Author Topic: Honda CB250N build  (Read 1171 times)

Offline busse

  • Posts: 3
Honda CB250N build
« on: Mar 28, 2017, 08:24:21 »
Hi, I'm Bo and I'm from Sweden so I hope you could understand my English.

I bought a 1981 Honda CB250 last summer with a broken Engine and this is my first bike and also my first build ever, the plas for this bike when I bought it was to do a cafe racer. The engine was not running but the seller said that a valve was broken and when I took it apart I found a broken inlet valve and it was because the clips had loosen, but I also fins a broken cylinderhead bolt wich I get loose after alot of work.  I ordered the parts I needed for the engine but in the north of Sweden it seems to be long delivery time on old Honda spareparts, I bought som parts from a Honda dealer and the parts the dealer coulden find I buy on eBay.

Whil I was waiting on the engine parts I started to planning for the cafe racer build, I think we can agree that the CB250N dosen't got the best gas tank for a classic cafe racer but I deside to use the stock gas tank but to still get some of the straight line under the tank  and the seat I was was thinking about to let the front of seat go under the back of gas tank where the original sidecovers should be fasten to make the line. Here's a picture of a cardboard template that shows my Idea of the new seat.

After thinking about the first plans for the build I took the bike apart for cleaning it up, after geting the dirt of the frame it show it was so good that I decidet to not do anything about it for the time.

When I finnaly got the enginge running I stated to fabricate the new seat, I choosed to do it from 1 mm thick iron plate, I started to make the front part that fits to the gas tank and the upper side och the seat. Then I made a plate for the rear fastening brackets that I unsrewed from the original seat, like this I can easy take away the seat like you can do with the original seat.

With this done I started to do the upper part of the cuts, I desided to try to make it to match the back part of the gas tank and after it was tac welded I started to made cardboard templates for the sides of the cuts.

The I starded to do the the sides of the cuts and tac weld it to the seat, with the sides of the cuts on it I trimed the under line for the seat and put some supports under the seat to make it stiffer.

A new rear frame was build to hold turners, licenceplate, licenplate light and a red reflector. This rear frame was made and fit in to the original bolt holes in the frame.

After this was done I started to look at the ugly, big plastic meter house, sidecovers and a new exhaust, a pair of new mufflers and a 38 mm diameter pipe was bought and I welded new pipes between the downpipes and the muffler. A friend of mine who alos got a CB250N made a pair of new cups to put the original meters in. A new controlpanel for the signal lamps was made and 6 mm LED:s is used as control lamps.
New side covers was alos fabricated out of metal and I used the screw holes for the original side covers brackets to screw the new side covers in place.
Next I was to get of the black paint in the aluminium parts around the handlebar and after a lot of grinding and polishing it was lookig good.

Next step was paint the panel and new meter houses black and mount it on the bike

Then I started to prepare the gas tank for new paint, before I striped the paint of the gas tank I was clean it from rust on the inside with lemmon acid but when I strip the paint I got a  some holes on the upperside, so I called a friend  who do tig welding and he changed the whole area around the gas cap and I ordered a new flip-up gas cap. Then an other friend paint the parts with 2K epoxi primer before starting to put filler on it, I first use fiberglass filler to fill the deepest parts.

To get a better riding position I decided to move the foot pegs backwards, and to do that I order a rear set on eBay. I designed new fastening plates in AutoCad for the foot pegs and the plates was laser cut in a local shop. An mockup with threaded rods was done to get the correct mesures of the brake and the gear shifter rods.
I design new logos for the gas tank and the cuts and a friend of mine did the printing of thoose at his company that do stickers and other adverticing stuff but It was hard to deside if I shouild have white and black or white and orange so I order both.

A new tail light was made from a flush mount tail light and an other tail light that I bought on eBay. This was done because the flush mount light had festoon lamps so I couldent have both tail and brake light in the same rear light.

After a lot of work with filler and grinding I finnaly got the seat, gas tank ready for paint, the color is an VW color called urban grey. A friend of mine did the paint but I have done all the work with filler before  paint my self. I have started to fabricate the bottom part of the saddle from 6 mm nylon plastic.

A new shorter aluminium front fender was baught on eBay and I will fabricate new fender brackets out of 3 mm thick aluminium. I think this fender looks better than the long stock one but I hop it's still enought long to do the work as a fender to protect you from getting dirty in bad wether.

Here we are now about eight months after I started the projekt, the next step is to make new rods for brake and grear shift pedals and a stop for the brake pedal backwards movement, fix the front fender, wait to the paint to get a little bit harder before mounting  the parts on the bike and put on some decals and countinue with the saddle.  The plans for this bike is to do this things for this spring to get  the bike able to drive it in the comming summer and maby do some small things on it.  I really would like to get rid of the clearcoat of the engine side covers and valve cover and polish the aluminium but just now to focus is to get the bike going for the summer and drive it. If it runs well and I like it I mabye tear it apart next winter and paint the frame and some other things on it.

Offline busse

  • Posts: 3
Re: Honda CB250N build
« Reply #1 on: May 07, 2017, 13:13:15 »
The build is now a almost finish for this time, mabye I tear the bike apart and paint the frame and do a real polish of the engine. What's missing now on the bike is the stickers with the Honda logo and the racing stripes, seat cover, strip the cover on the engines right side from clearcoat and polish the cover, wrap exhaust bandage on the exhaust system. The new front fender will wait because I broke my left wrist so I cant finish the mounting brackets with one hand.

Here's the new rear brake switch placed behind the foot peg bracket.

The rear set painted and in place

The valve cover and the left enging side cover stripped from clearcoat and polished.

A seat bottom made of 6 mm thick nylon.

Gas tank and seat mounted on the bike

Upholstery made of sleeping pad waiting for a black seat cover.

The bike what it looks like now.

Offline SoyBoySigh

  • Posts: 185
Re: Honda CB250N build
« Reply #2 on: May 07, 2017, 20:13:35 »
Hey busse - very cool project. (Though I can't see the pics, which is probably due to MY computer - I'll double-check later. I'm rather curious to see whether you're going WITH the given aesthetic, or whether you're needlessly trying to fight it..... AHA1 There they are!)

Nevertheless I am well familiar with the CB250N as it's a miniature version of my beloved DOHC-4, of which I've had three in a row now, two CB750F's and a CB900F aka "CB900K0 Bol Bomber" - I should think the CB260N & CB400N are a great influence on the DOHC-4 and vice-versa. It's not just the bodywork & Comstar wheels that are similar between the two - like the DOHC-4 series the CB250N/CB400N also has a "Sport-Kit" with special rear-set pegs and shorter pedals, lower bars & alternative throttle housing with the cables pointing forward & upward (so they don't catch on the gas-tank & scratch your paint when you use a lower handlebar) These can be both expenive and hard to find for EITHER series, the twins or the fours, but the nice thing about having a big flat alloy plate around the pepg/pedal area, is you can use that plate as a base for alternative foot-controls with OR without the special "Sport-Kit" components. The nice thing about Aluminum is you can drill it and tap the holes for threads, very easily, and cut/carve with a hacksaw & hand-file, even create entirely new brackets from flat alloy plate if you like, 'cause these brackets are similar to both the Dunstall aftermarket parts for '70s Honda AND the original adjustable foot controls from the '60s Honda twins such as the CB72/CB77 Hawk/SuperHawk, Meanwhile the awesome "Sport-Kit" throttle is a standard parat on the CBX550F - And as for handlebars, the cheap clip-on bars from eBay/China can be made very nicely adjustable through inclusion of a bar length with a slight bend at one end. The trick with the foot controls, is to mix-&-match the pedals which have the same spline & shaft, plus a linkage type shifter which can be located anywhere you like via the pivot bolts from the aforementioned CB72/CB77 Hawk/SuperHawk, and folding pedals which mount with a single bolt, so as to get 'em as close to the pedal pivot as you like - So too, there are ways of using a cut-down pedal with a linkage rod and Tarozzi style pegs with pedals included ie "Universal rear-set"foot controls. They needn't be expensive though, as the OEM parts can mix-&-match to create a beautiful factory-original style of controls, both for the feet and for handlebars.

I've often speculated on the possibilities of a CB250N/CB400N project. As a DOHC-4 Honda 'F-reak this model is practically right up my alley. As it is, I'm already looking to pilfer the things for parts, but I suppose there's more to it than that. It' a miniature version of my bike, so naturally whenever I'm rider slower, in traffic or "with" traffic I should say, and the bike feels heavy & ungainly at lower speeds, the mind naturally drifts to the "what if" scenario, of a smaller version of my bike, strictly for NON-HIGHWAY use, that is.

A nice lightweight commuter twin makes for a fantastic inner city run-about bike. These bigger bikes aren't nearly as nimble. While I had my first 750 on the road I also kept a C70 Passport, and when I took a KZ440LTD as a middleweight I found it seriously lacking in EITHER of my two favourite bikes' characteristics (Hence the "KZ440LOL" I'm still trying to turn it into!) What I'm getting at of course, is that the CB250N/CB400N would be the ideal "in between" - If you can get the weight of the C70 with more power, the "flick-able" nature of a smaller bike with the stability of the '80s Honda DOHC-4 series or close to it? I find it very intriguing. SOMEDAY, I'm gonna get my hands on a smaller bike once again. I've always been curious about something like, say - a CB400N engine in a CB250N frame. Well, my DREAM would rather be something more like the MVX250F with an NS400R engine, done up as a tribute to the famous JAWA Type 673 - Which is to say, a wire-spoke conversion and a re-paint, 'cause Honda already BUILT the MVX250F as a tribute to the Jawa! But yeah there are similar builds out there, especially in countries where the 250cc & 400cc classes are the "learner" category for introductory licenses, where people will put a larger engine into the lightweight nimble chassis.

Well I supposes what YOU'RE doing is all the more commendable, rescuing a "dead" bike, bringing it back to life!

Strangely enough it's not an engine swap that I'd suggest for this model. I'd urge you to look into some upgraded front brakes - Where with the CB650cc & CB750cc from this same era I would urge people to upgrade from 276mm discs to 296mm from the contemporary CB1100RB & CB1100R-C/D, I'd say that the CB250N & CB400N are perfect for the "hand-me-down" parts from the four-cylinder models. The 240cc dual-discs still have some good uses, but as a REAR disc where such is needed!

I've got a lot of similar ideas so far as COMSTAR wheels are concerned. Such as, if you don't already have the 18" front wheel you should switch to one if and when you can find it. And finding wider rims for the Comstar wheels, lighter rims even, in the form of Akront "NERVI" center-flange rims. Another possibility with the CB250N/CB400N might be to find some XBR500 "Boomerang" rims, paint 'em GOLD, perhaps a CB900F2/CB1100F/CB1100R-c-d/CBX750F-II/VF1000F-II etc 2.50x18" FRONT rim, of the "Boomerang" type, and bolt up a compact cush-drive and one of those 240mm discs to it, for a truly effective miniaturized CB1100F/CB1100R replica - And of course this all would ALSO work quite well on the CBX550F, I suppose that it might be the more appropriate CB1100R version, what with the shape of the tank.

But all in all there are far more PRACTICAL things to do with these bikes. Probably the best & easiest way to shed the most weight from this model would be to swap out to some lightweight alloy rimmed WIRE-SPOKE wheels - and more to the point a DRUM brake up front!

Setting up with wire-spoke dual-disc front end, let alone TRIPLE discs which is what all of the Superbike freaks are after, can be not only expensive and an absolute hassle to set up, it can also be rather HEAVY - And though these '80 Honda Comstar type disc brakes can be VERY lightweight for a given diameter, it's very difficult to pair TWO of these 5-bolt discs with a wire-spoke rim, at least not without a huge WEIGHT penalty (such as those bolt-up flange-plate Comstar to wire-spoke conversion kits) Besides the disc brakes of this period are in their infancy with stainless steel providing a poor coefficient of friction -drum brakes meanwhile were at their Zenith, and while a disc has a NOMINAL value which is numerically superior, that doesn't represent the true working diameter and leverage of a disc brake, while a drum has all of it's action taking place at the nominal value. Most of the negativity you'll hear about drums is due to people not having 'em SET UP correctly. So this is why I'd rather use a DRUM wherever it's still feasible to do so.

There are a ton of very undervalued drum hubs out there, such as the Honda CB450K 40-spoke 200mm or the CB72/CB77 36-spoke version of the same thing, OR the T500 Titan 200mm 2LS - Probably one of the most under-valued good drum hubs would be the KZ400 40-spoke, and there are several other good rear drums in 36-spoke, the key being to match 'em to the RIM you're planning to use:

The 40-spoke rims could lace up to the many rims available for/from CB750, KZ900, KZ650, GS750-GS1000 etc - which can also be found in 16" diameter for pennies on the dollar - I've bought a 3.50x16" "Super-Akront" rim, the most light-weight rim of it's kind, for as little as $25ea! That KZ400 rear, as well as the 160mm-180mm 40-spoke FRONT drum, could lace up to the same rims as were taken off of a CB750K or KZ900 rear drum, but they weigh a heck of a lot less!

MEANWHILE, these 36-spoke hubs could lace up very nicely to the very affordable alloy rims sold for the Yamaha XS650 over at "Mike's XS" where you could find either 2.15x18" & 2.50x18" AND similar rims in SIXTEEN inch, for the new low-profile MAXI-SCOOTER tires, such as I'm doing with the "KZ440LOL" here -

One might pair 2.15x18" & 2.50x18" for pretty standard tires for this model, using a wider rim on a narrow tire so the shoulder sits straight upright & the profile is relaxed, rather than pinched in too tight with the profile arched extra narrow.

OR, all the more interesting IMHO, one might pair say, 2.50x16" with 3.00x16" or 2.75x16" with 3.50x16" if the swing-arm & chain-line would take the extra width, and say, 100/70-16 with 130/70-16 or the same as my KZ project the 110/70-16 with 140/70-16 on the rear - Like I say, IF the chain-line could take it?

There are also some fantastic deals to be found in the form of vintage MX wheels from European marques like Husqvarna & Bultaco/OSSA etc. Lightweight Akront 36-spoke rims on conical drum hubs, sometimes they're even Magnesium hubs in them - typically with the sprocket on the same side as the drum. If it's at all possible, I'd want to lace 'em up to some of the conical drum hubs from Japanese MX bikes, with a 2.50x18" rear and 2.15x18" front - ideally with a 200mm drum or better yet 230mm for that matter, which one might be able to fudge into a re-drilled rim using larger spoke nipples to realign the spoke holes etc.

You'd want to find the rims which have the bead retention ridges, so you can seal them tubeless with aquarium silicone. Or the rims which are light enough as to warrant the lack of ridges & inclusion of an inner-tube.

Or, conversely, the CMX450 and/or Monesa Cota hubs which lace up to reversed spokes, with the nipples in the HUB and a bent head spoke through a center-flange rim just as you see on the COMSTAR wheels - and again, ideally with the lightweight Akront "NERVI" rims for the 50% weight reduction  - the TRICK being, how in the heck are you going to put the better front BRAKE into a rim like that? It would sure be nice to figure out how to put even the one Comstar type 5-bolt rotor onto a hub like that, using a 296mm  single disc with a good solid fork-brace to get the most from a single-sided brake (I'd also want this for the single-sided DRUM) The reverse-spoke wheels could make for a VERY light-weight set-up....

But yeah, any which way you slice it, I'd say that the most important stuff to do with these 1980s bikes is to stiffen the front end and steepen front end geometry for quicker steering - meanwhile beef up the front brake, all the while shedding weight from the wheels, get more rubber down to the road for better grip etc.

Of course one can have all of this WITH the original Comstar wheels, you've just gotta be really dedicated to the idea, 'cause it ain't gonna happen quick & it sure won't be cheap either. Nevertheless it's some of the coolest stuff one could DO with an '80s Honda!
« Last Edit: May 07, 2017, 20:29:08 by SoyBoySigh »
Even a stopped clock gives the right time twice a day.

Offline busse

  • Posts: 3
Re: Honda CB250N build
« Reply #3 on: Sep 10, 2017, 12:01:00 »
This is what the looks like now, I have run the bike about 1500 km this summer.

Things to do is rebuild the front fork and I also would like to find some softer rear shocks, I often run the bike on bad roads and the rear end is to stiff. Any one that have any suggestions of good working rear shocks? I have new rear shocks (think the brand it Emgo) bought on eBay but they are to hard.

Other tings to do is this coming winter is a new exhaust in stainless steel, and mabye a bigger rebuild of the bike with a Suzuki GS450 gas tank and a new or modified seat, it depend on what time I have to put on the bike.