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This probably belongs in the "Tech Talk" section but the General Discussion does say bike talk.

So heres the deal...I currently have a 2008 KTM 144SX that is slightely moded. Will a KTM 300cc motor fit in the 144 frame? I have been told that the 250 motor will but I was wanting to get something a little more beefier.

The 200 will. For sure. Been there. Done that. It's a simple matter of motor and engine head stay plates. The ignition. CDI unit will be different too as is the pipe.

I think the 250/300 cases are different and might be fun unless you have access to decent fab equipment.

slowjoe31 wrote:This probably belongs in the "Tech Talk" section but the General Discussion does say bike talk.

So heres the deal...I currently have a 2008 KTM 144SX that is slightely moded. Will a KTM 300cc motor fit in the 144 frame? I have been told th at the 250 motor will but I was wanting to get something a little more beefier.

been there too....the biggest motor with out modding frame is a 200 motor...the 250 and 300 need more space around the lower cradle area, and have different bolt spaces. any motor from 125-200 will fit in there, i have a 200 i would trade you if you wanted a 200 with out spending cash....new back tires 816-721-9169 collin

I may just have to retire the ol girl and look into a new 300. But for now the 144 has plenty of get up and go for woods racing!

Will the 200 jug bolt directly onto the 144 crankcase? If so what years of the 200 will be compadible?

slowjoe31 wrote:Will the 200 jug bolt directly onto the 144 crankcase? If so what years of the 200 will be compadible?

Well beyond my willingness to experiment.
David D's area.........David, do you know???

you need a new junk, head pv timer and a new crank. how much would you sell your 144 for?

slowjoe31 wrote:This probably belongs in the "Tech Talk" section but the General Discussion does say bike talk.

So heres the deal...I currently have a 2008 KTM 144SX that is slightely moded. Will a KTM 300cc motor fit in the 144 frame? I have been told that the 250 motor will but I was wanting to get something a little more beefier.

Honestly, I wouldnt change...you have a great engine in the 144. The 300 is one of my least favorite engines in KTM's lineup and is going to be counterproductive to the light handling of the 144 chassis

What others have said, but if you do get to tinkering in the engine. This is what I did over the winter and my 200 went from fun trail bike to being a rocket on the trail. Not everyone would like this set up, but when I started specing everything, I decided that I wanted to keep about what I had on the bottom end, really hit big in the mid, then carry all the way up.

Head - Milled to clean up the combustion and to knock it down to a zero squish height. This is supposed to be the biggest bang for your buck mod you can do, and plays a huge part in throttle response.

Cylinder - Ported with the focus on cleaning up castings and improve airflow throughout. This helps with the pull through out the RPM range.

Powervalve - Completely go through and cleaned out. Valve polished. Not sure it made a huge difference, but it's something I'll be doing regularly from now on. Just moving the assembly with a finger, and you can feel a lot less resistance, so it's got to help. Also, I have my PV adjusted to about the ticks width under the mildest setting as I find this helps me maintain traction in the slicker stuff.

Carb - Stock is 36mm. I had mine bored out to maintain the 36 size down low, but got it oval bored, so as you open it up, it pulls harder, it has a 38.5 mm verticle dimension now.

Clutch - Got to get that power to the ground and having 1/8" deep grooves in the fingers of the stock basket don't do so hot on that. So, I went sponsor hunting and got a full Hinson setup. Not sure if it was just the difference from a failed clutch to a factory team setup, but it's smooth and hooks up amazingly well.

And one more thing for the small bore...I switched to TuBliss last year. I had been running the 4mm ultra thick tubes and they weighed a ton. Switching to the TuBliss was possibly the best bang for the buck as it made handling instantly much better, let the suspension work much better, and acceleration and braking were hugely improved. It can still get puncture flats, I've had quite a few, but the benefits outweigh that only con.


I know it's a lot there, but after the 100 miler, I was left with essentially a cement filled engine and had to either rebuild or part out the bike. After riding it and getting some races on it, I have zero regrets. It really does pull like I want it to, and keeps the light handling of the small frame.

The 200 and 125/144 do differ in the crank, head, and cylinder. I believe the other pieces swap over. Also, the 200 is essentially the same engine from quite a while back, but I believe in 2001 or maybe 2003, they changed a few things they could be odd if you do start hunting for used parts to add the displacement.