CB250 Fork Swap - Honda Rebel Forum
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post #1 of 43 Old 01-06-2015, 01:40 PM Thread Starter
 
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CB250 Fork Swap

My next planned modification to my future Farmhawk would be swapping out the stock 91 Nighthawk forks with a 81-84 Honda XR200 fork set up. I have done some research and both share the 15mm front axle diameter and the 31mm fork tube diameters. So I think it would be a straight bolt in operation. I am looking for thoughts and concerns on the subject since I don't have the money for this as of yet thus I have plenty of time to ponder.

Now this mod would add two inches of extra clearance height to the front but I am concerned about the effects on the handling, I have also considered adding longer rear shocks to compensate for the additional front height. This would give me more ground clearance as a whole which would be great but I replaced the stock 33 tooth rear sprocket with a 38 tooth rear sprocket and I am left with very little clearance for the chain. I am afraid that an extra two inches on the swingarm angle from longer shocks might throw a wedge into the whole system.

The eventual goal of these mods is to make the hawk more farm friendly. Apart from when I am chasing trespassers off I would remain below 40mph perhaps more if I am going to a neighbors farm, all within a 25 mile radius of my house. If your interested in my sprocket odyssey you can read about it on another post here http://www.hondarebelforum.com/f77/c...ted-50978.html And before anyone chimes in with get a dirtbike let me explain that apart from some of the 60s scramblers, dirt ready bikes fit neither my tastes nor my budget.

Chef Vodka,
1991 Honda Nighthawk CB250
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post #2 of 43 Old 01-09-2015, 07:59 PM Thread Starter
 
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Ran into a slight research problem, the axle diameter on the front forks of the 81 to 84 Honda XR200 is listed at both 12mm and 15mm. So I wonder if the 15mm axle goes with the beefier 35mm tubes on the Honda XR200R.
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post #3 of 43 Old 01-11-2015, 12:03 AM
 
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Are you trying to swap just the fork tubes themselves or the entire fork assemblies? If it's the latter fork width and axle compatibility come into play.

"Ride Safe, Chop Safer" Motorcycles are not unsafe. However; they are extremely unforgiving of inattention, incompetence, ignorance, and stupidity.
Dismantling, sawzalling, and rattle canning does not make a bobber.
Those are STEPS toward customizing, not customizing unto itself.
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post #4 of 43 Old 01-11-2015, 05:35 PM Thread Starter
 
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I think the whole thing Shadow Shack, but I don't know for sure. Swapping just the tubes never occurred to me as an option. I have looked at replacing the fork springs with some heavier ones from progressive suspension but that's starting at $250. Fork tubes off a 81-84 XR200 run about $100 and they are for dirt riding. The tube diameters of the 81-84 XR200 are the same 31mm as the 91 Nighthawk 250, but research into the axle diameter is running at both 12mm and 15mm.

I was unaware you could just swap the tubes out while keeping the bottoms, would that give me a better suspension for dirt then the stock assembly? I am not mechanically inclined and I haven't yet taken a fork apart. Do you think I would be able to swap all the guts into the hawks lower assembly's as well?

Also I could do an entire swap, the wheel, rim, and brakes included. That however runs a fair amount more money then I have budgeted for the front end.
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post #5 of 43 Old 01-11-2015, 05:39 PM
 
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People have stiffened up the stock Rebel springs by adding a 1 inch long piece of PVC pipe to the top. A lot cheaper than new springs.

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post #6 of 43 Old 01-11-2015, 05:47 PM
 
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Quote:
Originally Posted by ChefVodka View Post
I was unaware you could just swap the tubes out while keeping the bottoms, would that give me a better suspension for dirt then the stock assembly? I am not mechanically inclined and I haven't yet taken a fork apart. Do you think I would be able to swap all the guts into the hawks lower assembly's as well?
Assuming the bottoms are milled the same it's definitely doable. However all this does is alter the fork length, you still need to modify the spacers up top accordingly to retain the lower and inner guts.



(just a random fork tube pic I found to illustrate what the bottom milling would look like...bottom on the left/top on the right)

Quote:
Also I could do an entire swap, the wheel, rim, and brakes included. That however runs a fair amount more money then I have budgeted for the front end.
Assuming the fork width is the same. Otherwise you may be looking at triple clamp/steering stem compatibility as well. For off-roading a full MX/enduro fork assembly would serve you better than longer street forks.

"Ride Safe, Chop Safer" Motorcycles are not unsafe. However; they are extremely unforgiving of inattention, incompetence, ignorance, and stupidity.
Dismantling, sawzalling, and rattle canning does not make a bobber.
Those are STEPS toward customizing, not customizing unto itself.
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post #7 of 43 Old 01-12-2015, 02:52 PM Thread Starter
 
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Excellent point on the fork width, I had checked the triple tree stem dimensions and they are different for the XR200. Until you reminded me it had slipped my mind so an outright tree swap is out of the question without milling modifications and I don't think I can afford that.

I need to do more research into the rest of what you are saying before I can fully understand that enough to continue the discussion. My brain is just having trouble thinking that way. I will check out some youtube fork disassembly videos later and work from that point. Thank you for pointing out that path to me.
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post #8 of 43 Old 01-18-2015, 03:45 PM Thread Starter
 
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Thanks to some people over at ThumperTalk I have confirmed the axle size for the 81-84 XR200 is 12mm. This has thrown a slight wrench into my drop in fit hopes. However the same person that helped me pointed out that its fairly common to drill out 12mm fork axle holes to 15mm holes and had done so several times successfully on his bikes.

It had also occurred to me that I could pick up a 12mm axle and get a 15mm outside diameter 1.5mm wall thickness steel sleeve to run the smaller axle through the forks and the larger hawk tire hole.

If I went the drilling route I would have to buy a drill bit, and get someone with a drill press to do the work. With the sleeve route I would have to find and buy the sleeve and a 12mm axle.

Any opinions?
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post #9 of 43 Old 01-22-2015, 02:25 AM Thread Starter
 
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I just arranged a swap today for a pair of 1981 XR200 forks. I found a farmer over in PA that was willing to trade them for 200 rounds of 7.62x54R ammo, so about 50 dollars worth with gas. I really love the barter system.

This front fork swap is no longer theoretical thanks to the arranged swap, and I am leaning towards drilling the forks out.
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post #10 of 43 Old 01-22-2015, 04:14 AM
 
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Last fall 7.62x39 ammo was over a dollar a round. Are you using todays prices?

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