Converting the YZ250 motor into a 250X motor?

[rjpjnk]

I am considering turning my 2011 yz250 motor into the 250X motor since it easy to do and so many reports say it is a smoother engine. The lowest costs I could find online show it will be about 850 in parts for Cylinder, Head, PV, Gov spring/washers, CDI.

 

Has anyone else tried this yet?

 

[southutdez]

I want to second this request. I have a yz250 and a 250x. I want them both to be X's. I followed a few of the threads for awhile as you guys went through some of the testing with the powervalve, cdi, etc. I'm hoping that you guys can post a dummy's guide to converting to an X. What parts will give me the best bang for the buck? I ask this, recognizing that you guys have put in a lot of time and effort to get this information. I would be extremely grateful to be able to benefit from your efforts.

[rjpjnk]

To make your 250 motor into a 250X motor you need the following parts. The best prices I could find online come to about $850.00 for everything. To my knowledge this list includes every part of the engine that is different except the pipe. From what I've read the changes to the pipe were more concerned with making it smaller and tucking it up and away to avoid damage from off road hazards. I suspect it does not contribute much to the 250X feel but I could be wrong.

 

So basically, if you swap these parts you have an exact copy of the new 250X motor.

 

 

(1) Head, Cylinder 1

Yamaha item: BF1-11111-00-00  

(2) Cylinder 1

Yamaha item: BF1-11311-00-00 

 

(3) Valve Assy

Yamaha item: BF1-1131D-00-00 

 

(4) C.D.I. Unit Assy

Yamaha item: BF1-85540-00-00 

 

(5) Spring, Compression

Yamaha item: 90501-290A2-00

 

(6) Washer, Plate (T=0.8)

item: 90201-154F5-00     (Quantity 4)

 

[E36M3E]

Didnt you just put together an EG mobetta 250 motor?

[YZDOC]

Are you not forgetting transmission gears, clutch springs and a whole bunch of other stuff? 

[rjpjnk]

Didnt you just put together an EG mobetta 250 motor?

Yes. Now I want to try the X motor.

[rjpjnk]

Are you not forgetting transmission gears, clutch springs and a whole bunch of other stuff? 

 

This thread is only about the motor. Someone else started a thread about the transmission.

 

I think I like the gears as they are, but I did already move to the X clutch springs. I like the easier pull.

[YZDOC]

Then you are only converting the top end and CDI into the X.

 

Carry on.  ?

[rjpjnk]

Then you are only converting the top end and CDI into the X.

 

Carry on.  ?

 

I don't understand your point. Are you considering the transmission to be part of the motor?

[Snider]

Its a engine, NOT a motor.. motor is electric..... 

[rjpjnk]

Its a engine, NOT a motor.. motor is electric..... 

Haha! Yes, I know what you mean, but just for fun...

 

Do you ride a motorcycle or an enginecycle?  ?

[Snider]

Haha! Yes, I know what you mean, but just for fun...

 

Do you ride a motorcycle or an enginecycle?  ?

Well,motor means other things but you are talking about a engine here... Ha ha.. And I should add not the transmission...

[YZDOC]

A play on words is so fun. Top end, not motor or engine. Making the YZ250 top end to be like the X by changing the top end and CDI.

 

 

Carry on some more.  ?  ?

[southutdez]

Thanks rjpjnk, that's what I was looking for. My boy is racing the yz250 and I'd like to smooth the power delivery out for him a bit. The gearing on the non-x will be fine. As far as all those x parts, are they all big contributors to the x feel, or do some play a minor role, like the cdi?

[asian195]

Its a engine, NOT a motor.. motor is electric.....

My grandfather always said this. Lol

[Snider]

My grandfather always said this. Lol

Well that makes sense.. I'm 55 yrs old LOL!

[mikenash]

Just a heads up guys if you hard on the clutch don't do the X springs in the clutch you"ll only wear the clutch out faster.

[rjpjnk]

A play on words is so fun. Top end, not motor or engine. Making the YZ250 top end to be like the X by changing the top end and CDI.

 

 

Carry on some more.  ?  ?

 

I honestly don't know. Are the cylinder and powervalve system considered top end? I guess they could be.

 

In any event, I'm changing everything except 3 of the gears.

 

Other than gears 3-5 in the transmission, are there any other parts of significance that are different between these two engines?

[southutdez]

Did anyone test just the cdi and how much of a difference did it make?

[rjpjnk]

Did anyone test just the cdi and how much of a difference did it make?

I don't remember if anyone tested only the CDI with no other X parts. Didn't you say you have both the YZ and the X? So you would be the perfect candidate to test. It is simple to swap the CDI. 

 

I suspect that the CDI and the PV system are designed to work together though. And you can't really do the PV without the cylinder.