Engine Trouble Broken Crank where mag bolts onto

Discussion in '2-Stroke Engines' started by sactownie, Sep 1, 2013.

  1. sactownie

    sactownie Member

    Hi all, this is a newer build, I have a little over a gallon of run time on it.
    I was happily cruising along in 7th gear about 30mph when the motor just quit as if I pushed in the kill switch, Had to pedal home 4 miles and upon inspection of the magneto cover the bolt coming out of the crankshaft snapped. Motor ran great before this but I did notice it would slightly cut out, just barely noticeable going over bumpy roads sometimes and I noticed a vibration for a second or 2 right before it quit..
    Anyone know what caused this and is this easily fixable? If fixable what parts and where do I get them? I'm posting pictures of the damage. I sure hope its fixable, riding this thing seemed to be bringing me out of the depression I have been in the last year.

    mag 002rr.jpg mag 003rr.jpg mag 004rr.jpg mag 005rr.jpg

    EDIT Looks like my motor is scrap after 1 gallon of fuel through it after looking at other post it seems i have a broken crankshaft? How could this have happen?
    Last edited: Sep 1, 2013

  2. BigBlue

    BigBlue Active Member

    Looks like one of the pins holding the magneto rotor together came loose and became wedge. Or maybe the magneto rotor came loose. Remove the spark plug, let out the clutch and rotate the rear wheel to see if the engine turns over.

    AKA: BigBlue
  3. sactownie

    sactownie Member

    motor turns over fine, It wasnt getting spark, I was only expecting to replace a bad coil when I was opening the cover.
  4. Purple Haze

    Purple Haze Active Member

    Looks like the nut loosened on the mag, or was not tightened correctly from the factory. The mag then cocked and got bound up in the coil, breaking the crank and the pins in the mag. Man, I feel your pain! I've never seen this happen on a new engine before. But it goes to show that you can't take anything for granted on these China Girls. If you're up to rebuilding it, at the very least you'll need a new crank, mag, a new gasket set as you'll have to split the case, and probably a new coil and woodruff key. If you go this route, I strongly recommend putting in better quality bearings while you're there. At this point, though, the cost will be close to a replacement engine. These things can break your heart!
  5. HeadSmess

    HeadSmess Well-Known Member

    take comfort in the fact that what youve achieved here is pretty unusual :jester: that magneto gets stuck to the fridge, forever! nut washer and all!

    you could try whinging to the guy that sold it to you...maybe...iunno?
  6. Fabian

    Fabian Well-Known Member

  7. sactownie

    sactownie Member

    The guy I got it from wont even sale me an engine only so im looking at ebay and this engine claims to be a true 80cc http://www.ebay.com/itm/Genuine-80c...Parts_Accessories&hash=item4d0b0ae688&vxp=mtr
    If this is true it would be alot better then the 66cc i had?

    Ahh nevermind I see this is just a BS ploy to sale new engines. Im really hesitant to buy another motor and something like this happening again. Im going to look into fixing this one. looks like a crank is only $12.50 at kings motorbikes but I don't know if it fits?
    Last edited: Sep 3, 2013
  8. HeadSmess

    HeadSmess Well-Known Member

    one. its 80cc if its bore is bigger than 47mm, otherwise its a 66cc like all the others.

    two. in australia, if someone sells us something that breaks like that did... we turn around and either get our money back or get a replacement. by law :)

    three. i said it was unusual. dont expect another one to break so soon. in other words, you seem to be the first. to document such a thing at least...

    four...that washer fabian hilighted... was it there when it was snapped, or is it just one you dropped when you removed the magneto?

    if its the former, it shouldnt be there, and see point two again for clarification. you got sold something faulty. start whinging. surely you have some kind of consumer rights? then again, america...cali forn eye ay... bad luck :jester:

    five.$12.50 isnt bad for a crank, just remember that you will still need a magnet, maybe a new magneto coil, and new screws for it. when splitting the case, if you bought a complete prebuilt bike, i doubt the guy included the clutch/sprocket puller that is critical and comes with every kit purchased.. he sounds like that kind of vendor. that way you can charge money to work on bikes for people cus you so kind hearted :)

    also, you may or may not need lower cylinder gasket, and crankcase gasket. an idea to change crank seals while its open, and possibly install nice new quality bearings. and its recommended to replace piston rings whenever the cylinder is removed. you definitely need new spring/c clips for the wrist pin! never ever be tempted to reuse them.

    an impact screwdriver or hammer and drift is also required.

    crank should always fit, so far as i can tell a 48 is identical to the 66 etc... though i do recall there being an issue with the shoulder/step that the main pinion gear rides on... may have just been bad manufacturing tolerances.

    probably best to get a new engine. AND a new crank.

    reassemble what you have with the new crank, but use the complete engine. if and when it dies, you got the magneto and stuff all there ready to swap over. the work is a good lesson, and if you stuff it, no probs. you have a working engine still :)
  9. HeadSmess

    HeadSmess Well-Known Member

    and...just the final point...


    who sold it, and whats his reason for not selling engines by themselves?

    people like that should be blacklisted and brushed under the rug.

    a real vendor would be sending you a new engine the second this happened if they valued their business.

    if i can buy a whole kit for $150, what are they paying for engines, wholesale? $50? go figure.
  10. Fabian

    Fabian Well-Known Member

    I have "NEVER" seen a crankshaft fail in that manner on any of my engines, and i have never seen this kind of failure from the "warranty returns" that ended up at the vendor who supplied my bicycle engines.
    This is close knowledge because i've gone through his warranty returns stack and picked out engines for $30, of which i have mixed and matched parts to rebuild good running engines.

    ***Never*** have i seen this kind of failure, and such a failure most likely would occur is if a flexing moment has been introduced onto the crankshaft or a sudden torque spike was imparted on the crankshaft to shear it in half; a washer being trapped in between the magnet and affixed magneto arms would be in line with the failure depicted in the photos.
  11. BigBlue

    BigBlue Active Member

    Be aware that there are two styles of crankshafts, depending on the stroke of your engine. One has a 40mm stroke crankshaft and the other has a 38mm stroke crankshaft. GT-5A, GT-5SR or PK-80 motors which have 40mm stroke crankshafts. Engines currently available from Gasbike, Kings and Piston Bikes are GT-5 type and have a 38mm stroke crankshaft. This information is from CR Machine: http://www.shop.crmachine.com/Stage-2-GT-5-Skyhawk-Cylinder-Body-66cc-BCBS2.htm

    AKA: BigBlue
  12. sactownie

    sactownie Member

    I never saw a washer in there or I didn't notice it. I think thats just part of the stack of plates?
    When I pulled it apart from the coil it just had a lot of metal flakes on it.
    Looks like a new engine is going to cost about the same as getting all the parts to fix this when shipping charges are figured in assuming that one of the $95 sellers on ebay will ship it to me in good ol california.
    Maybe I should do that and keep this one for parts. I know everything but the crank and magnet are good on it having only ran less then 3 tanks of fuel. It was just starting to make good power, I never kept the rpm's high, allways shifted it low in the powerband, basically I just putted around on it.
    The seller was enginesonlineshop.com He states right on his site 30 days warranty well its been about 45 days because it took me awhile to install it waiting for the shift kit then doing the actual install wich was my 1st motor bike build. He did include the tool to remove gears but It stripped out the 1st time I tried to use it, it was all crooked where the tool screws in to. Basically garbage. I figure I can pick up a gear puller cheap at harbor freight when I need it.
    I really miss riding that thing, When I can afford it I think Ill build a 2nd bike for a backup. Would be nice to have one in running condition at all times.
  13. sactownie

    sactownie Member

    I have no idea what mine is, I asked the seller and all he knows is they come over in a container from china. He claims to manufacture them himself on his web page but thats BS or he would know the specs!
  14. sactownie

    sactownie Member

    Here is my communication with the vendor. If you look at his website it clearly states they manufacture and import there own engines. This goes against what he told me in the email!
    So Basically I am not going to purchase another motor from him, he isn't even offering to sale me another kit for a discount, I think that would be the "right" thing to do, at least sale me one at his cost. I understand the 30 day warranty and all but the pictures clearly show this catastrophic failure wasn't my fault.

    replacement engine?

    Dan S
    Sep 1 (3 days ago)

    to enginesonlines.
    Hi, I purchased a engine kit from you on july 13. I ordered a shift kit and didn't get everything installed until 3 weeks ago.
    Engine ran fine up until 3 days ago when it just quit on me while riding. After getting it home and pulling the mag cover I discovered that the crankshaft has broke where the mag rotor bolts onto.
    This happened after only 1 1/4 gallons ran through it. I am sending you pictures , the 1st 2 pictures are right as I removed the cover. I will call you on monday to see what we can work out with this.

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    enginesonlineshop .
    Sep 2 (2 days ago)

    to me
    Our return and exchange policy is 30 days from the day it arrives. Because the engine doesn't have a odometer on it to show how many miles actually was put on it. Time is the only thing we can go by.

    Dan S Sep 2 (2 days ago)
    so how much will you sale me an engine only for?

    enginesonlineshop .
    1:43 PM (11 hours ago)

    to me
    Sorry but we don't have just the engine for sale at this time.

    Dan S <danrschaffer@gmail.com>
    8:26 PM (4 hours ago)

    to enginesonlines.
    Where would I purchase a crankshaft from? Are they all the same with the 66cc/80cc ?

    enginesonlineshop .
    10:57 PM (2 hours ago)

    to me
    66 and 80 is the same. But we don't know where to purchase one of those too. Our company is strictly a distribution center. Our role is like costco. We don't manufacture anything here. We import it in containers and then distribute to the public. That is why we offer only 30 days on all our items. We don't fix or sell replacements for these engines.
    Last edited: Sep 4, 2013
  15. HeadSmess

    HeadSmess Well-Known Member

    false and or misleading advertising. get legal on the suckers backside! thatll teach em to be... i cant say it here :(

    i cant see that small 1mm thick washer having been enough to destroy that magnet that way. plus it would be in a different spot what with rotation.

    somethings obviously really been in there and had a go. possibly the key for the magnet, having been assembled incorrectly, they just stick to the back of the magnet... i can see the things not only been split apart, but sort of twisted like a potato crisp as well.

    hit one with a sledgehammer and see how much damage you can do ;) pretty tough, them magnets are.

    if anything, id say it was the crank itself, had a flaw in the steel that passed all highly stringent qc tests :jester: maybe even dropped and they tried straightening it at one point! just bad luck. bit of imbalance combined with a stressed area...wacka wacka wock!

    if it had snapped right at the shoulder on the crank, id say the fillet was too sharp. it didnt :(

    man. ive had $30 refund on a $130 kit because i had a dented tank! tiny lil dent and i sorta felt bad but it wasnt for me so i had to :(

    easier and cheaper to just buy a new motor and sigh a lil bit
  16. Purple Haze

    Purple Haze Active Member

    If it were me, I'd buy another engine, then you can be riding while rebuilding the other one. It'll be good experience, even therapeutic. Yes, some of these so-called vendors need to be banished to the gates of hell, watch out for high shipping costs, that's a dead giveaway. The California laws don't apply to the engine, it's considered "parts only" as it can't be operated without other parts in the full kit. Good luck and don't let this experience sour you on the hobby.
  17. sactownie

    sactownie Member

    My wife thinks I broke it doing stupid stuff like I used to do in my car, burnouts, drifting, ect. but I try to explain to her where the crank broke has nothing to do with over-revving, abusing it , ect... This seems like a low stress area of the crank, I think I could just about epoxy it back together but I have no way of knowing where the magnet key should mount on it (engine spark timing would be way off).
  18. Fabian

    Fabian Well-Known Member

    That kind of thing isn't considered "stupid", it's called "fun" :banana:

    that could be considered to be a stupid idea.
  19. sactownie

    sactownie Member

    So fabian do you agree that crank broke where it broke could not have been caused from over revving the little motor? Would like to have at least 1 semi expert opinion to show her so she cant mention this as another one of my "failures"....,...............

    I also agree on the "fun" part of burnouts and drifting, unfortunately my wallet disagrees. I still have the perfect truck sitting in my driveway to do it though, a 2000 dodge dakota R/T with 97,000 miles that hasn't been driven out of my neighborhood in almost 2 years. Haven't paid the license on it, its on non op.
  20. Saddletramp

    Saddletramp Member

    May we hold back the sorrow, an $80 motor has bit the big one. Keep it for parts, all you can do.