CB250 RS - Project "Phoenix"

paddyshepherd

Active Member
Hi I'm Paddy & I'm from the North East, UK.
New member here and a new build too.

I'm currently building an old Honda into either a brat or a cafe racer, probably the latter, but since the base will be the same for both, I'm not stressing too much on it yet.

The base bike is a 1980 CB250 RS - this was the single-cylinder, 4 valve version that they did. I picked the bike up from a guy that works at my local MOT garage. He'd mentioned a few years ago that he had a few bikes that would be ideal for what I'm after. Fast forward a couple of years and I went to his house to have a look. It's been sat since around 2006, outside but with a cover over - so rust wise it's not the best but it's not too bad either. I gave the old bloke £300 and the result was he now only has 36 motorcycles.



First things first, we needed to see if that old engine ran. Quick check of the bores, some oil down them, some fresh fuel, carb cleaned and a battery - to our amazement it started on the 3rd kick! The best part was, it didn't just start but it ran - beautifully. No coughs, no splutters, it just ran.

Knowing that the engine was sound, the strip down began. The bike was completely stripped to a rolling chassis. Many parts will never see the bike again so a pile of bits now needs sorting through as to what's worth selling and what's straight to scrap.

This is the end result:



I decided that the stock 250RS fuel tank was too modern looking for what I was after, so a tank from a CB400/4 was sourced from good old eBay. Apologies, but it's not the best photo, lighting is difficult in our garage!



Next up, I decided that I wanted upside down forks, so I've decided to go with Aprilia RS125 units. After a bit of a cock up on eBay, I ended up winning two auctions, the first for a set of forks, yokes and wheels - the second for a job lot, which includes fairings, frames, swingarms, suspension, wheels and various other spares too. I now have a garage full of Aprilia parts. However, not all bad, as having paid only £58 for the job lot and £66 for the first set of bits, I'll easily be able to make more than my money back which can then go back into the build.

Next on my list is to drop the Aprilia front end in loosely so that I can begin to get an idea of my riding position before cutting the frame - being 6'3" this bit might take a bit of playing around with.
 

The Limey

Evil English Villain
Underatted bikes, and rare now too. The XL500 motor of then same era is a virtual straight swap, but biazarrely doesn't make the bike much quicker.

I'm liking where this is going with that tank, so I'm in.
 

paddyshepherd

Active Member
The Limey said:
Underatted bikes, and rare now too. The XL500 motor of then same era is a virtual straight swap, but biazarrely doesn't make the bike much quicker.

I'm liking where this is going with that tank, so I'm in.
Thanks mate - I've read quite a bit about the 500 swap. The plan is for now to build it back as a 250 but keep an eye out for a 500 to then do up and drop in.

Yesterday evening I dropped the Honda front end out and loosely dropped the aprilia one in, so that I can get a better idea of my riding position.

Before:



After:



(I really must get a remote flash for my camera so that garage photos turn out a lot better lit. Either that or actually fix our lighting system.....)

The front end sits really nice on the bike. It's also shown me that the original passenger peg mounts may work perfectly for my rearset mounts (shame they're pretty ugly looking). Unfortunately having a 34" inseam prevents me from having the pegs very high for ground clearance.
However, now that I know where a comfortable(ish) seating position is for me, I can now start marking the frame for cutting and de-tabbing.

My plan is kinda as follows:
Cut/loop the frame, get rid of any unnecessary tabs.
Weld in an under-seat electronics tray. This will house a slim battery, reg/rec unit, fusebox and any other electrics. Since the bike is kick-start only and will have minimal electrics anyway, I can get away with a tiny battery (I could probably run it batteryless, but I feel that is only asking for trouble).

I then need to make adapters/spacers for my front wheel and swap the stems from the bottom yokes of each front end. This will mean I can just buy off the shelf Honda bearings for the headstock.

I think I am more swaying towards a humped seat. The bike will never carry a passenger anyway (especially as I'd never get the Mrs on a bike!) so the seat options are purely down to styling. A hump will need to be fabricated such that it suits the line of the tank once that is in its final position. I envisage quite a low profile hump.

I think colour-wise I'm swayed towards a silver and metallic purple kind of thing. It'll quite possibly be a two-tone set up on the tank, with a Honda lettered logo bridging the two colours.

This will be a long old project and I don't expect it to see the road at any point in 2018 - early 2019 would be nice.
However - before anything else, I need to sell some of those aprilia parts before the old man kicks me out of his garage!
 

paddyshepherd

Active Member
Today I bought an angle grinder so the more serious stuff could commence. We started de-tabbing the frame and cleaning up some of the rear triangle. The rearmost seat mount was left on for now because it's a reference point for where I need the frame cutting at the moment.




Items like the helmet lock, bodywork mounts and lock stops were removed. A new lock stop will be welded on since the aprilia yokes have the stops at the back, compared to the honda which has them at the front.




Not a massive amount to show, but it's starting to take some shape now. The rear triangle needs the top bars cutting and new ones put in which will run horizontal, rather than running slightly downwards like the current ones do. I have now decided that I will definitely have a seat hump, though it will probably only be very low profile and may be made as a removable cover revealing a brat seat underneath.

 

paddyshepherd

Active Member
Not done a lot today (well, not that was worth photographing!)
I cleaned up a few more tabs and took the swing arm off to cut some stuff off there too. Before I did so I laid a spirit level from the crest of the tank down to the back of the bike. Gives a nice idea of the lines and where my rear hump will go. I've now decided I'll run a battery eliminator instead of a battery, so the hump area should be completely empty - instead it'll be used to house a bit of storage space for whilst out on a ride. It probably won't be lockable so it'll have to be for low value items only. The only way I can see it working with a lock is if I had a hinged bit of metal or something with a swivel lock mounted in it, then the hump padding cut around it. To be honest though I may end up with just a fabric hinge in the seat with some clips so that it folds up against the hump and latches into place - a system I've seen on quite a few builds on Instagram and Pinterest.

I think next up I need to get my frame chopped and the seat loop and electronics tray welded into place. Then I can start mocking up for a hump and for a seat. Whilst the frame is with my fabricator I'll probably start to strip the engine down to replace some oil seals etc. The engine ran a charm so I don't see this being a big task.

I think realistically my biggest challenge will be getting the front end sorted out with bearings, stem replacement and wheel spacers etc. I really cannot wait to get some paint on that tank!

 

teazer

Over 1,000 Posts
DTT BOTM WINNER
That seat bump looks really small to my eyes. I would make it longer and taller to better match the lines of the tank. Then I have to admit that I really like the stock tank on those bikes - so slim and sexy shaped. But it's your bike so you get to make it look how ever you want.
 

paddyshepherd

Active Member
teazer said:
That seat bump looks really small to my eyes. I would make it longer and taller to better match the lines of the tank. Then I have to admit that I really like the stock tank on those bikes - so slim and sexy shaped. But it's your bike so you get to make it look how ever you want.
Due to the length of the tank and the seat (I'm tall so need some shuffle room!), the hump was always going to be small - I don't want any bodywork past the centreline of the rear wheel to keep visual weight to a minimum. If anything it may get slightly taller and steeper. I hated the original tank - not because I actually dislike the shape, but more just because I thought it was too modern for what I was after. The hump I've sketched on follows a "swoop" from the tank, but I may modify the swoop line since it comes off the tank a little early at present. I need to download photoshop so I can do it properly - on paint if I try to erase anything it removes the background too, whereas PS I can do it on layers instead.

But thanks nontheless for your opinion - I do appreciate anything people have to say, regardless of whether or not they agree with me!
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
Just out of idle curiosity, how do you plan to get around an MOT and Construction and Use regulations? I thought the UK required rear bodywork to extend to the rear of the rear tire.
 

paddyshepherd

Active Member
teazer said:
Just out of idle curiosity, how do you plan to get around an MOT and Construction and Use regulations? I thought the UK required rear bodywork to extend to the rear of the rear tire.
You're correct in the C&U Regs aspect, but it's not an MOT issue as well.
However, the C&U gets greyer and greyer the older the vehicle is. The official wording is "as far as reasonably practicable" a mudguard must catch any spray from the rear tyre. A guideline is 2/3rds to 3/4 of the tyre should be covered - by the time I get a number plate attached to the back, it won't be far from this region. I can't see any issues arising from it in my area.

Edit: as a bit more background info, I'm loosely using this article as a guide for my build, since a lot of the bikes I'm taking inspiration from follow most of this theory: http://www.bikeexif.com/build-cafe-racer

So the reason for the small hump is to do with the Visual Weight. I am however, planning on shaping the side profile of the hump to match the squared tank, so the back end of the bike might be slightly more squared off to match the steep sides of the tank.
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
Sorry to be the bearer of bad news but that article was a bunch of BS with nonsensical ideas such as "bone lines' which mean absolutely nothing on a bike.

Go with what looks right or balanced to you and if that's big butt or tiny arse, that's all fine. It's what looks right to you and obviously has to be ergonomically sound and safe. Some of us lie sixties Tritons with slightly larger seats. Some prefer MotoGP or Ducati WSB rear ends. The seat hump just has to look like the correct proportions to you.

Many people use a second tank from the same model bike to get a matching back end, but not all tank shapes lend themselves to that approach. I use a combo of CAD (cardboard aided design) and analog photoshop - a print and pencil/crayons and a pack of plain white labels and a large eraser a.k.a. the "delete" function.
 

paddyshepherd

Active Member
teazer said:
Sorry to be the bearer of bad news but that article was a bunch of BS with nonsensical ideas such as "bone lines' which mean absolutely nothing on a bike.

Go with what looks right or balanced to you and if that's big butt or tiny arse, that's all fine. It's what looks right to you and obviously has to be ergonomically sound and safe. Some of us lie sixties Tritons with slightly larger seats. Some prefer MotoGP or Ducati WSB rear ends. The seat hump just has to look like the correct proportions to you.

Many people use a second tank from the same model bike to get a matching back end, but not all tank shapes lend themselves to that approach. I use a combo of CAD (cardboard aided design) and analog photoshop - a print and pencil/crayons and a pack of plain white labels and a large eraser a.k.a. the "delete" function.
Oh don't get me wrong I'm not following it word for word, (hence loosely! ;D) but I've noticed that a lot of the bikes I have used as inspiration do follow those theories to some extent. I think the reason I like a smaller back end is because I also like the Brat bikes with no hump at all.

Having said all that, I've had a complete rethink on the back end yesterday and had a bit of an idea. It sounds a bit bonkers at first but I plan on using a natural wood skateboard deck, (varnished and polished and trimmed to match the frame width), to form the seat base, hump mount, and back of the bike. I've seen it done on a couple of bikes and for my build it makes sense (being a longboarder and snowboarder, it adds a bit of personal quirk to it too). It's easier to explain with a sketch. It's easy to work with, cheap to fuck up, easy to mount stuff to and fairly lightweight too.

You're welcome to call it out as a stupid idea, but I reckon with the right varnish and finishing touches, it could look pretty cool.

 

cb250nproject

If you can make it better do so
mate the bike looks really good, I'm running a similar seat also. beauty is in the eye of the beholder mate,if you have a clear idea of what you want she will come out fine.

I'm hanging to see this build progress
 

paddyshepherd

Active Member
cb250nproject said:
mate the bike looks really good, I'm running a similar seat also. beauty is in the eye of the beholder mate,if you have a clear idea of what you want she will come out fine.

I'm hanging to see this build progress
Thanks mate - I've had a look through yours too.

Hopefully we'll be back on with some progression in a week or so, off to France in the meantime. I can't really do much now until I get the frame cut and welded (need the top of the triangle making a bit more horizontal!) before I can start looking at tank mounting and seat unit.

After that I'll move to the front end and the engine.
 

paddyshepherd

Active Member
Back from France now so started making a little bit of progress and mocking up.

I've removed the rear mudguard mount so that I could drop the skateboard deck into place and review the lines of where I want it to finish the back end off etc.



Roughly where I expect it to sit, just behind the shock mounts with the frame tapering up to it using a triangular piece of plate. That piece of plate will also form the rear seat base (i.e. skateboard deck) mount.


This pic shows where I expect the back end to finish frame wise, and I'll be having the top bar of the rear triangle raised up and shaped so it comes in level with the back of the shock mount where the spirit level is sat. Sent these over to my welder so he knows what to expect when I bring the bike to him.

 

teazer

Over 1,000 Posts
DTT BOTM WINNER
It all comes down to personal taste and it's your bike. To me "Brat" style is going back to a basic standard bike and they don't get me excited, but that's just me. Lots of people like that look. I do like your sketch of what you are trying to do.

Do you have a decent welder close to you? It would be possible to modify the frame to make it a flat top leaving the rear shock mounts in place but changing the tubing in front of the mounts.
 

paddyshepherd

Active Member
teazer said:
It all comes down to personal taste and it's your bike. To me "Brat" style is going back to a basic standard bike and they don't get me excited, but that's just me. Lots of people like that look. I do like your sketch of what you are trying to do.

Do you have a decent welder close to you? It would be possible to modify the frame to make it a flat top leaving the rear shock mounts in place but changing the tubing in front of the mounts.
Yeah, I know what you're saying there - I do like brat bikes but it takes a lot for one to really stand out. This won't be a brat, but it will have a couple of small cues from brat bikes (like the seat base), but it will definitely still have a small rear hump and a more café style colour scheme, probably with quite a lot of polished/brushed parts too. I'm kinda seeing it as a combination of styles. Hopefully it'll work out nice in the end. I'm focussing a lot on aesthetics so I'll be making sure it doesn't just end up looking a dogs dinner of parts. It may sound that way at the moment but I've got a clear image in my head of how it will all flow together - it's just difficult to visualise and show when there's only half of it there!

As for the frame, what you've described is exactly what I'm planning on having done. The new top bar will join at the top of the shock mount such that it's perfectly level. I'm lucky in the fact I've got two good friends who are both very good welders. I've said I don't mind how they do it as long as the end result is the same, but I envisage they'll cut the top bar out completely and weld a new one in, which will taper at the rear end to merge with the top of the shock mount.

datadavid said:
Oh no not a skateboard seat!
Not sure how that input is helpful in any way, shape or form.
 

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