Well, I failed.  NO PLASTIC was one of the design principles I followed.  And in my enthusiasm, I failed to appreciate that a battery’s case is made of plastic and no other material is available.  How could I not realize that?  What was I thinking when I declared NO PLASTIC? Was I blind?  No.  The battery just wasn’t installed until the very end so it was out of sight.  And out of sight is out of mind, they say.  How true.  But until I picked up the battery to install it in the bike, I was serious about no plastic.

The HONDA CB550 motorcycles have only a few original plastic components.  One of them is the throttle tube.   A part of it is hidden in the housing and the other is covered by the grip, so you will never actually see it.  But knowing that it is there and that it is made of plastic was certainly enough for me to make me want to replace it.

There are many aftermarket aluminum throttle tubes made by Moose Racing, PROTAPER, J27 MX, etc.  They appear to be well designed and of very high quality.  I was really tempted to get one of those.  But I had to ensure that it would fit the handlebars, the housing, etc.  And that wasn’t easy.

Probably the only unpleasant challenge in building a custom motorcycle is the time consuming effort of figuring out if an aftermarket part you are considering will fit your custom application.  To determine fitment, you need to know all dimensions, thread sizes, etc.  The problem is that nobody provides such detailed information on their websites, or in brochures, etc. and dealers never have it.  So you may end up spending several hours on the phone trying to find out the length and diameter of a certain part only to learn that nobody seems to know.  They all look at a list of what that part will fit and that’s all they have.  If the part is actually made locally and if you end up talking to the engineer who designed it or the machinist who made it, then you just might get the info you need.  But such luck is rare.  If I could have any of the time I spent on this project back, I would ask for the time I spent hunting technical specifications.

In the end, I sent the original throttle tube and an aftermarket throttle housing  to Tom Giovine, who came to the rescue again and machined all the parts I needed.

Throttle Assembly 3

If you decide to go this route, make sure that you use a quality graphite based lubricant when putting the assembly together.

THROTTLE ASSEMBLY complete compressed photo

P.S.  The battery’s case is not the only plastic component. BLACKSQUARE’s  other two plastic components are the side covers and the modified inner rear fender that is mounted between the seat and swing arm and whose purpose is to stop any dirt from being thrown into the velocity stacks by the rear wheel.  So, I failed the NO PLASTIC principle on three counts.  When things like this happen, I pin a few notes on the board in the workshop and try to move on.  Here is one of them:

Success is stumbling from failure to failure with no loss of enthusiasm. – Winston Churchill


Leave a reply