manchovie

Hey guys! Long time lurker, first time poster.

I’ve just acquired a ’92 miyata TI-6000 with a separating downtube (at the headtube lug). Is there any advice/help you can give me? I’ve been looking high and low on how I can get this bike running again and I kept running into dead ends in my research.

I’ve got access to a prototyping shop with all their machinery/materials and some great brains but I need to know how to tell them how to do it. That is unless it’s easier to do it at home or ship it to you or maybe have someone more local help me out! I’m in Toronto.

Here's what the failure looks like:

Andrew R Stewart 

Harry Havnoonian Bicycles - Bing

Harry is one of the most experienced repair/builders with bonded AL. in North America. Andy.

manchovie

I gave his company a shout on their facebook, hopefully I hear back. Thanks man! Has anyone had to do this on their own bike?

manchovie

I think the way to go might be to remove the head tube assembly entirely by somehow defeating the glue where it attaches to the top tube. Then clean/reglue. Does anyone know how to do this?

Andrew R Stewart 

If you want to ride this bike again be REALLY careful what you do. Do you have experience with catalyzed bonding agents (epoxies)? How about the ability to hold a frame in alignment while said bonding is curing? I strongly suggest a bunch of practice before doing to this frame that might compromise it's future. Andy.

manchovie

Thanks man! I don't personally have much experience with epoxies but I'll have help from some guys with a product engineering and prototyping background with a ton of experience with that stuff. They've put me in touch with their loctite rep to help find just the right one and I'm confident we'll be able to do better than what Miyata had access to in the early 90s. Jig-wise again I'm confident the engineers I'll be doing this with can sort me out here, if not, I guess I'll have a crooked bike . I've reached out to all the local frame builders as well as some others and have a few places I'll call today to learn more info.

There's a bunch of chatter about this problem online but really not a whole lot of evidence of people actually doing much about it, nor much information about getting the frames apart to access the lugs. I'm guessing either they gave up partway through or didn't follow up. One Bosnian fellow fixed up his Ti mountain bike with this method so I've got some hope.

Bradleykd

I just feel like way too much credit is being given to engineers here.

-Love,
A maintenance guy (the people who fix engineers' ideas)

Nothing else to add as I would not attempt this without a frame jig.

manchovie

Ok, I'll look around and see if I can borrow one locally. I fully understand the need for an idea fixer so fortunately one of the guys is a machinist/tool maker, he's been fixing our goofy ideas for years now and will definitely be in charge once the weird adhesive sourcing and frame disassembly stuff is out of the way. My hope is that we'll be able to bend that junction open far enough to access it but it's not looking likely.

FastJake

I'm not an expert on bonded frames but I've owned a few over the years and done some reading on them. From what I remember the tubes/lugs usually fit together as a slight press fit and the epoxy is just intended to keep everything in place.

If you want to repair this frame my guess is that you'll need to remove the headtube from both lugs, then remove those lugs from the top and down tubes (I don't know how to do that part!) You should be able to leave the rest of the frame alone. Then clean everything up and put a fresh layer of epoxy on all the surfaces and re-assemble.

When this type of failure happens most people throw the frame away. That's why you're not finding much. If this is a common issue with your specific Miyata frame I suspect it's a design issue that will probably not be fixed by new epoxy. I would expect it to be a design/fit issue that will simply happen again. But maybe not.

RubeRad

I don't understand why a frame jig would be needed. Why not just pull apart, clean off old epoxy (those will be the two hard steps!), add new really strong epoxy, squeeze back together, clamp, cure and ride? How much play can there be between the tubes and lugs? And besides, it's just the headtube, if it's off by a degree or two, so what, it's a very small lever being misaligned, and the steerer tube is still free to rotate inside it and point the front wheel forward. Worst case, the plane of the front wheel is off from the plane of the rear wheel by what, a mm or two?

Andrew R Stewart 

For someone who has the skill and tooling the difference between a hack job and the right job of reassembly (and it's here that the skill counts, IMO) isn't too much more effort. This can be a very nice riding bike again or it can become a bike who always turns to one side on it's known. That is what a degree or two in the wrong direction will result in. But what does straight steering have to do with a bike? Andy.

froeschli

Not sure how to say this. I have the bike now and it rides beautifully. Some research showed that Miyata used a double lug and the chance of the frame actually moving is very slight. I had an aerospace mechanic check the alignment and it is perfect. The tubes are actually splined and the frame was designed this way for repairability. It does not favour any side and has no quirks, except it is exceptionally light and nimble. In the fall I am having the rear triangle made of HM Carbon and fitting carbon forks. It will be legnedary...

RubeRad

Good job, congrats, I say if it is already exceptionally light and nimble, don't fix it!

Andrew R Stewart 

So I'm confused. Did you take the joint apart and reassemble with fresh bonding agent? Or did you decide to ride the bike as it was when you first posted?

My post, #11 , was more in response to RubeRad's post of how easy it should be to maintain alignment when repairing. I've only done a very few bonding repairs (on bikes, skis is an all together greater experience) and found the process to be frustrating at times. There are reasons that bond fail and these reasons need to be dealt with in addition to the mere mechanical aspects of joint disassembly and cleaning. Case in point was the Vitus that had it's brake bridge bond fail on one stay and that side of the rear triangle spread out a bit. Andy.

xavier.bike

Hey guys,

Just got a 1990 Ti-6000. I have the exact same issue with my downtube.
Did anyone ever succeed a repair ?

Thanks

WizardOfBoz

Love and kisses from us engineers, Bradleykd.