Single Coil

I just acquired a 1980's Miyata 710. The external finish is in near mint condition. Little or no scratches or scrapes, very bright and shiny. There is almost no external rust and what little there is is, for example, in the crevasses in the bottom bracket cable guides or in a few paces around the lugs.

When I repacked the bottom bracket bearings a literal cascade of rust, like more than half a 3 oz. bathroom dixie cup, poured out of the chainstays. I could barely keep it out of the bearing grease.

I've only put about 50 miles on it, and I have been very sensitive to performance issues, but I cannot perceive any. The bottom bracket plenty stiff, maybe even stiffer than my Trek carbon fiber and certainly stiffer than my aluminum bikes.

1. Any thoughts on structural concerns?
2. I plan to strip the frame and use Metal Rescue on the exterior surface rust. Thoughts?
3. What to do aboiut the internally rusted chainstays? I was going to get as much of the loose rust out as possible and then apply some kind of rust sealer, like anEvaporust product? Any ideas?

Thanks so much.

Unca_Sam

I'd be concerned with the quality of the rust. Was it powdery, thin flakes, big chunks?

My 912 I bought this year also had rust in the chainstays, but it seemed like flash rust, not pitted rust where I'd worry the chainstays would be compromised. I put some inner tube over the vent hole at the back of the chainstay with zip ties, then poured Ospho into the tube through the bottom bracket.

10 minutes later I drained it and let it dry, no more rust.

dsbrantjr

Evaporust to remove existing rust followed by Frame Saver or equivalent (there is an auto parts store clone whose name escapes me ATM) to resist further rusting would be my choice.

Single Coil

Powdery with some thin largish flakes. I was thinking I would do something like what you suggest.

HillRider

The auto parts store's (NAPA specifically) equal to Frame Saver is Amsoil's "HDMP" Heavy Duty Metal Protector. It and Frame Saver are exact duplicates but HDMP comes in a much larger spray can for less money. By either name the product is very effective.

Unca_Sam

Miyata proudly produced their own tubing, so I'm interested to hear a similar problem. It seems Miyata gave no treatment inside the tube, like a phosphatizing dip. My frame apparently lived in San Jose for part of its life, and I've been chasing rust that crept under the primer for 33 years. I was blaming the rust on living so close to the ocean, but it might just be a miyata thing.

I use evaporust when i wasn't too removed the rust from a part. Rinsing is recommended, with follow up preventive coating. Ospho is paint and forget. It fixes rust as iron tannite rather than removing it, making its own primer.

Unca_Sam

Evaporust is easier to come by. I had to order my quart of Ospho from Amazon.

Single Coil

That's what's odd about this. The exterior finish on the bike is really pretty spectacular considering it is 30+ years old. To the extent I could see into them, the other tubes had what I would think of as pretty standard surface rust, nothing serious at all. It was only the chainstays that have the problem. My guess is someone rode this bike a little bit and then stored it somewhere with a modicum of moisture in the air, like a basement, for a long time, and there must be something about the microenvironment (?) of the chainstays(?) that caused the problem. Or Miyata used crummy steel on the chainstays (which seems unlikely) I appreciate all the helpful suggestions.

Andrew R Stewart 

I suspect the factory cleaning wasn't as complete as it might have been (left over brazing flux can be worse then salt in advancing corrosion), there was no after finishing rust inhibitor applied and the environment the bike lived in wasn't nice either (I had a chromed Fuji that after only 2 months of Santa Cruz humidity was showing rust on every scratch). I seriously discount any claims of "crummy steel". Andy

Unca_Sam

Thanks for the insight as well, since I was hoping you'd chime in. At least on my frame, the brazed on shifter bosses and cable guides hosted quite a bit of rust. I had considered flux, because i didn't see much other reason for the rust "worms" under the primer.

Single Coil

This sounds like the most plausible explanation since the rest of the bike is practically rust free. And no, I didn't mean to disparage the product, the fit, finish and ride quality is otherwise pretty flawless. There's a reason why these bikes are as popular as they are 30 years after they were built.

Unca_Sam

I agree! Good luck with your rebuild. I'm getting close to satisfied that I have all the paint bubbles handled. I really don't want to sand, prime, paint, and clearcoat more than once...