250 cylinder interchange????

[Mr. Torque]

So, im trying to get this KX put together so I can do some woods racing with it   I have 2000 KX250, and I found a smoking deal on a good cylinder from a 2006 KX on Ebay.  I found it at the last minute so I placed a bid and won it and im waiting for it to get here.  I know that the 05-up swapped to an o-ring style head gasket vs. the steel one and other changes are evident.  I havent bought a pipe or reeds yet, im waiting to see if the cylinder fits.

Can anyone tell me Im wasting my time trying to get the 06 cylinder to work before I let other cylinders get away from me?  Thanks!

[The Flyin Hawaiian]

The 05-07 cylinders are completely different from the older 04 and below cylinders. The KX250 got a brand new motor in 05 and pretty much everything is different.

[Mr. Torque]

Indeed they are totally different, and the cylinder wont work.  Everything from the base gasket, to the head gasket, right down to the power valve....everything is totally different.  FYI for any of you wondering the same thing I was.

[DoldGuy]

Mr. Torque,
The 92 thru 04 cylinders will bolt on to your bottom end, but you will need specific parts for each particular year as the 92 you need the complete power valve assemb & head most other years you will need the power valve assemb only.

[Mr. Torque]

Mr. Torque,
The 92 thru 04 cylinders will bolt on to your bottom end, but you will need specific parts for each particular year as the 92 you need the complete power valve assemb & head most other years you will need the power valve assemb only.

So to clarify what you are saying....As long as I buy the cylinder complete with the power valve, I should be OK?  What about the expansion chamber, do I just need to buy one for the year of the head I use only?  Im aiming to get a 99-04 head, but I dont know what the differences is in the pipe.  If its just mounts, I can fabricate but I dont know if the exhaust port is raised or lowered ect...

[DoldGuy]

Mr.Torque,
If memory serves me, the different year pipes bolt on also to your chassis. What exactly is it that you are trying to accomplish? Do you currently have a cylinder on the 2000 KX250 that is in working order? You posted that this will be setup for woods riding, are you looking for a bottom end motor? As certain years were very good on bottom but lacked topend.

[Mr. Torque]

Mr.Torque,
If memory serves me, the different year pipes bolt on also to your chassis. What exactly is it that you are trying to accomplish? Do you currently have a cylinder on the 2000 KX250 that is in working order? You posted that this will be setup for woods riding, are you looking for a bottom end motor? As certain years were very good on bottom but lacked topend.

I am building a bike from a box.  I have now found a cylinder (2000 model, same as bike) and Im looking for a pipe only now.  Yes, im building it for woods but at the moment I just want it running so I can get some seat time in before running an 8 hour woods race.  Having said that, in the future I plan to buy a new pipe for it...possibly of the pro circuit sort, but now Im looking for a cheap pipe to put on it for seat time.  I have seen the factory part numbers listing a different pipe for almost every year so I was wondering if they just had small changes, or if they actually would not physically fit.

I am in it for more bottom end so In the future along with the pipe I will also install a flywheel weight and do some experimenting on my chassis dyno with it to tweak it in just right.

[DoldGuy]

Mr.Torque,
If I were in your position, I would locate a stock or FMF Gnarly pipe (stock will be very inexpensive) for a 1999 or 2000 model as any other pipe moves the power up the RPM range. I have tried just about every pipe out there for the KX250 (DEP,SPES,FMF,ProCircuit,Dynoport) and always end up running the FMF fatty, which takes away a small amount of bottom, but yields great mid & good over rev (not a woods type pipe). If you have access to a dyno, you should see similar results, & just by turning the base of the cylinder down (retarding port timing)& rechamber the head it will add alot of bottom and take some off of the top. You can also take away some of the hook (angle) in the rear transfer ports to add even more bottom (& take away top). If you run across a 95 KX250 cylinder that would be even better as they had very small ports, especially the exhaust, and can be turned into little tractors (with no top end). Keep us posted on the build as I am looking forward to this build.

[Mr. Torque]

Hey Doldguy, thanks for the info!  I have the access and ability to use to a lot of great tools, even machining tools.  Ive built many 4 stroke engines (I was on a drag racing expedition from 93-2002) and asides from refreshening/building them or adding bolt ons I havent dealt with many 2 strokes.  I will take your tips into consideration, especially with access to a dyno I can tune right up till Im sick of it.  Its not a dynojet, its a Mustang that uses eddy current and beleive me, it can do things unimaginable for tuning.  Once I make my 10 posts on here, Ill post up some of my research graphs on stuff ive already done with it.

[Mr. Torque]

Ok, finally project "Oscar the Grouch" had came to completion.  I have got everything on this bike freshened up and just like brand new.  I finished it a couple of weeks ago and Ive put about 10 hours on the bike and it runs like a dream....nice and crisp.  My wife made me go to Daytona for the last 7 days and its been killing me to ride!  Just got home this evening and im ready to hit the dirt.