'20 RXB250L - NC250 Motor Swap [Build Thread]
 

In June 2020 I purchased an Orion RXB250L (223cc) from Orion Powersports. Beyond a few small issues, I've had a great time putting 2k miles on my little air-cooled dual sport.


https://i.ibb.co/Jqxd6hn/IMG-20210822-130119935-HDR.jpg


I spent most of 2020 and 2021 making modifications to the lovable little CRF230 clone. If anyone cares, a full run down can be found on my instagram:

Ursa_Adv

Fast forward to 2021 and the announcement from Orion that a new frame & engine design would be used on the '21 model RXBs. Needless to say, I was extremely jealous of extra cc's, counter balancer, and sixth gear. I had seen Jack of All Master of None's Loncin RE250 (LX166FMM-3) swap, but not gonna lie....I wanted something more.

I looked at doing the Loncin swap with an Athena big bore and maybe an oil cooler. In the end however I kept coming back to wanting to do something more.

After hours of pouring over Orion documentation and my own bike, I came to realization. The '20 RXB250 is a rebranded X-Moto XB-39. But Orion put an air-cooled 223cc motor in it. That isn't what the X-Moto XB-39 comes with stock. Queue the google translate and some internet sleuthing and I discovered the answer to my swap problem.

The X-Moto XB-39 can come from the factory with 3 different engines. One of which is the NC250 ZS177MM commonly found on things like the SSR250/300, GPX250, and CSC RX-3. :doh:

Double checking all my measurements, knowing this would not be a cheap mistake if I got it wrong, I had a few adult beverages to think it over. About an hour later, I threw caution to the wind and pulled the trigger on an engine.

https://www.alibaba.com/product-deta...7bc23e5fICGgsj

Less than two weeks and 1k later, 88lbs of Zongshen 250 showed up on my doorstep.


https://i.ibb.co/JRbM7GN/1faddd3737a...dab3123992.jpg


This thread is going to my experiences swapping the NC250 into the XB-39 frame and, hopefully, provide a sign post for other bored lunatics :crazy: who decide to go down this path.

I should have taken a picture of the box before I opened it up, but it was pretty well packaged. The engine was in a plastic bag with a Styrofoam shell around it, inside a carboard box, and then wrapped with packing wire at intervals along the box. This was then wrapped in some thick packing tape. I can't complain about packaging. I was unable to find any indication of damage due to packaging or lack there of.

Only complaint I have is that I now have styrofoam on everything that I have to remove. All airways and opening into the engine were covered in silver reflective tape.


Contents of the Engine (and engine kit):

Engine/Trans:
- NC250 249cc motor (engine code: ZS177MM)
- 14 tooth front sprocket
- Kick starter lever (anodized red aluminum)
- gear shift lever (anodized red aluminum)

Fuel:
- Maikuni 34mm PWK Carb
- Fuel lines

Cooling:
- x2 Aluminum Radiators
- coolant houses and clamps

Electronics:
- Engine Harness. Note: Harness appears to be from a dirt bike, not a "dual sport". may have to splice in existing lights and indicators later.
- Rectifier
- CDI box
- Starter Solenoid

In order to make sure I can adapt my current setup to this new engine I ordered the following from CSC Motorcyles:

- RX3 Clutch Cable
- RX3 Throttle Cable


https://i.ibb.co/MRS1Pvw/IMG-20211021-180133369.jpg


Note: Please ignore my messy as hell workbench.

sounds like alot of work,hope it works for you. like to hear more about this build.

:thanks: I will do my best to keep this thread updated. Might be a few days between posts, but I'll try to keep the flow going.

I'll have a pretty massive photo dump in the next few days. Just need to find an image host that will actually show the pictures. Google Drive doesn't play nice with inline posting in forums for whatever reason. :shrug:

Thanks looks good

Awesome! I have had some thoughts myself about the need for sustainable power increases the cost versus the reward. A good documented thread will be invaluable. NC strong! Ride Hard!

I'll be watching thhis one!
The RX3 is fuel injected. I hope the throttle cable will hook up to the Mikuni carb.

You are absolutely right on this one. The CSC RX-3 does have fuel injection, but I couldn't find any difference between the fuel injected throttle cable and the carb'd version of the same bike they got overseas. I am working with a friend of mine to try to get one of the carb'd throttle cables to compare them.

I also have an SSR SR250 throttle cable on the way just in case. A back-up to the back-up plan.

After this is all said and done I will put together a "Needed parts list" for the swap. That way people can know what they need going into this project instead of having to do all this guess and check.

Today is going to be a pretty boring day. I'll be removing and labelling the old wiring harness (just in case this all goes wrong and I need to re-install the 223cc).

I'll post up some photos tonight of my progress.

I removed and labelled the stock Orion wiring harness this afternoon/evening.

The first image is the harness about halfway disconnected and the second is with it fully removed from the bike.


https://i.ibb.co/7nC9ZzC/IMG-20211023-194350144.jpg


https://i.ibb.co/9npF2RL/IMG-20211023-204533669.jpg


This last image you will see the old harness (TOP) and the NC250 harness (BOTTOM). As you can see we have some major differences right away. Length alone is going to be a problem. Also, this clearly came from a dirt bike not a dual sport. I can see a bit of wire work in my future as this project progresses.


https://i.ibb.co/3kbw486/IMG-20211023-204646150.jpg


We are going to set that aside for the time being and focus on the main elephant in the room. The engine. I am going to try to spend tomorrow moving the old engine out of the frame. More pictures and info to follow.

Man, I love threads like this! :clap:

Great posts! Just a suggestion. I see you are using IMGbb for uploading pictures. If uploaded with the " “BB code full linked” you can click on them and they open in another window, click again and gives you full resolution and another click will zoom in. Fantastic function for seeing small detail in a picture. I wanted to see how the frame was put together and the carb orientation with that zoom function I could see some more detail. It would add something to the analysis so I thought I would make the suggestion.

You, sir, are a nut. I approve of all of this.


If I ever blow up my Orion, I know what my next step will be!

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.

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! :tup: I'm going to keep up with this, I may get some ideas!

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!

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.


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.

https://i.ibb.co/Q8wVbvr/IMG-20211024-133047422.jpg
https://i.ibb.co/D1XRV3x/IMG-20211024-133032554.jpg
https://i.ibb.co/YQfkSRs/IMG-20211024-133024239.jpg
https://i.ibb.co/SNtQsBm/IMG-20211024-130556551.jpg
https://i.ibb.co/hH8dgX9/IMG-20211024-130544556.jpg
https://i.ibb.co/Jm89Jrs/IMG-20211024-130525859.jpg

Great pix! Amazing detail!

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

https://i.ibb.co/9NkwtMN/image-from-ios.jpg

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".

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.

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.

I do:

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

you are the man! Thanks for that :tup:

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.

https://i.ibb.co/x3Y3gHq/IMG-20211027-120255920.jpg

https://i.ibb.co/RQQF09Z/IMG-20211027-120437723.jpg

https://i.ibb.co/Kbpr6YP/IMG-20211027-120442844.jpg


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.

https://i.ibb.co/zN660VX/IMG-20211027-123527302.jpg

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.

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.

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

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.

https://i.ibb.co/k8XNGs0/IMG-20211028-125854295.jpg

https://i.ibb.co/sVKfRtg/IMG-20211028-131007481.jpg

https://i.ibb.co/FK5nqBL/IMG-20211028-125934974.jpg

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.

https://i.ibb.co/RgKrkhc/IMG-20211028-130011635.jpg

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.

https://i.ibb.co/4d2TtnQ/IMG-20211028-130843069.jpg

https://i.ibb.co/GCLTWqr/IMG-20211028-130858992.jpg

https://i.ibb.co/s3Ktssz/IMG-20211028-130849094.jpg

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 :shrug:

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!

Not a silly idea at all. As I was sitting there looking at it, I had the same thought. Like how could we "redo" these pipes back here. I, of course, rabbit holed into "Why don't I just make a new a frame?" That was my "too far" moment. lol.

As the goal for the swap was to use the stock frame, I am going to see what my fabricator says about options. I need to take the frame up there to have them plot out my engine mount situation, which will involve hauling the motor up there too, so we'll see.

I have a back-up option in the wings, if I really need it, but I'm trying to stick to the original goal of putting more power into my RXB. If I start swapping frames we get into that philosophical arguments of "is a thing still a thing if you take away all the parts", "cost vs. effort", etc.

Another stupid thought I had looking at your pics……. Looking at the bike from either side, look where the two tubes attach to the spine. Follow them down to where the meet, forming a Y. At that point, cut the larger of the 2 tubes just above where they meet straight across, following the tubes angle. Rotate that tube 90 degrees inwards toward the spine, trim the top edge of that tube and flange it to reattach to the spine. It looks as though that could gain you and inch minimum clearance, all while utilizing the OE frame and it’s materials. It’s merely, “modified”. Like I stated, just another silly thought, hope it makes sense…..

I think I'm following. Something like this (simplified I know), right?

https://i.ibb.co/h2qYtJV/Untitled.png

I think you are right to explore all options by taking off those valve covers and see how they are put together. I was thinking putting a stud in but doesn't look like there is enough room to
work. Grinding down the cover where the bolts are located? Custom valve cover? Just some Thoughts. Looks like it will work just question of how.

Bingo!! You think that might work?? Granted, I'm just going off pics.... Just thought rather than spend a lot of time, and of course money, on fab work, utilize what is already there. Just tweak it a tad, all while still remaining solid, and safe. Thoughts? Besides, I think the tubes would be of length needed (you probably trim off an inch or so), because their new attach points would be lower than before, due to the drop of the spinal tube.

You may also think about using the engine as a stressed member. This would allow you to rotate the engine down a bit more to allow clearance for the intake valves. It may be just the way the photo is taken (first photo, post #29), but it looks like the engine it rotated clockwise too much so that it clears the frame.

Currently, it does have to sit more clockwise than I would like due to the frame. Which further causes the valve cover issue.

If I am following you, by using the engine as a stress member, I would be able to remove a bit of the frame and use the overall strength of the engine as part of the "triangle".

A bit like this?

https://i.ibb.co/CvqNVn8/Inked-IMG-2...-125854295.jpg

Yes. You'd still be able to add a skid/bash plate to protect the underside of the engine. Also, by doing so, it looks like you would have an easier time attaching the top of the engine to the cross brace.

Looks to me like this frame was not designed with the counter balanced case protrusion in mind.

I personally wouldn't move or alter any of the upper frame structure.

The way it appears clocked the sprocket to swingarm and rear hub line seems like it would possibly lead to chain wear interference.

I think the main focal point or frame alteration is around the counter balance case protrusion.

There's a couple of options. You could shave out frame material around the counterbalance, I don't think there is enough meat to the frame for this.
You could make a cut where the bottom red arrow is in the photo and put a pie cut kink/dogleg moving the frame towards the front wheel and filling in the lower frame section extension.
Or you could cut out the whole section and fabricate an engine mount/frame tie in bracket. A bit like my Honda Xl185.

You might be able to incorporate a lower engine mount with the infill frame extension section.

The upper front mount might also be able to be incorporated into the frame adjustment pie cut portion where the frame will bend out towards the front wheel..

However not sure if these fixed mounts will make taking the engine out or putting it back in impossible due to space constraints.

Just throwing ideas.