, I'd first think it was just your clutch slipping
  7. built_not_bought

    built_not_bought New Member

    It moves with it on and off. I adjusted the clutch cable and the flower nut/pressure plate (guess that describes it) When I pull the clutch lever it releases and rolls smoothly. Release the lever and it still rolls just wont catch and crank...
  8. crassius

    crassius Well-Known Member

    f it doesn't move well with head on, it is just your clutch slipping
  9. Steve Best

    Steve Best Active Member

    Things will fall off a 4 stroke with the same care they do on a 2 stroke.
    I have over a thousand miles on my 2 stroke bicycle and this weekend met a guy who has put many more thousands on his 2 stroke bike since 2012. Wow, I'm getting a little defensive, sorry about that. Just that I love these little 2 strokes. Cheap, light, simple, easy, powerful. Remember; "a poor tradesman blames his tools".

    First off, buy a torque wrench and tighten all bolts to the proper torque. That is why your pipe fell off.
    Not too much, not too little, just right tight.
    Second, do not continue to ride with a problem. First sign of trouble, stop and solve it or use the pedals.
    3rd, pipe falling off did not damage the clutch. It was not set up well originally.
    Read up back posts about how to set it up.
    Set up the clutch, check your compression, check for spark and gas, repair any problems and try again.

    A prime rule in trouble shooting is "put everything to the as-designed state".

  10. built_not_bought

    built_not_bought New Member

    I do love them as well. This is my 8th build. I end up selling them or giving them to homeless traveling vets... We pressurized the motor this morning with smoke. Seems as if the gasket on the bottom of the jug has a 2" piece missing... So I have found the compression leak. Now to figure out an easy fix for that. Any tips on making a gasket? Keep in mind this is my only means of transportation (temporarily) our nearest auto store is 60miles (give or take) and we do have a walmart (yay us) I dont really know anybody since I just moved here so asking for rides is out. Anything I can make a homemade gasket with?
  11. Steve Best

    Steve Best Active Member

    Cardboard box and scissors! Regular paper will work. Soda cans cut to shape. Use one or stack them to height.
    My present cylinder is raised a bit with thick cardboard and a soda can on either side to protect it from tearing.
    The aluminum cuts easily with scissors. You can use the soda can alone to drop the cylinder.
    You can grease the cardboard, paper or cans, or use dry.
    I leak test on assembly by pressurizing to 7 psi max. More will blow your seals out.

    I hate using sealer but will use sealer alone on some builds if needed.
    I file and sand the cases flat first. RTV sucks, I prefer ThreeBond for this.
    This is a last resort due to sizing issues and it won't come apart easy.

    4-6 sheets of paper are about the stock gasket height.
    Soda can gaskets on either side keep the paper reusable many times.
  12. built_not_bought

    built_not_bought New Member

    Now we are cooking with butter... Im using some cardboard first thing in the morning. Ive got an entire day to work on my bike.... A small list of things as well... 1. Make gasket 2. Cast my new custom levers 3. Oil all my cables 4. New brakepads 5. Source a new freewheel for pedal side 6. Clean carb 7. Begin building new fuel tank rear mount.... Woohoo
  13. built_not_bought

    built_not_bought New Member

    Update... Pulled motor apart to fix the gasket and found a new problem. I dont even know which piston to order... SMH 20160908_184730.jpg
  14. Frankfort MB's

    Frankfort MB's Well-Known Member

    Just order one for a regular 66/80cc engine

    Look for any other scratches or rub spots and make sure they aren't going to affect anything
    (I'm guessing you don't have a 49cc?)
    (And I don't think they ever made a black Grubee)

    I can't tell what even happened but your piston is fried, if your like me then you would want to upgrade to something better since it broke.... I would look for lightweight pistons then polish it when it arrives

    This should add a decent power increase:)
  15. Steve Best

    Steve Best Active Member

    Ouch! You need both a piston and a cylinder. Looks like it overheated, noting the discolouration on the piston and perhaps slight signs of detonation beads. The lack of scuffing on the skirt says your oil mixture was fine. Piston got hot and swelled until it rubbed.

    Why did it get hot? Fuel mixture/jetting wrong? I don't think so, no huge signs of detonation. I suspect hot weather and hard load. More cooling air speed and more pedaling might have helped this poor engine.

    The Grubee cylinder and piston will work, even if it comes in the different height. Assemble it and check how high the piston comes in the bore. It should be level.

    If the piston is too high, Use a thicker or stack basgaskets or stack headgaskets to get proper squish (@1mm) with the head.

    If the piston is too low, thinner base gasket (cut paper) or file the top of the cylinder (finish by sanding on sheet on glass plate) to get proper squish with the head.

  16. crassius

    crassius Well-Known Member

    look at the mzmiami site on ebay and it will show the measurements - measure your piston to see which to order
  17. built_not_bought

    built_not_bought New Member

    Thanks everyone. Yes its a good time to upgrade. Ordering new parts soon. On the bright side, good time to break the bike down to the frame and give it that new Black cherry pearl paintjob Ive been putting off. Lesson learned, GA heat and my weight = more breaks to cool the motor... *Side note* What would happen if I took the 90cc off a small ATV and installed on a bike? Motor seems to fit the spot. Im sure I can whip up some brackets. Its chain driven.
  18. FurryOnTheInside

    FurryOnTheInside Active Member

    I thought a seized piston was from heating and expanding the piston _before_ the cylinder has time to warm up and expand ("hard load"!). So I don't know if taking breaks is the answer, perhaps just a more gentle first ten mins would be better (and build to prevent detonation too) so the piston and cylinder warm up together. Not an expert but that's the impression I got from my reading.
  19. Steve Best

    Steve Best Active Member

    Been there, done that too!
    Mostly happens with watercooled engines with forged pistons. exactly as you describe.
    Waterjacket doesn't warm up as fast as the piston.
    Causes a "four-square" scuff on the piston. Also called a "cold seize".
    Forged pistons swell much more than cast, much more prone to it.

    Even without detonation, engines can overheat.
    Richen the mixture will liquid cool the piston. That liquid being fuel.
    More rpm helps, as does more speed for air flow if it can be done with less throttle.
    Cooldown breaks and lower loads and slower on the hills or a lower gear help too.

    Hey Built,
    90cc bike engine weighs over 3 times what your China Girl does.
    I'm sure it can be done, but getting kinda heavy for a weak frame and wheels.

    Last edited: Sep 14, 2016
    FurryOnTheInside likes this.
  20. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    it's a GT5 or high wrist pin hole piston. 47 mm diameter.

    Which way are the ring pins facing? Towards the exhaust or intake?