Boxerworks.com

I have the straight front to back (CC products style) frame braces on my Cafe Racer. To that, I added a 3/8" X 1 1/4" steel crossbar that attaches to the top engine to transmission bolts. The bar has the ends kicked up in order to meet the frame braces. That configuration seems to me to not put undue stress on engine parts that were only designed to fasten dust covers. The points I used are heavily cast and are meant to take a load. If that helps anything, I can't say. There are so many differences in my Cafe and a stock bike that I think the riding position makes the most difference.

Here is what a respected guru of BMW-dom said about my Cafe when he saw it: The frame braces are not needed. They may help with extreme braking forces. (I have stock brakes and there is nothing extreme about the forces they can apply.) He was non committal about the cross brace. He said my clip ons are an ergonomic mistake and that the bike needs a lesser (?) fork rake (he has a mod he likes and I think it's mostly less rake) for the steering effort to be correct for clipons. I like the steering feel of the bike with the clipons. He really liked the way I used the existing passenger peg wings and mounted the working bits inside for making my rearsets. It is the fact that they don't put the rider's feet in a wider stance that he praised.

Some random thoughts on the subject:

For cross frame bracing, I think my cross brace to the frame braces is more effective than a triangle that reaches up to the top tube. Whether or not it does any good is something I can't back up.

As far as it goes, wobbling is not an issue of not having added frame braces. I am sure of that.

From what I've seen, ME109 could outride, on his stock RS, most anybody, frame braces or not. That is worth considering.

I did not expect my frame bracing to do any good at my riding level, if any. At some point, it is an exercise in not doing stupid stuff but doing most of what people have thought would lead to better handling. I don't think it has hurt anything and that is a bonus. I made my bike to be, first, an example of a style I like (Cafe Racers) and to not be one of those where they just strip off most of the bodywork and put a hump seat on it. It turned out to be a super fun bike to ride.

Chuey

As I've said before I want to use the 'Clamshell' air filter housing and stock filter along with the /5 tank I have, the CC type braces would be too high at the rear and too low at the front with this arrangement so I've been playing around with carboard, perspex and body filler to roughly mock up my recent ideas.
I'd like to share these ideas with you and ask for feedback - not really whether they're necessary because that debate goes on and on but rather whether they will work - have a look -



This is a brace that would go from the rear of the engine to the rear of the top frame tube, I'd have to machine it out of billet aluminium so that it would clear the air filter - this will put the frames mounting point a little too forward - more thinking needed there. The Filter shell will need cutting to clear this brace as well as the next one -



This would brace the swinging arm pivots to the engine sitting under the air filter. This would brace any fore and aft loading but not any up or down.



To complete the bracing I was thinking of a headsteady as with the Norton Featherbed frame.
Here I would weld a couple of lugs to the top of the timing housing and bracing these to the frame tube via the Mono's coil bracket (I'd have to make another for the L/H side) - one either side and bolted together with a spacer. I'm really not sure about this one as the Featherbeds steady connects the headstock directly to the engine but it would complete tying in the frame to the engine.
So do you have any constructive thoughts?

It seems as if you're using the engine to do what the fore/aft CC Products braces do. You may end up with the same effect I have but with the radial bracing of the two top trans to engine mounts a bit less effective due to being braced up so high above the mounting points.

I approached Vanzen on the subject of trying to get permission to use his design and of course, I offered to pay him for the right to do so, much as one pays for the right to use a boat designer's design. His response to me told me he wasn't into the idea and thought that anything approaching that would be sort of like plagiarism on my part. To be fair, he posited that he did not know my abilities to construct the frame competently. I gave up on that idea in honor of his feelings. I had seen it as being respectful and as having honored his design but he saw it as some dude trying to catch his wave.

Nourish, I see your rear braces as a fresh new idea that has merit. However, the guru that I mentioned would no doubt say that it is something that answers a question that hasn't been asked by the frame. As for his credentials, he's an engineer who worked at the BMW factory in the design of the flying brick but now lives in So Calif. and finds employment fixing BMW motorcycles. I think he likes me because I listen when he pontificates.

Chuey

I approached Vanzen on the subject of trying to get permission to use his design and of course, I offered to pay him for the right to do so, much as one pays for the right to use a boat designer's design. His response to me told me he wasn't into the idea and thought that anything approaching that would be sort of like plagiarism on my part. To be fair, he posited that he did not know my abilities to construct the frame competently. I gave up on that idea in honor of his feelings. I had seen it as being respectful and as having honored his design but he saw it as some dude trying to catch his wave.

Has that bike been completed and tested?

Hi Chuey

something that answers a question that hasn't been asked by the frame

Could you expand on this? as I thought this would be the same question that the CC type braces answer.

Good to see your interest and experimentation in frame strengthening Nourish.
I've seen so many variations of bracing and different places being braced.
As a metal fabricator/welder I can appreciate the skill required to produce structurally sound components used to brace a frame.
I do question the information on which many of these braces are designed from.

The precise weaknesses of say a /7 frame should be should be known in full by now. By that I mean the exact places that need to be braced, and the ideal shape of the brace should be known. No more, no less.
Seeing so many variations of bracing sort of says we don't really know what we're doing?

Whether or not a brace is necessary sort of goes hand in hand with whether it will work, or not.

I would think that any type of bolted brace that has any clearance around the bolt, is less than ideal.

I think your tube brace needs to be in line with its anchor point at the tranny. Being offset to the bolt allows for increased leverage on the top tranny studs. Perhaps your tube could have an internal threaded boss at the tranny end to screw onto the stud?

Thanks for your thoughts, I can't see that I would be able to put the tubes directly onto the studs as these would interfere with the air filter outlets instead of going under them.
I was thinking of using 14 guage plate (2mm - 0.080") folded at a right angle to brace the two 16mm tubes and bolted down in the three places as shown to help spread the load, the tubes would fit right under the two engine studs to keep deflection to a minimum. Any forward load would be directed into the engine cases, do you not think the 8mm studs would be man enough to hold onto the loads that would be pulling on them or am I missing something? Although I could use high tensile studs.
How much do these frames deflect - surely more than the clearance required on the bolt holes?

Vanzen - Where is he? - I don't think I've heard from him in ages - his web page has gone.

Nourish wrote:Thanks for your thoughts, I can't see that I would be able to put the tubes directly onto the studs as these would interfere with the air filter outlets instead of going under them.
I was thinking of using 14 guage plate (2mm - 0.080") folded at a right angle to brace the two 16mm tubes and bolted down in the three places as shown to help spread the load, the tubes would fit right under the two engine studs to keep deflection to a minimum. Any forward load would be directed into the engine cases, do you not think the 8mm studs would be man enough to hold onto the loads that would be pulling on them or am I missing something? Although I could use high tensile studs.
How much do these frames deflect - surely more than the clearance required on the bolt holes?

Vanzen - Where is he? - I don't think I've heard from him in ages - his web page has gone.

Ah yes, those air thingies. There's always pods.

2mm is on the light side for the intended job, however a triangular brace bracing the 'foot' with the bolt hole in it, would help significantly. If the brace is intended to stop either side of the swing arm from moving forward or backwards, the 'plate' component of the brace is not really required. The small bolt in the centre of the tranny would need to be a very close tolerance fit or it would do not much more than stopping the plate from rattling. Besides, that bolt is totally unsuitable for a long term anchor point.
There is no problem with the studs at all. They are supreme here. The possibility of a stud being pulled (case threads yeild) over time is real. Of course, this depends on what forces exist. Or not.
Any movement at a brace's connections is counter productive.

How much do these frames flex? That's what I'm talikin' 'bout. And where, to be precise.

I miss Vanzen too.

I could fold a lip from left to right behind the center bolt - that would stiffen the plate up to stop the tubes from flexing. That bolt really wouldn't take any fore and aft load as the gearbox studs should take that - I thought more likely to keep it clamped down and rigid.
You talked of a triangular brace - do you mean an extra verticle fillet at the tubes gearbox end?
Should the thread strip we would then know if the frame was flexing around here! Possibly then tap it out for M10 studs.

Nourish wrote:I could fold a lip from left to right behind the center bolt - that would stiffen the plate up to stop the tubes from flexing. That bolt really wouldn't take any fore and aft load as the gearbox studs should take that - I thought more likely to keep it clamped down and rigid.
You talked of a triangular brace - do you mean an extra verticle fillet at the tubes gearbox end?
Should the thread strip we would then know if the frame was flexing around here! Possibly then tap it out for M10 studs.

A folded lip will stiffen the plate, particularly if it extends to the brace tubes, and the plate will stiffen the tubes.
I'd think a sufficiently strong tube would negate the need for the plate,

You're correct re the vertical bracing at the gearbox end of the tube. The vertical height should be at least as high as the top of the retaining nut. This brace should extend along the tube at least twice it's height.
Where the vertical brace best attaches to the tube depends on what obstacles may be present.
There's also the question of what handling characteristics may be changed by removing flex.

All this of course is just the way I see it. I've never strengthened a frame.