'20 RXB250L - NC250 Motor Swap [Build Thread]

[China Rider 27]

Originally Posted by Ursa_Adv

I'll try that with the pictures from tonight. I'll make sure to snag a few of the frame. Is there any specific points you want to see?

I also try to get another light out there so I don't have to rely on the flash as much.

I was just thinking how do all these frames match up, the HAWK, X Pro Titan, etc. I was just curious about all the attachment points. No need to spend your time taking special pix. As it sits now that black all blends together and the resolution is reduced I think when the pix is uploaded to the forum, hence getting full resolution gives a better view of detail and opens in a kinda zoomed in look.

That old saying a Picture is worth a thousand words. This is the first time I have seen the RXB250L frame. A good build thread has good pictures and you have started with some good ones.

Somebody taught me how to upload with imgbb and when I learned I went back to my build thread (edit function which the original user can modify the post) and re-uploaded the same pictures and erased the original links to have them appear in the post. Rather than take new pictures you could just upload the original with the full link code and fix the original post, try it first to be sure the link works (that you are getting the picture loading in a new window with full resolution).

A build like this, with all the clearance issues, those close ups angles and any zoom ability will improve seeing how it all fits and maybe taking your idea and work to apply it to another bike. I only say all this because you have done a great job getting started so I can't resist trying to make it better. Keep up the good work!

[Ursa_Adv]

Originally Posted by China Rider 27

I only say all this because you have done a great job getting started so I can't resist trying to make it better. Keep up the good work!

Any way we can make this thread a better reference is an excellent idea. I resized the images in the first few post so they didn't just load as massive 4k images within the thread, but it definitely does reduce the visible details.

Originally Posted by Plump Kibbles

Man that gas tank looks awesome - I wonder if it would fit my X-Pro CRF clone!

It all comes down to the mounting points. I lucked out in that X-Moto literally copied the KTM style of tank mounting. Spent a few hours on Acerbis's website looking at installation manuals and found one that I felt was super close. It was a gamble for sure, but worked out. Check with who ever you decide to buy the tank from and make sure they take returns. Worst case, send it back and remount the stock tank.


Today's Update:

The stock motor is out. It was way less work than I anticipated. The only problem on the horizon I can see is that rear mount bracket for the original engine requires the removal of the swingarm bolt. Not really a problem, I guess, I've just never done it before so I've got some reading to do.

Quick measurements on the NC250 front mount points, they will fit between the ears welded on the frame. The same for the rear mount point which allows the swingarm bolt to pass through it.

I'll get started on the swingarm tomorrow after work. Here are some pictures of the progress so far.

[China Rider 27]

Great pix! Amazing detail!

[Ursa_Adv]

Turns out the Swingarm removal is way easier than I thought.



Loosened the bolts up last night, I'll be pulling the swingarm in its entirety this evening. Then we're on to test fitting.

Note: I'm a turd and I labelled the 21mm nut on the swingarm a "21mm bolt".

[China Rider 27]

With that full resolution zoom function you can get right in there and see it. That suspension looks beefy. Adjustable for rebound? Any issues with it?

[Ursa_Adv]

Originally Posted by China Rider 27

With that full resolution zoom function you can get right in there and see it. That suspension looks beefy. Adjustable for rebound? Any issues with it?

Yup. Dual adjustment on the front and rear shock.

The only "issue" I had with it was my fault. I never set my preload properly, which was fine when I was just tooling around town or some light forest roads.

However, when I started pushing the bike harder things went south quick. Needless to say I chunked a very nice tire off the muffler. No one to blame but myself on that one. Live and learn.

Other than that I can't complain. I know Dave (Dirtbike Channel Dave) and Joe Henner have made some modifications for usability, but they are strictly motocross. For the average user, the stock suspension is probably going to be fine. Heavy riders might benefit from swapping the coil out though.

[OffRoadToad]

Originally Posted by Plump Kibbles

Man that gas tank looks awesome - I wonder if it would fit my X-Pro CRF clone! I want a bigger tank but have no idea what fits.. rocking a 1.5gal I believe.

Awesome build man! I'm going to keep up with this, I may get some ideas!

I thought the same thing when I saw that tank. I was just looking at tanks this weekend.

You wouldn't happen to have a part # or link for that, would you Ursa?

Oh, and subbed. Great thread since I have the same bike.

[Ursa_Adv]

Originally Posted by OffRoadToad

You wouldn't happen to have a part # or link for that, would you Ursa?

Oh, and subbed. Great thread since I have the same bike.

I do:

2015 KTM 250 SX
Acerbis Fuel Tank 5.3 Gallons Natural
Link to RMATVMC

[OffRoadToad]

Originally Posted by Ursa_Adv

I do:

2015 KTM 250 SX
Acerbis Fuel Tank 5.3 Gallons Natural
Link to RMATVMC

you are the man! Thanks for that

[Ursa_Adv]

Test fit is complete. We ran into a few clearance issues. The front mounts for the motor are in the way. No matter which was you slice it, but we kinda knew that was a possibility going into it. So no real deal breaker.








The other place we had a "hit" was the stock skid plate mount under the frame which was impacting the oil drain plug on the bottom of the engine. I used what was left in my angle grinder disk to remove the mount for the skid plate.



I've got to pick up a new grinding disk and then I'll get started on the front mounts as well. At the end of the day, I need the rear mount (swingarm) to slot and align. The others, I can fab in later.

[ExMxer]

Tilt that engine “up” about 3-6 mm….. from the front of course. Look at it from a down the road perspective. Raise up, before grinding down…..anything. Room is above, using the swing arm as a pivotal point, don’t use the cradle as a crutch. The more you can upright that cylinder, while keeping the cases somewhat level, the better off you’ll be. Sounds dumb as shit, but it does work. Hell, go 10 mm if needed….. that cylinder has a hell of an angle ahead of it. I really admire your work progress, swaps are a real test, keep it up!

[Ursa_Adv]

Originally Posted by ExMxer

Tilt that engine “up” about 3-6 mm….. from the front of course. Look at it from a down the road perspective. Raise up, before grinding down…..anything. Room is above, using the swing arm as a pivotal point, don’t use the cradle as a crutch. The more you can upright that cylinder, while keeping the cases somewhat level, the better off you’ll be. Sounds dumb as shit, but it does work. Hell, go 10 mm if needed….. that cylinder has a hell of an angle ahead of it. I really admire your work progress, swaps are a real test, keep it up!

You got it in one. The plan is to get it in the back mount (swingarm) and tilt the whole engine up.

It's only in that position in the picture because it won't sit any other way.

The front two upper mounts hit the counter-balancer just enough to keep me from tilting it up.

The end result will have the cylinder sitting more in a vertical position, but I have to clear those two front mounts.

[ExMxer]

Originally Posted by Ursa_Adv

You got it in one. The plan is to get it in the back mount (swingarm) and tilt the whole engine up.

It's only in that position in the picture because it won't sit any other way.

The front two upper mounts hit the counter-balancer just enough to keep me from tilting it up.

The end result will have the cylinder sitting more in a vertical position, but I have to clear those two front mounts.

You got this! Looks like kind of fun that makes a man cuss from time to time Seriously though, that engine looks impressive, bike should rip. Enjoying watching your progress, keep up the great work!

[Ursa_Adv]

With the front mounts removed, I was able to rotate the motor into the proper position and boy did it feel good to get the swingarm bolt slotted in to place. Small victories.







There are a few areas of concern. The first is the front of the engine, there is a bolt that keeps the left/right side of the case together.



It rests ever so slightly against the frame. Removing the paint from the frame in that area was enough to allow it to slide freely without hanging up.

The next concern is the rear valve cover is right against the frame. Specifically the bolts are right against the frame. This is going to present an issue for valve adjustments.







I am going to check the length on the valve cover bolts, some creative spacing might give me a better clearance, but unsure if it will work. I don't like the idea having to take the swingarm off to slide the engine sideways to get clear of the frame each time I do the valves. My experience, however, on this build has shown me removing the swingarm takes a whole 5 minutes. So who knows

[ExMxer]

That looks great! As far as your frame issue with your valve adjust, could it be possible to have two new tubes contructed that attach to the upper spine? I don’t know the trouble you are willing to go to, but having two “shorter” rails connected to the spine would still maintain a solid structure, but giving you room to adjust your valves without removing the back half of your machine. Just a silly idea, this swap reminders me of a 2 stroke swap I helped a friend on years ago. Your work looks really good, hang in there!