[Alan F.]

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...

 

[J-T]

Sounds like fun

 

[longdistancerider]

This will be fun to follow

 

[Alan F.]

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.

 

[Paul F]

sounds interesting, i look forward to following the progress!

Lol

 

[Alan F.]

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

 

[Paul F]

DIY rules, imo. nice job! totally agree getting things off the floor, much easier to work on.

 

[Alan F.]

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.

 

[Alan F.]

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.

 

[Alan F.]

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.


[]

 

[longdistancerider]

Some nice machine work there and great creativity

 

[Paul F]

I think I need a lathe now, and ... a bridgeport, and ... hmm.

 

[Alan F.]

Some nice machine work there and great creativity

Thank you Sir.

I think I need a lathe now, and ... a bridgeport, and ... hmm.

Years ago I got interested in making my own parts, I picked up a Harbor Freight Micro Mill/Drill for something like $179 new shipped to my door. That one was light enough to ship FedEx then, now it's not available anymore. A year or so later I found a barely used Harbor Freight 7x10" Mini-Lathe model 33684 for $299 local pickup, it's the original green model from the early 80's that was actually a 7x8"... I recommend a lathe first because you can mill on a lathe, but you can't turn parts on a mill. I've been searching for a South Bend 9" at a low price for a long time, they're out there but timing is everything. It seems that big, heavy lathes can be had cheaper because nobody wants to move them. If you're interested in small machinery have a look at http://www.littlemachineshop.com they have everything and a lot of useful info as well.

 

[Alan F.]

Not much progress to report lately, my mini-lathe's motor controller fried and I need to get that back up and running.


Over the weekend I picked up two parts bikes, a 92 and another 93. I traded an old electric winch I got from my old landlord, he thought it didn't work and gave it to me. There are no tanks, seats or bodywork, one is missing it's starter and both have bent forks. Otherwise they seem complete minus a few nuts and bolts here and there. They've been out in the weather for a long time, but the wire harnesses look uncut and connectors still look corrosion free. I'll tear the engines down to assess the damage this winter.


I'd never traded for a whole bike before, I was very surprised at the absence of any buyer's remorse.

 

[Alan F.]

Ok, I finally found some time to get my lathe back up and running. With a little luck I should have some progress to report soon.

 

[Alan F.]

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.

 

[longdistancerider]

Whew, I read this on my phone and the pictures wouldn't come up. I though you were going to be using aluminum as a bearing race in which case it's an almost instant failure. I like the adapter cups, those should work fine.

 

[Alan F.]

Whew, I read this on my phone and the pictures wouldn't come up. I though you were going to be using aluminum as a bearing race in which case it's an almost instant failure. I like the adapter cups, those should work fine.

I just viewed it on my phone now and no pics either. So I cleared web cache and tried again, there they are.

Aluminum as a bearing surface? Not for anything faster than a lazy-susan

Bearing cups like these are an old low-tech idea, they're available commercially for American bikes.

 

[Alan F.]

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:

View attachment 211697

View attachment 211705

View attachment 211713

View attachment 211721

 

[Alan F.]

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 from this section of frame as well. The slugs are made from stainless steel round bar (not sure of the grade), 4.75" x .710" with a quarter inch center bore (.230" wall) and I rounded the ends, they're a bit heavy but fit inside the frame tubing nice and tight and shouldn't rust permanently in place in case I want to do a frame loop later on. I also unbolted some parts from the rear section, removed the helmet lock (no key anyway) and the seat latch cable. I removed the seat latch, cleaned and re-greased it before bolting it back in place. Without the cable actuation for the seat latch it's just a matter of reaching under the rear of the seat and pulling the latch open with the loop that the cable used to attach to, simple.


While my drill batteries charge here are some new pics: