From CB450 Racer to Bobber

RevheadR

New Member
Hi fellow bikers,

When I say CB450 Racer, I do mean racer:

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I used to campaign this in the Belgian Classic Motorcycle Racing Championship until a crash in Chimay put me off racing. No major damage was done to me or the bike, but I didn't want to take the risks anymore.

Anyway, the bike was dismantled and boxed up for a few years. About a year ago, I had figured out that it was going to be changed into a hardtail bobber, with a racing twist.

Put the frame in a jig with the rear swingarm to locate the rear axle plates, cut-off the rear section bit-by-bit to be replaced by 25mm x 2.5mm seamless steel tubing. Before anyone wants to comment, I know the headstock should be held in the front of the jig. As Mr. Sinatra said: "I did it my way", checked the trueness of the frame and welded the downtube and bottom rails to the jig. Trueness was checked throughout the building and welding of the frame.

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As I am not a professional welder, I only tacked the tubes together. This was then TIG-welded professionaly by a friend.

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The simplicity of the design showed when it came out of the jig.

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Time to get it back on its wheels, so a pair of old CB450 wheels were fitted.

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The frame needed more strengthening, so two tubes in front of the rear wheel (top ans bottom) were put in:

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A mock-up engine went in and it was time to see where the seat was going to go. Note the position of the original footrest... Way too high!

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So the footrests were lowered, the sidestand shortened, the rear brake-mechanism was build (from some CB500Four and CB350K4 parts I found), the rear fender (aka original front fender) was tweaked to closely follow the radius of the tire and fitted.

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Time to go back to the welder and get it all welded up professionally. First the top:

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... and then the bottom:

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A lot more work has been done since, updates will follow shortly. Enjoy!
 
You've got some serious skill. Subscribed with interest.

Sent from my DROIDX using Tapatalk 2
 
Thanks for your kind replies. I had an overall look in mind when I started but am figuring out a lot of smaller details and technical solutions as I go along. Have already tried and thrown away some things that didn't work or I didn't like the look of. As the build continues I will take more pictures...

In order to give the seat springs a bit of movement I chose to secure them with a hairpin clip. Also saves from having to fiddle with a bolt or nut where you can't get to it :D
You can also see the beautiful aluminium Borrani rim and the de-chromed fender.

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Another few hours were spent on the license plate/rear light carrier. I wanted it to be easy to remove (to keep the racer twist, I do have more racer details in mind). It is fitted with two tubes into the frame.

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The very first picture shows the Grimeca 4LS front brake that I used to race with. Very decent brake (when set-up correctly), but not very pleasing to the eye... Luckily another member of the raceteam had his Suzuki GT750 4LS brake for sale. Laced to another Borrani rim, it fits in with the looks of the bike.

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Very happy with the overall look of the bike. Still lots of work to do and details to figure out, but we're getting there!

Since I do a lot of travelling for my work, there are weeks that I won't be able to work on the bike :( Updates will follow, but might take a bit longer to materialise...
 
RevheadR said:
The very first picture shows the Grimeca 4LS front brake that I used to race with. Very decent brake (when set-up correctly), but not very pleasing to the eye...
WHAT? That giant drum brake is killer..... on ANY bike. You just don't see them that often. I love it.

I like a more traditional hardtail back end though, so I'm not crazy about you not following the angle of the stock backbone, or the odd rear axle plates, but the overall profile still looks good. Too bad about your crash. That racer looked great.
 
In order to keep the original registration of the bike I can't extend the wheelbase of it, therefore the angle of the top rails is different to that of the backbone, otherwise it would be too long...

I still have the Grimeca brake and that will find it's way into a future build, I just think it is too square and boxy for the lines of this bike.

As for the racer? That was a lot of fun to build and race, it ran very well. In the end I am glad that it wasn't damaged too much, so I can now turn it into this and keep enjoying it!
 
RevheadR said:
In order to keep the original registration of the bike I can't extend the wheelbase of it, therefore the angle of the top rails is different to that of the backbone, otherwise it would be too long...
Is that some weird Dutch law? I think that here in the US, if you have the original numbers visible on the frame and/or motor, it's still considered the same model of bike, regardless of what you do to the frame.

Do you have inspectors actually measuring your wheelbase and comparing it to Honda's original specification from 30+ years ago?
 
Guys, your comments are much appreciated!

It is indeed some weird Dutch law. When you modify your frame and the wheelbase changes by more than 6cm (shorter or longer) the registration needs to be amended, with all kinds of paperwork and inspections to go through. Not worth the hassle in my opinion.

If you do change the wheelbase and don't get it documented officially, you could lose the registration if you get stopped and it gets investigated. Doesn't happen very often, but would be a shame after all the work that has gone in... 8)

Another week of travelling ahead, so new updates as of next weekend!
 
It looks decent as garage art but you went from a seriously cool and proper race bike to a machine that is for all intents and purposes unrideable due to the terrible ergonomics. Please tell me you're fixing that with some new handlebars.
 
Not sure why you think the ergonomics are terrible, but please give me some pointers if I am missing something. ???

The relative position of the seat, footrests and handlebars/clip-ons is not to far off from an original CB450. All three are just lower and the clip-ons are of course narrower. The seating position is similar to a standard bike with flatbars.

When I'm back I'll take a picture sat on the bike, so you can see what it looks like.

And hey, if it doesn't ride well, I'll just change it until it does ;)
 
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