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Discussion Starter · #1 ·
Ok, as promised here's a build thread. I'm cutting and pasting here so hopefully my photo links all work...

Last fall I picked up a titled basket case 250 Nighthawk with 14K miles on it, it had been stored poorly by its first owner and the second owner tore it apart except the engine which he spray bombed flat black. Compression was good and the title was clean so I plunked down my 200 bucks and loaded it up. He had Bratstyle delusions and hacked off the frame behind the rear shocks, thankfully he kept the back half.


I figured with the rusty spokes and rims that this would be a good place to learn to lace wheels, experiment with rust removal techniques and experiment with diy zinc electroplating techniques. I did plenty of research and sourced the parts I'd need, but then life popped up and the build budget went away. So I came up with the same old plan to build what I can around the parts I have on hand.


SO, the 90's 750 Nighthawk rear wheel, 41mm fork- single disk brake front end, 88 CBR600 front wheel and set of 17" Michelin Pilot Activ tires I had originally planned for my 750K a few years ago were in. 5 minutes of measuring and note taking and it was settled, it could be done.
I've poked around the web but it seems nobody ever bothered to try this one before, so here goes.


I'm drawing inspiration from some scramblers and small bore hooligan bikes like the ducati scramblers of the late 60's

and more modern bikes like the 390 KTM Duke

and some of the custom bikes being built and ridden in southeast asia, I'll upload a few photos of those below.




I'm hoping it turns out more hooligan and less like





I'm gearing it low for more (maybe some) useable torque, I have a set of CB700SC rear shocks (2" taller than stock 250) with 4 way adjustable rebound damping and chromed Progressive springs (rated coincidentally for my weight) from craigslist, I picked up an All Balls brand fork rebuild kit, and the other day I picked up a 525 120 link Tsubaki roller chain on clearance.






I'll post some photos of my progress soon, photobucket work around in progress...
 

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Discussion Starter · #2 ·
There are a few corners that I'm just not willing to cut on this build, but then again there are corners that I'm decisively running with scissors toward.

Sometimes there's a fine line between cutting a corner and writing the check for a shiny new part.
 

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Discussion Starter · #3 ·
With plans to go through this bike in depth I decided I needed a bike lift or work table of some sort, I'm done building bikes at floor level. After looking around there seemed to be two options.


Option one:



But at 200+ pounds and an iffy reputation, I didn't think I'd like lugging it down to my basement workshop.


Option two was to build some type of wooden work table that would support the right amount of weight but at the same time to not go overboard with weight bearing capacity, maybe a little storage beneath would be nice and casters always make a great addition.
after some consideration and research I decided on one.
Dropbars Bikeworks: January 2011
Theirs looks like this:



And mine came out looking like:

Rock solid with lots of screws and glue holding it together. I added a 6' black vinyl runner to the top for looks function and protection.


Total for this was about $75
 
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Discussion Starter · #4 ·
I bolted up the swingarm and mocked up the CB700SC shocks, I like the look and they're about 2" longer than the 250's stockers.
Here's a photo mocked up with a CB750K tank, the rear mount was close but this tank was just too wide for the frame.





Here's a CB350T tank mocked up, I like the look but this tank is a little rough and much smaller than the stocker, nope.





On with it then, I'll be adapting the rear wheel from a 90's vintage 750 Nighthawk. I have it lying around for another project and opted to use it here, just like most of the upgrade parts I'll be adapting.





This wheel already has an unused Michelin Pilot Activ 130-70/17 and new All-Balls wheel bearings installed.
To adapt this wheel I simply had to center the wheel in the swingarm and mill the sprocket carrier for chain line, there is plenty of room for a wider tire later on.


First order of business is to adapt the 15mm axle to the 17MM wheel bearings, it's easier for me than cutting the swingarm slots to accept the 17mm axle, which would be way too long anyway. Since the bearings were new there was no sense in swapping them out to fit the axle either. So I turned some steel sleeves with a 1mm wall and a flange on the end from stock I had on hand, not stainless but it hasn't rusted in a damp basement for 6 years either so it's a good alloy choice. Starting out with narrower stock would have been easier, but the stock was free... I'm no machinist, and my machines are best classified as toys, but I'm confident I can get this done.




 

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Discussion Starter · #5 ·
Next I needed to get the wheel centered in the swingarm. (Centered yes, just like the stock wheel was. Not all rear wheels are actually centered in their swingarms to be in the center of the bike though, so look out for this if you ever get into this situation) Unfortunately to center this wheel I needed to take off a little material from the drive side, specifically the area that the seal that rides around the wheel spacer is driven into. So I'd have to figure out a new way to replace the seal.
With a little consideration I figured a thin spacer with an o-ring would do the job, this area is only sealed from the elements to protect the spacer on the sprocket carrier and it's sealed bearing, not all that critical but necessary.
This is what I came up with:





It's a bit thinner than the stock seal:



But it fits and with a little grease behind it, does the job without binding.
























It fits and does the job of keeping the wheel centered and most of the elements out of that area.
 
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Discussion Starter · #6 ·
On to the Brake side of the hub.


One simple spacer over here to fill the gap. However it was late and I didn't feel like rounding a square piece of stock to get the right spacer length, so I made a two-piece spacer for this side.














Looks like plenty of room for the brake stay and actuator rods.


I had to mill down the sprocket carrier to restore chain line center, and while I was at it I shortened the sprocket studs so they won't contact the swingarm.


I soaked them in plain 5% Acetic Acid White Vinegar (safe enough to drink) for a few days, the acid will affect the rust but not the steel, unless you're very patient. Then I zinc electroplated them with the solution left over from some experimenting last winter. They came out looking more galvanized than I'd hoped (and there is still some rust seen inside the nut threads) but I can always throw them into the vibratory polisher with some corn cob to shine them back up when I replate the rest of the hardware.





Here is a shot with the rear wheel mounted, stock seat set in place, and that 350 tank in place (too bad the seat gap is so bad) and the engine mounted.


 

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Discussion Starter · #7 ·
To Adapt the 750NH steering stem to the 250 frame I'm using the bearings from the 750NH and making bearing cups to adapt to the 250's frame. The steering stem is long enough to do the job unmodified if I play my cards right.


I finished up the upper steering bearing cup first, I'm making them from aluminum to keep weight down, but they're pretty chunky. It's probably overkill but all stressed areas are minimum .300" thick. I'll clean up the finish on both after the bottom cup is done and all dimensions are finalized.











 

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Discussion Starter · #8 · (Edited)
The bottom bearing cup looks so much like the upper that I didn't bother taking any photos of it on the bench.
I finished it up earlier tonight and the 750 triples bolted up flawlessly to the 250 frame using the tapered roller bearing set from the 750.
Here's a few pics:







 

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Discussion Starter · #9 ·
I was getting tired of that detached back half of the frame getting underfoot so it's time to get it back in place. Since I'm working in a basement shop welding is probably not gonna fly so the plan is to make some slugs, square it up, drill some thru holes in the frame and drill and tap some holes in the slugs, then just bolt that sucker back on. I'm also planning to cut some tabs off this section of frame as well.
While my drill batteries charge, here are some marked up pics:





 

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Very interesting project!
I am curious about the details of your 1 mm wall thickness axle sleeve adapter. By definition you will always need to be able to withdraw the axle through this sleeve to remove the rear wheel, so it is essential that the sleeve never becomes deformed so the axle slides out of it easily. It is also essential that it be clamped rigidly by the axle nut when the wheel is in place to prevent possible spinning of the inner bearing races.
For the stock axle, the 2 bearing inner races are clamped hard against a spacer between the bearings in the wheel by the axle shoulder on one side and a spacer on the other side allowing the axle nut to be torqued up tightly without binding the rear wheel bearings. Since you are adding a second spacer in the form of the sleeve over the axle, it must be clamped tight by the axle nut as well to prevent it from spinning on the "real" axle. Unless the length of the sleeve is precisely correct it would seem it would either be too long (compressed before the bearings) or too short in which case it would be free to spin on the real axle. In any case it seems to me to be very important that the sleeve not be free to rotate inside the bearings or on the axle when the wheel is installed.

All in all I would be inclined to simplify the installation by eliminating the sleeve and replacing the wheel bearings with a couple of new ones of the correct size for your application. Bearings are relatively cheap and not that hard to change out compared to all the work you have already done. Just my 2 cents.
 

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Discussion Starter · #13 ·
Don't be too concerned Duckster. When the axle nut is tightened, my spacers are all against the bearings' inner races and all is as it should be. I adapted these bearings to the 15mm axle because they're new with zero miles on them, I installed them myself a few years ago after refurbishing these wheels.
 

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Discussion Starter · #14 ·
Thanks flitecontrol, 01-7700 and Duckster. I'm sure to use some unorthodox methods and materials in this build, but I'm using what I already have (or already made for another stalled project) to keep the cost down and to avoid hauling major components out for welding or machining.
 

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I'm curious about how the 2" longer shocks will affect the chain run. I used 1" longer ones on my Nighthawk and worry about the increased friction and wear from the chain's increased angle against the upper swingarm guide. Maybe it's nothing, but I'll be looking forward to hearing how yours works out.
 

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Digging the build and watching the progress, more please sir, may I have some more?
 

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Discussion Starter · #17 ·
Hey there Bob.
I actually measured my shocks against the stockers just last night and they're only one inch longer than stock.
I'm not concerned though as i've had the stock shocks from my CB750K3 on my CM400C (1 inch longer) for several years now with no ill effects over thousands of miles. And I haven't adjusted chain tension often enough...

Also the rear sprocket i'll be using on this NH is 5 teeth over stock, so there's more chain angle added there as well.
 

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Discussion Starter · #18 ·
Hi kryton, this is actually a few months worth of progress condensed into a few posts, I had some trouble with my lathe's motor controller and lost momentum for almost half the summer.
 

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Discussion Starter · #19 ·
I measured the stock shocks against the CB700SC shocks I'm using, they're only one inch over (13" eye to eye) not two as previously stated.



Here's a look at the fit of the steering stem with my bearing cups added with the stock fuel tank in place.



Here's an overall view of where i'm at today.




And a shot of the frame slugs joining the cut rear frame to the front half, all bolted up. Chopping a frame with a light saber really does vaporize a lot of material...
 
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