Slightly Cafe CB250RS Project

[xwhatsit]

Unless I'm missing the obvious and it's an electric start model (so he just can't turn it over) CB250RS's will start just fine even with a dead-flat battery. They'll run fine even if you just connect the positive lead to the negative lead and leave the battery out altogether -- however you won't have any lights. Might be a good thing to try before buying it.

I've got some red side-covers... can't fully recall condition, they're buried with a whole bunch of crap. I think they're decent enough though. I'll flog them on very cheap if you want them (like $10 each); I'd give them away but I need some money for a new camchain, gaskets etc. (doing up another stock 250 engine, my gearbox is getting worse and worse -- I've got a bottom end and a top end but they need to be joined together ). There's a red tail/seat too... the tank is pretty farked though.

There's some good forks too but I'm considering hanging onto those to keep a complete rolling chassis for bucket racing or something.

Let me know if you need bits and bobs, chances are I have it and might be persuaded to get rid of it.

[tychver]

I might take you up on those side panels if I don't get this parts bike.

I'm pretty keen on it though, because there's a whole shitload of little things I want. Brake reservoir, side panels, tank, possibly some gearbox bits, the unrestricted cab and intake, exhaust system etc.

I feel like a kid in a candy shop just looking at the pictures. It's seat is fucked though, and the plates are dead so I don't really know who would want it apart from a person already with a CB250RS.

[tychver]

Well, I won that CB250RS parts bike auction. The owner lives 300m away from me! I'm picking it up thursday night, hopefully I can have mine running and WOFed on Sunday. I need to drain the synthetic I put in and get some decent oil in there, degrease the entire engine and find the leak (if any).

I'll then start stripping the clean bodywork off the parts bike and repainting it in a nice coat of modern honda red. I'm thinking of a silver honda wing on the tank, and CB250RS on the side panels in black, but with the "RS" in blue.

Starting to think about the engine...

If any work needs doing internally I'm going to spring for the wiseco and have the entire engine rebalanced. I'll get the cams reground at kelford to something like the Megacycle specs and do a light port and polish on the heads my self.

Should end up with 30-35hp, a fat spread of torque, smoother engine and several years of good riding for $500.

[xwhatsit]

Nice! If you want to get some Honda wings made up cheaply, send a PM to MSTRS. He does all sorts of vinyl cutting, could do the `CB250RS' lettering too. I got some 1960s style ones instead, they look quite neat I reckon, but I'm sure he'll have designs for the more modern ones too.

In terms of rebalancing, what's the story there? When I was first mooting the idea of a 350 piston I asked about this, I got told because it's a single, you can balance the crankshaft weights as perfectly as possible but you won't achieve anything, only shifting the vibrations around 90 degrees (I think that was the figure). Hence the need for the balance shafts.

The Wiseco piston won't be substantially different in weight... maybe you could just leave the crank alone?

[tychver]

Hey, thanks for the tip about the wings, but I've gotta strip, sand, seal and and fill the new tank first.

Well yeah a single can never really be balanced all that well due the fact that the conrod has a greater movement mid-BDC-mid than mid-TDC-mid.

But making sure the balancers aren't adding any undue virbrations themselves and that the crank is actually balancing the vertical momentum of the piston can go a long way to making a single run smooth.

[tychver]

My second rusty piece of shit. Note the much better side panels and tank and exhausts without holes?

I've yet to start it, it needs a new fuel line and a bit of electrical work. If the engine is in better shape I might drop it and fit it to the my bike, which is already road registered, unlike this one!

[tychver]

Pic of my new beastie:

[tychver]

Bodywork and exhausts came off the whore bike last night.

Dad's teaching me to strip and fill. There's a couple of small dents in the nicer which are getting smoothed over.

I'm also going to brillopad the exhausts.

[tychver]

I'm measuring up for some CB250N comstar mags. Still can't decide whether to use the CB250N 270mm disc. It's a fair bit bigger than the little 243mm POS on the RS. Caliper is probably better too, and the headlight would look nice.

Bah, this is turning into the entire front end :|

[tychver]

Oh gawd.

Now I want to build a CB400 four RC160 replica.

[xwhatsit]

I'm measuring up for some CB250N comstar mags. Still can't decide whether to use the CB250N 270mm disc. It's a fair bit bigger than the little 243mm POS on the RS. Caliper is probably better too, and the headlight would look nice.

Bah, this is turning into the entire front end :|

The CB250/400N has a 19" front wheel so that might be tricky. Interesting that the later Japanese 250RS had a two-pot calliper. Nissin I think... would be better than the original `no-name' (i.e. Honda) one-pot calliper. The later electric start models you see in NZ and the UK only had a one-pot calliper, so maybe it was the final Japanese domestic model that had this fitted (they did a CB250RS-R, red and white livery, gold forks and rims etc.).

Oh gawd.

Now I want to build a CB400 four RC160 replica.

I like the later Honda 250cc race models, much sleeker tank/seat combo. Although the RC160 is a special bike for being the first 250cc four since the pre-war supercharged bikes, and Hondas first four I think? The CB400 four is a gorgeous bike though on its own -- you mean the CB400F, 70s model?

[tychver]

Measured up the CB250N wheels. Which turned out to be Nighthawk wheels. 18" front 16" rear.

However I might be able to pinch the drilled disc

Changed the oil and cleaned the strainer yesterday. Don't know why I did it on such a windy day, trying to catch the oil was a bit of a laugh. Put some of that oil cleaner stuff in it before I drained it. Dunno if it got much out but it seemed pretty sludgy. Filter screen seemed fairly clean though, so I guess it's just a lack of the oil being changed for like 9 months. It's done all of 8km in that time though...

Started removing the carb from my parts bike today. It's completely missing the choke cable assembly. Ah well, I've got one on the other carb. Also discovered that it's not siezed. Merely stuck in gear. Maybe the barrel is in better condition than mine? Hmm, need to get that off.

Did some more cleaning rust off the exhausts. Tis fun.

Brakes are on the list next. Stealing the reservoir from the parts bike as it's much less warped. Leaver is in fine condition on mine so I'll keep that. Not sure what to do about that back brake. Seems pretty fucked. It's not returning properly at all and is sticking on. The one on my parts bike is much better, and with less wear on the shoes. Maybe I should swap it over. Hmm. Sounds harder.

[tychver]

Saturday:
Finish cleaning up the headers; the interior welds are horrible
Get the rest of the rust off the mufflers
Drill out the rivets and gut them
Dismatle the carb after it gets dark

Sunday:
Drain brake fluid and swap the reservoirs over. Flush through and refill with nice new Ferodo DOT4 fuild (came in conveniently motorbike sized bottles). Hope it doesn't eat my brakes. Ah well. I've got 3 sets of front brakes handy.

[tychver]

Exhausts got done. Sounds fantastic, runs much better. Pulls strong from 3k to 7k. Not sure what's happened to the top end, maybe I've still got the restrictor plate in there? I'll check when I rebuild this carb.

Never got around to rebuilding the 2nd carb as I've decided to throw it away and get a VM34 for my more highly strung bike. It's fairly seized so I'm definitely going the performance rebuild route.

[xwhatsit]

Yeah I get the same thing with that more open Cycleworks pipe -- pulls strong midrange, but the top end tails off.

I just snaffled the XR250 cylinder head that popped up on Tardme. Bargain -- $70, no cracks, that's a rarity. So I'm going to rebuild the other bottom end I've got into a nice-running reliable standard 250 engine, then get to work on my current engine to bore out to 336cc (piston arrived a few days ago), as it's shagged anyway and needs to be opened right up and split the cases (first gear in the gearbox is toast).

I so nearly bought a VM33 out of Japan a while back but the bidding got too high. It was a Yoshimura-badged thing -- apparently the VM33 is completely different from the rest of the VM28, 34 etc. series. Yoshimura collaborated with Mikuni to make this VM33 pre-jetted for the CB250RS. They made different sizes for other bikes too. At least this is what the auction said (I think, translating from Japanese). Only problem is the VM series don't have an accelerator pump, so you can't snap open the throttle like you can with the PD70A. I'm more keen on a Keihin CR33 (again, sold pre-jetted for CB250RS in Japan), don't know how the prices compare though. Might have to go a little bigger with 336cc.