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Miyata 512 - Ugly Duck or hidden swan ?

Old 04-22-19, 07:54 PM
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Miyata 512 - Ugly Duck or hidden swan ?

I picked up a Miyata the other day intending to use the frame as the basis for a 650B conversion. Miyata 512, splined triple butted tubes, 63cm.

Ugly duckling

In 700c format, it has clearance for 25mm, tires - maybe 28s. I saw it had some surface rust and lots of parts I'd donate to the coop, but I have plenty of bits to hang on the frame that would make this an easy conversion.

But after stripping it of parts and cables, I paid attention to this surface rusting around the forward rear brake cable entry hole into the top tube:

And then this rust and what appears to be the start of radial cracking of the top tube at the exit hole of the brake cable.

I had hopes of making a swan from this, but I'm wondering if it is too far gone to be reasonably fixed.

How serious is this cracking? Can the top tube be repaired or replaced? Is the frame otherwise potentially worth the effort to do that? Or should I just move on to the next frame? Any ideas or suggestions?

Last edited by S28546; 04-22-19 at 08:57 PM. Reason: Add details of what is shown
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Old 04-22-19, 08:12 PM
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Whats dat? A hole or something?
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Old 04-22-19, 08:18 PM
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You can't really reasonably replace the top tube but you could just pull the plugs seal an touch up over and use a couple of classic cable clamps these are really tough well built frames so there shouldnty be an issue unless it's rusted through, That said I think this bike should be fixed up and road close to stock it is not a good candidate for 650b conversion you would have issues with brake reach.,crank strick on turns and still really wouldn't have clearance for fenders or bigger tires
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Old 04-23-19, 06:13 AM
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Gonna go "ugly duck" on this one. Part out and cut your losses.
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Old 04-23-19, 06:25 AM
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Are these cracks? Because this is the exact location where they form on these frames, very bad engineering decision to use them. Miyata only used them for a couple of years. Once the cracks start, they grow each time the frame flexes.

Assuming no damage, these splined triple butted frames are rare enough to save, and worthy of a repaint, IMO.
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Old 04-23-19, 12:55 PM
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Those are cracks, Save the fork, headset and other parts, and toss the main frame. It's toast. Sure, it can be repaired by a frame builder. Price of repair will exceed the value of the frame, unless you can get a buddy price.

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Old 04-23-19, 09:03 PM
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I had the same crack issue with a Miyata 312 frame. The cracks didn’t appear until I stripped the oaint from the frame. Everyone here was pretty adament that the frame was dangerous and shouldn’t be ridden with the cracks. So . . . I had the holes patched by a frame builder. The bike now belongs to my grandson.
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Old 04-23-19, 10:24 PM
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Unless you can have the cable-routing holes welded up, I'd put this frame into the trash -- maybe cutting it up first so nobody tries to use it as is. IDK what Miyata was thinking with putting holes in the toptube without some sort of tubing doubler welded on to spread the stress. And WHY have the holes on the top of the toptube where rain water can get into the frame???
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Old 04-25-19, 09:39 PM
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Thanks for all the feedback - ugly duck it is. I noticed the tubing around the rear cable hole has deformed in addition to cracking. I've decided to cut bait with this frame..
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