49cc GY6 Clone Piston Pic

[DoubleWasp]

This is the old piston from my girl's scooter. I'm doing a big bore kit on it so she can keep up when we're riding together on the beach. Pretty sure I'll get her on a Harley soon.

Not sure of the history of this engine. She picked it up used with 10k miles on it. Cylinder looked good, but piston looks pretty worn.



I don't feel so ridiculous filling it with VR1 anymore. These engines clearly undergo serious stress and heat.

 

[bioburner]

10k on a Chinese scoot is very good. Most of them don't have a oil filter and I don't consider a piece of door screen a filter.

 

[DoubleWasp]

I stick to 500 mile oil changes for that reason.

 

[FCD]

Dumb question this is a 4 stroke right

 

[Chris142]

Originally Posted By: FordCapriDriver
Dumb question this is a 4 stroke right
yes because it has an oil ring.

It's been very hot and had lots of blow by.

 

[JTK]

I've heard of these fan cooled Chinese GY6's racking up some miles, but 10K on a 49cc is unreal!

 

[Trav]

I wonder if you could get a moly coated piston for that?

 

[tomcat27]

that piston sure did its time! what does the big bore kit bring it up to?

and are you looking to put her on a Night 500? Night 750? Sporty?

 

[spasm3]

I'm suprised to hear the cylinder looks good, as that piston looks scarred like it swelled with heat.

 

[DoubleWasp]

It actually made 14k. She just bought it with 10k on it.

Yes, cylinder looks flawless. Hash marks unmolested.

I have a big box of coatings that I am going to use on this thing. Dry film lubricant on the skirt, thermal barrier on top, thermal barrier in the exhaust port and combustion chamber, heat dispersal coating on the outside of cylinder and head.

This is going into an Italica QT50:

*47mm piston and cylinder (39mm stock)
*Big Valve head with matching 47mm combustion chamber 23mm intake and 19mm exhaust valves (18mm/16mm stock)
*A9 Camshaft (more lift/duration)
*17/49 final drive gears

After seeing this piston, I consider the coatings mandatory. It's not going to be living an easier life with the new parts, so I'm doing everything I can.

Edit: Also adding an oil cooler kit that comes with a small filter.

 

[Popsy]

What oil cooler kit will you use?
I think it looks quite ok for a 14K miles 49cc piston.

 

[spasm3]

Rejetting the carb for the cam?

 

[alex_at]

I wonder what causes the piston to look like this. I have seen 2 Suzuki Boulevard C50 pistons that look exactly like this, but the Suzukis are known for piston slap (mostly when cold started). I also wonder if the choice of oil can prevent this from happening.

I'm also wondering if an Moly coated piston will actually help - is the moly coat really strong enough to withstand the piston scraping at the cylinder walls?

 

[Jarlaxle]

Originally Posted By: bioburner
10k on a Chinese scoot is very good. Most of them don't have a oil filter and I don't consider a piece of door screen a filter.


Neither does a Honda Helix!

For that matter...neither did an old VW Bug.

 

[DoubleWasp]

I forgot to mention that I have a 23mm carb replacing the stock 18mm carb. I have am full set of tuning jets ready to go in. I'm starting with a rather fat one (#105) and working my way down. I know exactly what these engines feel like when running rich, so I can start out safe and go down from there, watching my plug condition.

I'm using the Scrappy Dog oil cooler kit.

I have no idea whether the coating will hold up or not. These engines and parts are so cheap, it's worth it to find out the hard way. I don't expect to be disappointed. The thermal coating will keep a lot of heat out of the piston.

A major contributor to the whole thing could be the simple fact that people usually start these scooters cold, and have pretty much no choice but to knock them straight to redline, or be run over. That could cause a load of piston slapping as the engine sees 9000rpm while still cold.

I usually let all of my 2 wheelers warm up before cracking on them.

 

[Silk]

Originally Posted By: bioburner
10k on a Chinese scoot is very good. Most of them don't have a oil filter and I don't consider a piece of door screen a filter.


Honda clone - but it's ok for Honda ?

 

[DoubleWasp]

Started it up tonight. Ran really hot. Turns out the carb was loaded with an #88 jet. Not even close. Had to turn out the idle mixture screw until it nearly fell out just to get it to idle, doing 230 degrees in the process.

#105 is going in tomorrow.

 

[spasm3]

I hope the lean condition did not kill the new rings.

 

[DoubleWasp]

Did a compression test to be sure, and popped the scope in. Over 220 psi, and all looks good.

Turns out that even the #105 jet will not be enough. Getting the 24mm performance manifold and 150cc carb.

Between the cam and big valve head, a 50cc carb doesn't stand a chance, even with the fattest jet.

Once I have everything down, I'll have a fool proof formula for the future.

I consider this engine sacrificial. Hope I don't screw it up, but if I do, I'll do it right the next go with all lessons learned. But so far, so good.

 

[DoubleWasp]

Yesterday, I got the right carb and manifold in and got her going. I still had to fatten the carb way out in order to get her to idle.

Once I got the rings broken in, I was able to lean her idle out and reduce the idle speed to a normal level.

I can tell I now need a leaner main jet, but it made its way to 45 MPH with surprising ease. Once I get the fuel mixture under control, she should make 55-60. These engines are practically inoperable when running as rich as this one is.