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Author Topic: CB250 RS - Project "Phoenix"  (Read 6272 times)

Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #70 on: Jul 25, 2018, 04:30:36 »
Couple of bits and bobs done the last few days.

I was at Silverstone Classic weekend just gone and picked up an AntiGravity Lithium battery while I was there. This thing is tiny and weighs next to nothing! So as soon as I got home I immediately offered it up. I've decided to hold off on shocks until I get my rear wheel and tyre sorted, so for now I'm not moving the battery tray until I know if it's necessary or not.



I offered up most of the key electrical components to the bike. The coil and reg/rec sit underneath the tank like they used to & the CDI unit can sit next to the battery within the battery tray. I'd already cut out a cardboard template for the main electronics tray but it appears there'll be very little for it to house now as most of the items already have a home! I'm also slightly concerned about the risk of over-stiffening the frame if I put a big panel in there... is that a valid worry or do we not think it'll make much difference?



I've also now decided I'm going to reuse the standard 250RS switchgear and simply refurbish them. The housings are metal so I'll either rub them down and leave them with a raw finish or I'll re-paint them black. At the moment they're kind of a faded grey. I originally planned on replacing but they actually look pretty nice, and very period. I'll probably run a separate quick-action throttle housing and some stubby levers since the clutch is so light.




In other news, I've also purchased a Daytona Velona combined speedo/tacho, I've finally received my reworked camshaft and I've started removing more of the engine casings etc ready to get them blasted and painted. Progress is a nice feeling!


Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #71 on: Sep 17, 2018, 16:23:44 »
Well, this has been very slow.

Due to various personal goings on, along with currently raising a puppy, work in the garage has pretty much ground to a halt.
I got 10 minutes or so to have a mooch at stuff a while back so I started fiddling, and instantly spotted an issue. With the disc removed from the wheel so that I could centralise the wheel to my previous measurements, the caliper hits the spokes of the wheel. This is due to the fact the caliper is mounted inboard of the fork, since the yokes on the monster front end are spaced for a wider wheel than the aprilia ones are. The ducati forks and caliper simply will not work, not without machining either the caliper or the mount - neither of which I want to do. I kicked the tyre and went back in the house.

A few weeks of sulking later I finally had a bit of a rethink, and the solution is much more glaringly obvious than I ever imagined. When I first started looking at fork conversions I looked to All Balls Racing for a conversion set of bearings. They didn't do anything for a 250RS, it's simply not common enough. Today however, thanks to a conversion list on here I accidentally stumbled upon, I discovered there's a lot of much more common hondas using the same bearings as the RS. One of those happens to be a CB750, which All Balls do several (and I mean several) sets for. Scrolling down the list for some smaller bikes that the kits are available for, I came across a kit for the KTM RC 390/Duke 390. These run a similar width front wheel to the RS, and are less than 3kg different to one, dry. With this kit I can run the yokes and forks of the 390, a wheel bearing is available for the spindle, since it's the same size spindle as the RS125 one I previously fitted. To eBay we go, armed with my ducati forks and brembo caliper to try and buffer some of the cost!


Edit: Had some measurements through for the KTM. Forks are a bit longer at around 745mm, so approx 20mm or so longer than original.
The stem is also longer, including bearings and seals between yokes there is approx. 200mm, compared to approx 180 on mine. I think it may still be workable, just with the forks dropped through the yoke a little and having the stem machined down to suit, I suppose? What do we reckon?
« Last Edit: Sep 18, 2018, 08:11:41 by paddyshepherd »

Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #72 on: Sep 25, 2018, 09:02:00 »
OK, we're doing this properly this time.

KTM forks and bottom yoke collected. The stem can't be shortened as it does actually have a taper on the stem below the bearing seat. So instead, and to save faffing around with conversion bearings that I'd have to import, I'm having a new stem made to fit the KTM yoke but with the standard Honda bearings. The forks are black, which completely goes against one of the bad points of the aprilia forks, since I wanted to change to silver. However, they are in absolutely immaculate condition, having only covered 800 miles. I'm going to leave them as they are for now, and if I still don't like the black when it's all finished I'll strip them and send them off to be reanodised. I've ordered a top yoke from Tyga Performance, this is a race-orientated yoke which doesn't come with the ignition barrel mount, since it's part of the casting on the stock one. I now need to order some clip ons as well, but that's in progress. I do however intend to replace the seals on the forks - not because they're leaking, just because they're well... orange! Oh and of course, get rid of those silly reflectors!




Offline Kunphushun

  • Posts: 9
Re: CB250 RS - Project "Phoenix"
« Reply #73 on: Oct 08, 2018, 21:55:15 »
Really cool build so far!

Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #74 on: Oct 09, 2018, 16:47:07 »
Really cool build so far!

Thanks mate!

So here goes, big update.

I got my new stem made and received it back today, but I'll come to that shortly.

So recently I was wondering what to do with the front wheel, since the hub I was using had that weird disc brake adapter on it that I didn't really like (which would also need modifying for the new alignment), and I'd have to make wheel spacers to suit it in the new forks as well. Fast forward a day or two, trawling the internet to see what was available for the KTM's. I decided I'd get a custom hub made by a company that had cafe'd a 390 and made their own hub. However, whilst waiting for a quote from them, through a complete accident, I discovered that the new Husqvarna Svartpilen/Vitpilen 401 is a Duke 390 with a dress on. Now, no big deal, until you discover the Svartpilen has 17" spoked wheels. A quick phone call to my local Husqvarna spares dealer and I had a brand new hub on it's way to me. This would drop straight into the forks, brake would line up, no funny adapters to make and no new spacers needed. It's a lovely item.



So I've packed that straight off to my wheel builders to finally get my wheelset built with the honda rear hub in it and that new one in the front. Once I get those back, I can get tyres on, allowing me to finally sort out the rear shocks!

So onto the front end then.

Good news and bad up here. I got my lovely Diamond Racing clip ons, and they really do look fantastic.



I then got my new custom stem today and set about fitting the yokes up. Now unfortunately this is where it turns a little more sour. The stem doesn't quite fit right. No fault of the machinist, it matches the honda stem perfectly and looks bang on:



The difference is however, the KTM top yoke is significantly thicker, making the stem too short. I managed to make it fit by removing the rubber dust shield and washer from beneath the bottom bearing, but there's still only a few threads available to fit the nut to. B*gger.

So. My last hope was that the Tyga top yoke may be a little bit thinner than the stock one. But I've had a right old nightmare trying to get my hands on one. The place I ordered it from didn't have any in stock, and his next batch got stuck in customs clearance. So two weeks after I sent him my money I've cancelled the order and gone back to the drawing board. Now in order to fix the mess I've now got I was discussing with my machinist potentially shortening the stem slightly, and rather than using a nut use an internal thread and a bolt. Would work. But we then both had a light bulb moment. Just get a custom yoke, which he has offered to do for the same price of the Tyga one that I can't get my hands on. By doing this, he'll be able to make the mounting a little bit thinner around the stem, and in general make everything fit a little nicer. So I need to pull it all apart again tomorrow night and send it back off to him.

But anyway. Here's some pics of how it will all look.


(not the best lighting, but you get the idea)

and from the top:



and here you can see how close it was to being perfect. (I can get the nut on by a few threads here, but this is without the seal and washer underneath the bottom bearing, and I'd much prefer I got them in)





So close, yet so far...





 

Offline Brodie

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  • Posts: 2356
  • Gold Coast, Queensland
Re: CB250 RS - Project "Phoenix"
« Reply #75 on: Oct 09, 2018, 19:09:28 »
Just a thought for the top yoke.
My BSA A10 has a threaded sleeve that screws onto the stem between the yoke and stem.

The yoke then clamps onto the stem.

Why not make a sleeve with a hex shaped shoulder and bore out the yoke to accept it.

Food for thought.
I'm not sure, but don't ask Brodie.

Way to many build and half done projects to list here.
Sr250, Gs750, Z50A, XV1100, A10, Z160A.

Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #76 on: Oct 10, 2018, 07:02:11 »
Just a thought for the top yoke.
My BSA A10 has a threaded sleeve that screws onto the stem between the yoke and stem.

The yoke then clamps onto the stem.

Why not make a sleeve with a hex shaped shoulder and bore out the yoke to accept it.

Food for thought.

That indeed would work - however as I say I was going to be buying a race top yoke anyway (to remove the ignition mount and other tabs), so it makes sense to just get a new one machined instead!

Cheers though!

Offline teazer

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Re: CB250 RS - Project "Phoenix"
« Reply #77 on: Oct 10, 2018, 11:51:12 »
Leave the top yoke and just get a sleeve nut machined up with a hex top, so machine it out of hex bar stock.  It can be alloy or stainless - either will work.

Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #78 on: Oct 11, 2018, 04:48:35 »
Teazer, again I appreciate the suggestion but I'd be changing the top yoke regardless - the stock KTM one would need a lot of work to get it where I'd want it to be. So if I was going to be spending 150 on a race one, I'd much rather that money was going into a mate's pocket and getting a completely custom product for the same price.

A little more progress, anyway.

I got a phone call from my wheel builder yesterday asking me to pop in. I only dropped the rims off with him monday night and it turns out he's already had both rims polished and my front one was all built, just needed truing and tension - and it looks bloody fantastic!


Rear rim after the polishers:


They haven't managed to get every mark out, but considering there was some nasty dings in those rims here and there I think they've done extremely well to get them looking that good.

and the front one built up with the Husqvarna hub:


Looks bloody lovely if I do say so myself.

As an aside, I'd been looking at what tyres I want to run when I get the wheels back.
With dropping to 17's, I get plenty of choice for sticky rubber - but only if I can get them in narrower widths. One set that I've been having a look at is the ContiTwist Supermoto tyres. The skinniest they do for a rear is a 130/70 R17.  This would just about go on my rear rim & the conti is supposedly a "pointy" tyre, so that should hopefully counteract the slower handling of the wider tyre. I was concerned that it wouldn't fit in my swingarm, so I borrowed one from my local tyre place to check.

It's probably bigger than my 250 will ever need, but it looks bang on and in proportion to me - would you agree?



I do now however need to check if it'll be compatible with my rim, being a tubeless tyre I will probably use a tubeless kit anyway but it depends on rim profile too. Outex say their kit is fine on any rim, WM type or not.


Offline paddyshepherd

  • Posts: 64
Re: CB250 RS - Project "Phoenix"
« Reply #79 on: Oct 14, 2018, 12:44:04 »
Tyres ordered for getting my wheels back this week.
Gone for Bridgestone BT-39SS, 100/80 front, 120/80 rear. I decided the 130 was more than too wide.

The BT-39ss was produced for production class racing for 125's, so should be nice and sticky. Not fussed about wear life as it's not a bike that will see a massive amount of miles.

I'm planning on doing a tubeless conversion if possible though to remove the weight of the tubes.
Hopefully by next week I'll have a full rolling chassis again, as I'll get shocks ordered as soon as I've got the rear tyre on.