Slightly Cafe CB250RS Project

[xwhatsit]

No, that's a very different setup from how the RS pegs attach. The footpeg bracket on the RS attaches by the swingarm pivot bolt running through the bracket. That has three small bolts around the circumference. And at the end of the day they're still about the same position as the RS pegs, maybe a cm or two different.

Personally I made up my mind long ago to hang onto my RS and never sell it -- therefore any stupid time and money I spend on the thing I don't have to worry about `overcapitilisation' and `return on investment'... all the effort I put into it is just for my own pleasure. However the sensible thing would be just to tidy it up and buy a VFR400

[tychver]

So you're still running the standard rearsets?

Mine don't suit me, even worse once I get some clubman bars or clip ons.

I'm going to have a look at having some simple ones machined out of of a plate of aluminium, relocating the gear selector and rear brake pedal is going to be a bitch though.

How related are the CL250S and the CB250RS? They look pretty similar.

Just been checking Yahoo Japan out. Saw some FCR35s being sold for CB250rs? 35mm seems a bit big but maybe they work!

[xwhatsit]

Yep still standard pegs. Making one yourself wouldn't be completely ridiculous I suppose, the plate is fairly simple. Mind the drum brake actuation rod though, you could always chop it off and use a die to carve some more thread on it. Making a longer linkage for the gear shifter would be a piece of piss with some threaded rod.

CL250S and CB250RS same thing really, I don't think many came to NZ (at least through official channels?). Might even be same frame, dunno, but basically another in the line of the original XL250S family. The high pipes are so cool

[tychver]

I've actually found that you can get universal rearsets that you get just mounting brackets made up for and adapt the gear selector/brake linkage. Cheaper than getting own plates made I think. The standard ones are kinda uncomfortable for me even with the standard bars, I'm only 5'8 with incredibly short legs. Kinda like an orangutan.

How close is the CB250N frame to the RS? Looks almost the same, but I guess a lot of those Honda 250-350(60?) frames are pretty similar. The rearsets look to mount in the same palces on those bikes, and aftermarket rearsets are available for them.

http://img.yezzz.com/zm4207942.jpeg

The entire rearset seems to sit higher to clear the exhaust though. Dunno if the peg position is any different to the RS, or even if they will fit and not look stupid.

Custom mounted universals it is for me I think. Damn being short sucks. I can't even get my feet down on my uncles XR650L!

[tychver]

http://www.trademe.co.nz/Trade-Me-Mo...-206566396.htm

CB400Four for 1500 anyone? Just look at those headers!

[tychver]

Engine is coming out of the frame tomorrow. Along with the tank and seat unit coming off. Better put a tarp over it to keep the electrics dry.

[xwhatsit]

Blimey! Fiddling with the engine or painting the frame?

I did it on my own (out and back in again) by dropping the bike on its side and pulling the mounts out, was easy like that, although it's not a heavy engine anyway.

[tychver]

Both

I'm reconditioning the engine. Emailed econohonda about getting a complete XR250 engine and gearbox. If it's not ridiculous money, I might grab it and get a sorted RS head on it. Otherwise it's just a new topend, including the damn leaky rocker cover gaskets lol.

I played around in DynoSim setting up a standard CB250RS and playing with it. A simulated curve looks worse than the bike feels. I'm thinking of raising the compression while I have the engine apart. It'll be ok if I just increase the valve clearances by however many thous I have taken off the deck right?

I'm wondering if I can get anything close to 10.5:1 without taking too much. Maybe an XL/XR wiseco is just going to be easier.

It's also getting a new coat of black on the frame, honda red on the body panels, relocated/smaller battery and a nice chrome filter.

[xwhatsit]

I'm going down the 335cc big-bore route, but it's not straightforward and I'll have my existing engine to fall back on if it blows up.

You can take the standard engine out to about 270cc using the standard cases (i.e. you don't have to machine out the crankcase). They were pretty popular mod with the XR250 back in the day I think, there were possibly a few companies who made kits.

I reckon Wiseco might be smarter than shaving the head. Wiseco do a 10:1 for the pre-RFVC 250s, +2mm oversize too, that would put you at 262.2cc instead of stock 248.6cc. If you wanted to shave it I don't think you'd get so far as needing to fiddle with the valves (remembering if you have to add too much slack to the valves, the rockers wear faster and you'll get less opening as well, so that will hamper performance). The stock piston has little cut-outs for valves, you could just machine a little bit more with a dremel until the valves clear it, allowing for a bit of rod stretch.

My RS will ping at low RPM with a stock piston (what are they, 9.3:1 or something?) and 91 octane. So be careful lol.

The later electric starts had more compression in the official literature but Honda never changed the horsepower/torque figures with it though.

I reckon Wiseco 10:1, +2mm (you'll need to give it a rebore anyway) and you'll be laughing. 9.3:1 to 10:1 is pretty good.

Who ever heard anything about hot cams? They must've made a fancy cam for the XR250s, surely. Then again the CB250RS cam is better than an XR250 or XL250 cam anyway.

[tychver]

That's interesting. Mine doesn't ping at all, although it's running stupidly rich.

The rocker covers are leaking bad, and the outer oil seal on the headgasket is going (who knows how long before the inner?), so I figured it was better to save my self some expense in the long run and do it properly.

Option A: Gearbox is in decent condition and it's just an oil seal. Bore is fine, drop in new piston and rings.

Option B: Gearbox is in decent condition and it's just an oil seal. Needs rebore. Go for wiseco and have engine rebalanced plus a hot cam and new valve springs. 28-30hp.

Option C: Gearbox is fucked. XR engine and 6 speed box from econohonda. CB250RS topend with a wiseco 10:1. FCR35. Could get a couple of extra HP by going for a more agressive cam and revving the tits off it.

Oh dear.

[xwhatsit]

The rocker covers as in the two little silver valve inspection covers? Just an O-ring on each, easy -- but if you're talking about the rocker cover as in the whole valve cover on top of the cylinder head, this one is a bit of a tricky one.

There's no gasket, and I don't think you can really add one as the cam runs directly in the head/rocker cover, so you'll change the cam bearing clearances which can't be good. I've wondered about machining out the valve cover and adding a rubber O-ring type thing that sits in a groove? Might be tricky. It needs a gasket because the cheap aluminium warps and you'll be lucky if some bastard hasn't nicked the surface.

The real problem though is that the rockers themselves wear out a little sealing O-ring on their shaft (see what looks like two screw heads on the outside of the rocker cover) and leak out of there... a prick to get access to, the retaining pins seize in there, not looking forward to it.

Making the top-end oil-tight is not easy, heh.

I'd love to discover one of these aggressive cams. I should ask Malcolm at Econohonda if he has anything lying around

[tychver]

http://www.megacyclecams.com/catalog.../page%2025.pdf

http://www.xlintperformance.com/performanceparts.htm

Those are both for XR/XL engines so probably different grinds to the CB250RS but it looked to me like their first cam was pretty much the same as a CB250RS cam.

Standard CB250RS timing is 5/30 and 35/5. Not sure about the lift.

The first megacycle cam is 4/32 and 35/8 so it has a little longer duration with slightly more overlap. Overlap reduces effective compression so engine manufacturers tend to avoid it.

If I end up going to XR engine route I'm going to get a cam ground by kelford and clean up the head my self. I've got a dremel and a flexible shaft and experience ruining VW aircooled heads

Did the megacycle exhaust improve your performance at all? I'm debating whether to get a custom system made up or just clean up this one with a proper silencer.

[xwhatsit]

Thanks for the link there -- interesting stuff! Needle-bearing billet cam? That's a great idea considering the plain bearings which are often shagged.

Can't imagine the 134-50 grind being particularly docile >_<

It's a Cycleworks zorst (they still make and sell them new -- maybe $300-400 or something?). It's improved mid-range torque to the point where you can short-shift it and make nice progress, but it's lost some top-end. May be just a jetting thing; all I've done is pull the plug to check it's not dangerously lean. I'm not going to be too fussed fiddling about with the carb as I'll need to start from square 1 with the 336cc engine.

[jester_parks]

got a "hot-cam" in the shelf waiting for the big engine.
Can`t say anything about the timing yet, but it is obviously a regrind done for (the identical) XL-engine and gives more lift.
Got it a while ago and will take the timing as soon as its in the head

[tychver]

I'm attempting to buy a parts CB250RS in Dunedin. It's pretty rough but the exhausts are still there and the bodywork is completely straight and not cracked like mine. Not sure about fork corrosion, haven't checked. Still
+1 for straight tank.

Apparently it's a non-starter though, possible electrical fault, although the owners swears me blind it'll just need a battery.

I've decided to just get this bike put together and running, in a nice but mostly standard configuration. It'll be as close to factory condition as I can get it without spending large amounts of money I won't be able to get back.