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verticaltwin
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Date Posted:05/13/2011 12:27 PMCopy HTML

I'm wondering if anyone has tried de-raking an xl350 frame... While I'm monkeying with the 350 motor I need to be setting up a frame for it. My choices are to adapt a Bultaco frame to hold the 350 motor (original plan), but I've been looking into modifying the xl350 frame. Pulling in the steering head to 26 degrees, then lengthening the swingarm a bit to get the right wheelbase for flattrack.

Any tried and true methods for pulling in the steering head a bit? Swingarm lengthening?

Might be too much trouble and better to stick with the Bultaco frame... Just thought I'd ask around. The goal is to have a bigger motor than my 250 for the Stockton, KS 1/2 mile in August.

midnight340 #1
  • Rank:Gold Member
  • Posts:130
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/18/2011 5:19 AMCopy HTML

I don't know how others have done it, but I did bring mine in to approx. 27 degrees and lengthen the swing arm 2 1/2" although for a street bike.  I did do it while looking at a lot of flat track bikes, so that was a big influence.  I haven't had it in the dirt (strange for me) but I do like the handling on the street.

I was kind of radical about it I suppose.  I cut the back lower backbone loose where it meets the "box" by the rear motor mounts and swingarm mounts.  I cut the seat stays/rear frame loop tubes loose, then slightly notched  the back side of the down tube just under the stamped head bracing.  When heated ahead of that notch, I pulled up on the back bone which brought the front end in to where I wanted it.  Used an angle gauge on the head with bike level.  (by raising the backbone it steepened the head)  I then welded the rear frame/seat supports back to the backbone.  Welded up the slight notch I made in the down tube. 

This left a gap of about 1-1/4" or so where the backbone separated from the "box" at the rear of the engine.  I then used plate and large tubing pieces to lap the ends of the backbone where I cut it about an inch above the "box".... basically made sure it was reinforced and very well welded back together at that point.

Unlike some "heat the head and pull the wheels together" methods, this avoided any chance of getting a twist in the head angle, thus keeping the alignment true.  (without any frame jig)

You can see photos of the bike on the XL350 page ("XL350 project update photos" near the top of the threads now)

If you have a good Bultaco frame it might be easier?.... but I liked working with the Honda frame.

Hope this helps.
-Del
verticaltwin #2
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/18/2011 7:26 PMCopy HTML

Hey, thanks for the info. Sounds like a pretty good method, although I will need to look into the effects of raising the backbone on tank mounting, etc... You gave me some things to think about though.

Where did you cut the swingarm to lengthen it?

Your bike looks great. Nice job on it! Wheelbase looks a little long for flattrack, but perfect for your intentions. Ready to paint it yet?
midnight340 #3
  • Rank:Gold Member
  • Posts:130
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/19/2011 5:03 AMCopy HTML

 Yes.. I'd think the swing arm is too long for flat track.  So 2 1/2" would be too much.  But an inch or 1 1/2" would compensate for the loss of wheelbase when the front end comes back.   As for the swing arm, I just picked the straightest section, sawzall-ed it, got some tubing that slipped inside the stock pieces + plus some that matched.  Cut the inside tube a couple inches longer than the filler piece so everything was doubled up.  Left a 1/8" gap or so to get penetration into the inner tube and welded it all up.

With the backbone method, it doesn't change hardly at all up front, and the back raises only the 1 1/4" - 1 1/2" (whatever it is to get the front angle) so doesn't interfere as much as you'd think.  Also, I wanted more room thinking that maybe I could pull the motor apart without taking it out of the frame... but haven't tested that yet.  But it does give some more room over the head.

As for paint.... I was looking for a tank, saw some of the fake "distressed" finishes on some customs where they tried to make it look like an old worn tank... then walked in a bike shop and saw this CB200 tank looking just like this (for FREE!) so I cleared it with a spray can and installed it.  Just an interim step.  I will eventually decide on some paint treatment I'd guess.  (Workin' on getting halogen/LED lights worked out right now.)
verticaltwin #4
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/19/2011 5:02 PMCopy HTML

I agree... Just not adding as much length to the swingarm would keep the wheelbase correct. Not that there is one wheelbase that everyone likes. I like it short, like 54.5-55.5 or so, for turn 4 at Jeeps mainly... that wall comes at you fast on a D-shaped track. I think the bigger tracks would be ok with stock wheelbase.

As for the backbone, I'll take a closer look at the effect on bringing it up. Maybe you are right and it won't affect things too much. I have a couple different old fiberglass tanks that I may be able to use, depending on the angle of the backbone. Just trying to keep the center of gravity as low as possible. That cb200 tank sits on your bike pretty nicely. Looks good as is... by the way... I was just making an assumption that you were getting it ready for paint based on the very clean look of the rest of the bike!

Thanks a lot for the help and input! The more I mull over the options, the more inclined I am to stick with the Honda frame. I can alter it as necessary as I build and test. Heck, we've had a couple of guys on stock framed xl350's that got around the track pretty good!

midnight340 #5
  • Rank:Gold Member
  • Posts:130
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/21/2011 5:28 AMCopy HTML

Let me know what you end up doing.  I'd be interested...
verticaltwin #6
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/23/2011 2:52 PMCopy HTML

Well I went ahead and got started on it over the weekend... Mainly taking things off the bike, except motor/wheels/forks/bars. I measured and compared the C&J Baker frame to the stock xl350 and they are really not all that different. Biggest differences are the motor being 2" more forward on the Baker frame, steering head angle, and the distance from the front of the seat to the steering head. Started removing brackets to fit fiberglass tank/seat, I have a set from my old Trackmaster DT250 that I hung on to. Seems like they will fit ok, with some more cutting and grinding.

I had an interesting idea on pulling the steering angle in a bit, kind of a variation on what you did... I thought about partially cutting the front down tube below the bracing, like you did, but instead of cutting the backbone down by the swingarm I would cut it just in front of where the seat section attaches. This would allow me to bend to the steering angle I want. Then I would have to partially cut the front of the backbone (from the top down) just behind the steering head brace and bend down to line back up with the severed end of the backbone near the seat rails. In the process I would have to reposition the brace between the lower steering head and the backbone... Not sure about this, may be too comlicated. I was just brainstorming last night and haven't really worked out all the details. Might not work well, but it would help with forward positioning of the tank/seat.

[IMG]http://i17.photobucket.com/albums/b79/verticaltwin/xl350framecuts.jpg[/IMG]

Something to think about anyway... although I may just try it stock before doing anything radical. I have enough chassis work to do with changing footpeg positions, figuring out tank/seat mounting, and adapting the rear wheel to disc brake setup... at least for now!
verticaltwin #7
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:05/26/2011 5:34 PMCopy HTML

Got the seat and tank setup.. Lots of cutting and grinding, but seems like they fit well. The seat is more forward than the stock one was, in fact it mounts in the tank mounting hole... but you can see the rider position is still too far to the rear of the bike. I think that the steering head and swingarm will need to be done after all... We'll see!

[IMG]http://i17.photobucket.com/albums/b79/verticaltwin/xl350seattank2.jpg[/IMG]
midnight340 #8
  • Rank:Gold Member
  • Posts:130
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:06/23/2011 2:30 AMCopy HTML

 I was going back over the thinking I did when I did mine.   (I was wanting to raise the backbone in relation to the head, but you probably don't want this with your tank set up.)  So:

One thing to consider is the lower on the down tube that you notch, the less it shortens the wheelbase...  Think of it like this, if you notched way down at the fr. motor mount, when you twist the head angle down you will have the head going forward AND down... stretching the head forward from that pivot point.  This would also raise the engine height as the head moves downward...if my thinking is correct.  Probably not what you'd want.

On the other hand, if you could notch the down tube right  under the head, there would be negligible movement of the head in relation to the rest of the frame or engine.  You would simply steepen the angle with little change otherwise, other than your front wheel would move back thus shortening the wheelbase some.

For simplicity and to get what you want without changing much else, you could notch the down tube just below the head... say right below the tank mounts and ABOVE the stamped triangle bracing to the backbone (that you have your X on).   Cut the backbone where you have your top mark.  Then simply weld plate or tubing to fill the gap you make in the backbone when the head angle swings forward a tinch... and of course to add strength back in at that point.

Simple... nothing else would change.  You'd de-rake the front, bring the front wheel back a bit  (in effect moving the seat and engine forward, as they'd be closer to the front wheel.)  Then you could compensate with the swing arm length a little.  Or just run a short wheel base which you said you liked. 

I think you'd probably like the quicker front end a lot more than the stock geometry.  And this would be fairly straight forward with only a couple of cuts.

That's my thinking....  let me know what you think.
verticaltwin #9
  • Rank:Bronze Member
  • Posts:26
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:06/23/2011 7:29 PMCopy HTML

Thats a great idea... I think you are right about cutting as close as possible to the steering head. I'm glad I didn't get a wild hair and pull out the sawzall yet! I've been looking at it and stewing on it for a couple of weeks. For some reason I had been trying to stay away from cutting in the gussets, but in reality they just give more material to reinforce the altered frame area. Cutting through the welds eat up a sawzall blade, but sacrifices must be made. 

I'll have to wait until I get the steering angle set and the forks set up properly until I'll know the wheelbase for sure. Then I can look at lengthening the swingarm in necessary. I want to set it up as close as possible to my current flattracker, and just last weekend I finally got it set up right.. after two years of tinkering and tuning. Turns out all it needed was properly set up rear shocks! Go figure. You'd have though I had another 100 cc's, even beat a couple big bore tt540 Yamaha's on the little xr250... (Big thanks to Durelle Racing) Now I know the geometry I want to try to duplicate.

Thanks again for the ideas!

 

suzukijo #10
  • Rank:XL Board Member
  • Posts:13
  • From:USA

Re:De-raking '75 xl350 frame

Date Posted:11/26/2011 9:21 PMCopy HTML

when the '79 cr125 came out with the 23" front wheel, changing to a 21" wheel was the way to go, taking a little out of the top frame tube, just above the carb was easiest. I would think that cutting the frame in the same area, and adding an inch or so would get you where you want, and still allow the front motor mount to fit (maybe with some movement of the hole location, there is a lot of slop there stock). its not a highly stressed area, i would think tucking the wheel back would offset any frame lenghthening. just a thought. i did this on a suzuki once and it was noticable in steering, which it needed, easy to do, tank still bolted up with little change. and it leaves the gusseted steering head area alone. imho.



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