85$ Polini Piston VS 8$ China Replacement

[SEANIA]

Completely destroyed the piston for my Polini bore.

 The Polini replacement is 85$ (without sh/h/tax), for a kit worth 200$ (180, but, no head gaskets/pin bearing/exhaust gasket). I grabbed one that's extremely similar, for 8$, or 13.50$ all said and done. Since the bore may very well be trashed anyway- I'm not worried about a cheap piston destroying it. Am melting the aluminium off the bore with pure sodium hydroxide, and then then am shoving it all back in there with a heavy Castor927 or Yamalube mix (not sure which would be best for dealing with a questionable bore).

Anyway ,picture time! Lets see how they stack up before hand.








Not too bad for the price I think! Again, considering the Polini piston isn't worth buying at its price, for a bore that might not even come back to life.
Skirt starts at the same height relative to the pin.
The top is a bit shorter, but I can always shorten the cylinder or head a little to compensate if the compression is substantially lower. 
Has thicker rings, which I like.
Both seem to be the same diameter, but the cheaper one has thinner walls.
There is more support around the pin on the Polini, but the Polini is also cut into further up around the pin.

Is weird that the Polini didn't have piston windows, considering the intake is on the case, but, if that's what Polini paired the bore with- then that's what the replacement is going to be. Plus, the last thing the cheap china piston needs is more points of failure with even less supporting material.

Will update when the boy gets installed.

[118118]

First thing I'd want to know is why did it seize in the first place. 

[SEANIA]

First thing I'd want to know is why did it seize in the first place. 

never seized. piston was off center slightly, ground/melted all over one of the walls till it lost compression.

off topic though

Not important rightnow. All  possible isues were adressed in another post.

 This is seeing what a jank piston will do in nice cylinder instead of buying the $$$ polini one that costs half the price of the kit.

[JJJoseph]

Small-bore Kymcos are all made in China, and the parts are interchangeable.  Why not just buy the complete Chinese BBK kit?  They're not expensive, come with all the gaskets, etc, and they work just fine.

[KymcoRockr]

Small-bore Kymcos are all made in China, and the parts are interchangeable.  Why not just buy the complete Chinese BBK kit?  They're not expensive, come with all the gaskets, etc, and they work just fine.

None of this is true.

[Viper254]

If you make a statement like that, a little more detail would be good... do you know some more about it?

[JJJoseph]

None of this is true.

Don't be too harsh if you know nothing about the topic!  Here's my Kymco Sento rebuilt with all totally interchangeable Chinese GY6 parts:

[SEANIA]

Have had it installed, and running for a few weeks.

Works! Sorta.

It drops a lot of compression since it's shorter, and I mean, a lot of compression. Before I started using it daily, I took a zuma2t head and ground it down a fair bit to raise the compression back up some. Still not as high as it should ideally be, but is loads better.

Power wise, it feels the same as a well tuned stock bore. Likes 9 gram weights the best, but stuck 10's in it for the break in.

Has been solid. Been using it as my daily, and have put over 300 miles on it. Again, could use more compression since I'm still shoving 93 through it, but, is stable.

However- have dropped the whole engine/arm now. Is getting swapped with a 100% stock engine to scoot around on...while this one gets rebuilt with aftermarket form the ground up. Only stock thing left of it should be final drive- fun.

Important thing learned here-

Do the cheap china pistons work?
Yes
....but sand your head down to get usable compression.

[KymcoRockr]

Don't be too harsh if you know nothing about the topic!  Here's my Kymco Sento rebuilt with all totally interchangeable Chinese GY6 parts:

It's common to get more than 20K miles out of a stock Kymco 50cc engine. Let's see how long it runs.