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does a stock gpx head have enough cc,s to run a 153cc setup

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just seen rkfinch is running a lifan big valve head in a 153cc motor just want to no if stock lifan or gpx head has enough cc,s in it to run a 153cc motor as these head were designed for a 125

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nope, the most a gpx can be bored out to is 140cc, which is 56 mm. dratv sells the lifan big head i think if your interested.

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thats not wat i am talking about i am saying that if i have a 153cc piston and barrel does the stock head have enough cc,s in the combustion chamber to run a 153cc motor i would say no i would say it would then blow the compression threw the roof

can someone like rkfinch answer me

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the valves in the stock gpx head won't flow nearly enough to keep up with a 153cc configuration

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Yes, that is how we have ordered them, so unless we get a surprise they will be complete.

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dont any of u guys have a answer for my original question i need to no about the copmression do these big valve heads have enough volume in the combustion chamber to run a 153cc motor i would think not i would think they are designed for a 125 motor and once put on a 153cc the compression would be way to high

i am just going on my 2 stroke expereance i may be wrong carnt anyone help with this

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wat makes u think i dont no wat i am talking about i wasnt trying to insalt u i admit i am only new to 4 strokes all i no is wen i put a 134 kit in my cr125 i had to up the cc,s in the head to end up the write comp for what fuel i was using

does it not work the same way with 4strokes do u not have to cc the motor built to work out wat copmtession u will end up with

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no i was just use the 153 as an example i am about to buy a 143cc kit here i AUS

so do u suggest i cc the motor biult a few times adjust the piston to head clearance until i get the comp i am chasing

i have a big valve zong head do u no if it has the same cc,s in it as the lifan head

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wat do u mean that there is no squish band. pls help me bro i am only trying to learn

one thing i dont understand is that u can bolt a lifan head up to a 125 and a 153 and still come up with write comp

once again im only trying to learn bro

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Man........ I wouldn't go above a 140cc kit on any of the motors.........For reliability Only and anything above the 140cc kit now you got to look into the Tranny to hold up...... Unless your a Expert or Pro Rider with madd skills you cant even use the power these motors produce

And Maybe people would bennifit More Kenny, if you would have patiance and take the time to explain things "In Detail" if you dont have the Time dont comment........ Ha Ha Ha

GPX 140cc kit with Dr ATV Parts:

Lifan 120cc Cylinder

Lifan Monster Head

Dr Atv 56mm Piston

Thin Copper head gasket

Miss Parts:

TB 26mm Carb or 24mm Kehlin

Crower G-2 Cam

flywheel and oil sling machining

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i was just using the 153 as an example i am about to get a 143 kit here in AUS and yes bro i have raced motocross and supercross for 10 years

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I Know how long you have been racing.... But alot of people think Bigger is better Maybe so with you But chances are The lower end will not hold especially if its a Lifan Bottom end Just trying to save you money.

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It's all a matter of matching the piston to the head. So, if you get a 58mm piston, you want to make sure that it's domed or dished enough so you've got the right combustion space/volume at TDC to put compression where you want it. Using your 153cc example... lets say you want 12:1 compression...

You're going to need 14cc's of space. CC the GPX head, CC the top of the piston, and then tune by varying the thickness of the head and base gaskets.

Totally made up numbers because I haven't cc'd a GPX head...

Head volume - 8cc

Piston volume - 1cc (Slightly dished piston)

Ok, so assuming that piston comes right up to the head with zero squish clearance, you've got 9cc of volume. At 153cc displacement thats 18:1 compression, a WEE bit high. We're using a theoretical 58mm bore, and we need 5cc of additional volume, so we need a head gasket that's 1.9mm thick. That gets us the 5cc of additional volume, and presto, 12:1 compression.

Lets say you got a popup piston, and the popup displaces 4cc.

Head - 8cc

Piston - -4cc

Now your volume at TDC is only 4cc, you're going to need to mill the piston, or get a head gasket that's 3.8mm thick, which may require a longer cam chain.

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cool i am starting with a zong head

does the clearance have as big of affect as on a 2 stroke. i have been told 0.3 is the limit on these little 4 strokes.

would u agree that the ideal setup is 13.1 with 0.3 clearance but if i had to raise it to 0.5 or 0.8 to get the write comp the claerance wont have as big of affect as on a 2 stroke its more about getting the comp write

if i have to machine the piston is it best to do a dead flat cut acrooss the vavle releifs then if if the valves or to close to the head can i just dremel the releifs carefully or do i have to get them machine cut

thanks kc................

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The clearance can have a big impact, especially if you've actually got a proper squish band. Too tight and you'll detonate early, too loose and combustion suffers. One of the areas holding back the 52.4mm motors, the combustion chamber is too big to really have much of a squish band in the head, and the stock piston isn't shaped to help.

The main reason for listing a .3 clearance is to avoid piston to head contact at high RPM. Any less, and well... do you like gambling? : )

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