Bracing the front of the frame

[Chuey]

My Cafe Racer has been on the back burner (or worse) for about a year. The LED lights I had for turn signals had not worked out very well at all. I'm really a nut about turn signals and brake lights so that was taking some of the fun out of riding the bike. Now the two other projects I had are out on the road and the Cafe is back on the work stand. I think the lights are coming around.

As I've done various steps of "development" on the bike, I've put it together and ridden it. The main last step before calling it finished (?!?) is to brace the front of the frame. I'm thinking that I want to brace it without taking it apart completely, spray a quick coat of paint on it and ride it to make sure it's good. When I'm happy that it's ready to go, I'll take it apart and cosmetically upfix it. After all, it started out to be a poseur bike but I love the way it rides. It may someday be able to fulfill the role of posing. It's gotta be shiny to do that, right?
'
Since I don't want to take the whole head bearing assembly apart, I'm thinking of having someone else TIG weld the head tube gussets on for me. My way is to use what I know and that is brazing or gas welding. Both fine, but more heat and hence, more trauma to the bearings, etc. I figure that TIG will cook out the grease but not as badly as brazing it would.

If anybody can post up some pictures of bikes with the head area braced or even sketches of ideas you'd like to share, I'll appreciate it. Thank you.

Chuey

[ME 109]

Dunno if this helps chuey.......

Well, the photo I put up didn't show much. I'll put another one up.

[Deleted User 72]

Dunno if this helps chuey.......

Well, the photo I put up didn't show much. I'll put another one up.

That one shows even less.

[ME 109]

That one shows even less.

What one?

Sorry Chuey, I've completely run out of time for a photo today.
I was sure the original photo I put up clearly showed the brace.........too much.....outback I think.

Here's a photo someone left lying about on the internet.

http://penforhire.files.wordpress.com/2 ... g-head.jpg

[vanzen]

One of a few methods commonly used in the day,
this one on a bike that is/was owned by Ted Witting:



More common was to simply use the plate without the diagonal tubing,
as in the white frame below:



Another popular method (as used by HPN) was simply to "double" the side plates.
Where and how these plates are welded will be crucial to "keeping it straight" –
and ultimate effectiveness.


Or, (pictured in progress) a somewhat more radical approach:

[the quinner]

this one on a bike that is/was owned by Ted Witting:

Still is...we have a secret society of Krauser-powered bikes here in the PacNW.

[ME 109]

I see....... extra bracing.

[vanzen]

Still is...we have a secret society of Krauser-powered bikes here in the PacNW.

Care to share any of those secrets with an old friend stuck in the lost corporate take-over state of Mi ?

[Chuey]

Thanks. What exactly, are the forces that need to be braced against?

Is the head tube trying to twist sideways? Is it tending to move back or forward during certain conditions?

Chuey

[vanzen]

...Is the head tube trying to twist sideways?

Yes. Chubby Checker would be proud – it can do the "Twist".
Lateral forces imposed during the transition of a curve will call the tune.

Is it tending to move back or forward during certain conditions?

Yes, absolutely - typically "back" and caused by forces imposed during rigorous braking.


... But if these effects are not real and perceived, thought of as "trying" or a "tendency" –
The operative question to consider might be, 'If it ain't broke, why fix it ?'

Ultimately, then, one might consider that the experience of "pushing" limits
will be the only true validation for a desire to be actively involved in "extending" those limits
as the experience of chassis flexure and the amount of that flex
will be (almost) entirely dependent upon a very aggressive riding style.

Conversely, we must consider
that much of contemporary MC tire, brake, and chassis engineering and development
which has provided vastly improved performance characteristics
also has had the very tangible benefit of requiring a lesser degree of rider input
to realize any chosen level of those performance characteristics.

Other factors to consider:
Non-stock modifications that will change one aspect
of an otherwise integrated chassis performance package.
i.e. Bigger & Better front brakes
that perform beyond any possible consideration of the BMW engineers' balanced system approach -
Will have the potential to stress and perhaps surpass design limits of both the forks system and the frame.

In fact, with very aggressive braking, 80's era dual Brembo F08s
are capable of introducing enough force into the chassis to produce these distortions -
Similarly, with very aggressive riding in the curves, the "Twist" will be an all too obvious phenomenon.
If, perhaps, only at levels determined to be commensurate with systems design parameters
intended to provide a majority of the consumer market with a compliant chassis
having the ability to perform adequately well in any of a wide variety of riding scenarios.
Subsequently, as a rider's chosen performance intent is brought into focus,
that versatility might now be considered as a limitation, a disadvantage.