I... blew it up. Rebuild?

Discussion in '2 Stroke Bicycle Engines & Kits' started by Earbiter, Dec 30, 2016.

  1. Earbiter

    Earbiter New Member

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    Towards the end of last summer while riding home from work, bike was running great, then when i was coming to a stop the engine just died.
    After i started going again, i tried to start it back up, it struggled but finally started. But now the exhuast was very loud and had a serious lack of power.
    I finally got a chance to dig into it, found one of the piston retainer clips had broken and made it's way into the cylinder, where it dug two large gashes into the cyl wall and the piston skirt.
    Found no evidence of bottom end damage, or the clip.

    I know there are top end rebuild kits, but will this be ok? Or should i just replace the whole damn thing?
     

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  2. Kioshk

    Kioshk Active Member

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    Are you sure it was caused by a retainer-clip? I'm sure you verified that one was missing when you removed the piston. I ask that since the indentation-damage to your cylinder looks a lot like the indentation of a needle from the upper needle-bearing. Check that bearing too to make sure it's still in one piece.

    That said, it's easy to rebuild the top-end; you'll just need to make sure you clean out the bottom-end properly. I usually remove the entire engine, fill the bottom-end with gasoline, and slosh it around by cranking the flywheel. Dump out the waste and repeat a few times. This should clean out any offending particles there. You'll need a new cylinder, piston, rings, and gaskets: lower and head. You may need a new needle-bearing.
     
  3. Earbiter

    Earbiter New Member

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    Ya im sure, i was planning on getting this kit http://www.ebay.com/itm/191550568760,
    i know it's cheap but it's all i can afford right now.
    Just wanted to know if it would be ok. Ty.
     

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  4. Earbiter

    Earbiter New Member

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    Sorry if i misspoke regarding the clip being gone, i have them both but one is clearly broken. What i meant was it wasn't in the bottom end. I'm guessing it got thrown out the exhaust. I'll prolly have to clean the pipe to make sure it's not floating around in there.
     
  5. ultralight01

    ultralight01 New Member

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    You could buy a new engine for $30 more, or a $50 49cc pocket bike engine. I have no knowledge of how to fix two strokers, but I'm sorry this happened.
     
  6. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    There are 2 kinds of 47 mm / 66cc pistons.

    Your piston is a high wrist pin hole for a Skyhawk type motor.

    The ebay piston "photo" is a low type for a PK 80 type motor.
    Whether that is the correct pic is anyones guess?

    If that piece of the clip is in your bottom end you will destroy
    your new top end.

    I don't like those double clips, the single arm ones don't fail like that.
     
    #6 MotorBicycleRacing, Dec 30, 2016
    Last edited: Dec 30, 2016
  7. crassius

    crassius Well-Known Member

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    motors are cheap, when parts become chunks, why take a chance on trashing a new top end if an old chunk appears after the rebuild

    if it were a cleanly seized piston or suchlike, that would be different
     
  8. Kioshk

    Kioshk Active Member

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    That's a decent replacement, but as MBR advises: verify the piston size.
     
  9. cannonball2

    cannonball2 Active Member

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    You can buy the complete basic engine in the $75 range shipped if you search around on eBay. Problem I have had with parts was not always getting exactly what was listed.

    Just be sure if you go for a replacement that the intake\exhaust spacings are the same
     
  10. Earbiter

    Earbiter New Member

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    Good advice all ty, i think i will just buy a new engine, and keep the old one for parts or something.
     
  11. crassius

    crassius Well-Known Member

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    if your motor is wide front mount, be sure you get that again
     
  12. sbest

    sbest Member

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    Actually your piston and cylinder will work with a new set of rings.
    There is no damage above the transfers.
    Not exactly a rebuild, but it will run again with rings only if you wanted to try it.

    I had the exact same fail. wristpin clip broke one of its legs.
    Had about 1000 miles on the engine at very high speeds.

    Steve
     
  13. Earbiter

    Earbiter New Member

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    So i got some funds and decided that it's not much more to buy a whole kit, rather than just an engine. Extra parts is never a bad thing, right?

    So the new kit is coming later this week. With that said, I plan to port and polish it before it goes into my bike. I've done this a few times before on several different kinds of engines, with a very cheap dremal, so I bought a very nice pin die grinder from the cornwell to make it easier.

    But I'm still left wondering, I've read about the "transfer port correction mod" does anyone have pictures of what this should look like? I know they need to be pointed at the spark plug, but I'm not really sure how this can be done without raising they're roof/messing with timing, and I'm not really looking to mess with that too much. Prolly just an extra base gasket or 2. Please help me understand.
     
  14. Tyler6357

    Tyler6357 Member

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    Your engine looks like a GT type and the link connects to a PK80 type. That won't work, the GTs have a longer connecting rod. Here you can see the differences in the wrist pin location on the piston. The GT is on the left and the PK80 on the right.
     

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  15. Earbiter

    Earbiter New Member

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  16. Kartooo

    Kartooo Member

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  17. Earbiter

    Earbiter New Member

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    Nevermind, I think I've got the transfet ports figured out. Thanks maniac57!
     

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