I picked up a barn fresh Miyata 912 today. The only real issue is this dent in the chain stay:







It is somewhere between 1/8 and 3/16 of an inch deep. Is this a serious concern? I'm sure breaking a chain stay at 30 mph would be unpleasant. Is this something a frame builder could fix? The bike was cheap enough that I wouldn't mind spending some money for peace of mind.

Chain stays are very thick in that area, I personally would not be concerned. Any frame builder could do a quick fill with some bronze also..

you shouldn't have to send the bike a frame builder, any good welder should know how to fix it. If you want the bike to look brand new with a fresh paint job then send it to a frame painter and they can usually do repairs like that, just ask before you send it. If you opt for a local welder then buy some paint to match the original paint and touch it back up when it's done.

someone tried putting a triple on there at one point. they tightened it down before they realized they needed a longer bottom bracket ;(

Cosmetically, a little Bondo Glazing and Spot filler (the red stuff in a tube)? It also looks like you have a little kickstand crimpling. Wouldn't really worry about it. Looks like the bike has seen some use, which is the way it should be.

I definitely wouldn't worry about it. Just take a wire wheel to the dent to clean the rust off, hit it with some etching primer, paint, done. That dent shouldn't be a problem as long as the rust isn't deep. I bet you'll like the bike, though. I just piced up a 914 and it's a nice, fast rider.

Cosmetically I'm not worried about it. This bike is going to get a good cleaning, rust removal and some touch up paint. Other than greasing and new cables and bar tape, I'm hoping that's all it needs.

Without looking at the problem in person the initial reaction would be how long can the stay last with that damage before getting worse and failing? I would not trust bondo unless the damage is superficial and not compromising the integrity of the stay. But if that damage cut through the stay, which it appears it had, then I would repair it with bronze filler to give it strength. Stays are strong, true, but they also do a lot flexing, and a cut flexing over time will lead to the cut getting larger and larger and larger then boom down you go. How long that will take depends on the initial cut, rider weight, frequency of riding, and riding surfaces, so it could take 6 months or it could take 6 years or longer.

Steel frame? No worries.

I wouldn't bother with a frame builder or welder; fill it with lead solder or even Bondo and ride it.

Better pic:

Really no big deal. Sand and either paint or fill (JB Weld works well) sand and paint. Ride on.

Thanks for the better pic, no cut that's good. I wouldn't even bondo or JB Weld it unless you want to look perfect, just get the surface rust off and touch up paint it. This dent won't fail the stay.