CR steering stem specifications(pics)

[kawamatt2]

Ok guys, add one more to the list of riders attempting the USD fork swap to an XR frame. Quite a bit of research here on TT and ebay hunting brought me a pretty good deal on a set of forks, triples, and stem from a 00' CR 250.

There are a few different options for adapting CR style forks to an XR. Bushings for upper and lower CR triples can be made to allow use of the stock XR stem. Specialty bearings can also be purchased to allow use of the stock CR stem in the XR neck. And finally what seems to be the most common; modification of the stock CR stem to allow use of XR sized bearings.

I obviously chose to pursue the third option for a few reasons, the most prominent of which is serviceability. I wanted to keep as many wear items at possible as stock parts. This has two advantages; availability and price of replacement parts. $45 dollar a pop "specialty" thin section tapered bearings don't sound too appealing especially when being used on a 12 year old dirtbike.

So now we can get to the meat of the issue; modification of the CR stem. I should begin by saying that i am NOT a draftsman. I've taken a few classes on engineering measurements but am far from an expert and probably only mildly proficient reverse modeling components. With that said, the first order of business was comparing an XR stem and bearings to a CR stem and bearings. Shown below.

A little closer look at the XR setup.

And the CR setup.

Now to get out the calipers and model up the stock CR piece. I used a cheaper set of calipers and suspect their tolerance is +/- .01mm. Good enough for gov'ment work though! All dimensions in millimeters.

Now to modify the CR stem to work with the XR bearings while remaining compatible with CR triple trees. There are a few things to say about why i did some things the way i did but most of the thoughts are included in the notes section of the drawing.

With a resized stem we run into the problem of mounting the top triple clamp. The hole is too large for the stem. An insert bushing must be made to resize the hole in the clamp.

Finally what the stem and bushing look like together.

Last one. The difference in how the top triple clamp is located on the stem. The CR is equipped with a chamfer that provides a stop for the tree while the XR's triple appears to be limited only by the threads for the castle nut.

So... would like to hear your opinions on the execution of the stem modification and bushing. I think having these drawings will make it simpler to have the modifications performed as opposed to asking the machinist to completely reverse engineer the part him/herself.

And a final query: Anyone know the thread callout for the two threaded portion of a stock XR steering stem? My drawings show the outside diameter of the threaded portions and i have a cheap plastic pitch gauge that tells me a pitch of 1.0 but i am looking for something more concrete than what i have.

Thanks for your thoughts and opinions.

[JoeBlow Kokomo]

WOW, you da man!

About time somebody put the specs down for posterity.

[Triple B]

Print and take to the machine shop........Thanks kawamatt

Gas for you ?

[Alex 400]

with how many people are starting to do this conversion and how informative this post is, this should become a sticky!?

[YZDOC]

Very good post. By the way, are you an Engineer or just gifted?

[sirr1]

Maybe this will help you visualize what needs to be done to the CR stem.

Stem A is the XR4 stem. Stem B are 2 CR250 machined stems to fit the XR4.

If you machine the CR stem there will be a gap between the ID of the top triple's hole and the OD of the CR stem.

Emig racing sell a bushing that eliminates the gap for 30 bucks, I cut a SS hose clamp and wrapped it around the stem and it works fine.

Somewhere here are pics of my fix under a USD post.

pm me if you need more info!

SIRR1

[kawamatt2]

Thanks fellas!

Engineer in training.?

sirr1, do you know specifically what the threaded portions of the XR stem are? If i could just get get the call-out for those the drawing would pretty much be complete. I am sure any competent machinist could tell me but i'd like to have all the info right there when i take it in. ?

[sirr1]

Thanks fellas!

Engineer in training.?

sirr1, do you know specifically what the threaded portions of the XR stem are? If i could just get get the call-out for those the drawing would pretty much be complete. I am sure any competent machinist could tell me but i'd like to have all the info right there when i take it in. ?

Sorry I sure don't, it been a year since that job was done!

The machinist asked me when he did the two stems if I wanted a jig made for future production and like a dummy I said no.

I could have retired selling machined CR250 stems to XR ridiers:banghead:

In the begining I had a difficult time finding a shop to turn the stem because of how busy the shops in my area were.

I got lucky because the shop I used had some down time waiting on specs for another job, it still cost $100.00 per stem but worth every cent!

FYI once machined and pressed into the lower triple the CR stem will be shorter than the XR.

I had maybe 1/4-1/2 inch of thread to work with on the top triple to spin the nut on.

I used an Emig top triple and this unit may be thicker than a stock CR top triple so it may not be an issue for you.

And you will need some type of bushing on the top triple between the stem.

Feel free to pm me if you need assisstance.

SIRR1

[Triple B]

Maybe this will help you visualize what needs to be done to the CR stem.

Stem A is the XR4 stem. Stem B are 2 CR250 machined stems to fit the XR4.

If you machine the CR stem there will be a gap between the ID of the top triple's hole and the OD of the CR stem.

Emig racing sell a bushing that eliminates the gap for 30 bucks, I cut a SS hose clamp and wrapped it around the stem and it works fine.

Somewhere here are pics of my fix under a USD post.

pm me if you need more info!

SIRR1

I would give you gas too but where is your fuel jug?

[sirr1]

I would give you gas too but where is your fuel jug?

TT Administration does not like me any more:cry:

[The Regulator]

Nice job guys! ? Now to find a deal on some CR forks. ?

Gas for you!!

What years CR forks/stem does this apply to?

[kawamatt2]

I would assume all late model (00' and on at least) are going to have a stem larger than the XR so any could be made to work. Its going to require machine work any way you look at it.

Updated one of my drawings. According to a couple of Journeymen at work the XR stem has what is referred to as a "b@stard" thread. I.E. not a standard die size. I guess this is to be expected as the shaft was made to fit the bearings being used and not to conform to common machine sizes. I figure they originally turned these things out a dime a dozen on a CNC lathe that can cut any sort of threads. SO, the major thread size on the XR stem is M23.82 X 1.0 for the upper nut and M25.83 X 1.0 for the lower castle nut. These transfer to 0.9378" and 1.017" respectively in standard units. I have updated the drawing accordingly.

Now to find a shop that accepts small jobs.?

[JoeBlow Kokomo]

So how does this get to be made a sticky? Or is there a 'garage' section here?

[u000533]

Hi everyone, I just completed my third USD conversion over the weekend and have to say it was the easiest yet.

Conversion no:1 was with CR/CRF parts and an emig stem and bush. Probably the best quality conversion but not cheap.

Requires cash and a press.

Conversion no:2 was CR parts and had a custom stem made and pressed in as described in this thread.

Requires a machinist and a press

Conversion no:3 and hopefully the last was CRF450 forks, stem and wheel with the special bearings from Twin Works Factory and I'd recommend this to anyone who wants a conversion done very quick, easily and cheaply and yes the XR brake caliper and bracket bolt straight on.

Requires bearings and some elbow grease.

All that was required was to make or buy some 5mm spacers to lift the bearings, as they're thinner in profile than the stock bearings.

I'm going to write it all up on my website, rockseven.com, this week so that there is a reference for each conversion.

For anyone considering this conversion CRF450 forks are the ones to go for as they're a much better fork than the CR ones.

And for all those wondering why 3 conversions, too many years as an engineer being taught theres always a better option ?

[TWIZLR]

Is the xr400 stem the same size as a xr250? I want to do the swap to usd forks too, but most just list for xr400s. Also, what mods do you make to the rear shock to keep up with that front end?

[fasterfaster]

Is the xr400 stem the same size as a xr250? I want to do the swap to usd forks too, but most just list for xr400s. Also, what mods do you make to the rear shock to keep up with that front end?

Get your shock valved and sprung for your weight.

[JoeBlow Kokomo]

Is the xr400 stem the same size as a xr250? I want to do the swap to usd forks too, but most just list for xr400s. Also, what mods do you make to the rear shock to keep up with that front end?

Unless you're going to motocross your xr you need to get USD's revalved as they are setup for things like huge jumps with sharp edged landings. Will be very harsh for trail riding.

So you send BOTH ends off to a tuner.

The biggest expense of this mod is having them tuned, not buying and installing the forks.

$600-700 from most places for both ends. ?

(plus shipping)

[JoeBlow Kokomo]

Hi everyone, I just completed my third USD conversion over the weekend and have to say it was the easiest yet.

Conversion no:1 was with CR/CRF parts and an emig stem and bush. Probably the best quality conversion but not cheap.

Requires cash and a press.

Conversion no:2 was CR parts and had a custom stem made and pressed in as described in this thread.

Requires a machinist and a press

Conversion no:3 and hopefully the last was CRF450 forks, stem and wheel with the special bearings from Twin Works Factory and I'd recommend this to anyone who wants a conversion done very quick, easily and cheaply and yes the XR brake caliper and bracket bolt straight on.

Requires bearings and some elbow grease.

All that was required was to make or buy some 5mm spacers to lift the bearings, as they're thinner in profile than the stock bearings.

I'm going to write it all up on my website, rockseven.com, this week so that there is a reference for each conversion.

For anyone considering this conversion CRF450 forks are the ones to go for as they're a much better fork than the CR ones.

And for all those wondering why 3 conversions, too many years as an engineer being taught theres always a better option ?

I was going to use this method but the CR and XR stems are different lengths.

[u000533]

TWIZLR - Is the xr400 stem the same size as a xr250?

Allballs http://www.goallballs.com list them as using the same head bearings, so it should be possible.

MindBlower - I was going to use this method but the CR and XR stems are different lengths.

The longer stem is accommodates the thicker CR or CRF top yoke, if you try to use the XR stem with the CR/CRF top yoke you'll get this

regards

Mike.

[XR_RON]

TT Administration does not like me any more:cry:

I wouldnt say that!