MOUNTOPZ 3125xr8-u piston size???

[POPtimusPrime]

We got blue smoke! How do I know if I need the 52.4mm or the 54mm piston. Plate does not seem to give any indicators either (152I, 154I, etc. that I read tells you what size it is). My bit of research says the 52.4mm but, I read that's for the 110cc and I'm pretty confident it's 120cc (despite labeled 125). Only other visible marking is the 124cm3 on side of jug/case. I had trouble uploading pics. I can do the work but, lack confidence in knowing the riggt part. I'd be interested in upgrades too!? Pls help before she blows!! (I'll keep trying for pics)

[david3921]

If you need parts for your ATV, they are available from the Coolster website.

https://coolster.com

Piston and rings:

https://coolster.com/product/piston-...-120-lpj-c004/

[dirtbkr188]

The only sure way to get the correct parts is to take the head and cylinder off and measure the bore with a digital caliper. Then you can measure to see if you need a piston with a 13mm or 14mm wrist pin.

[POPtimusPrime]

Are you saying that the wrist pin is an indicator to piston size?

[POPtimusPrime]

The coolster website was my first stop. Primarily for the part number, which then led me down this rabbit hole of figuring out if I got a 110cc or 120cc. Coolster website only shows skirt length and wrist pin center to top of piston and no further info is found in the description. I don't know if the engines where switched during a specific year or series or something!? I understand chinesium quad curators are hard to cone by but, maybe somebody knows something?

[dirtbkr188]

Originally Posted by POPtimusPrime

Are you saying that the wrist pin is an indicator to piston size?

No, I'm saying that you have to disassemble the top end to find out the cylinder bore size and which wrist pin size the crank uses.
The Chinese engines are very unreliable when it comes to the information in the engine VIN and the displacement on the cylinder wall. You cannot assume that you have a 52 or 52.4mm bore going by the numbers, the engine has to be taken apart and certain parts measured for accuracy.

[david3921]

Originally Posted by POPtimusPrime

The coolster website was my first stop. Primarily for the part number, which then led me down this rabbit hole of figuring out if I got a 110cc or 120cc. Coolster website only shows skirt length and wrist pin center to top of piston and no further info is found in the description. I don't know if the engines where switched during a specific year or series or something!? I understand chinesium quad curators are hard to cone by but, maybe somebody knows something?

I think you might be over thinking this. According to the Coolster website, the piston and ring set fits your model number. My first response above was the same as dirtbkr's but I deleted it all to give you what you asked for. Looks like you'll have to do what we've all done when ordering parts for our China vehicles; take a chance and hope we get what we need. I've ordered parts from Coolster before. I've received what I ordered, quickly, and at a good price. They've got a great website where you can find parts for your ride and download manuals. You have to register to download stuff but it's pretty easy.

[dirtbkr188]

+1 on what david says above, join the website and you will be able to access a lot of specific information for the quad you have.
I nosed around on there for a while, I found out the bore is 52.4mm and the stroke is 55.5mm.Using the formula to calculate the total displacement, I came up with this:


5.24 x 5.24 x 5.55 x .7854 = 119.68 cc


Not only is the piston listed, but there is also a gasket set with all of the top end gaskets you'll need.

[POPtimusPrime]

Dude! Thanks for taking the time to do that digging. I guess I need to register with the site. I've ordered parts from coolster before but, it was parts that were more easily discernable. My other concern was that the website didn't specify that it came with rings and pin I'm cautions with Chinese sites as they show ya 1 thing and...!