ADVrider (
-   Some Assembly Required (
-   -   building a custom trailbike: Honda CRF chassis + XR250R engine (

jesusgatos 03-30-2011 02:21 AM

building a custom trailbike: Honda CRF chassis + XR250R engine
I killed my WR250F a few years ago riding Gifford Pinchot (totally worth it) and although it was a fluke thing and wouldn't have been much work to fix, I was over it. Just don't like having to deal with the maintenance that those small-bore 4-strokes demand. So I thought about buying a 2-stroke. Something like a KTM 200, or a YZ250 set-up for woods riding. But, well, I like building things and what I really wanted to be riding was an updated XR. Something like an XR250R engine in a modern chassis. Air-cooled, stupid-simple, reliable engine with a good chassis, suspension, brakes. Dwight Rudder started a thread on thumpertalk on this topic several years ago. He decided to build a customized CRF230. The CRF230 was appealing because it's based on the XR200 engine, and has a 6spd and e-start. But the XR250 also has a 6spd, has a 4-valve head, and makes a little bit more power (16 vs. 20 stock, according to info I read online). The '96 and newer XR's are dry-sump engines, and are a little bit more compact than the earlier XR250 engines. Found this image somewhere online that illustrates the differences.

So I started shopping. Watched the classifieds and found a clean 2000 XR250R. Bought it. Pulled the engine and sold the bike. Started taking some measurements and it looked like it would almost bolt right into my 2003XR250F chassis. Had just blown-up the engine in that bike, so I was tempted. But that Yamaha wasn't a particularly great-handling bike. Found out a few months later that one of my buddies had just blown-up his CRF450R while he was riding in Mexico. Called him. Hey sorry to hear about your bike, but, um, what are you gonna do with it? He thought I was nuts for wanting to put an old air-cooled XR engine in a racebike, but was happy to be rid of it.

Took a few months to get it from San Diego all the way up to Bend, OR, but I tore into it as soon as I rolled it into my shop. Checked a few critical dimensions, and it looked like a good fit. Would have to cut the engine cradle out, but that was no big deal. Took me less than a day to get it stripped-down and cut apart. And there it sat. Got pushed aside (literally) to make way for another project. Decided to pack everything up and hit the road. Spend some time traveling. But first I was going to build a custom motorhome out of an old 2.5-ton military 6x6 called a deuce and a half. Took this picture right after I brought home this water-damaged camper to strip a few appliances out of (vintage stainless steel oven/stove). That's my buddy Duane, and I think he was saying something about what a hillybilly I am.

Been several years now since I 'started' this project, but never really did much more than collect a bunch of parts. Motorhome is coming along slowly-but-surely, am almost finished rebuilding my desert truck, and don't know... just seemed like it was time to get back to work on this bike. Making time to work on this project in between all my other projects though, so it's going to be mostly nights, weekends, and rainy-days. But I'm motivated and this is actually a pretty straightforward deal. Made some space in the garage today and got started.

Not a bad fit. It's sitting in there cock-eyed because I have to clearance the frame and I'm doing that with a die-grinder a little bit at a time so I don't remove any more material than absolutely necessary.

The twin-spar frame clears the head with plenty of room to spare and should make working on the bike pretty easy.

Stock gas fits too. Am planning on putting the bike back together with the stock tank and plastics (minus the radiator shrouds) to see how it works, and if I like it, then I'm going to make a new tank, subframe, seatpan, and plastics. Already have a pretty good idea of what it's going to look like and it's gonna be sexxay.

crankshaft 03-30-2011 04:09 AM

Very cool, I've often dreamed of the same project.

911racer 03-30-2011 04:19 AM

Thats going to be one bad ass bike! I really like your Toyota truck as well. :clap

jesusgatos 04-01-2011 06:02 PM

Thanks guys, but you might want to hold off on the compliments until it's done. Lots of people take stuff apart and start these kind of projects. Hell, it's taken me over two years just to get to this point. Guess we'll see if I can finish this one in any kind of respectful fashion.

Next thing I need to do is figure out exactly where the engine needs to sit (side-to-side) because it affects how/where I have to clearance the frame. So I spent a few minutes taking some measurements and it looks like the distance from the centerline of the engine cases to the centerline of the front sprocket is within 1/16" from the centerline of the rear hub/swingarm to the centerline of the rear sprocket. So that means I can just mount the engine dead-center in the chassis from side-to-side. Not a big deal, but makes it a bit easier to locate and design/build engine mounts, etc.

jesusgatos 04-03-2011 06:15 PM

Just posted this on thumpertalk:


Originally Posted by jesusgatos (Post 10218890)
Am building a custom trailbike, putting an XR250R engine into a 2005 CRF450R chassis. Fitting the new engine right now, and would like to know where the CRF front sprocket is located, relative to the chassis. Would sure appreciate it if somebody could take a quick measurement for me. All I need to know is the height from the bottom of the forging to the centerline of the sprocket (pic shows measurement requested). Thanks in advance.

jesusgatos 04-03-2011 06:19 PM

Have provided enough clearance to locate the engine side-to-side, but need to get a measurement for the countershaft sprocket before can do much more. Pretty sure am going to need to rotate the engine forward/down a bit more and that will require more clearance, but don't want to remove any more material than necessary.

Hodakaguy 04-03-2011 06:31 PM

Sweet! :lurk:lurk:lurk


jesusgatos 04-04-2011 12:00 PM

Have just about got the engine in the right place. Just need to machine some bushings for the swingarm, then I'll be able to do the final clearancing and cut some gussets to weld into places where I've weakened the frame. Took a few pics to show how I test-fit the engine, mark-up the frame, and then clearance a little bit at a time.

Also slid the engine cradle tubes back into place to see how they fit and it's very close. Think I could probably just barely almost have made it work without cutting out the engine cradle. But I wouldn't have known that without doing it this way, and more importantly, I couldn't physically fit the engine into the frame with the engine cradle in place. So as I see it now, I've got three options:

1) Bend-up some new tubes and weld them into place. Easy enough. But the main clearance problem is the oil drain bolt, which I'd still have to notch the left engine cradle tube to clear. Would most likely just pierce the tube and weld a short section of round tubing into place, through which I'd be able to remove/install the oil drain bolt.

2) Reinstall the engine cradle tubes I've cut out. Not quite as sketchy as it sounds, as I was really careful about how I cut everything apart and will be gussetting the swingarm junction anyway. No real advantage to doing this though either. Cutting off the old engine mounts and cleaning-up the tubes would take more time than bending and notching new tubing.

3) Buy a new frame. Seriously considering this option. Mostly because I'd kind of like to cut apart one of these frames anyway. Want to modify it to carry oil in the downtube, and maybe even fuel in the twin-spar part of the frame. If I go this route, I'd need to cut out the tubular hoop over the engine. Think that would give me just enough room to squeeze the engine in there. Going to watch ebay and see if anything pops-up.

VxZeroKnots 05-15-2011 08:54 PM

I don't really understand option three, if you bought a new CRF frame wouldn't it need the same treatment to get the engine in? What am I missing? as always nice work Jesse.:clap

jesusgatos 05-15-2011 09:51 PM

Think it might be possible to fit this engine into a CRF450 frame without cutting out the engine cradle. Instead, would try to modify/clearance the left-side of the engine-cradle tube and then maybe cut out the horseshoe-shaped tubes overhead. But this project has been on hold for a little while. Am going to ride up to Fremont tomorrow to talk with Curt at BTR moto about building an all new custom steel main frame. Never wanted to build an aluminum-framed trailbike, but was going to hack this together using what I had laying around because all my tools are in storage.

KASUYAHO 05-15-2011 11:47 PM

Cool mate,
but i can not help thinking 650R in there :D

jesusgatos 05-16-2011 12:06 AM

Already got one of those.

VxZeroKnots 05-16-2011 05:59 AM

okay, that makes more sense. I keep thinking about making a steel tressel framed dual sport with fabbed tanks and everything a la your composite thread. We'll see what happens when winter swings around.

shoein 12-07-2011 03:53 AM

Any updates? Sounds like a fun project.

jesusgatos 12-07-2011 08:38 AM

Sadly, no. Have sold most of my bikes, and this was the one that I was keeping to travel with, but I've got my hands full with other projects (motorhome, mini-motorhome, XR600/650L scramblers, etc.). So I bought a 2010 450XCW to ride for now, and with the new Freeride 350 being announced, am not sure if/when I'll get around to finishing this bike. Kind of a shame, because it wouldn't take much. Guess I would consider selling it at this point if anybody wants to finish it? Send me a PM if interested.

Times are GMT -7.   It's 06:17 PM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015