Engine Trouble Broken Crank where mag bolts onto

[sactownie]

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.



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?

 

[BigBlue]

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.

Chris
AKA: BigBlue

 

[sactownie]

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

 

[Purple Haze]

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!

 

[HeadSmess]

take comfort in the fact that what youve achieved here is pretty unusual 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?

 

[Fabian]

 

[sactownie]

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?

 

[HeadSmess]

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


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

 

[HeadSmess]

and...just the final point...


NAME AND SHAME.

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.

 

[Fabian]

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.