CB250RS café racer project

[mylittletony]

This may not be totally relevant to this thread anymore, it seems to have become a general CB250RS Q&A!!

Could anyone tell me whether cbX250rs forks fit? I need to do fork seals, but have found some cbx forks locally in better condition for half the price of the repair work.

How about an easy front brake upgrade to improve the feel and power? at the moment I squeeze and it slows down a bit but there's zero feedback and i'm using the rear brake a lot...

[xwhatsit]

Could anyone tell me whether cbX250rs forks fit? I need to do fork seals, but have found some cbx forks locally in better condition for half the price of the repair work.

Haven't got a clue, but the first thing to check would be what diameter the stanchions are -- CB250RS forks are 33mm.

Length would probably be all right as long as it's not too far off; the CB benefits from a slightly lowered front-end (sharpens up the handling noticeably), so if they're slightly too short that's no big deal. If they're too tall you can drop them through the yokes up to a certain point.

Axle diameter would be the other issue. The CBX runs 17" wheels, so mudguard height would be off. Unless you ran a complete CBX front wheel, mudguard, brake etc. (probably better brakes than the CB item too).

Seals on the RS are really easy to do yourself. I see David Silver has aftermarket seals very cheap... once you pull the forks off you can strip the forks and rebuild them in an hour.



Brakes are rubbish... I've completely rebuilt my calliper and used a couple of different master cylinders but they're terminally crap. I see a lot of photos of Jap RS clubmans running the front end off an SR400, which has a twin-leading-shoe drum brake. The later Japanese CB250RS Deluxes (the RS-Z and the RS-Z-R which was all blinged up in red/white/gold colour scheme) had a twin-pot calliper which might've been a bit better. I haven't seen any in NZ, dunno if they reached England, might've just been a Jap domestic thing.

[jester_parks]

I bought and fitted CB400n-forks, which have the same diameter (33mm) and give you the option of double-disc 240mm or - with CBX750, CB900F (or FT500?)-calipers - 276mm brake-disc....and this combo does work!

[mylittletony]

cool, thanks for the advice, speedy as usual!! Not 100% about the home rebuild, it took me 3 months to change the lights and relocate the battery!! Don't have a vice at home, or a stand, or most of the correct tools! Should give it a go though i guess, hopefully work would let me build them up...

as for the CB400N forks, can you keep the same wheel? It looks like you have. I can't recall a spoked wheel version over here and wouldn't go near a comstar...

edit: actually, aren't cb400n the same as cb250n forks??

Was ideally hoping to kill 2 birds with one stone and get better braking with a fork swap, so i'll have a search for some.

[xwhatsit]

Jester_parks: Nice!

mylittletony: I don't have vice/stand either... you can leave the bike on the centre stand. About the only `special tool' you need is a broomstick with a wooden handle to hold the damper rod in place when you loosen the bolt that retains it on the underside of the forks.

I always thought CB250N forks are 32mm.

[mylittletony]

Unfortunately no centre stand either, only a large flower pot come workbench I do have a broomstick though!

Just doing some research on David Silver, the oil seal (Honda p/n 91255413881) listed for CB400n is the same as the CB250N AND the cb250rs... The superdreams also share LH fork bottoms according to the site.

By default, does this mean the forks are the same (maybe diff length)? I'd be surprised if a manufacturer the size of Honda would use different forks for 2 similiar 250cc commuter bikes the same age... Or could DS spares be wrong? *head scratch* I did see an RS advertised here fitted with superdream wheels a while back. If so, presumably the larger disk/caliper Jester mentions could fit 250N forks fitted into 250rs yokes??

Sorry for the ramblings, need to sort out the forks and don't want to blow £80 if at all avoidable

[xwhatsit]

Just doing some research on David Silver, the oil seal (Honda p/n 91255413881) listed for CB400n is the same as the CB250N AND the cb250rs... The superdreams also share LH fork bottoms according to the site.

You're shittin' me! I had no idea. I always thought they were very different, although that might be the CB250T I was thinking of.

Just sharing fork seals alone doesn't mean too much though (although means they're 33mm so that's great), as they're a generic thing (just need same inside and outside diameter). The Superdreams have the calliper mounted on the RHS though... so if the fork legs are different on the RHS then that could give you pause to see if the calliper mountings are different.

CB250N is much heavier than the RS so the springs/damping might be better by necessity... that would be nice.

Have you come across some cheap 250N forks?

[tychver]

I've got an entire cb250n superdream to go at. I plan on stealing the wheels for my rs. Comstars just really complete that 80s ratbike look eh!

[tychver]

Having ridden a CB250N I can tell you the suspension probably isn't any better. I doubt they changed the damping, just the spring rate. It feels slightly more planted due to the much better and bigger tires, but you really notice that extra weight. They're not as much fun but I bet they're less insane for long trips on the motorway.

[xwhatsit]

Having ridden a CB250N I can tell you the suspension probably isn't any better. I doubt they changed the damping, just the spring rate. It feels slightly more planted due to the much better and bigger tires, but you really notice that extra weight. They're not as much fun but I bet they're less insane for long trips on the motorway.

You're right, the couple of Wet Dreams I've ridden feel like a sack of soggy shit... they are up near 180kg dry compared to the RS at 125kg dry -- no wonder the RS was considered `sporting' in its day lol. A sleeved down 400 so they were never going to be good. I suppose tauter springs is a start.

They still had FVQs on the back... possibly worse because it was an earlier iteration. A fellow on here named Magua has the 400 and it has broken (i.e. snapped) two FVQs over a year or two.

[Magua]

Tom, if you're interested in 250/400n forks, then try this guy. He's the one I bought my 200 from. http://www.trademe.co.nz/Members/Lis...?member=716336 I noticed he had a cb250rs or two lying around, too.

[jester_parks]

Just posted a lengthy "howto" to Tony not considering that only he can read it!
Please Tony, copy and paste my pn to you into this thread for everybody to know!
Thanx.
To be understood:
It is NOT IMPERATIVE to change to CB400N-forks - it only gives you the benefit of double-disc.
The cheapest is keeping the CB250RS-fork, getting the Bol`dor-caliper and a disc and you are done. Inclusive bleeding the system you are on the road again "with working brakes" within 2 hours.
btw. braided-stainless-steel-line does help a lot!!

[mylittletony]

As requested:

Hi, this conversion is straight forward and you can do it step by step! The CB400N-fork has got the same diameter - so just slot it in! The tubes are a bit longer, but this is no roblemas you can push it through abit further (or - alternatively, fit longer shocks - I am working on that matter).
The caliper CB250RS will fit as well as the disc or the front wheel as a whole - but the you have no benefit: it will brake just as bad!
Solution 1: CB750/900/1100 Bol`Dor-caliper and one of their discs = 276mm = Plug`n Play!...thats what you see on my photograph.
Solution 2: The CB400N-fork gives you the benefit of fitting two calipers = doubledisc. Unfortunately the frontwheel of that particular model is 19inch. Get a wheel ot Yamaha XTZ750 Super-Tenere and redo the wheel for 18inch (it is 21inch), so you have a spoke-wheel with 2 x 240mm discs - Haven`t done that yet, but I am positive it will work and look perfect.
Solution 3: Get a Yamaha TZ-Front-Wheel, fit FZ400 discs =280mm, fit Bol`Dor-calipers and you come up with a 280mm-double-disc. This I have done and the setup is waiting to be fitted.
Just ask for mor information if needed!

Thanks Jester - very informative as always!! I think i'll re-seal my existing forks and do the single disc brake upgrade. I've found a CBX750 caliper but the discs look totally different to the one you show. Can you clarify which model and year discs and calipers are compatible (to the best of your knowledge)?? I'm sure everyone reading this will be interested!!

Xwhatsit: There seem to be a lot of "wet-dreams" over here, especially 250 so i was hoping to score some decent forks more easily. I also wasn't sure which calipers fit which forks, solved by Jester!

[jester_parks]

So sorry - I was too little specific!

The disc itself MUST BE off a CB750/900/1100 Bol`Dor, the CBX disc CAN NOT be used!
The caliper of a CBX750 and FT500 can be used, but the mounting-bracket must be off a Bol`Dor-type....alternatively look for the whole Bol`Dor-setup.
Go for the double-piston-type & go for the later discs, as they are lightened....
Sorry. the picture shows the one-piston variety: this is not correct but I hope you will understand what to use of which model!

[HenryDorsetCase]

So, uh, I have a garage full of CB750 parts, and need to sort out what to keep and what to not keep.

WHat I would like to do is get a wire wheel with dual discs with better calipers than the SOHC CB750 ones (one moving pad, one fixed, on the pivoting bracket). My intention had been to try and source a GL1000 front end complete (a relatively common (in the US) mod in the day for racing apparently). but something like what you've posted above would be perfect.

Sorry to hijack the thread, but any ideas? I want to avoid if possible using a comstar wheel but would consider using a CB750/900 rolladoor front end. Discs and wheel would be the issue there.