Engine EXPLODED... can it be saved?

[justthisguy1292]

I was ridding my PK80 up a steep hill and the engine just stopped. i let it cool off a little and tried starting it. there was little resistance to me pedaling to start it(there should be since i have a shift kit). When i finally walked it home and took it apart i discovered the upper piston ring had broken in half and tore a chunk out of the piston and the cylinder. The other half of the piston ring is somewhere in my muffler. I can hear it jingle when I shake it. I wanted to just buy a new top end assembly but i can't find one. I almost bought a skyhawk top end by accidently. I didn't know there was a difference. Does anyone know how to either fix this cheaply or find PK80 parts? If i wasn't planning on going to college in a few months I would just buy a new engine but thats a little too pricey right now.

[2door]

Justthis,
I'd try several of our sponsors. I know PistonBikes has them.> Motorized Bicycles Gas Bike Engines Gas Powered Bikes Motorized Bicycle Parts You should be able to find the necessary parts to fix that little guy cheaper than a complete engine.
Tom

[Prasinos]

Getting the whole assembly doesn't make much sense, a new piston/ring set and a cylinder should be all you need, these are the cheapest i can find:

Bike Motor Engine Piston Set 80cc/66cc Parts - Motorized Bike Piston Set 80cc/66cc Parts - Bike Motor Piston Set 80cc/66cc Parts - Motorized Bike Parts

Bike Motor Cylinder Body - 49cc Parts - Motorized Bike Cylinder Body - 49cc Parts - Bike Motor Cylinder Body - 49cc Parts - Motorized Bike Parts

as long as your writs pins ok this should be all you need, you can make a base gasket pretty easily but if you want to buy that too....

Bike Motor Parts Cylinder Base Gasket 80cc/66cc - Motorized Bike Cylinder Base Gasket 80cc/66cc Part - Motorized Bike Parts

So that's all you'd need for 36 bucks, 14 bucks cheaper than top end assembly at spookytooth.

If you think there's damage to the writs pin and/or the head you can just buy the whole top end for 50 bucks:

55cc & 60cc Complete Upper Engine Assembly

That should do it, good luck on the rebuild, and be sure to keep any parts that still look ok...

[Riding Rich]

I would call Justin at Pirate Cycles.

His site dosen't show the parts available but he has them all.
Thats where i got my PK80.

I broke the rings trying to put the jug back on.
He's sending me a new set.

Shipment is fast and service is good.
Call him he will take care of you.

[POPS]

Zoombicycles.com

They are PK....POPS

[Humsuckler]

any idea on what contributed to the failure?

[Riding Rich]

My guesses would be.

#1 ring flutter caused by high rpm.

#2 locating pin came loose from piston.

#3 excessive heat caused rings to bulge out into the ports and get caught on a sharp edge or Casting flash.

#4 Bore Distortion caused by excessive heat.

Other than that the rings are close to the top of the piston.
only a little over .100 inch.
Typically .200 inch is reccomended allthough closes to the top is the best except it exposes the ring to more heat.

[Prasinos]

i would go ahead and say it was a faulty engine, that shouldn't happen...

[Riding Rich]

Yep it shouldn't happen.
But like i said the top ring close to the piston crown.
We know alot of these engines come with casting Flash in the ports.
All it takes is a little junk in the wrong place at the wrong time.
I just orderd 2 sets of rings for my PK.

The brand new one.
I broke a ring trying to put the Jug back on.
So they are fairly brittle.

2DOOR

How many miles were on the motor?

[justthisguy1292]

I was getting close to 1000 miles. i think I can find the parts. Not entirely sure how it all goes together. I'm betting there are some posts on how to do that. I just took another look in the cylinder and theres a second gouge. it looked like just a smear but when i felt it it was definitely a gouge. Its maybe an 1/8 inch wide and almost runs the entire height of the cylinder. probably happened when the half of the piston ring was banging around in there.