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converting a '07 125sx to a 150xc

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hello all, I have a chance to pick up a 2007 ktm 125 sx really cheap.  needs a top end and cylinder replate, but the rest of the bike is in excellent condition.  plastic and tires are great and bike is complete.  bike hasn't ran in 5 years and the cylinder is removed from the motor.  seller says the clutch and trans is perfect. it has been stored inside.  suspension is good also. comes with 2 complete exhaust systems.   

 

this is what I have in mind for this project bike:  rebuild engine, increase bore to make 150cc, and while it is apart, add in an xc or xc-w transmission gearset. add a lighting coil later and factory headlight/taillight.  also want a pro moto billet kickstand.   

 

so is all of this possible?  is there a 150xc, and a 150xc-w, or just the xc? 

 

will the porting be changed in the cylinder to make it a true xc, or do I have to swap cylinders entirely? 

 

do I change all of the gears in the transmission or just some of them?

 

just trying to figure out all of the details before purchasing the bike.  this will be my first ktm and am hoping you fine folks will point me in the right direction. 

 

I have a 02 Suzuki rm 125 that I dearly love, and a 04 gasgas ec300 that has been awesome.  my goal is to build a bike very similar to my 02 rm 125 in regards to handling but with a wide ratio transmission, headlight/taillight, and a kickstand. 

 

I primarily trail ride and endure/woods race.  my Suzuki just doesn't have the appropriate gearing, even with +4 teeth on the rear sprocket.    

 

thanks.

 

        

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hello all, I have a chance to pick up a 2007 ktm 125 sx really cheap.  needs a top end and cylinder replate, but the rest of the bike is in excellent condition.  plastic and tires are great and bike is complete.  bike hasn't ran in 5 years and the cylinder is removed from the motor.  seller says the clutch and trans is perfect. it has been stored inside.  suspension is good also. comes with 2 complete exhaust systems.   

 

this is what I have in mind for this project bike:  rebuild engine, increase bore to make 150cc, and while it is apart, add in an xc or xc-w transmission gearset. add a lighting coil later and factory headlight/taillight.  also want a pro moto billet kickstand.   

 

so is all of this possible?  is there a 150xc, and a 150xc-w, or just the xc? 

 

will the porting be changed in the cylinder to make it a true xc, or do I have to swap cylinders entirely? 

 

do I change all of the gears in the transmission or just some of them?

 

just trying to figure out all of the details before purchasing the bike.  this will be my first ktm and am hoping you fine folks will point me in the right direction. 

 

I have a 02 Suzuki rm 125 that I dearly love, and a 04 gasgas ec300 that has been awesome.  my goal is to build a bike very similar to my 02 rm 125 in regards to handling but with a wide ratio transmission, headlight/taillight, and a kickstand. 

 

I primarily trail ride and endure/woods race.  my Suzuki just doesn't have the appropriate gearing, even with +4 teeth on the rear sprocket.    

 

thanks.

To truly make it a 150xc you'll have to stroke it as well. The KTM 150's are a larger bore and a longer stroke than the 125's. There is no 150xc-w, and from what I know the KTM 125 cylinders can't be bored out. There isn't enough material between the water jackets and cylinder wall, plus it's likely that trying to fix the ports after the bore would be a nightmare.

If you do it I assume you will need a 150 cylinder, PV, rod and crank kit, CDI, xc stator, 150 pipe, and that's leaving the tranny alone.

I'd buy it just to have it, but making it into a 150xc is possible, but expensive.

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Thanks poldies4.  I'm going into this project with the attitude that the piston, crank assembly, and cylinder is shot.   

 

Haven't seen the bike yet in person and seller states it seized up in 2009.  Don't know yet if the crank is good or not. But I am betting on the cylinder being scorched and needing a replate.    

 

I knew that I would need to purchase a 150xc stator in order to get lights, but that's no big deal.  What about the exhaust system?  Is the expansion chamber different when going from a 125sx to a 150xc?      

 

 

It might be cheaper to just to purchase a complete engine assembly from a 150xc or a 200xc and go that route.  Just gotta be patient. 

 

I purchased a non running 02 rm125 in 2012 for $900.  had a new crank, tires, and plastic was excellent shape.  suspension did not need service.  Less than $2500 later for the total purchase of the bike and parts, I had a minty blinged out rm125 with new motor, exhaust and lot of other goodies. 

 

I guess I enjoy buying a project and building it up.  I think as a whole, a person will get a better bike going this route, and you know what the condition of the internal parts.      

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