Jump to content

XR400 USD Fork Conversion Complete

Recommended Posts

Some back story of drawing up the new stem can be found here. CR Steering Stem Specs

Some of these pictures are repeated.

Add one more to the list of those who have converted to CR style inverted forks. This will be a long one so grab the popcorn.

So i started out like all the rest; wanted an upgraded front suspension system both for the later model equipment and the improved performance inverted forks can deliver. Began by hunting ebay for a set of forks from a late model CR. It would have been a plus to get the triples as well but i was willing to take whatever i could get. The first stroke of luck was finding a nearly complete front end from an 00'-01' CR 250 for a pretty reasonable price (~$250). In one swoop i got the forks, upper and lower triples, steering stem, bearings, nuts, and front axle. So the only other thing i needed was a front wheel assembly. Figured i would worry about those details later. I get the forks and associated hardware and, as expected, the seals were shot. They leaked oil in the package!🙂 Another detail to worry about later.

Now the task was getting these fancy forks on the old primitive XR. I was aware of the options already available from Emig Racing and special sized bearings. I abstained from them because one, i wanted the personal challenge of designing my own part and two, i wished to keep all stock wear items. These ideals left with me the responsibility of studying, comparing, and drawing a new part based on the measurements i could glean from both the stock XR parts and the stock CR parts. We began by disassembling the XR and CR to bare triples and stems.


Obviously there are considerable differences. Mainly, the CR uses larger neck bearings. There is no possible way to reuse stock CR bearings as they will simply not fit into the neck of the XR. On the same token XR bearings will not work as shown because they will not fit on the CR stem. Nor will the XR stem work with the CR triples as pictured. Its diameter is too small.


What to do? Make a hybrid with both shafts! A few hours of caliper and computer work later netted a design that i was pretty sure would work to fit the CR triples to the XR frame. The route chosen was to use a stem that would press into the CR lower triple yet still allow the use of stock XR stem bearings. Additionally a bushing would need to be made to allow the top CR triple to fit the new stem. I'll spare you the different design issues that had to be taken into consideration and just post my initial drawing. Keep in mind that this was the initial design and there have since been some revisions. In other words DON'T TAKE THIS ONE TO YOUR MACHINIST!



So now it was time to see about having this part made. That was the biggest pain in the butt of all. I ventured to cnczone.com to hunting for a smallish one-off type shop that wouldn't be afraid of working with a relative newbie to machining. As you can see Here i ran into some pretty critical individuals. The good came with the bad though and i got 3 or 4 PM's inquiring about quoting this job. I eventually settled on a shop called Axis Machine located in Butler Pennsylvania. The machinist in charge there is Jim Wobb. He was very understanding of my desires and design intent and was willing to work with me in whatever way possible to get this part made. I will not reveal what his quote was out of respect for his business interests, but safe to say that it was VERY reasonable and in the end it proof enough as i chose this was instead of the Emig setup. For future reference his email is axismachine@zoominternet.net. He is very helpful and had no qualms with answering all my little nagging questions. If you pursue the same method i did i would encourage anyone to contact him. He has my drawing and my full permission to use it as he sees fit.

With all that said here are copies of the drawings i sent to jim. Sorry for the mega link but i know no other way to host these .pdfs.

CR Stem Conversion

Elapse a few days (did i mention he was fast!) and i had my part. Here is the new stem layed next to the stock XR and CR.


And a close up of the threads and bushing. Is a nice fit.


So now for some small details. Removing the stock CR stops courtesy of an old school machinist at work.


Went ahead and rebuilt the forks with new seals and oil while i was waiting for the stem.


It was time to break down and get all this stuff off the workbench and get this bike back on the road(trail really). Step 1: Install bushing to top triple. I froze these in the ice box overnight to shrink them slightly. Hoped to ease installation somewhat.



Fits well.


Now to press the new stem into the CR lower triple. Froze this one also.




It was a tight fit. Good.

Hammer bearing on. Funny thing here. If you'll notice i forgot the lower bearing seal. :hammer: Oh well, next time i guess.


Now its just time to put it all together.




Funny thing here. I bought a complete front wheel from a guy on thumpertalk. If i recall correctly it was was an 04' CRF250. I guess there have been some changes through the years because the later model front axle was considerable shorter in length. No problem there as the forks came with an axle. The problem was the wheel spacers were not nearly wide enough. It must be that the smaller bore bikes have closer spaced forks or axle mounting points. In the end i just made a little spacer out of some 3/4" water pipe from Lowes. It turns out that its a nice fit over the axle.


*Continued in next post.

Link to comment
Share on other sites

Getting close.


And we are done!



I think it looks pretty darn good and i can definitely tell a positive difference just riding around the neighborhood. My stem worked perfectly and everything went together well.

I would recommend again to contact the above mentioned machinist if you are attempting this swap. He did an outstanding job for me.

Thanks for looking!

Link to comment
Share on other sites

It looks good and I am so darn tempted to go inverted on my 650L, I just don't want to lose my steering lock,and I have so darn many other considerations with headlight signals, etc. I just like the inverteds a lot.

Link to comment
Share on other sites

Very Nice Job Indeed!

But I have to nit pick here just a little, I noticed that you did not incorporate the clip on the new stem?

I am sure the stem won't come out of the lower tripple, I hope....

Clip? I did not know that there was a clip on the stock setup. I assume it is supposed to be some sort of circlip or c-clip to keep the stem from backing out of the lower stem? That is a good point but i am must've either misplaced it or never saw it.

I would hope it never comes apart. That sucker was TIGHT. I was worried i was going to bend something pressing it in. In the end though, unless the threads on the spanner nut let go the stem will not part from the bike.

Also wanted to add that your bike is a big inspiration to me. As you can see i have a long way to go to street ready but i'm leaning heavily on yours for ideas. 👍

Link to comment
Share on other sites

Very Nice Work. I did my USD conversion much the same way, except I used the XR Stem and machined some bushings, much like you did on your top triple, for both ends. I have a 90 XR250R, which has a shorter stem, making it so the Emig approach not feasible. I measured and drew my stem and the proposed bushings up in Autodesk Inventor, making it easy to converse with my machinist riding buddy when we were discussing how to make and fit these parts together. I've had mine for almost a year, including one major wreck in an enduro where I broke a bar clamp bolt, and the stem/triple clamp combo is no worse for wear. (I needed new rubber cones and new bar mounts though.)

I disagree with sirr1. The stem can't come out anyway. The spanner nut pre loads both bearings, (pulling them together), and the top nut sandwiches the whole thing together. Combine that with a healthly dose of shrink fit on the bottom triple/stem interface, and you have a setup that wont budge.

Excellent work with Solidworks! Thanks for writing up such a descriptive and informative thread!!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

  • Create New...