Vince
Changing the shape or dimensions of the bracket could be a good plan. It is vibration that kills these things so making the same design out of heavier metal may not be the answer as you have increased the mass and stiffened the bracket which means that it will probably vibrate at the same natural frequency.
What you need is either a mount that does not transmit the vibration or an assembly that vibrates at a frequency that the SuperHawk does not. A stiffer bracket (not necessarily heavier gauge steel) will push the frequency upwards beyond the normal operating range if you are lucky.
That particular arrangement clearly does not like the 180 degree crank arrangement of the Superhawk. I'll bet good money that if you installed a CA77 motor in there the chain guard would never fracture. That's maybe a little drastic though......
G
Japan Meets Britain
I think also the fact that I ride the thing so darned much increases the likelihood of these chain guards fracturing.
Now it has been suggested by more than one person that the chroming process caused the metal to become brittle. I asked Ronnie Brown / Brown's Chroming about this, and here is his response to me: "I don't think we could have made it brittle, that comes from being put in acid for hours, and we only do it for minutes, I think it was just thin metal and it need reinforced to absorb the movement." Problem with this guard is the fact that you only have one mounting point in the rear, and I've had even stock painted ones fracture twice before. I think it's just a design issue, and hopefully the combination of a rear clevis mount and metal reinforcement in that area should result in a much stronger design. Of course, there's always titanium......
I was told a long time ago that plating causes hydrocarbon embrittlement. When I get parts chrome or zinc plated i have them baked in the oven to release the hydrogen.
My plater told me that's absolutely necessary for any stressed bolts like say axles etc. We have had spokes plated in chrome and in cad and zinc and always have them heat stress relieved afterward. I think it's something like 450 degrees for an hour, but you should check. Ask another plater that does commercial type plating.
In one of my earlier posts above, I did mention that I asked Ronnie Brown about that, and he said with their method it wouldn't happen. Plus, I've had two black-painted chain guards fracture at that very spot too, so the chroming wasn't a factor in those two cases. I think as far as the chromed one that fractured goes, it was a new reproduction that was not an exact copy, and it did not fit perfectly (it was too squared-off, and too tall at the front end). And I don't know if the chain guards are more prone to fracture on my particular bike because I ride the thing so darned much, and frequently on bumpy urban highways at 70mph. I really think it's a design issue -- you have two mounting points up front, and you only have that one mounting point in back, and it's located at the bottom of a very thin piece of metal, and that part of the bike is subject to lots of bumps and impact (might that be a reason why it's hard to find a CB77 chain guard for sale???). I think this clevis mount is the best solution - it looks good, that whole area has been reinforced on the back, and this (original) guard fits properly. It should be on the bike within a week, so the proof will be in the pudding, as they say.....
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