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Thread: Crazy inverted tricks on a ATCR250R!

  1. #1
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    Crazy inverted tricks on a ATCR250R!

    Well the time has come for me to get inverted (forks, that is) as well. I've been wanting to do this since the CR's broke onto the scene with inverted forks back in 1990. I started getting serious about this project a little over a year ago. I measured several of the 250cc motocrosser's forks & quickly ruled them out because they were a tad too long. While I was at a Honda dealer, I measured a CR85's forks and quickly realized that they were the perfect length, but their 37mm diameter was a step down from my 250R's standard 39mm forks. I happened across a "Mini Rider" magazine that had a 85cc shootout, and that was when I saw the perfect set of forks, the KTM 85SX's. They're the perfect length once again, but their 43mm diameter is a step up compared to my stockers. I set up my eBay account to notify me of any 85SX forks for sale and then kept this new found "fork knowledge" to myself, as I didn't want any additional competition when it would come time to start the bidding. Well, I've never seen any of those forks on eBay yet, but all of the other 85's (KX, RM, YZ, & CR) come & go all the time. Then Billy (Honda ATC) let the cat out of the bag with his "Inverted fork ramblings" thread. He now posessed the same inverted fork knowledge that I did! He quickly acquired a set through the KTM Talk classifieds, and now his Z is "Rolling on inverts", as his thread was titled. I followed his lead and acquired a set the same way just after Christmas of last year. I finally got to start the conversion process a few weeks ago, and here's the progress so far.

    Pic#1 shows the forks as they arrived, in a gun case no less.

    Pic#2 compares the stock, standard fork to one of the USD's. The USD (Upside down) fork is shorter in total length than the stock fork, but when measured from the top to the front axle attach point, they're almost identical. As far as weight, each USD fork leg weighs almost a pound less!

    Pics#3 & 4: I've got the spacing set & can start taking measurements for the triple clamps. Luckily, I was able to use the same fork spacing as the stock forks, 10 5/8" on center.

    While Billy made all new triple clamps out of steel & changed the fork rake at the same time, I plan on keeping the fork rake the same while modifying my existing aluminum triple clamps. The only other option is to have completely new triple clamps machined, a la Speedbump and his ATCR250R conversion project.
    Attached Thumbnails Attached Thumbnails 102_0240.JPG   102_0248.JPG   102_0245.JPG   102_0247.JPG  
    Last edited by Red Rider; 04-20-2006 at 12:04 AM.
    Red Rider's Sand Machine Updated 07/23/14

  2. #2
    Billy Golightly's Avatar
    Billy Golightly is offline Always finding new and exciting ways to not give a hoot in hell Catch me if you can
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    Welcome to the club!

    That is something else that you were thinking about the KTM forks before and around the same time as me. Looks like it wasnt such a bad idea afterall if we both came up with it on our own

    I remember you asking me in the one thread what the weight difference was, I was pretty sure they were lighter but I'm glad you ended up weighing them. Thats a considerible difference considering their bigger and stronger in every way.

    Whats your theory on the tripples? Cut off the existing 250R fork mounting holes and weld on new ones that fit the KTM forks? I had considered that before I started making mine. Interested in seeing how it turns out. Keep us updated

  3. #3
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    Sweet RR! I remember seeing an ATC250R at the dunes a few years ago with CR80 forks on it. It sure looked good and the owner said they were light years ahead of the stockers.
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  4. #4
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    Quote Originally Posted by HondaATC
    Welcome to the club!
    Thanks Billy, although I won't actually be a card carrying club member until it's rideable.

    Quote Originally Posted by HondaATC
    Whats your theory on the tripples? Cut off the existing 250R fork mounting holes and weld on new ones that fit the KTM forks?
    Exactly. I only got the forks. No axle, fork guards, triple clamps, or front brake came with them. Even if the triple clamps did come with them, I wouldn't have used them, as they're pretty puny. I had some 49 & 53mm holes milled in a block 1 1/2" thick aluminum that I'll cut up & have welded onto my triple clamps.
    Attached Thumbnails Attached Thumbnails 102_0241.JPG  
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  5. #5
    Billy Golightly's Avatar
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    What kept me from doing it like that was the fact that in order to cut the stock clamps, and weld the new ones on there was going to have to be a heck of a lot of beveling and angle cutting to make enough room for the weld to penetrate and stack up. I didn't have any real way to do that since I dont have a vertical band saw. If you can pull it off this way though you'll sure have saved yourself alot of head ache. I'm getting ready to start on my second set in aluminum. Just bought the 3/8 6061 last night

    I was going to ask you about the brake. Any ideas on that yet? The stock 85SX caliper is useless, way to small for anything but a mountain bike.

    Also, FYI KTM105SX front forks are exactly the same as the 85s. KTM 200MXC front forks are the same diameter but are longer. Seals, ect are the same. Dont know about the internals. Just a little tidbit incase you decide to make another set or someone else does

    If you have trouble finding a set of springs try finding some for the 200MXC. When I got mine from Moto Pro I only had a few hours to put them in or I wasnt riding. The springs because they were a larger diameter winding made the ID of the springs smaller. Cant increase the OD of them or it wouldn't fit in the tubes, so they wound inward and it caused some problems. Thats where the fork bladder rides at and sadly the springs wouldn't even fit over it. I had to grind it down for the fork to make it over it and not drag. I also trimmed some off of the end of each spring and them fit the length as they were off of a fullsize. They ended up being plenty stiff even without any revalving.

  6. #6
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    Congrads...RedRider...

    That R of yours has been begging for inverts!!

    Love your 1989 R...always have!! Please show us tons of pics!!

    SEND ME PM HERE - CLICK HERE

    1986 ATC 250r, 1986 Tri Z, 1990 LT 500R "Quadzilla"


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  7. #7
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    Quote Originally Posted by HondaATC
    I remember you asking me in the one thread what the weight difference was, I was pretty sure they were lighter but I'm glad you ended up weighing them. Thats a considerible difference considering their bigger and stronger in every way.
    Whenever I change or modify something on my bike, I always try and weigh the before & after product. If I'm gonna change it, it better be lighter when I'm done! It's been pretty easy making things lighter, since most of the stuff that I changed was originally steel, and now it's aluminum, but I was worried that the inverted forks would be heavier, so I was pretty happy when they wound up weighing less.

    Quote Originally Posted by HondaATC
    I was going to ask you about the brake. Any ideas on that yet? The stock 85SX caliper is useless, way to small for anything but a mountain bike.
    Actually, my stock caliper matches right up with the mounting holes on the forks. The pads are nowhere near the disc, but it bolts right up! Obviously, I'll have to sort that out later. I am hoping to use the stock caliper and just change the mounting bracket, but first I need to get the forks mounted up.

    Darius, I know what you mean about the bike screaming for inverts. I'm going to miss the red fork boots though. Do you think I should retain the fork boots, and just slide them down to the bottom?
    Red Rider's Sand Machine Updated 07/23/14

  8. #8
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    It's about time you broke this news Red. My lip is raw from chewing on it to keep the big secret ever since I found out that you were doing this. Hurry up and get it done so I can see/try/ride the final product. Then I'll find some new legs for my R and you can start building another set, only better, and without the bugs.

    Thanks for the news on the other KTMs Billy. Knowing this will help me to find a set of USD's much easier.
    Current Ride (Purchased new in Oct. 84) - 1985 Honda ATC 250R w/ ESR 310cc big bore kit
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    got sand?

  9. #9
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    Quote Originally Posted by Red Rider
    ...Do you think I should retain the fork boots, and just slide them down to the bottom?
    Stretch 'em out over the upper portion! So they look normal.


    Those KTM 85SX forks look like just about the perfect USD 3-wheeler fork. I bet they would improve the 84 or 85 KXT250 immensly. Tecate's are leading-axle anyway. BigGreenMachine, oughta grab some and slap on your 85!

    This has got me day-dreaming of resurrecting my 84 KXT with a set of those forks up front. Sadly, about all I have left of it is the frame and an 85 front wheel assembly.

    More than enough to start a restoration!
    Last edited by Jeb; 04-20-2006 at 05:03 PM.
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  10. #10
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    Jeb, could you post some more pictures of your "big three" Tecate, Tri-z, 250r

    Ive got the rarest of the three, and one day I'd like to have the other two.

    I Needs some motivational snaps

    Cheers
    My toys 85 KXT250A2, 85 ATC250R, 85 Tri-z 250, 06 LT-R450, 04 YFZ450S, 07 125 typhoon x 3, 06 FPV GT.

  11. #11
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    Quote Originally Posted by OZQUAD44
    Jeb, could you post some more pictures of your "big three" Tecate, Tri-z, 250r

    Ive got the rarest of the three, and one day I'd like to have the other two.

    I Needs some motivational snaps

    Cheers

    Hi OZQUAD! Maybe this evening I can get some up.

    Thanks!
    1986 Tecate
    1984 Tecate
    1985 Tri-Z
    1986 ATC350X
    1985 ATC250R (2)
    1985 ATC125M (2)
    1982 ATC70 - Original Owner

    175 TriMoto Frame with Pro-Tec Rear Suspension

    3-Wheelin' since '82

  12. #12
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    Very nice mod to any trike these days as the conventional forks are dated in design.

    Jeb, would love to put some USD's on my fat tired machine but the cash flow won't allow.

    James

  13. #13
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    Well, I made a little more progress my last few days off. I've been building a jig that will hold everything nice & straight (I hope) while the ends are welded back onto the triple clamps. It was going along smoothly, and as always, I ran into a setback (read as: I made a mistake!) that really slowed me down and required redoing some work that was already done.

    The pics show the almost completed jig with the forks in place. I'm going to have only one side welded up at a time. That's why one of the original forks is mounted up in the jig alongside the USD fork. This will help hold the triple clamps straight, while the jig holds the forks straight & parallel. Once the one side is welded, I'll reset the fork guides on the jig to accept the other USD fork, and then have that side welded as well. In the final pic, you can clearly see that I'm passed the point of no return with the triple clamps, as I've already cut the ends off of the left side. That was scary.

    The jig is made out of 3/4" partical board, and is reinforced on the backside with 1/4" thick 2" x 2" angle steel. All of the forks guides are made out of the same angle steel. It's all very stout & should work as planned. Before anybody asks, gravity & a tight fit is holding the forks in place right now, but they will be clamped to the jig as well, when welded.

    Billy, thanks for the additional spring & miscellaneous info. Also, you mentioned that you'd purchased some 3/8" thick aluminum for a set of aluminum triple clamps. Are you going to make those the same way that you did the original steel ones?

    Sandman, thanks for keeping the news under your hat. I hope your lip heals soon.
    Attached Thumbnails Attached Thumbnails 102_0249.JPG   102_0250.JPG   102_0251.JPG  
    Last edited by Red Rider; 04-24-2006 at 01:57 AM.
    Red Rider's Sand Machine Updated 07/23/14

  14. #14
    Billy Golightly's Avatar
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    Jig is looking good so far! Just becareful that when it goes to weld that you dont burn a hole in the wood Been there done that. Do you have the KTM clamps where your going to cut those ends off, or are you making all new pieces to weld on? Hows your front fender gonna fit using the original mounts? Mine is kind of a tight fit because the notches in the fender for the forks/fork boots werent big enough for the KTM forks. I kind of had to mount it at a funny angle for it to fit in there.

    On my aluminum ones, Yup, pretty much. Going to keep a 3/8 thickness on most everything. The problem I'm having right now is locating a good source of the rubber handlebar clamp antivibe pieces. I need to have those so that I can have Ronnie (Yamahondaman) turn out some of the weld in pieces that they (the dampners) will sit in on a CNC lathe, that way the taper is perfect and the handlebars wont have any slack. Thats the main problem with my steelies right now. We used a custom made tapered drill bit and it didn't come out to good.

    I think I'm seeing things, but have the bar mounts on your top tripple been cut off and re-welded closer together and solid? Just looking at the underside of it in the one picture it looks like there was a place where the antivibe rubbers and stuff would have sat but its like a round welded up circle now? I cant remember if the 250R clamps were a solid mount or not originally, Must be going crazy.
    Last edited by Billy Golightly; 04-24-2006 at 03:32 PM.

  15. #15
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    Quote Originally Posted by HondaATC
    I think I'm seeing things, but have the bar mounts on your top tripple been cut off and re-welded closer together and solid? Just looking at the underside of it in the one picture it looks like there was a place where the antivibe rubbers and stuff would have sat but its like a round welded up circle now? I cant remember if the 250R clamps were a solid mount or not originally, Must be going crazy.
    Good eye there Billy! Yes, the 250R has solid-mount handlebar clamps, and mine are still solid-mounted, but they are closer together as you thought. You're not going crazy, yet. A few years ago, I decided to switch over to some Magura X-Line bulge bars, and I didn't want to use those fatbar adapter clamps that bolt onto the original handlebar clamps, so I cut off the old clamps & had some billet fatbar clamps welded on. The original clamp spacing was too wide for the fatbars, so I had to move them closer together, which opened up a hole on each side of the handlebar clamps.

    The fender, like the front brake, will have to wait until the triple clamps are done, but now that you've asked, I'm curious also. Thanks for the fire warning. I'll be sure and keep a fire extinguisher handy while they're being welded. As Fire Marshall Bill used to say, "Everybody remain calm! I am a fire marshall!"
    Last edited by Red Rider; 04-24-2006 at 02:19 PM.
    Red Rider's Sand Machine Updated 07/23/14

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