CB250RS café racer project

[HenryDorsetCase]

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.

I always liked the brakes on my GB400. that should (you'd think) be not too far off. If I had kept the 400F, I was going to play about witht that as an option.

Now Ive a bunch of 750 bits again though so need something beeeeefy.

[tychver]

Just thought I'd drop in an let it be known that the Keyster XL250S carb rebuild kit works fine with a 122 main jet to rebuild the CB250RS's carb.

[tychver]

Oh, one other thing. Is the Cycleworks exhaust any lighter than the stock pair?

[dogsnbikes]

Hi Guys

Well as the lucky owner of 2 x CB250RS's I have one in orginal condition and Im rebuilding the 2nd well redesigning the 2nd into something fun but different

First of all it will be a single seater,the frame will be cut off just rear of the rear shock mounting point,the mudgaurds are CB650 steel front gaurds will be used front and rear the rear shocks will be GS550 shocks and the headlight is also GS550 the instruments are off a GB400 and the front brake master is of a GN250 the Bars are Drag bars the single 250 is being replaced by a 250 twin which I picked up the other complete with headers,wiring loom,coils,carbs etc for 500 so was a bargin and alot cheaper than buy parts to rebuild other motor

will add more picks and progress reports as the rebuild goes and hope to have this little beasty up and running by xmas intime to ride too the boxing day races in wanganui

[xwhatsit]

Oh, one other thing. Is the Cycleworks exhaust any lighter than the stock pair?

I didn't weigh them, but yes -- I picked them up to compare. It felt like the Cycleworks 2-into-1 was about one to one-and-a-half stock exhausts. Could've been lighter but it's built very robustly, much better than the stock pair.

First of all it will be a single seater,the frame will be cut off just rear of the rear shock mounting point

Cool man! So I suppose that spare engine I almost bought is going to be rebuilt and chucked into it?

You can get rid of most of the frame past the rear of the shock mounts just by unbolting it. There's only a bit left, sort of a `hoop' to support the pillion seat but the rear wheel almost reaches that high in full compression.

[tychver]

I'm thinking mine might fail next WOF on chain/sprockets.

520 chain isn't too hard to find, but where do you know where to get sprockets from?

[dogsnbikes]

I
Cool man! So I suppose that spare engine I almost bought is going to be rebuilt and chucked into it?

You can get rid of most of the frame past the rear of the shock mounts just by unbolting it. There's only a bit left, sort of a `hoop' to support the pillion seat but the rear wheel almost reaches that high in full compression.

everything is unbolted the rest will be cut off....as for the spare engine It will be done up in time think thats about #7 on the things to do list in the shed

[dogsnbikes]

I'm thinking mine might fail next WOF on chain/sprockets.

520 chain isn't too hard to find, but where do you know where to get sprockets from?

parts@econohonda.co.nz

[tychver]

I searched for them on econohonda before but couldn't find any. Found them now. Thanks!

[xwhatsit]

I searched for them on econohonda before but couldn't find any. Found them now. Thanks!

That list they have on the website dates from about 2006... better to ring or email.

A cheap, good-quality sprocket is made by JT Sprockets. They're available from almost any bike shop.

The part numbers for an original kick-start model (the hub doesn't have a `proper' cush drive, there's 4 bolts holding on the sprocket) is JTF 281.14 for the front sprocket, and JTR 248.44 for the rear (the number after the full-stop is for the number of teeth, so 14 teeth front and 44 teeth rear... after trying some different sizes my personal preference is stock gearing).

If you have (like me) an electric start rear hub (I have kickstart engine in an electric start frame... weird), which has a `proper' cush drive, and 6 allen-bolts holding the rear sprocket on, then the part number is JTR 245/2.44 for the rear --- same front sprocket as the kickstart motor.

[jester_parks]

Why not converting to a 428-chain?
Thats my plan after having upgraded my 350 Yamaha from 428 to 520....and lost 15km/h topspeed!
Thinking the other way round, the little Honda doesn`t need a "big" chain, but could do easily with 428 - and could gain topspeed!
As there are no sprockets in the required measurements, I will have them fabricated to size...not the cheapest option, but if there are more people interested it will work out cheaper for the individual.
Drop me a mail if so!

[Kickaha]

Why not converting to a 428-chain?
Thats my plan after having upgraded my 350 Yamaha from 428 to 520....and lost 15km/h topspeed!

Was that with keeping the same ratio?

[jester_parks]

lost topspeed with same ratio!
No wonder if you compare the weight of the two chains!
....and the small RS definitely does not need a big chain!!
428-chain-conversion will be manufactured in Germany with whatever ratio will be required.

[tychver]

Why not converting to a 428-chain?
Thats my plan after having upgraded my 350 Yamaha from 428 to 520....and lost 15km/h topspeed!
Thinking the other way round, the little Honda doesn`t need a "big" chain, but could do easily with 428 - and could gain topspeed!
As there are no sprockets in the required measurements, I will have them fabricated to size...not the cheapest option, but if there are more people interested it will work out cheaper for the individual.
Drop me a mail if so!

You lost 15km/h top speed going from 428 to 520 chain? 428 chain is about 1kg per 100 links and 520 is about 1.5. Even taking into account that it is rotating mass, it is not enough to make 15km/h difference. Something is wrong there!

I wouldn't go for a smaller chain. The CB250RS eats a set of chains and sprockets every 10,000KM already. Single cylinder engines are hard on chains in the first place and the RS doesn't have a proper cush drive to absorb some of the chain shock. The relatively small 14T front sprocket doesn't help much either.

[jester_parks]

"Something is wrong there!"

NOTHING WRONG THERE!!
It is as it is as I have the direct comparison!
No reservations in the least to use a smaller chain on the RS!! - It is a road-bike after all with a very moderat power-output.
Chain-stretch will be bigger, chain-adjustment more often .....but it is as always: there`s a price to pay for everything