The s/trx250b9sf3 build thread

Discussion in 'Some Assembly Required' started by TedT, Dec 31, 2011.

  1. TedT

    TedT Adventurer

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    Well I've been meaning to get a thread going on this bike for awhile now. Some of the local inmates have seen the progress, slow as it is, and I figure it's time to let the project be seen by the interwebs at large.

    First of all, what it is. The frame started life out as a yamaha srx 250 that was bought locally by someone who over the years beat it with what appears to be several large hammers until I got it a few years back. Now the stock motor ran, but poorly, and the electric starter had been removed and replaced with a piece of cardboard, if this tells you anything about the state of the bike. The clip-ons were bent, the tank had been caved in several times and generally the bike looked to be on its last legs.

    Enter my father and I. We had a couple of old racing motors from my superkart days in the basement: A '95 CR 250, and this '85 ATC250R (which is identical to the TRX250R engine). We went with the ATC motor, because the CR vibrates to kingdom come and it lacks a sixth gear and lighting coil.

    Now you can see where we're going with this. Out with the old 250, in with something a little (or a lot) faster. While I'm at it, why not update the suspension out of the Regan era and make it handle and stop a little better? Enter the Buell xb9s suspension and wheel setup. Why? Well the ZTL brake setup looks cool, and it was available. Plus, why not?

    The rear swingarm has been an issue, one which I hope to solve with the use of a swingarm off of a CBR 600F3. Why the CBR? It has a chain drive, drives off the correct side, it's cheap, and they're plentiful. The stock Buell swingarm would have worked, but for the fact that it's a belt drive that drives off the right. So the first order of business is to get this swingarm on the frame and figure out the shock and rear axle/pivot bolt. Once I have parts in hand I'll know if I'm going to be making linkage setups or not. Then the back tire, motor mount, radiator mount, get the old DA system set up and running (I'm going to need to see what this motor is doing, it's a fully-built motor and I'm going from scratch on jetting/gearing), then wire in the lights, and it's done. Sounds simple, right?

    The goal for this whole bike is to weigh as little as possible (I'm shooting for 250lbs as a target), handle well, and basically just be a little fun bike to ride around on.

    I'll have pics up soon, once I find my camera and take a few of them.
    #1
  2. TerraRoot

    TerraRoot Adventurer

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    well you had a day where are those pics? in my imagination this project sounds awesome.
    #2
  3. ben2go

    ben2go Moto Flunky

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    I iz waitin patiently.I swearz.:augie
    #3
  4. jake28

    jake28 Riding to the horizon.

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    Subscribed. Do great things.
    #4
  5. TedT

    TedT Adventurer

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    Got the camera and a few pics! Now my computer is making ominous noises. Let me see if I can get on another compy to upload them.
    #5
  6. Daamud

    Daamud Life is like a box of Old Milwaukee

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    :lurk:lurk
    #6
  7. TedT

    TedT Adventurer

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    Okay so I'm going to give this a shot here to see what happens. Hopefully my computer stays running long enough!

    This first shot is of the frame in the jig. It's an engine hoist, but it does the trick well and makes welding this frame up much easier. I've so far stuck to just reinforcing/finishing the welds that are currently on the frame, since I'm putting a lot more power in there I figure that I might need to also do some additional bracing to deal with it.

    [​IMG]

    Here's a close-up of the work I've done so far:

    [​IMG]

    Here are the footpeg mounts, lots of hours of hand-sanding and blasting later, they're looking good! I can't believe Yamaha would let a bracket like this go with such poor quality.

    [​IMG]

    The tank. Previously filled in with so much bondo that paint would not adhere to it, and yes those are some serious holes in the bottom of it. The metal is too thin for welding, at least with a MIG setup. Might have to teach myself how to TIG or ??? to get this thing back into shape, since finding these tanks is next to impossible anymore.

    [​IMG]

    So that's where I am as of right now. Going to go do some more work on the frame and hope that the swingarm arrives tomorrow so I can get that on and start work on the motor mounts.
    #7
  8. TedT

    TedT Adventurer

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    Well I did a few more things here, only got a pic of the potential frame brace. I'm thinking that this will allow easy access to the motor, yet still stiffen the frame.

    [​IMG]

    Now that's the main bar, or a scrap alternative for now, held up by a really long magnet. I'd also tie it in trellis-style to the bar just above it.

    I also knocked a very large pile of rust out of the tank, and judging by the sounds in the tank, there is a lot more to take out. I'm starting to think that I better hope for an Ebay miracle.

    Okay, enough of me. Time to leave the shop and head home.
    #8
  9. DRjoe

    DRjoe Long timer

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    When you say you have finished the welds have you welded the gussets across the tubes?

    I'm using my Phone so I can't see in the photos.
    #9
  10. TedT

    TedT Adventurer

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    Yeah, basically all I've done so far is to finish the welds across the tubes that were not done from the factory. I haven't started in on any major bracing or fixing the broken mount on the frame just yet because I'm still waiting on the swingarm to do the final engine placement. The way I saw it, a fully welded tube would give me a little more strength than one that was only welded enough to keep it from breaking off entirely.
    #10
  11. SwedeMix

    SwedeMix Adventurer

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    ["Why? Well the ZTL brake setup looks cool, and it was available. Plus, why not?"]

    That´s well put, I have nothing but respect for that kind of thinking! It´s your bike, a kind of a master of your own destiny type deal, and I applaud whatever type of bike´s being handbuilt :clap
    I´ve had my fair share of failed projects, finally coming to terms with not being capable (on my own at least) to pull off one of these huge builds. Therefore, I have even more respect for those who actually do, and make it look good too!

    Good luck, keep the focus and dont forget why you started the build in the first place! (personal experience..)

    Cheers :1drink
    #11
  12. jake28

    jake28 Riding to the horizon.

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    I'm a huge fan of these projects and have a few in the garage right now. I'm no engineer, but I can't see what that length of flat bar is going to add to the frame. The frame doesn't flex across the span that you have filled. And it is heinously ugly which I would forgive if there weren't few great street builds out there.

    I think you would be better off in performance and looks gusseting the frame at the steering head and pivot points. Adding flat bar across the frame just because you can isn't the answer.

    Post a copy of the photo in this thread for some real expert insight.

    Still a huge fan and looking forward to following this.

    jake
    #12
  13. DRjoe

    DRjoe Long timer

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    Oh
    Um as far as I know the factory do that on purpose to stop cracking.
    From my very limited knowledge on the subject I think what you have done is focused all the stress in to one point by welding across the tube which can lead to cracking across the tube.

    There is a great thread on here called "some advice required" that you could ask about frame reinforcing, Your garuanteed to get a better explanation from there.


    #13
  14. TedT

    TedT Adventurer

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    Thanks for the comments and advice so far, guys! As far as the brace situation, I'm not using that piece I put up there. I'm just attempting to get an idea of what will work where. I'm definitely going to be seeking out advice here, please do keep it coming. This is definitely new ground for me, things I haven't touched on in any aspect since my karting days. Most of my other builds have been relatively tame in comparison, but this time I figure it's time to go big.

    The issue I'm trying to combat now rather than after I have the bike together is to eliminate the torque flex (the side-to-side rotational flex) that this motor upgrade will probably bring. The mounting system is going to take up a lot of it, but I'm trying to see if I can stiffen it up more. I'd hate to build it only to find out that I can't enjoy it like I want to be able to!

    The steering head is well- braced stock, I'll get a photo of it here in a minute and upload it.

    No swingarm yet today. Good time to get involved in some chassis theory though, and get to work on getting a new steering stem made for the Buell front end.
    #14
  15. garrett the nerd

    garrett the nerd Sprocket Protector

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    Hey buddy. In for the duration. I'll stop by the shop soon to offer some thoughtful nods and affirmations without actually knowing anything :rofl
    #15
  16. TedT

    TedT Adventurer

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    Thanks Garrett! And yes, I was a little hasty in my welding. Lesson learned! Next time I think twice, weld once rather than now figuring out how to fix what I did here. I've got to get on the compy at home to upload the steering stem pics, this computer keeps making hard drive death sounds. Onwards!
    #16
  17. Throbbing Missile

    Throbbing Missile Stuck in a rut

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    I've recently been doing some frame work where I've had to remake some gussets of that style. I did some research and found out that, as has been mentioned, welding across the frame creates stress concentrations at the point. The problem with not welding is that water can get in through the gaps and rot from the inside out.

    [​IMG]

    My replacements in progress:
    [​IMG]

    I haven't welded the ends of these but will incorporate filler plugs through which Waxoil can be sprayed once the frame has been painted.

    Full details are on this blog post: http://www.throbbingmissile.com/2012/01/gussets-and-other-innuendo.html

    There is also a link to Tony Foale's book, Motorcycle Handling and Chassis Design on my blog. It's quite an expensive book but covers in huge depth all the elements that you're looking to work with on your SRX frame, I can't recommend it highly enough.
    #17
  18. TedT

    TedT Adventurer

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    Thanks for the link and the info! I was actually going to touch on that subject myself on this frame. Some of the exposed tube ends actually had started to rust on the inside of the frame. Now, it's not a gusset joint, so I'm thinking to close it off especially since it's towards the tail of the frame and could see some road debris getting in there. But after having ground down my prior attempts, I was thinking along the lines of what you just said to keep the tubes solid. I'm going to have to see if I have a copy of Tony Foale's book here. I saw some of the work he did on his website and it's given me a few ideas as to where to go next on the frame.

    In other news, the swingarm is here! Going to take a little work to make it fit, but it looks like it should take the stress of the swap a lot better than the stock swingarm. Plus it's a little longer, which might not hurt in the grand scheme of things.
    #18
  19. TedT

    TedT Adventurer

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    Here's some more pics, first of the steering head bracing:

    [​IMG]

    [​IMG]

    And one of the new swingarm vs. the stock piece. It's red on red for the stock one, sorry if this makes it difficult to see.

    [​IMG]

    More work to follow, but for now I need to sleep.
    #19
  20. fleshpiston

    fleshpiston Been here awhile

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    Hey that frame looks familiar! :1drink

    Cool build....so how much HP will you get out of the new motor?

    Keep an eye on ebay for a tank, they show up every once in a while.
    #20