I'm painting an 81 Raleigh Team Pro (Reynolds 753) with a rusted bottom bracket shell. The Cinelli shell originally had grooves to guide the cables. With the rust and time, the cables have worn all the way through the shell, so there's a thin hole about 1/2" long.

My thought is to add a plastic cable guide and just put it over the holes. Would this work? Do the holes need to be filled?

Every bottom bracket shell should have a small drain hole to let tramp water escape so if yours has one either patch the grooves or just leave them and add the guide over them.

That's what I love about this forum. Every once in a while we get new and "impossible" situation.

I don't believe it's possible so saw or rub through a BB shell with a gear wire, but here it is. I suspect that it was more of a rusting process with the wire serving to hold water against the shell, letting the rust etch it's way in.

BTW - a few good closeup photos would be nice.

Clean it up as well as possible, and close it with body filler, or a "metal" epoxy. But you'll need to reroute the wires, so I suggest screwing or gluing a steel or plastic guide.

Wet road grit can serve as a nice abrasive paste between the cables and guide or BB. You'd likely make it through many cables before making it through the BB, but IMO given enough cables, time and shifting, it would be inevitable.

Yes to your idea of buying a plastic guide for the cables. Most bikes of the 80s that had down tube shifters had a delrin plastic guide under the BB.

I suppose it is possible, after all, even water cuts through miles of solid rock eventually as witness the Grand Canyon. However, it must have required a lot of shifting with gritty cables to do this. I have a '96 Litespeed with 70,000 all-weather miles on it and the original plastic Shimano bottom bracket guide is still in good shape.

Even if you used coarse lapping compound, it would take eons to saw through a BB shell. If wear could cut through steel that way, we'd be seeing hundreds of posts about the screw on guides wearing out or falling apart.

Back in 1968 I went to BB routing for the ft derailleur. It took over 10,000 miles to cut through the paint.

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Looks good, but I would have loved to see a photo of the etched groove before you fixed it.

BTW-take a moment and use an Exacto knife to cut about 1/2" from the outside (bottom) of your plastic noodle. The ear wheel throws water, mud and silt at the open end behind the seat tube and it'll rapidly fill and bind your cable if you don't provide an easy exit. This is one reason the original design was made open at the bottom.

It might be interesting to see the BB Shell in question. It's not clear whether the shell rusted through from the inside, or outside. Nor is it clear how stable the shell is at present. As I'm sure everyone knows, the blue bike above is a 'nago, not a Raleigh Team Pro.

Thanks to all for the input. I have no pix as I took it straight from the LBS to the painter. But the shell seems otherwise entirely stable. I've had the bike a little under two years and removed the surface rust (although not under the cables) when I first got it. Then got caught in the rain a number of times this summer and the problem recurred with a lot more paint flaking off, so I decided I needed to get some paint on it. It's sufficiently superficial that I'm relatively certain the structural integrity isn't otherwise compromised.

(I had a 'that really shouldn't be possible reaction myself. But there's no indication it happened from the inside and I can't think of another explanation.)

Maybe it was made that way- combination cable guide/drain hole.

I can find no other example and everyone with great familiarity with these frames says they've never seen or heard of it.

DRAIN HOLE????

There's a clover 1" across cut through the shell. I don't think another mall hole 1-2mm is going to make a difference.

I was referring to the frame in question, not the Colnago pictured...

I gathered that, and could have said that companies don't put weep holes right on the cable run, but this was more fun.

Oh, now I see what you were doing there...

I was thinking of the recent post about dented seat tube, that was in fact manufactured that way,

and the unlikeliness of a shift cable sawing through steel by moving an inch or less X times a week for X years.

But then again, that club shaped hole could have been caused by impacts from road debris....

I agree that it's virtually impossible for a cable to saw or abrade through the shell. As I posted earlier, it took my FD wire over 10,000 miles to work through the paint.

But it is conceivable for a wire to chemically etch it's way through. If you've ever stored steel outdoors, you know the effect. You get rust where there's imperfect contact which traps water causing rust line. So once the wire is through the paint it'll hold water (salt water if ridden in the winter) against the shell, causing rust. With some use the cable will rub off the rust layer exposing fresh steel and setting up the next rust cycle. Do enough of these rust/rub cycles and it'll etch it's way through the shell much faster than would be possible through mechanical abrasion.

Combination drain hole/cable guide

Tidy. I'd use a bit of noodle sleeve in there myself though

God I want to see a pic of this. CudaK has a site with an image of a team pro bb shell from that era- https://www.kurtkaminer.com/TH_raleigh_serials.html

I have a frame I built in 2001 using a Henry James bb shell. the cables run across the bb through guide eyelets. Bike was used for everything including gravel road riding and commuting in all weather (including salty snow). Put 20,000 miles on that thing, and there is not even the slightest groove where the cables run.