Questions about broken crankshaft....

Discussion in '2-Stroke Engines' started by Joeeastman, Nov 15, 2011.

  1. Joeeastman

    Joeeastman New Member

    Hey guys and gals, I have an issue and need some help from the masters in this forum.

    I had received a replacement motor from kingsmotorbikes and after about 2 weeks of riding it, motor started acting weird. Let me explain: Im going to meet up with my riding buddy and as I approach his place, motor started wanting to shut down, I had to give a little more throttle to keep running. As i get to his house the motor will not stay running and was making some strange noises. Now, prior to this incident, the motor was running like a champ, way more powerful than the original skyhawk gt-5 that i got from them. Ok, moving along...

    I popped the cover to the magneto and the clutch to see what was going on and here is what I noticed:

    With the spark plug out, I rotated the magneto to get the piston to rotate, which it kind of did, but when I did that the small bevel gear on the other side would only sometimes turn. I thought maybe the keyway had fallen out or something but in reality the journal on the crank had sheared. The play that was in the shaft was the flywheel "catching" at the location where the journal had ground its way into it. ok.....

    I took the motor apart and checked out the damage, there was no damage to the con rod, but the piston was scored on the sides pretty bad. I also noticed that the main bearings were dry. Shouldnt they have grease packed in them from the factory? I wonder if this was the culprit... Now to the point:

    I ordered another crank and piston from Piston Bikes but did not get my piston, no problem though, cause i talked with them and it was just a simple mistake and hes sending one out to me. However, the crank I received was not the same as the one that was in my motor originally. The broken crank had the markings "ZAF60" on the connecting rod and looked to be of the 4 piece design. The new crank from Piston Bikes has the markings "Z-L". I could not see any difference in the 2 but when I put the motor back together the piston (which i borrowed from a gt-5 my friend had) would hit the head. I tell you, I was soooo bummed about this, i knew it was too good to be true. Anyways, I swapped back to my original damaged piston to see what would happen and the piston skirts would now hit the flywheels. I took the piston out and made a comparison, they were different. The wrist pin locations were different. The one from my ZAF60 con rod had the pin higher up in the piston and the other one was further down. Ok, i am lost......

    I read here in a thread that the ZAF60 came from GT-5 motors while the Z-L came from PK-80 motors. but when i opened up my friends GT-5, you guessed it, It had the Z-L and not the ZAF60. Now, I know someone out here knows whats up and can enlighten me on this matter. I'm gonna send back my broken crank to Kings MB but they only show that Z-L crank and I already have that one now and don't really like it compared to the ZAF60. What should i do? Does anyone have this ZAF60 crank and related Piston? Please, if anyone can help me with this I would greatly appreciate it! Otherwise, I'm gonna see if I can have a shop press sepperate my new Z-L crank and put the ZAF60 con rod on. But i still need that =(

    Attached Files:

  2. blue 48

    blue 48 Member

    hmm im gonna watch this post i never Touched the cranks in these engines YET
  3. motorpsycho

    motorpsycho Active Member

    wow. i think i would have just bought a complete new engine instead of going through all the trouble.
  4. a/c man

    a/c man Member

    So let's review the damage.
    Piston......all done
    Cylinder head.... must be all gouged up

    Bottom and top end both f...ed
    Why bother ?
    Not trying to be a smart a$$ but it's time to say goodbye to it and move
  5. Joeeastman

    Joeeastman New Member

    I know right, I didnt have the cash to put up for a new setup so i just purchased a new crank, it was only like $20 and i figured i could make it work plus it seems like if you go to order a motor, there is still no certainty in what your gonna get. I thought that these motors were pretty much the same but found out that there are many differences......My bike is running now and i have it running pretty strong but I miss that feel of the power that i had before that crank failed...
  6. Joeeastman

    Joeeastman New Member

    I feel ya on that a/c man, however, if i would have done that I wouldnt have learned anything. I have a sense of accomplishment now that I brought this thing back from the dead and now there is a sort of connection ahahaha. Anyways, gotta make do with whatcha got.....
  7. HeadSmess

    HeadSmess Well-Known Member

    lol. quality. broken crank. thats gold :D

    main engine bearings should be dry and unshielded. thats what the oil in the fuels for.

    swapping the crank over and getting it running is an accomplishment. well done :)

    considering how thin the key is, tis weird the crank busted first...probably machined slightly more off centre than usual :jester: i doubt it was due to having too much torque!
  8. jaguar

    jaguar Well-Known Member

    A scored piston is no big deal as long as the rings didn't get any grooves in them that would lose compression. I would just clean up the piston and use it as is.