RobinWinter

Hi guys, brand new to the forum, actually joined to get your expert opinion(s). I have a Miyata 912 that I absolutely love, but about 2 years ago I had a minor crash (wheel grabbed in a concrete seam in a parking lot and I got tossed), and I've recently noticed these little rusty scratch looking things coming from the rear break line frame hole....I'm worried they're signs that the frame is cracked.

If they are, what am I looking at as far as life for this bike? I don't think its financially feasible to get the frame repaired but I don't want to toss the bike either. So think I can get a few more years out of her?

abshipp 

Robin,

Welcome to the forum!

Unfortunately, I believe that your fears are well-founded. This is a known failure mode for Miyata frames with internal routing like this. You're definitely playing with fire here continuing to ride the frame, it will eventually propagate around the circumference of the frame.

User Colnago Mixte posted here with a similar issue. Unfortunately your frame is going to look like this soon if you keep riding it.

Crack at water bottle boss. Please help me assess.

RobinWinter

Thanks abshipp, that's exactly my fear. So now I need to either find a new bike or possibly score a frame set to swap all my components over. Would a Miyata Pro frame take the Shimano 600 components and the 912's wheels ok? I might be able to grab one.

Oh, and as for my frame, I might as well ride until its toast right? Cant possibly expect to be able to sell it...

Colnago Mixte

I would advise against riding it, not because it's dangerous (it probably isn't) but because every time you flex that frame or go over a bump, those cracks are just gonna grow.

I already attempted one sort of ghetto fix of brazing some hose clamps around the top tube. All four cracks returned in the gaps between the clamps.

So in the next couple of weeks, I will attempt a second repair using pieces of cro moly tubing from a donor bike to make a sleeve, and then I will braze that on. This is how I should have done it the first time, and I'm confident it will work, since I will be essentially replacing a 5-6" section of the top tube. Might be ugly, but how could it not work?

I plan to start a thread when I'm confident the repair worked. So hang in there. These Miyatas are simply too good to toss, and the repair should end up costing me $50 or so, as I will be doing all the work myself.

* crosses fingers *

ThermionicScott 

That's a shame. It has a neat kind of kintsugi look.

Colnago Mixte

Yeah, I was bummed, but I guess I overestimated how strong the repair would be, and underestimated how much frame flexing and torquing goes on with that particular part of the top tube. It was a major unforced error for Miyata to have approved this design.

I should have simply done it right the first time, but I was too eager to save $$$, just so I could brag to people the repair cost me less than $20, which it did, until the cracks reappeared after a couple long rides. It looked fine painted, I doubt anyone would have even noticed the repair.

I bet the repair might have worked had I only located the hose clamps directly over the cracks, but live and learn.

jetboy 

one think you CAN do which i am not sure you want to do- is just chop the thing in half and make a single speed collapsible bike out of it- you can take on trips and just tool around in low stress/speed situation.

I made a prototype one out of a bent up trek. it came out ridable! but i sort lost interest and its been sitting. got to get back to it at some point.

fietsbob

a section of the next larger size of tube , can be shaped to double the thickness around the hole ,
or just fill it , then use an external cable stop, on top of it..

By brazing drawing the molten brass under the patch is do able.. for someone with brazing skills..

I extended the useful life of a bike with down tube damage ,( from hitting a parking stop block at night ,
placed recently, for parking on half of a formerly 2 way street on Campus..) like that..




....

wesmamyke

That is interesting...what are the joint things made out of? They almost look like castings or something. Am I understanding it and those are hinges and it folds up?

dweenk

S&S coupler maybe?

JohnDThompson 

The nice thing about steel is that it seldom fails catastrophically, and those cracks are in an ideal location for you to keep an eye on them.


A possible fix: cut a couple patches from a derelict frame to braze over the cable holes and cracks, braze some cable guides onto the patches, and route the cable externally.

jetboy 

and S&S coupler would be the way to go. this is the $20 version - its an aluminum railing connector.

https://www.nurail.com/

the top one works great, but i could not find the perfect size for the downtube so its oversized and ugly. after I thought I should have done an insert inside the downtube so i could have used the same couplers would have looked way better. I did inserts in the top tube as well for strength: just epoxied them in,



then drilled and tapped in the railing fixture:




the fixture has another small pipe between so it can pivot, but not fully. its really there just to help with adjustment to make sure its straight and also to make it stiffer by making the force perpendicular to the insert pipe pipe, and not the top tube.. where it could fail with a good bump. .

no picture of it but there are 2 allen bolts on the fixture of course- just undo one (2 in total for the bike) and the bike comes apart.
someone else on the Internets came up with this- i just copied.

Colnago Mixte

The OP has more options than I do, the cracks on his are fairly short, so he probably could just do as you describe. But if he's gonna go through the trouble of brazing something, why not put a little effort into saving the internal cable routing? I think patches, combined with add-on external cable routing might not look the best.

As for Miyata, the cracks on my frame snake around probably 2/3rd's of the way around the top tube, when you consider the opening in for the brake cable. Mine needs some pretty radical surgery to ever get back on the road.

But I have flux, silver solder, and a MAPP gas torch. I've also played around with building brick kilns around the work, in order to raise the temps a few hundred extra degrees. If I can cut up a cheap frame and practice first, it should be a piece of cake.

Kontact 

If one has the ability to braze, why wouldn't you just replace the lugged top tube with a new one?

jetboy 

yours is far enough gone you might be better to just cut it clean off, then take a piece of downtube from another bike and braze on a sleeve over the whole thing. then drill a new hole for internal routing.

Colnago Mixte

Yep, that's the plan. And a damned fine one at that.

I figure I will cut the top tube sleeve in half long-ways, and then pre-drill the cable opening. Then silver solder the two halves over the cracked area of the top tube, using hose clamps to hold it in place while brazing. How hard can that be?

qcpmsame 

This was my thought, it seems more logical and safer all-around. Sleeves would be obtrusive to me, couplers sound reasonable if that is your thing. But, if the sleeve works for you, more power to you. I'd be for getting an estimate from @gugie, or some other reputable frame builder, about replacing that failed top tube. Miyata are pretty nice bikes and it it suits you for your riding, it might be the way to look at using.

Bill

gugie 

Replacing a top tube is open heart surgery on a frame. To be honest, I'd pass on that repair. If you're really interested in doing it, I'd have someone replace it that has already done at least one.

qcpmsame 

@gugie: Honest men are hard to find, this is why I mentioned you as a person to seek out.

Bill

Chombi1 

Putting such big holes on a frame tube without any reinforcement at the edges would always be asking for trouble.... What the heck were the engineers thinking of back then??......

CroMo Mike 

It appears that you overheated the steel tube while doing your brazing. That heat-damaged section of steel needs to come out too at this point. Brazing and silver soldering are a delicate balance between hot enough to melt and flow the filler rod, and not melting the base metal. Care and attention to what goes on at the work area are important.

Andy_K 

That's exactly why I keep trying to talk you into attempting such foolhardy repairs...so you'll be someone who has done at least one. If you ever decide you want the experience I've got a Voyageur I'd be happy to let you experiment on.

Colnago Mixte

I apologize, but I don't recall asking for your advice, or anyone else's in this thread. I don't wanna end up owing you guys money or anything.

Kontact 

Why wrap the tubes with strips of hose clamp instead of brazing on a gusset around the opening? It doesn't look like the hose clamps even overlapped the cracks. To reinforce against a radial weakness you'd want to use longitudinal reinforcement. Even a silver fillet would likely stop the cracking if you first stop drill them with a tiny bit.

RobinWinter

OP here, thanks for all the input around this. I've been looking for a shop that can do a repair with no luck so far so now I'm scouring craigslist and ebay for a new frameset. I now have even more questions. Are all Miyata frames with internal brake cable routing prone to this issue? Would a 914 be worth grabbing? Or a late 70s/early 80s Pro Miyata frame? There just arent any cheap options out there for Miyatas it seems. Frames are in the 250+ range and complete bikes are in the 350+ range...

Would like to stay with Miyata and stay in the 912 quality range if I can help it. Been looking at Univega as well but I dont know what the models equate to.