300cc Kit

[Weldangrind]

No disrespect intended towards Peter, when I say that perhaps the piston was 180* out from proper orientation. So hard to know, since the piston top could have spun when things came apart.
The arrow on the piston points roughly 80* to the right from forward, which means it could have spun 120* from rearward. The intake and exhaust valve reliefs appear to be identical, so it would be an easy mistake to make, if a person didn't spot the arrow. Again, no disrespect intended.

[2LZ]

Originally Posted by Jay In Milpitas

Please notice that Peter's picture of the top of the con rod shows the pin centered in the rod meaning that it hadn't shifted to one side. The shot inside the barrel also doesn't show a linear wear mark that would correspond with pin shift.

I wasn't referencing Peter's bike. I was talking about how bad my neighbor will feel and how many beers he'll feel obligated to get me. It could grenade because I forgot to put in oil and it will still be his fault. ;-)

[Duckati]

Originally Posted by Weldangrind

No disrespect intended towards Peter, when I say that perhaps the piston was 180* out from proper orientation. So hard to know, since the piston top could have spun when things came apart.
The arrow on the piston points roughly 80* to the right from forward, which means it could have spun 120* from rearward. The intake and exhaust valve reliefs appear to be identical, so it would be an easy mistake to make, if a person didn't spot the arrow. Again, no disrespect intended.

Really interesting thought... To my eye, the reliefs at bottom of your picture slightly larger. The skirts often aren't symmetrical either:

“On asymmetric piston designs, there is a wide skirt panel and a narrow skirt panel,” he explains. “The wide panel needs to be in the direction of major thrust. The major thrust direction is the side that is against rotation. For example, if the engine rotates clockwise when viewed from the front pulley the major thrust would be to the left (against rotation).”

(borrowed from http://blog.jepistons.com/piston-ori...ps-and-bottoms)

Peter had noted the ~50g or nearly 20% weight increase over the stock piston, despite someone here saying they should be within 3% as a general rule to match crank counterweight balancing, so that's where my brain had gone. Folks here had requested purchasers of the kit to weigh theirs before installation, but I'd not found anyone that did when reading this whole thread yesterday. Perhaps someone did but forgot to mention it...

Anyone? Bueller?

...but the fact that no one else has reported a change in vibration, yet Peter's was extremely noticeable to the point he was considering going back to stock, has remained a red flag in my brain.

[Juanro]

Weight quoted for the STD piston matches mine:

Cranckshaft/conrod Assy alone: 3,22kg
Conrod weight at the head, when horizontal 66gr
Piston, rings, pin, retainers 275gr
Balancer countershaft 475gr (Couldn't weight offset part alone, but estimated 200gr)

[2LZ]

Originally Posted by Duckati

Really interesting thought... To my eye, the reliefs at bottom of your picture slightly larger. The skirts often aren't symmetrical either:

“On asymmetric piston designs, there is a wide skirt panel and a narrow skirt panel,” he explains. “The wide panel needs to be in the direction of major thrust. The major thrust direction is the side that is against rotation. For example, if the engine rotates clockwise when viewed from the front pulley the major thrust would be to the left (against rotation).”

(borrowed from http://blog.jepistons.com/piston-ori...ps-and-bottoms)

Peter had noted the ~50g or nearly 20% weight increase over the stock piston, despite someone here saying they should be within 3% as a general rule to match crank counterweight balancing, so that's where my brain had gone. Folks here had requested purchasers of the kit to weigh theirs before installation, but I'd not found anyone that did when reading this whole thread yesterday. Perhaps someone did but forgot to mention it...

Anyone? Bueller?

...but the fact that no one else has reported a change in vibration, yet Peter's was extremely noticeable to the point he was considering going back to stock, has remained a red flag in my brain.

I didn't weigh mine and compare. I just assembled it so I could clear the shop to get my car project back up on blocks.

I wonder if Peter felt this vibration while reving in neutral too, not just in gear going down the road.

[NzBrakelathes]

Here is a pic of the piston in new state
I fail to see bad casting as a cause, but we are all arm chair mechanics
Here in China 100's are fitted to MX bikes and I think some new MX bikes get these kits too.

[Jay In Milpitas]

Originally Posted by NzBrakelathes

I fail to see bad casting as a cause, but we are all arm chair mechanics

Oh. Wow, I have been categorized to below the level I was in 1962.

[ChondaChondaChonda]

Originally Posted by Jay In Milpitas

Oh. Wow, I have been categorized to below the level I was in 1962.

I see no names mentioned.

Arm chair means we are not there in person to know for sure what happened.

I don't know who you are or what your background is by internet-osmosis.


Please enlighten us and add to the conversation.

[NzBrakelathes]

Relax relax
Plz don’t go reading in a ton of stuff into a simple post
Yes we all sit on our chairs by a computer or phone looking at photos
It’s not about our individual skills but the position we are when we look and post about our thoughts ideas and so on, I’m currently in my workshop area squaring down typing on my phone lol
I must be the squating mechanic etc
Lads I’m gunna solve more on my bike today so I’m a bit busy
Have a great one

[Sullybiker]

Well, something went wrong for him, and it sucks because like so many here he's a top ambassador for Chinabikes, and he's still choosing to keep himself in the game.

The valve strikes seem odd to me. That's a simple matter of clearance, but it might have happened if the cylinder failed and allowed the top end to drop as the piston was driven upward.

[NzBrakelathes]

Originally Posted by Sullybiker

Well, something went wrong for him, and it sucks because like so many here he's a top ambassador for Chinabikes, and he's still choosing to keep himself in the game.

The valve strikes seem odd to me. That's a simple matter of clearance, but it might have happened if the cylinder failed and allowed the top end to drop as the piston was driven upward.

It broke loose so yes valves got hit cause piston would go up unattended IMHO from my arm chair lol

[ChondaChondaChonda]

Well, I have decided that I will pull the big bore piston and cylinder out of my LXR and drop it into the new GPX. I have not even put fuel in the new bike yet, so it's a brand new motor.



I'd like to rack up some miles and see how it does. Plus this should give a potential LXR buyer some extra piece of mind.



I will see if I can find a small accurate scale and get weights on my pistons while they are out. I've not noticed any difference in vibration levels with the kit. I do really like the extra grunt, especially off road.

[Juanro]

How many miles / hours have you put on this kit?

[2LZ]

Originally Posted by Juanro

How many miles / hours have you put on this kit?

Under 50 miles. I have my suspicions but all we have are pics and report to go by for doing any forensic guessing.

Update on mine:
I took it out after work for another 10 mile putt around my area. I'm still being easy on it because I'm breaking in the new cylinder and piston. I briefly got it up to 7500 a couple times and no more vibration than normal, though I can still feel it's a bit tight. I'm going to do the usual break-in process, which isn't a big deal for me. Twisty roads anyway. Lots of up and down throttle.

Regarding how it's acting, it's what I've wanted it to be since I bought it. It's SO nice to finally have some usable torque between 3500 and 5000 rpm's. I don't have to drop a gear and ring its neck anymore just to climb up a steep paved road.

Liking it a lot so far and it has yet to grenade.

[Juanro]

Originally Posted by 2LZ

Under 50 miles.

Yes, I've read Peter post. I was asking Chonda about his.