How about a double front downtube?

I also started to query whether I should build a single-downtube frame in the first place.  Brough Superior bikes have them (Pic. 15) so from a strength and handling perspective they ought to be fine.  However Chief engines are not designed to easily become "keystones" or stressed-members of the frame, unlike Sport Scouts which have different front engine-mount lugs on the cases.  The Chief's wide mounting low down at the front, and that stupid bloody magneto deck, were going to result in very messy engine-plate arrangements (Pics. 16 and 17).  Almost as messy as those you see on the Norton Chief in Pic. 18.

Now fellow enthusiast Raymond, whose Tribsa chopper I showed you in Part Two, still has a few bike bits lying around the place.  Propping up one end of his hencoop was a 1960 Triumph duplex (that is, double-downtube) frame which he said I could take and chop up if it were absolutely vital, but if not vital then I was to leave it alone.  You can see from Pic. 19 that these frames have a very steep rake, as Triumph were busy experimenting with steering geometry at that time in an effort to get these things to handle.  But again, once you've tipped it back until the top tube is parallel with the Ariel top tube (Pic 20) it produces a rake of about 32 - 33 degrees with all tubes from the steering head being of the correct angle to give visually pleasing results.

Two things put me off reaching for my hacksaw.  Firstly, these duplex Triumph frames are fairly rare, as they only remained in production for two years before Triumph lurched on to its next phase of frame experimentation (using their customers as unwitting road-testers).  The Triumph Gods might get angry if I carved up a rare frame. 

The second thing that put me off is that the steering head casting on these frames is almost as ugly as the Indian Chief steering head.

Regarding the first objection, when I visited 6th St Specials in Manhattan last year I mentioned this frame option to proprieter Hugh MacKie, and he told me that he had one of these frames with a damaged rear section which he'd let me have for $50!  If I'd known this earlier, I would have gladly sawed off its front part and stowed it in my suitcase, but by this time I was committed to another option involving a Kawasaki Z1000.

Again, it was Raymond to the rescue.  He also had two complete but non-running Z1000's that he'd swapped a crate of beer for, and he let me have one for experimentation purposes.  I promptly sawed off the front of one bike (absolutely no heart-searching this time!) and offered it up to the Ariel frame.  As you can see in Pic. 21,  the visual results in terms of steering-head geometry are well within the ballpark. 

In addition to the top-tube/fork-rake angle being just right for a rake of about 33 degrees, there were two other things I liked about the Kawasaki steering head.  Firstly, the steering head itself is just a plain tube.  You can't get looks much more simple and elegant than that!  Secondly, the outside diameter of the top tube is exactly the same as the Ariel top tube!  Amazing.  In fact all the tubes on the Kawasaki frame have British dimensions.  Later, needing a spacer sleeve to go over two of the slugs being used to expand the Ariel rear frame section, I found that the two frame tubes each side of the battery compartment on the Kawasaki were a perfect match.  So I sawed those off, too. 

As for the rest of it … anybody out there want to buy a Kawasaki Z1000 basketcase, 60% complete?

Encouraged by these discoveries, I started sawing and grinding all extraneous matter off the Kawasaki steering head so that I could do a proper mock-up to check out the "look" of this bike.  When I'd finished, I was left with just the steering-head cylinder itself, and about a foot and a half of frame top tube, with the welded joint intact.  This joint is a tricky weld, because it has to be strong and because the tube end has to be "fish-mouthed" to make it a close fit against the curved surface of the steering head.  If I could use the factory weld rather than be forced to re-position this critical joint, then I'd be off to a big headstart in terms of structural integrity.

Next, I sawed through all tubes in the Ariel rear frame at the mid-points between their lugs, and shoved in some short pieces of old curtain rod so that I could slide each section this way and that.

Up until this point, I’d no idea really if the resulting motorcycle was going to be pleasing to my eye or not.  I could fool around with sketches and artists impressions until the cows got home, but pictures rarely do a motorcycle justice.  The only way to know if it will be cool or be a clunker  is to see something "in the metal".

So with quivering hands and rapidly-beating heart I shoved a Harley FXR front end (another story, which I'll tell you later) into the Kwacker steering head, and lined up its top tube with that of the Ariel.  I slid the rear frame section back by exactly 3" at the cut beneath the gearbox, and adjusted all other sections accordingly.  Then I lifted in my Chief engine, and completed the picture by adding the Triumph rear hub with Harley rim that I'd scored from 6th St. Specials last year.

I stepped back, and what I saw in front of me was … perfection! 

For now, I won't say anything more about it than that.  Go and look at Pics. 23 and 24 to see for yourself.   Suffice to say that, as soon as the cut through the lower frame tubes was separated by 3", everything suddenly looked "right". 

At long last, I’d struck upon a Minimal-fuckin'-ist Chief concept which lived up to the images floating in my mind's eye.

Its time to do some welding.  See you next month.
 
 

Next month:  Frame-building with Dr Frankenstein.

Pic. 16. Probably the neatest way to fit a Chief into a single-downtube frame, but it worries me that there isn’t any support for the downtube at the top front of the motor.

Pic. 17.  Additional support for the downtube can be provided by the top front of the motor if the magneto deck is utilised as a mounting point.  But it was never designed for that, and I was not willing to personally be a test-pilot for the necessary strength-testing under actual road-going conditions … 

Pic. 18.  A Norton Chief, somewhere in France.  Hopefully the many drilled holes made it so quick that nobody had time to catch sight of its rather ugly engine-plate arrangements

Pic. 19.  1960 police Thunderbird, with duplex frame.

Pic. 20. The duplex Triumph frame donated to Project Chief by Raymond.

Pic. 21. When the front of a Kawasaki Z1000 is cut off and lined up with the Ariel frame's top tube, we get a rake of 33 degrees!

Pic. 22.  The Ariel minus its front, and the Kawasaki minus its rear.  All I had to do now was dangle it with some electrodes in a tank of germplasm, and wait for a powerful-enough thunderstorm!

Pic. 23.  Now its starting to look like a motorcycle!

Pic. 24.  Technical consultant Kevin Lowe holds a tank in place, while your columnist bursts into fits of aesthetic superlatives.