1967 CB450K0 Black Bomber Rebuild - By Royhall

[royhall]

The rear mudguard was not as simple a fit as I was expecting as the space I had measured to put the extra wiring turned out to be much smaller than I thought. With the mudguard fitted it pushed the wiring right up against the Selenium rectifier that has me concerned about the heat damaging the wiring especially if the rectifier were to fail. As the rectifier is 53 years old there is a fair chance that it could fail so I decided to replace it with a modern unit. It was a fairly simple four wire fix and just a small aluminium bracket to make to carry it. Makes sense really as I have used a later model higher output alternator with a CB250 regulator and electronic ignition so it's already way off standard. May as well go the whole way.

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As you can see from the two pictures it was all pretty tight. Now the rectifier is replaced it has freed up quite a bit of space for the wiring. The wiring is now all accessible from the left hand side and just requires the removal of the left hand side panel and air filter.

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You can see in this shot just how much extra wiring is under the rectifier. Hope all my crimps are good or that would mean removing the rear wheel and mudguard to get a soldering iron in. All the crimps were done with a really good pro crimping tool and passed the pull test at the time, but now I wished I had taken the time to solder them as well. To be fair though I thought the access was going to be much better.

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At this point I fitted the rear wheel and chain, no issues there at all. The chain was sold as a CB450K0 specific item but was about 6 links too long. An easy job to remedy and always better too long than too short. I'm sorry Mr Honda but those mudguards are just massive.

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[royhall]

The assembly of the handlebars is a simple affair on this bike. The right hand unit simply contains the starter button and the left hand unit just the lights dimmer and horn button. The unit on the right polished up okay and the starter button tested okay so that went back on and the cable fed through the bars, the left hand unit had a damaged dimmer switch, so as new ones were still available that was replaced. All in all a very simple and quick job.

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The control cables were not as simple a job as I was expecting. I had bought all the cables early on in the build and expected just to take an hour to fit them. The clutch cable was correct but required a lot of research into it's routing as it fouled in many places, I got it right in the end though and once lubricated and adjusted the clutch works really well. The speedo cable turned out to be a K1 part as that's all that was available. It is the correct length and colour but the nut that fixes it to the speedo drive gearbox is longer than the K0 and bottoms out before the cable is tight. The remedy there was to simply hacksaw 6mm off the end of the aluminium nut. Simples. The front brake cable was impossible to source ready made as they are all too long. I was hoping Venhills would remove 110mm off the lever end of one and replace the nipple but they wouldn't do it. Instead they copied the old cable and made a completely new unit, unfortunately they didn't have all the fittings required so had to reuse the bottom adjuster. It's not been re-plated but you cant really see it on the bike when the rubber boot is pulled on.

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As I had already fitted the pattern seat I thought it prudent at this time to try the petrol tank on to see how the fit is between tank and seat. I had no cause for worry as the tank went straight onto it's new mounting rubbers with the aid of a smear of rubber grease and the seat closed with a perfect gap. Well pleased, and first time in years that the bike looks like a Black Bomber again.

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I have jumped ahead a bit with the pictures as I forgot to to take snaps at the time. Next job is fitting the carbs and air filters that from the above picture you can see are already fitted. A real Blue Peter car crash. I could have cropped the picture but to be honest I cant be bothered.

[royhall]

Next up was the carbs. I sent the original carbs off to the guy I always use for refurbishment, Matt Harper (sales@harpers-ultrasonic.com). I used to do them myself years ago but these days the old eyesight isn't what it was, nor is the patience with all the stuck tiny screws. After stripping and checking the carbs they were declared scrap as they were simply worn out. Taking advice from Matt plus a bit of research online, I decided to go with a set of CB500T carbs. These were restored with new 450 jets and needles (supplied by Ash) and the accelerator pumps blocked off as the pump diaphragms are not available. Matt was of the opinion that the pumps would deliver too much fuel to a 450 and flood it. Time will tell if he was correct.

They were an easy fit with new genuine rubbers and clamps. The pattern air filters also fitted okay as I had previously fitted them and got around the usual pattern part fitment issues. As you can see, the filter top mounting bracket is in the wrong place so required slotting to get the bolt in.

The weird spring steel choke connector took a bit of sorting out until I realised that the 450 and 500 items are different. Fortunately I had a 500 link sent with the carbs, so job done.

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[royhall]

Next up is the replica silencers that came from CMS via DSS with the proud boast that they are made to exacting Japanese standards. Well they don't fit. What a surprise pattern parts that don't fit who'd have thought. The problem is the standard Bomber mounting brackets don't fit, on ringing DSS they informed me I needed K1 brackets. After wasting a further £50 on K1 brackets I discovered that they don't fit either. Very annoying, I really wish these companies would actually test fit these pattern parts then they would know that they are wrong. It appears that there is nothing wrong with the silencers themselves it's just a rear bracket issue so I have decided to make some brackets myself. I could have used mild steel and painted them but instead decided to make life hard and use 3mm stainless.

I have started to make the brackets but have come to a dead stop. The problem is that I don't have a right hand downpipe at the moment as it's still at the chromers. So I have fitted the left pipe and started the rear brackets but need the right pipe fitted to get height and length alignment so all stop on that job. I am also waiting for the headlamp rim from the chromers so I can finish the wiring.

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Once I get the correct positions I can mark the mounting hole and drill it through. This stainless is a real pig to drill and cut. Once the drilling is done I can mark out a triangular shape between the holes and cut them out properly. Then deburr and chamfer and polish them to a nice finish.

So until the chromer comes through that's as far as the project can go. This is where its up to now. The last picture makes the seat look out of line but it's actually not closed onto the clamp. It fits perfectly when it's fully down. The seat itself is the lipped model that shouldn't really be fitted to this bike. I chose it because I like the blended to the tank look that it gives and it also protects the tanks paintwork as the bike will be getting some use. When it comes to selling it I am having the original seat refurbished so it can go with it, or be fitted before sale. The original flat seat and tall tank join reminds me of the 1970's nut crusher MZ250, not a good look but that's just personal preference.

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[Moorey]

Stainless requires good quality sharp drill bits a little Trefolex and a slow drill speed and you should be OK. It work hardens very rapidly.

[royhall]

I use Rocol but the same thing really. I use thin slitting disks made specially for stainless to cut it out and a sharp file to finish.

[philward]

Bike looks superb Roy!

[royhall]

The two remaining items have finally arrived back from the chromer, namely the headlight rim and the right hand exhaust header pipe. Now according to CMS the pattern silencers should fit perfectly as they are "Japanese perfection replica's". So what's the score here with the right hand silencer.

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On offering up the silencer the mounting bracket fouls the back of the crankcase by quite a margin. At this point I have no option but to cut into a finish chromed piece, not something I would do by choice. After marking out a line around the crankcase with a black Sharpie, it was just a very careful cut using a very thin disk in the grinder.

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The cut went quite well and after smoothing out and deburring with a fine file I masked the area off and sprayed three coats of cold galvanise to stop the rust (hopefully). If the cold galvanise fails to work the silencer will have to go out for chroming. I used a car scissor jack to lift the silencers into position so I could mark the final hole in the new mounting brackets which was then drilled 11mm to take a 10mm mounting bolt. With the holes drilled I then removed the excess material from the brackets to make a triangular piece, then polished them up on the buffing wheel. To mount the silencers into the correct position I first started with the left silencer and aligned it so the main stand cleared the cut out and hit the rubber stop correctly. To achieve this I used stainless washers to move the silencer left or right, that done I fitted the right silencer packing it so it was even with the left.

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Considering the fitment problems encountered with these so called perfect replica's I am really pleased with the end result. It's annoying that they say they are for the K0 when really they are K1 silencers, but that said I am glad they are available as without them it would be virtually impossible to finish a build like this.

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[royhall]

After aligning the silencers with all the bolts just nipped, I started at the front and tightened all the bolts and clamps. At this point the gremlins struck again and one of the 6mm header studs stripped in the cylinder head. It must have been close to going already as I barely got past a light nip before it went. In frustration the garage door got shut on it and I left it for a few days. On return I simply removed the left pipe and Helicoiled the head and put it all back together. Thirty minutes is all it took,  but when it happens it's just so annoying it's best to walk away and forget it for a while. The headlamp went on no problem whatsoever and worked perfectly first time.

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The petrol tank was the last item to fit although it had been sitting on the bike for a while. After removing I fitted the new fuel tap and put about 0.5ltrs of petrol in the tank and gave it a really good swill around then emptied it into a clean bowl. The petrol came out as clean as it went in so no problems there. I then put a full gallon of petrol in the tank whilst it was still on the bench to check for leaks. As it appeared to have no leaks I put the tank back on the bike and connected the petrol pipes. Unknown to me at this point I had set myself up for a big scare.

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It's finally time to prepare for engine startup. With the plugs removed and back in the caps I turned the engine on the starter and observed good fat blue spark at both plugs. At this point the electronic ignition is set to a scribed mark to give a rough setting for startup, afterwards it will be accurately set with a strobe light. The engine turned well on the starter so I gave it a short burst to circulate the oil again, the replaced the plugs in the head. I turned on the petrol tap to fill the carbs and check for leaks, once again all is good.

Time to see if the engine will start. Not being sure what the procedure will be I gave it half choke and no throttle. On pressing the starter button I got a nasty metal to metal sound and a reluctance for the starter sprag clutch to engage and turn the engine. The clutch was rebuilt with new rollers, springs, and cups into the old clutch as new ones are totally unavailable. It appears that the original was too worn to be saved so that' s my new problem. Anyway soldiering on, I tried to start the engine again and this time it fired up straight away. Now here's the previously mentioned scare, it went straight to 7000rpm before I could reach under the tank to kill the ignition. Scared the crap out of me and my hands were still shaking 30 minutes later.

A little investigation revealed that when fitting the tank I had trapped the throttle cable splitter box and pulled it out of its housing, as a result the throttle was at about 60%. To be honest I'm surprised the engine started from cold in that configuration. With that sorted I tried again and it started okay with just the tick-over a little high but that easily adjusted to a steady 1000rpm. Unfortunately the starter clutch doesn't want to play anymore so that will now be coming apart again.

Whilst it was running I checked for charging at the battery. Static the battery voltage was 12.7 volts, running it read 12.76 volts so not totally sure it's charging. It's a new AGM battery so I am uncertain if the 60's alternator has the output to better that voltage plus there's now a regulator fitted.

A couple of questions, can I safely disconnect this red wire from the rectifier and run the engine without anything melting. If I can I can measure the charge voltage without it being connected to the battery. Does that sound possible? And secondly does anyone know where I could get a replacement starter sprag clutch or can I replace it with a clutch from another bike.


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[MrDavo]

It looks excellent, shame about the starter clutch. Mine was fine but original and unworn, I know people have had trouble with them. Two of my rear rocker cover screw threads could do with helicoiling, but I’d need to pull the motor to get the space to do it properly. In the meantime I have a slight leak from there which I’ll put up with.

Looking at the photos the right side carb to air cleaner band doesn’t seem to be on properly. My air cleaners are the same as yours, and are also a pain to assemble, when I had all the faffing around with float levels and air leaks they were on and off like a naughty lady’s undergarments.

My CL450 doesn’t seem to charge at much of a higher voltage, which did worry me. That said I’ve never had the battery go flat, even with the lights on.

[K2-K6]

Very nice work Roy.

"Now here's the previously mentioned scare, it went straight to 7000rpm before I could reach under the tank to kill the ignition. Scared the crap out of me and my hands were still shaking 30 minutes later."

I bet that reduced the time for oil to reach the exhaust cam   

[royhall]

Well spotted Dave. I already rectified that since the photo was taken, strangely it was the photo that alerted me to it. Can you remember what voltage reading you got at the battery, static and with the engine running. My only concern there is that I have updated the wiring quite a bit so anything is possible. As for the oil pressure, it gave it a good leak test and nothing came out. As for blood pressure, well that went sky high.

[AshimotoK0]

The best way to check if the system is charging it to put a multimeter on 10A DC range in series between the +ve battery terminal and the positive wiring BUT don't operate the starter as this wil draw too much current and pop the fuse in the meter. You will then see a positive value if the system is charging (at different revs)  and negative value  if it's not charging. I don't have any experience with those Motobatt batteries, so I  can't really comment on those.

Your pattern silencers will definitely have been meant for a K0 as the K1 does not have the front mounting brackets. Don't ask me how I know this....  I bought a set of NOS 'K0' silencers, which turned out to be K1 (i.e no front brackets). If you look at the Bomber in David Silvers museum closely, it is fitted with K1 silencers with the front brackets bodged on and silver painted. Luckily I found some proper K0 NOS silencers and sold on the K1 ones.

One Achilles heel fault of the Bomber is the starter sprag clutch. On mine the retaining screws had come loose and chewed up the rear of the alternator rotor and also ripped out the stator windings. Also the sprag rollers had distorted and ruined the side plate. Plus the sprag clutch rollers had also badly worn the boss on the sprag clutch sprocket assembly. The parts are rocking horse poo parts. I have got my mate Graham Curtis looking at recovering the sprockets by grinding down the boss and shrinking on a hardened collar. I did get hold of a NOS CB500T --275-- rotor and it looks basically the same as the --283-- part (the taper is the same). People tell me you can fit the 5-speed parts but even these are very rare, even in the States. The ony place I have seen selling the clutch and alternator rotor relatively cheaply, in decent nick,  is the seller on eBay called BGM Cafe racers.

There was a discussion on Facebook Bomber closed group on the starter clutch .. I will copy it later and put it on here.

[royhall]

Thanks Ash will look forward to reading the Facebook thing as it may have some useful information.

I have taken the starter clutch back out and degreased everything. It was covered in some greasy goo that I think came off the new starter chain. I thought that may have been the problem but no luck as it was just the same.

After cleaning I miked everything up to check for maybe an odd roller but didn't find anything. I have assembled it on the bench and tried it, one of the rollers sticks out of position every time I tried it. Under a magnifying glass the roller mating face has two dents that are grabbing the roller and stopping it moving. All three faces have this wear but one is worse. Really this part requires replacing but they are available nowhere.

My plan for tomorrow is to polish the faces with a small fine polishing stone and try to remove a bit of material at the high spots to take away the dent and see how that works. I have nothing to loose if it doesn't work as it's useless as it is. If that doesn't work, to be honest I don't know what I will do. I doubt I will find a new or good used item as there are so many people looking. I was hoping that someone would have come up with a cunning plan to remedy this as it's a very common problem. All I can find on the internet is how to replace the rollers and springs. One lucky break is the roller face on the sprocket is in good condition.

Any ideas here would be gratefully received. Cheers.


UPDATE. Just noticed something here   https://www.cmsnl.com/honda-cb450k0-black-bomber-general-export-usa_model14564/rotor-ac-dyn_31101283013/#.X7lX7-VxeUk   This alternator rotor has lugs to centre the starter clutch, mine does not have these. I was wondering how it was supposed to centre as the starter is bolted down before the rotor is on the shaft. If its even slightly off centre it's going to cause a problem? Probably wont help as these items aren't available either, but looking at mine it does look like some arse of a PO has filed the lugs off. Looks like I need a replacement rotor before moving on.

Spot the difference. No wonder the starter wont work.

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[K2-K6]

Wondering if there are any close that could be machined as the basic design has mostly been copied from those early Honda I believe.

https://www.ebay.co.uk/itm/Anlasser-freilauf-Starter-CLUTCH-Yamaha-VMAX-1200-V-MAX-Kupplung-VMAX12-/111619692053

Is it the component in above link?