rickpaulos

Trek 1200 road bike. bonded aluminum construction. One piece cast head tube with internal lugs for the top tube and down tube. Similar for the bb shell and seat lug. IMO, with the internal cable routing, no chain stay bridge, these are very clean looking frames. the 1200 came with a steel fork in 1988.

Received recently at our local bike coop. A project bike for sure. Came in with a hideous 3 color fade paint job. I asked a local volunteer who specializes in polishing frame to a mirror finish to strip the paint and we'd take a look at polishing. He got quite far along before he revealed the hole in the frame which had been hidden under a beer sticker. Looks like someone tried to drill out a water bottle blind nut and got carried away. So now what? Fill the hole with Alumiweld or some epoxy like JB Weld? Replace the down tube? Make it a wall hanger?

I took the frame to a newbie local bike part artist and aspiring frame builder. He did some practice runs using Alumiweld on some aluminum rims and that was not the least bit promising. It looked like the rims were melting at a lower temperature than the alumiweld. We watched the vids on youtube about alumiweld and they state the material needs to be heated to 750F. Even a propane torch melts aluminum.

I don't know that kind of glues Trek used. Would they be thermal activated. Heat some to melt it to remove the tube sections? I would measure first, then cut a section of the downtube out so each end can be removed without needing to flex the frame open. The tubes on these Treks are not mitered, just right angle cuts at both ends.

unterhausen

Is there also a problem with the front derailleur that is frame related?

I think this one should probably be recycled into beer cans. But depending on the series of aluminum, you might be able to get someone to fill that hole with Tig. I don't think alumiweld will hold.

I like your signature.

rickpaulos

The bicycle had other issues. The seat post was too small and there was a wedge of metal shoved in to compensate. The headset cups are plastic and were cracked, shunk and loose in the frame so the fork wobbled in all directions. Left crank extractor threads trashed from the crank being hammered on to the axle. The front derailleur cage was mangled. And the paint. All adds up to a novice owner/mechanic. The parts can be replaced as needed from the vast supply at the coop.

The front derailleur inserts look okay. The "braze-on" bracket was held on with screws. Removed for the paint striping.

guy153

The rule of thumb with aluminium is that if the thing you're repairing wasn't welded in the first place (e.g. they used rivets and/or glue) then it's probably not a weldable alloy.

unterhausen

Didn't think that it might not be weldable.

That's good about the front derailleur, it's just that it was so crooked in the first pic I wondered if there was an issue

GrayJay

Google research indicates the frame is made from "Easton ProGram DB aluminum", most likely a 7000 series alloy (which can usually be TIG welded and then aged to restore the hardness.)

I think that entirely replacing the downtube and bonding in a replacement would be more difficult that it might initially seem unless you are very experienced with using epoxy. Longevity of a re-bonded frame would be highly suspect. Many of the bonded frames from this era had ongoing problems with the joints separating, probably why the bonded-metal construction process has largely been abandon for newer bikes.

zandoval 

I have used this Harbor Fright AlumaRod to fill holes in my aluminum boat. Still... I would get someone who brazes on a regular basis if I were to fill holes in an aluminum bicycle...

Trakhak

The bonded frames with problems were mostly the European ones. I sold Trek and Raleigh bikes during and after the bonded-frame era for both companies and never saw or heard of a bonding failure. People have reported being hit by cars, totaling the frame, but with the bonded joints remaining intact.

Trakhak

Why not wrap the damaged tube in carbon fiber?

rickpaulos

the seat stay brake bridge is riveted on. The shift lever mounts, rivet of some sort. The chainstay cable stop peg is stainless, glued on. All the main joints are glue.

rickpaulos

I once attended a lecture by mr Burke. He stated the first years production had issues but they got it figured out. I've seen some where all the paint blistered off from corrosion. I assumed those were the first year models he was referring to. Our local coop has had quite a few pass through that were all in good condition.

I found the specs for this model.. Posted above. Alcoa 6061 T6.

rickpaulos

humm. Easy patch. But I think the plan is for the bling factor of all polished.

rickpaulos

"As one of the most popular aluminum grades, 6061 is often chosen for structural applications, welded assemblies, electronics, and a variety of industrial and household items. 6061 aluminum tube, aluminum bar, and aluminum plate offer high-to-moderate strength, excellent corrosion resistance, and superior machinability and weldability. 6061 aluminum offers greater strength over other alloys in the 6xxx series, which is why it’s chosen for applications that require tough, yet light material.

6061 T6 is one of the most commonly requested versions of 6061 aluminum. The T6 refers to the temper or degree of hardness, which is achieved by precipitation hardening. This grade has a good strength-to-weight ratio and is also heat-treatable. With great formability and weldability, it is used for engineering and structural applications, boats, furniture, and more."

More info here:
https://www.kloecknermetals.com/blog...luminum-grade/

GrayJay

I saw another source citing the 1200 model as using easton tubing, might be that Trek changed tubing suppliers for the 1200 throughout the years?
Reason for all the bonding and rivets is that it allowed for construction of the frame without applying any welding heat. The frame could then be constructed from tube that were heat-treated prior to construction, no need to heat-treat the entire frame afterwards. For same reason, in early 90's Raleigh USA briefly built a technium model frame from strait gauge Reynolds 753 tubes, getting all the strength benefits of the 753 without need for highly skilled framebuilders capable of silver brazing 753.

Bonded lug bikes I remember that were notorious for failing joints were the the early carbon fiber tube specialized Allez frames, few of those early Allez frames would survive more than about a year before needing replacement.

rickpaulos

from company histories dot com:

Doug Easton started in 1922....

In 1986, Easton Sports Canada was launched and the company began to produce mast and boom tubing for sailboards and bike frame tubing. Easton then tried to bring out its own line of bicycles but soon found that the economics did not work: the company's frames were too expensive to factor in the other costly components of the bike. In 1990, the money-losing venture was brought to a halt.

I assume they mean selling bicycles was halted in 1990, not bicycle tubing.

In 1998, the company entered the aftermarket bicycle component business.

Easton's products are in most sports: arrows, ski poles, tent poles, hockey sticks, baseball bats, etc.

JohnDThompson 

The Trek 1200 series frames used a 7000 series heat treated aluminum alloy that isn't recommended for welding. That's why the front derailleur mount and brake bridge used rivets and epoxy. I don't recall the exact epoxy used, but we were reluctant to replace tubes on damaged frames and offered a discount on replacement instead.

Canaboo

Aluminum doesn't stay polished looking for long

The best solution is likely to form a decorative overlay for the bottle mounts that is glued over the holes and bridges the gap. It needs a fiberglass layer if it will be made with carbon. That would be easy enough to do and one of the specialty epoxies from 3M will work.

rickpaulos

ah yup, that's why most polished aluminum frames are clear coated.

Doug Fattic 

Another option using the concept of a decorative overlay is to use 2 decorative overlays - one on top and the other on the bottom (made from splitting a tube) - and mechanically bolt them together. I'd use what I have on hand and on the top overlay (made out of thin steel tubing) I'd braze on a a long M5 boss. On the bottom overlay I'd also braze on a water bottle boss and drill it out so an M5 bolt long enough to engage in the top boss. In other words the bottom boss is just for reinforcement. And then I would paint them so they wouldn't rust. A hole would have to be drilled in the bottom of the frame for the bolt to pass through. The bolt would have to be chosen or modified so it was just long enough to grab the boss in the top overlay.

Wicks aircraft has SS tubing to use as overlays if one wanted to get fancy. Of course brazing and painting are activities I do all the time so it wouldn't be much effort (although it takes time) for me to make 2 overlays that can be bolted together for a permanent solution so no welding or gluing would be required.