I am building up an unbranded team 2008 Kona King Zing frame (made by Dedacciai for Kona) and running into a weird problem with the BB cable guide. I have some generic ones and a proper Shimano SP-18 guide and they're all too tight a bend; the frame uses a normal English BB but the BB area is much larger than a standard shell (big enough for BB30, which they switched for 2009), so the guides I have won't sit flush with the frame. In addition, it doesn't have a threaded hole to accommodate a screw like for an SP-18, just a little hole for a nub. Obviously I don't want to tap out a hole in the carbon.

BB cable guides are sort of a weird part to find because they're included with most frames. Cannondale sells frame-specific guides but I haven't seen others, and none of the guides mention what sort of frame they're designed for. I imagine someone must make a guide for BB30 frames and similar. Where should I look? Or should I just manufacture something out of plastic pipe maybe?

Trek made a metal one for my 5200 that might work.

If you have a plastic guide, you can easily contour the back to match your larger shell. Then install it temporarily trapping it in place with the cables (don't bother adjusting the derailleurs yet). Jiggle it around to find the natural position where the cable routes are shortest, especially the FD cable. Trace the position with a crayon, remove the cables and glue the guide home with double sticky tape.

It won't go anyplace, since the cables will keep it in place, the adhesive is only to keep it from shifting around if/when the cables are slack.

How do I make the guide the right shape? I saw suggestions of heating it up and bending it. I suppose I could cut some material out to make it closer in shape. The plastic ones I have are too rigid to just bend into shape.

Am I the only bike mechanic that still uses these things? Or you can take coarse sand paper, wrap it around the BB shell, and rub the adapter back and forth to sand in the matching curve. (it'll be off by the thickness of the sandpaper)

Either way filing or sanding it to shape is less than 5 minutes work. You don't have to get it perfect, just reasonably close.

I'll give it a try with the file. There is a LOT of material to remove but I have nothing to lose. Thanks for suggesting the simplest approach.

Since you're filing plastic it'll go very fast. If you have one or are buying anyway, the file of choice is a half round bastard, or double cut file. The half round shape will let you contour the inside curve very easily.

try boiling some water , put the cable guide into the water to soft it up , when soften ,mount onto bb , bent to take shape , let it cool and it will keep it new shape .