Trials conversions

Discussion in 'Trials' started by plane_ben, Mar 7, 2011.

  1. Twin-shocker

    Twin-shocker Long timer

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    You might find that mounting the footrests so high makes the bike very difficult to ride in competition, as the high position will make the bike feel less than stable, and mean that balance is far from easy.

    I would suggest leaving the swinging arm stock, as reducing the length will mean grip is harder to find, and if the head angle is altered the right amount (to reduce wheelbase by at least 40mm), the shorter swinging arm will make the front end very light.

    Best possible set up motor wise for the old TL250, is conversion to 305cc, which is achieved with a bigger bore, and using the longer stroke crank fitted to XL350. Effectively this is what was used on the TL based works bikes, and provides a big improvement over the trail bike style stock motor.
    #61
  2. LarryDawg

    LarryDawg trials nut

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    but it looks like it will be even heavier then the TL250, I ride one its a tank.....
    Larry
    #62
  3. plane_ben

    plane_ben Adventurer

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    Yea, I was looking at those pegs yesterday. They are going to be dropped a couple inches. Don't know what I was thinking putting them up there.

    As for being a tank, yes, the TL250 was a tank. I rode one back in the day all the way to the expert class. I could hang with my 305cc mod and some other geometry improvements of the day. But it wasn't until I switched rides to a Yamaha TY250, that I started winning in my class again. Now at my age and class I would be riding, I could use one of my Yamaha XS650s in the sections. It's just all about the project for me and If I can use it on the trails and in a trials occasionally, I'll be happy.

    I remember doing 305 kits on my XL and TL 250's. They were new sleeve and piston kits. Haven't heard of using the 350 crank. Is it a straight swap using a 350 cam chain and cylinder spacer for the longer stroke? Or do you have to use a piston with higher wrist pin location? Powroll does a stroked crank then shrinks the con rod. But they are pricey. I want to do the 280cc piston at the least and would like to stroke too. If this 350 crank would work, I'll start combing e-bay ASAP.:D
    #63
  4. supermotosean

    supermotosean Been here awhile

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    Finished up the steering stem angle mod. Came out straight as an arrow.:wink:

    [​IMG]


    Apologies ahead of time if this is a repetitive question that I have miserably failed to search, here goes:

    I've noticed the cut/re-weld modification done to several older/noncompetitive/non-trials trials bikes in an effort to tuck in the front end, tightening(reducing?) the rake and gaining quicker turning and better "nimbleness" (I hope I didn't just make that up!?!). Noticing this and browsing through this thread has made me wonder: If someone wanted to quicken the steering on an older motocross/trail bike (for quasi-trials purposes), and said bike has a leading axle type front fork, could you swap the left and right tubes/sliders moving the axle behind the fork and get similar results? I do realize that this would be affecting the trail instead of the rake but I'm no engineer and am having trouble thinking of any nasty side effects other than keeping an eye out on front tire to head pipe/frame clearance. Just some food for my random thoughts and I'm looking forward to reading some opinions (or even better, some experience!) be it good, bad or otherwise....:ear
    #64
  5. plane_ben

    plane_ben Adventurer

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    In response to your question, a leading axle actually decreases trail making for quicker/lighter steering. Turning the leading axle backwards would result in negative trail that would be almost impossible to ride. Imagine a shopping cart wheel on the front of your motorcycle.

    My reasons for cutting the neck and de-raking was two fold. #1 was a shorter wheel base handy for tight turns in trials. #2 is making the steering quicker.
    #65
  6. supermotosean

    supermotosean Been here awhile

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    Got it..:clap

    For some reason I watch everyone on their hacks putting leading links on and moving the axle forward to reduce the trail helping with steering leverage and for some silly reason I thought going the other way would do the same on a two wheeler.


    I probably shouldn't have admitted that out loud:lol3 Thanks for the response!:D
    #66
  7. Twin-shocker

    Twin-shocker Long timer

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    The 350 crank is what was used on the 305cc works bikes, and yes a cylinder spacer is needed. The 350 wrist pin size is larger than the 250, so you would need to get a bush made if you choose to use a 250 piston.
    #67
  8. plane_ben

    plane_ben Adventurer

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    Wow. Can't believe it has been 8 months since my last post. Finishing up school and getting a job in December, plus being out of town for said job accounts for some lack of posting. I have acquired an XL350 crank and flywheel for the engine going into this bike. It's not going to be a drop in fit though. I will need to machine the case for the bigger diameter main bearings. I thought I would be able to just swap out the 250 crank bearings, but they will be the wrong size inside diameter. There is plenty of meat in the case to make it work. The only interference will be cutting into the top end oil feed galley. But as a steel shaft that feeds oil from the oil pump fits in that galley, I have room to grind it down so it will rest right on the outside of the bearing race. I will post up some pictures tomorrow of what I'm trying to explain. More to come.....I promise.:wink:
    #68
  9. lineaway

    lineaway Long timer

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    Interesting project. Sounds like you have been way too busy for a spring chicken.:rofl Will be glad to see the pics!:clap
    #69
  10. plane_ben

    plane_ben Adventurer

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    ^^^Thanks for the interest. Hopefully this project will move along a little faster.:1drink

    Here are the pictures I took for the engine crank swap.

    First pic is the 250 crank and the biggest bearing. It is a roller bearing with inner and outer races. It is impossible to get the inner races off without destroying the crank.

    [​IMG]

    Second pic is the 350 crank and one of the main roller bearings. They are the same size both sides, so I can machine the case to fit with one setup on my mill.

    [​IMG]

    Next are pictures of the cases each side and looking into the bottom case. You will notice that one dowel alignment hole is off center, so I'll have to re-drill one hole for center as both 350 main bearings are center pinned. Should be easy peasy.

    [​IMG]

    [​IMG]

    [​IMG]

    On the second pic of the case, you can see the caliper is right over the lower edge of the top end oil feed. There is a shaft that goes in there and extends to the out side of the clutch cover where it picks up an oil galley from the oil pump cavity. I should be able to just grind that shaft flat enough so that it rests on the outer race of the main bearing.

    This crank will give me a significant stroke and about 305cc all by itself. I'm also looking into a bigger bore as well to get me into the 335cc range.

    More to come as it happens.
    #70
  11. anonny

    anonny What could go wrong?

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    That pic is awesome! Your project is looking good, great idea!:lurk

    #71
  12. plane_ben

    plane_ben Adventurer

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    Took the cases to my friends machine shop for machining. I'm out of town until May. More updates to come soon.
    #72
  13. XR200R

    XR200R Homemade

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    Hello,

    When I was younger I put a Honda 160 twin engine in a CL90 frame with a big rear sprocket and wish I still had it.

    Next, I cut down a Yamaha DT360, using a plate seat, gas tank from a Yamaha 80, big rear sprocket, re-raked steering head, cut steering stops, rearset pegs, custom exhaust and shortened swing arm. It would go where the new TY350's were going, but of course I had to work harder to get there.

    My present ride is a stripped Honda XR200R with aluminum plate seat, XR80 gas tank, reraked steering head, shortened swingarm, narrowed frame, rearset footpegs, custom exhaust, cut steering stops, big sprocket and direct-acting monoshock. Yes, it's the twin-carb version (you're laughing). I added a butterfly choke to make starting easy. I strongly recommend starting with the single-carburetor motor if you want to do a conversion, becuse the twin-carb set-up is wide (you're still laughing).

    I can't put Michelins on it because the rear tire is 17" and I like the long suspension travel this bike has.

    It is a good woods bike and tough as a rock.

    Attached Files:

    #73
  14. lineaway

    lineaway Long timer

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    Interesting, I can see a use for it over the stock bike. The rear brake must take awhile to get used to? Thanks for sharing.
    #74
  15. r2wtrials

    r2wtrials Been here awhile

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    A guy that we meet whilst out practicing has this in a constant state of change ... never exactly the same when you see it next as if he wants something changed he goes home and makes it or welds it etc ... the wheelbase has since been shortened a bit.
    It doesn't so much as ride over things ... just through them!! :)

    [​IMG]
    #75
  16. wb22rules

    wb22rules Bourbon Tester

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    That gas cap looks a tad dangerous lol
    #76
  17. r2wtrials

    r2wtrials Been here awhile

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    That has been re-designed already :) ... i rode the bike the other day, a bit scary !!
    #77
  18. BEEF706

    BEEF706 King of the dumb dab

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    Is that a CRF 450 motor???????? :eek1
    #78
  19. 19673ontree

    19673ontree Adventurer

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    Here is a cool looking xl tl ? 250 :rofl

    [​IMG]
    #79
  20. r2wtrials

    r2wtrials Been here awhile

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    CRF250 i believe ... if he is out with us tomorrow i will try and get more info and images!
    #80