1980 CB250RS - Another Aussie newby

G'day guys,

I've finally gone far enough into this project to think it's worth sharing. Hopefully others can learn from some of the mistakes I've made along the way! A little background, whilst I am fairly mechanically minded and have worked with small engines before this is my first foray into the bike world, and it's been a hell of an experience!

I had been wanting to do a build for the last 12 months but was just waiting for the right bike to come around. Finally spotted this 250rs on gumtree for $200 in running condition. DEAL! "What a bargain!!" I thought to myself...After getting it home and pulling it down and having a look through, I'm fairly certain I got exactly $200 worth of bike and not much more haha.

Here's what I had when I got home:


Quick assessment: Front end off a completely different bike and didn't even fit correctly, there was a decent 3mm of play. Not sure how it was being ridden around! The front drum brake also didn't match the forks. Tank was beyond a bondo repair end very rusted on the outside (inside was great!). No chain and front sprocket so couldn't take it for a run (probably for the best!). Engine ran nicely on choke, but was a bit hesitant with the choke off (no air filter so I imagine the jetting wasn't quite right). Rear drum worked nicely. Tyres absolutely stuffed. Rear shocks bounced like there was no damping at all!

So it's at this point I was quite torn as to what to do. I know the right thing to do is get it on the road, get a feel for the bike and then decide on a direction. But the work just to get this thing on the road was going to be just as much as rebuilding. So after much deliberation that's the way we headed!

The inspiration:

First lesson: Research your bike THOROUGHLY before starting a project! After getting the bike home I did some reading about the RS to find out some unique problems. Like so many of the honda's, there were no bearings between the camshaft and head, so if it had ever been starved for oil they had a habit of chewing up camshafts and heads pretty quickly. Quick google showed that camshafts were as rare as hens teeth. Luckily this is what I found:



Next thing: The RS was one of the earlier 4 valve heads, there was not much meat between the valve seats and the spark plug hole so once they got a bit to hot they had a habit of cracking between the seats. I was not so lucky with this:



Cracks between the exhaust valve seats. F*&$. A little demotivated about rebuilding an engine with a cracked head. Started pricing up a repair job, not cheap. But I couldn't stand the idea of leaving it as is. Then the morning I was going to take it to the head shop, I was drinking my morning coffee and browsing gumtree... Must have been my lucky day!! A head from a 1982 CB250RS for $30! Had it in the mail a few hours later.

A trip to the wreckers had me equipped with 250RS front end, some corn stars from the 250n (more or less interchangeable) and another RS tank. Happy days! Or so I thought.

The next few days were stripping down the frame, adding to the list of parts required (boy was that list getting long!). After a bit of reading, I found that the RS was a notoriously nice bike to ride, with good handling. I really wanted to keep it that way so there will be minimal modifications to the frame and suspension/ride height.

Frame cleaned up nicely:



So turned my attention to the years of dirt and oil caked into the cooling fins of the engine. After spending nearly a full day cleaning the heads without successfully removing all of the paint I found myself a soda blaster. $150 later this is what I received (not pictured: barrel):



Had a good luck at the bottom end and gears during disassembly, and was very relieved. Everything was well and truly within tolerance. Turns out the bottom end and gears were all designed with the 500 in mind, so are somewhat overkill for the 250. Just the way I like it.



Attention turned to the brakes. Rear drum looked good, and after a bit of cleaning looked even better. Plenty of meat left on the (hopefully not asbestos) brake shoes. Front calliper was in alright condition (picked up from the wreckers as well). A little bit of oxidising inside that cleaned up alright. Piston was seized but pressed out beautifully with a grease gun and 10mm grease zerk. A bit of pitting right around the seal so it was back to the internet to try and source 43x38mm piston. Boy did that take some time, but now have a calliper I'm happy with.

New (old) tank cleaned up (love my wire wheel!). Turns out it was been painted about 5 different colours before it got to me! A few shallow dents that will need filling. I did however start to really appreciated the patina'd finish in raw steel, hmmm. Frame, swing arm, rims and a few brackets were sent off to the powder coater's for grit blasting and coating (satin black - boring I know).



I had decided to leave the swing arm bushings during powder coating after the manual said that drifting them out would destroy them. Well damned if you do damned if you don't because when I got the arm back the heat must have damaged the bushes and they dropped straight out when I tried to put the steel collars back in. Bugger. Luckily a friend of a friend had a machine shop and turned me up some new bronze bushings that should outlast the bike.

Turned my attention back to the engine, piston was looking a little sad, with scuff marks on the skirt and the liner wasn't much better with a few gouges. Probably a little deep for a hone so started looking for a 0.25mm piston kit, but the only one I could find that wasn't going to cost an arm and a leg was a 1mm over bore. Oh well, I don't see myself flogging this thing too much to require any additional over bores so that's the way we go. Plenty of meat in the liner for 1mm as well.



And bottom end rebuilt. This was the most daunting to me. Having never worked with motorbikes or gearboxes before, the whole things seemed a bit over my head. After pulling it apart and reading the manual thoroughly it now all makes perfect sense and she still shifts beautifully! Happy days! Spent about 2 hours double checking everything before sealing the 2 halves back up making sure I didn't miss anything....Of course I missed something.. F&$^!!! Split them back open, clean up the threebond and try again, this time with the counter balance chain guide in place .



And here she sits, waiting for the barrel to come back with the new overbore:

Carburettors!! All I can say here is that boiling lemon juice is absolute magic!! But don't let any small alloy parts settle to the bottom in any hot spots Nearly dissolved the cover for my accelerator pump. Luckily pulled it out just before too much damage, but did have to clean up the sealing surface on some glass with some lapping compound. Crisis averted!


A tiny bit of polishing on one of the covers, and a new seal kit (sourced from a cb750A just fyi) has it sitting ready for an engine:



Rebuilt and painted the forks with new seals and fork oil. Little bit of pitting on the stanchions. May have to do a modern front end eventually but this will allow me to atleast get a feel for the bike. Tripple tree's cleaned up and painted as well. Note: Hammerite satin black is absolute SH!T. Very difficult to use. Really missing my compressor and spray equipment right around this point in the build. Rattle cans just don't cut it.



This is where the next lesson kicked in: Just because your wreckers says that the forks are all good doesn't mean they are. Never assume!! Somehow during re-assembly I didn't notice the left stanchion was bent. Another bugger. There was about 5mm runout when it was rotated. It was bent just below the bottom triple from what I could tell. I just couldn't deal with looking down and not having the steering lined up with the wheel. So $50 later it was pressed out and I was much happier.

And here's how she stands right now! Old shocks on just to get a rolling frame. Progress will stall for a few weeks now, moving house (much to my displeasure) and work will have me interstate for a little bit. Certainly not lacking motivation now! Can't wait to hear this thing alive again!

Super excited to see what is to come.

Are you using a Haynes repair manual to assist you? If so where could I find one?

Welcome to the forum Chris,Nice Honda 250 8)

Welcome and well done so far! Wise move on keeping the frame mostly stock. This is the kind of experience that is missing in the world of motorcycling these days....getting your hands dirty, using your brain and finding out just how the machine looks and works from the inside out. When you get this on the road you will be closer to being 'one' with the machine than anybody who just 'buys and rides' can ever be. I've always had a soft spot for smaller displacement bikes (funny thing is when I was a kid, this would have been considered to be a mid-range bike), it ought to turn out to be a great little machine...best of luck and enjoy the experience.

eglintonw, I would be in a world of hurt if it wasn't for my Haynes manual. I got it from the ever reliable ebay. Was about $30 AUD in total.

Thanks for the welcome guys! I am absolutely itching to get the old girl running and on the road, but for now I'm at the mercy of the machine shop. Sent my cylinder in to be bored and valves/head to be reground about 4 weeks ago now. At the time I was assured it would be a 3 day turn-around .

Small progress in the meantime, clip-ons are on. New jets and a Uni filter are on. Switches and a few other small pieces have been cleaned up in preparation for installation.

Few questions for any cb250n/rs owners: Does anyone know if the cb250n calliper bracket will fit the 250rs calliper?? The disc I have at the moment is a little too big for the RS calliper and I'm trying to work something out.

Also, opinions on lubricating the piston/cylinder during re-assembly? 2-stroke oil or dry?

g'day chris, nice work so far, they're a fine little bike. i've got the front forks from one with an XR250 wheel inserted in my BSA C11, which one day will emerge from the garage disguised as a trials bike

for lubing up the topend during assembly, just use whatever oil you're going to use in the engine (if you're going to be getting it going straight away) or assembly lube (supercheap or repco should have it) if the engine is going to sit for a while before you get it running

where in australia are you? there seems to a fair few aussies on here from all over the place, i'm in (bloody cold today) melbourne

I agree with spotty, just use whatever you are using for engine oil on the cylinder, rings and piston, but be sure to give the cylinder a really good scrubbing before assembly...you don't want any of the honing abrasives sticking to the cylinder walls. Obviously, when you get it running, observing a proper break in period is critical to ring seating and long engine life.

Awesome, thanks for the input guys. Engine oil it is. Hopefully get the cylinder and head back the next few days. In the meantime I'm having a think about styling. Bit tricky with the lines on this bike but toying with the idea of using the stock seat and cutting the foam down flat to a thicker brat style seat.

Also still trying to source a 250n calliper bracket with the hopes it will fit the 250rs calliper so I can use the larger disc.

Fun and games!

Chris B.

maybe with the caliper/bracket/disc jigsaw puzzle, have a look through some microfiche/part number lists and see which part numbers match/re-appear between the two bikes

spotty said:

maybe with the caliper/bracket/disc jigsaw puzzle, have a look through some microfiche/part number lists and see which part numbers match/re-appear between the two bikes

Click to expand...

I agree,that's worked well for me also.
I've also found that Honda has sometimes changed part#'s only for a small cosmetic reason between some parts(color or lack of paint or a small extra hole or tab)and that the parts were essentially the same fit.

Been having a very close look at cmsnl to crosscheck parts, however can't quite determine the 250n hanger/bracket will fit the rs calliper. I suspect it will however rather than gamble $80 on a bracket that may not work, I picked up some 10mm aluminium to make up a bracket to adapt the RS calliper to the N's disc.

Also, Spotty, I'm currently based in Adelaide but I'm expecting work to move me back to Brisbane any month now. Aim is to get the bike finished before that happens!

chrisbchips said:

Been having a very close look at cmsnl to crosscheck parts, however can't quite determine the 250n hanger/bracket will fit the rs calliper. I suspect it will however rather than gamble $80 on a bracket that may not work, I picked up some 10mm aluminium to make up a bracket to adapt the RS calliper to the N's disc.

Also, Spotty, I'm currently based in Adelaide but I'm expecting work to move me back to Brisbane any month now. Aim is to get the bike finished before that happens!

Click to expand...

any cycle salvage yards you could get a used one from ?

Welcome mate. Good to see another Aussie.

grcamna5 said:

any cycle salvage yards you could get a used one from ?

Click to expand...

theres quite a few wreckers in adelaide, quick google just turned up 4 or 5, you may well find the bits you need or even someone who already knows

https://www.google.com.au/?gws_rd=ssl#q=motorcycle+wreckers+adelaide+north+east+rd

be warned, making your own bracket can be a RWC fail when you take the bike for rego, in theory anything like that should have an engineers certificate. i got away with it on my bike as i didn't have to take the bike to the rego branch and the guy who did my RWC 'looked the other way', it was going on club reg and you can just take paperwork in to the rego branch. lucky.

MR Cycles has been my go-to wreckers and has been a massive help. Picked up the tank, forks, wheels and more off him.

spotty said:

be warned, making your own bracket can be a RWC fail when you take the bike for rego, in theory anything like that should have an engineers certificate. i got away with it on my bike as i didn't have to take the bike to the rego branch and the guy who did my RWC 'looked the other way', it was going on club reg and you can just take paperwork in to the rego branch. lucky.

Click to expand...

Thank god I have you guys for guidance. Makes perfect sense that they wouldn't trust an amateur to mount his own brakes. That brings us back to the original plan: 250n bracket. I suspect it will fit, however the callipers are completely different parts between the two models. The RS has a bigger piston and no cooling fins.

Called the machine shop for the millionth time today, has been over 5 weeks since I dropped off the cylinder and head off. Unfortunately they still haven't finished as the "guys are out racing". Apparently Monday will be my lucky day! Here's hoping.

shame you're not in england, those sorts of things are plentiful (and cheap) over there

http://www.ebay.co.uk/itm/HONDA-CB250N-FRONT-CALIPER-CARRIER-MASTER-CYLINDER-/261821526383?pt=LH_DefaultDomain_3&hash=item3cf5c7716f

mind you, small hondas used to be fairly plentiful here too, but they all got used up and throwed away