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Crack in the head tube! Trek 600

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Crack in the head tube! Trek 600

Old 11-17-21, 10:53 PM
  #51  
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Wow! Didn't even know that some Treks had these one piece headstocks.
Might the step on the faux lug around the head tube section created a stress riser?
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Old 11-18-21, 06:58 AM
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Originally Posted by JohnDThompson View Post
Unfortunately, that pseudo shoreline creates a stress riser that can eventually crack.
My first thoughts when I looked at my picture after reading your initial description!

Since it is old enough, hasn't happened yet and isn't catastrophic, I am going to move forwards with my plan for this frame. What plan? There were several! One just got eliminated, gravel.
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Old 11-18-21, 08:12 AM
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Originally Posted by Chombi1 View Post
Wow! Didn't even know that some Treks had these one piece headstocks.
Might the step on the faux lug around the head tube section created a stress riser?
Yes, absolutely. But to be fair, the vast majority of them held up fine.

N.B. I know some weight weenies who used one-piece head tubes in frames because they were lighter than three-piece head tube/head lugs.
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Old 11-18-21, 10:06 AM
  #54  
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I dunno,.....
I'd feel kinda weird if I was a frame builder at Trek and had to see the use of these one piece, faux lugged headstocks. It would feel just wrong.
They must have been thinking, nothing could really go wrong with them, being all one piece.......
​Sure, other manufacturers used one piece headstocks like Vitus, but they did not go to the extent of faking lugs on them.
Unfortunately, I suspect this just mostly beancounter engineering at fault.
......

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Old 11-18-21, 11:39 AM
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The challenge is always ROI and impact to margins for the business.
f you can reduce assembly cost, this represents, along with the seat cluster with socketed seat stays, you can also increase production with assembly time reduction.
It is a risk decision associated with being innovative in manufacturing/assembly. I really can't fault them. I don't know, maybe JDT knows, if TREK did any FEM of the head tube portion of the frame. I suspect not with an assumption of an engineering safety factor built in .
Quality of the piece delivered is up to the supplier, adding to the risk of some having voids or inclusions that might contribute to the stress riser triggering a failure.
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Old 11-18-21, 05:40 PM
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Thanks for all the responses about this! I've definitely learned something about Trek history, reading these posts.

These 600 series bikes look to have had the rear (seatstays, chainstays) and the front (headtube, fork) done by outside contractors in Japan. That started in '82, the year of my bike. I had been under the impression that the whole thing was made in Japan, but looking at the Vintage-Trek website set me straight.

Maybe mine is brazed with silver, and I've misjudged the metals. I am looking deep into the headtube using a flashlight, and all the filler's corroded in there, making it difficult. The Trek brochures from '82 are pretty vague, they just say "low temperature" which is not very specific but could mean silver (or could mean they are very careful with bronze!!). I know the fork and rear triangle were done with bronze. In either case, gently heating and peeling the faux lugs will be the way I disassemble.

I've ordered a headtube and some lugs from Framebuilder Supply. I'm also grateful for the discussion about how big the vent holes should be, in the headtube where the lugs/tubes are brazed in. I will be making them small, probably a just one little hole to make snaking dynamo wire through the downtube easier.
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Old 11-18-21, 06:04 PM
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Here is a guide:



As done by Mr. Confente
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Old 01-06-22, 03:18 PM
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Here I go! I will replace this headtube.

Before I started disassembly work, I decided to take measurements of the frame. The top tube is bent a little (likely because of a dent in the middle), so the angles are hard to get. But basically, even though this frame was marketed as a 73/73 seat/head tube, it is not. If you put the top tube level, the seat tube is 73.5 and the head tube is 74.5. Wild! That might explain the ultra twitchy handling. With my raked-out fork, I had under 30mm of trail! That's French Tandem territory. I do have to say, it was quite easy on the arms for a tired rider, however. I may slacken the head angle by half a degree when I put the new head tube on, to make things a tiny bit less extreme.

First, for prep, I filleted (flayed??) the head tube, with an angle grinder and hacksaw.



Then, I torched it up and peeled the lugs off. The red you see is not me overheating the steel. It's dust on the steel glowing, not the steel itself. A lot of dust was created when I cut everything apart. You can tell in person, but not so much in pictures. In any case, I did not cook a tube. I only did it with propane, and it was enough.







After a chat with Jack at Franklin Frame, who is doing some chroming for my René Herse project, I got the same advice as elsewhere: peel the lugs off with low-moderate heat. So that's what I did. I only used propane for this - it worked fine - so it must be the bike was brazed with a high-silver of some sort.

Jack told me to expect the original miters to be wrong. Boy, was he right! I will have to redo both, to a significant degree!
So, next: the hard part, sanding and re-mitering!
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Old 01-06-22, 04:22 PM
  #59  
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Originally Posted by scarlson View Post
Here I go! I will replace this headtube.

Before I started disassembly work, I decided to take measurements of the frame. The top tube is bent a little (likely because of a dent in the middle), so the angles are hard to get. But basically, even though this frame was marketed as a 73/73 seat/head tube, it is not. If you put the top tube level, the seat tube is 73.5 and the head tube is 74.5. Wild! That might explain the ultra twitchy handling. With my raked-out fork, I had under 30mm of trail! That's French Tandem territory. I do have to say, it was quite easy on the arms for a tired rider, however. I may slacken the head angle by half a degree when I put the new head tube on, to make things a tiny bit less extreme.

First, for prep, I filleted (flayed??) the head tube, with an angle grinder and hacksaw.



Then, I torched it up and peeled the lugs off. The red you see is not me overheating the steel. It's dust on the steel glowing, not the steel itself. A lot of dust was created when I cut everything apart. You can tell in person, but not so much in pictures. In any case, I did not cook a tube. I only did it with propane, and it was enough.







After a chat with Franklin Frame, who is doing some chroming for my René Herse project, I got the same advice as elsewhere: peel the lugs off with low-moderate heat. So that's what I did. I only used propane for this - it worked fine - so it must be the bike was brazed with a high-silver of some sort.

Franklin told me to expect the original miters to be wrong. Boy, was he right! I will have to redo both, to a significant degree!
So, next: the hard part, sanding and re-mitering!
You might already be planning this via photos in a future post, but can you explain what's wrong with the mitering and what you'll be doing to correct it?
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Old 01-06-22, 05:53 PM
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Originally Posted by tricky View Post
You might already be planning this via photos in a future post, but can you explain what's wrong with the mitering and what you'll be doing to correct it?
Ahh, I think I forgot to take a picture of the ways they were off, so I will attempt to describe it.
Firstly, the tubes are mitered before being brazed in, so they were rotated a little relative to vertical. When I held the new head tube up to the frame, this was clear, because of some (1-1.5mm) gaps. Also, the down tube was a little short, so the head angle wanted to be closer to 75.5 degrees!

I corrected by filing the top tube a mm or two shorter and then wrapping sandpaper around the headtube and using that to sand the miters until they were en forme. Pics to come. I'm going to braze tonight.
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Old 01-06-22, 06:15 PM
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@scarlson

Timely post! I went down the rabbit hole late last night reading the Joe Starck interview in RR #12 (after seeing a reference in a recent BF thread) and he talked about a Trek frame he and another builder did some "destructive testing" on. Apparently it was a frame Starck had built some years before which had been damaged, and he was interested to see what kind of brazing material penetration his joints actually had. The description he gave pretty much matches what you've done here. Weird how you then updated this thread showing a similar process, complete with photos, the very next day!

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Old 01-06-22, 09:07 PM
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Really interesting post, love the pictures of the HT replacement process.

What I find interesting is that this is at least the third time we've seen documented issues with "handmade era" Trek frames, including the Ishiwata fork crown failures and numerous examples of poor brazing at the rear brake bridge. Hardly a pattern that should make Trek riders nervous, especially given the low numbers, but still, funny that things keep popping up.
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Old 01-06-22, 09:27 PM
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@Drillium Dude , I love those old RRs! Read damn near every one of them back in the day when they came out.

So, here's the brazing! First, it's a 73ST / 74HT, if the expensive digital protractor is to be believed.

Here's a closeup of my beautiful mitering job.


Tube in lug.

Top lug brazed.

Both lugs brazed!!


Cutting off the extra tube. I filed it square and checked it at multiple angles using a machinist's square, because I don't have a facing tool.


After this, I did a bunch of lug thinning and checked everywhere to see if there was any sign of voids. I think I got all the way through. I would start at the top and draw the filler through with the heat. Eventually it'd get to the bottom or come out someplace else, and that's how I'd know I'd done it. Used maybe 3/4 of a troy ounce on this. Based on what I've read, that seems typical.

Now, reaming it the next/final step. There is a 1-3/16" reamer at work, which comes out to 30.2, which should be correct according to Sheldon. The frame can be mounted in the lathe, using a centering cone on the tailstock. Often a Jacobs chuck has a tapered nose that can be used as well, but a centering cone is nicer. Everything's great, right?

Well, not exactly. The trouble is, I did a little test on a scrap piece of headtube and a 1-3/16" reamer, it turns out, is too big for a good interference fit with headset cups. The Park Tool spec page explains: 30.2 is the size of the headset cups. 30-30.1mm is the ID of the frame, for a proper interference fit. So, I bought a 30mm shell reamer, used, from evilbay. It was $15. I cannot afford the damn Park Tool, of course. I will probably do this frame in the lathe, but I'll build a guide, pilot, and holder from threaded rod and a cone I turn on the lathe in the meantime, so that I have a long-term solution when I no longer have access to a lathe. I won't sweat the facing. I figure if I can't find any defect using a machinist's square, it's faced well enough for me. I could get out a dial indicator and mount the frame in the mill if I really wanted to be serious, or buy a side facing cutter (another $15) but I don't think even the Park tool facer/reamer is that good.

So, waiting on reamer. I also have to braze back in the water bottle boss on the bottom of the downtube (the bottom lug point was partially covering this hole) and re-run the internal wire I burned up. Then toss some linseed oil in the frame and we'll be good to go!
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Old 01-07-22, 12:35 PM
  #64  
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Speaking of thinks being off, It took awhile before I noticed this CS bridge. It is off as the photo almost suggests. 1984 610 same as #49 above.
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Old 01-07-22, 02:30 PM
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Originally Posted by SJX426 View Post
Speaking of thinks being off, It took awhile before I noticed this CS bridge. It is off as the photo almost suggests. 1984 610 same as #49 above.

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Medici brazed mine cockeyed in 1979:



This kinda thing would've bothered me bitd had I paid full price. Since I got the bike for a song, not so much today

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Old 01-07-22, 05:59 PM
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Originally Posted by scarlson View Post
@Drillium Dude , I love those old RRs! Read damn near every one of them back in the day when they came out.

So, here's the brazing! First, it's a 73ST / 74HT, if the expensive digital protractor is to be believed.

Here's a closeup of my beautiful mitering job.


Tube in lug.

Top lug brazed.

Both lugs brazed!!


Cutting off the extra tube. I filed it square and checked it at multiple angles using a machinist's square, because I don't have a facing tool.


After this, I did a bunch of lug thinning and checked everywhere to see if there was any sign of voids. I think I got all the way through. I would start at the top and draw the filler through with the heat. Eventually it'd get to the bottom or come out someplace else, and that's how I'd know I'd done it. Used maybe 3/4 of a troy ounce on this. Based on what I've read, that seems typical.

Now, reaming it the next/final step. There is a 1-3/16" reamer at work, which comes out to 30.2, which should be correct according to Sheldon. The frame can be mounted in the lathe, using a centering cone on the tailstock. Often a Jacobs chuck has a tapered nose that can be used as well, but a centering cone is nicer. Everything's great, right?

Well, not exactly. The trouble is, I did a little test on a scrap piece of headtube and a 1-3/16" reamer, it turns out, is too big for a good interference fit with headset cups. The Park Tool spec page explains: 30.2 is the size of the headset cups. 30-30.1mm is the ID of the frame, for a proper interference fit. So, I bought a 30mm shell reamer, used, from evilbay. It was $15. I cannot afford the damn Park Tool, of course. I will probably do this frame in the lathe, but I'll build a guide, pilot, and holder from threaded rod and a cone I turn on the lathe in the meantime, so that I have a long-term solution when I no longer have access to a lathe. I won't sweat the facing. I figure if I can't find any defect using a machinist's square, it's faced well enough for me. I could get out a dial indicator and mount the frame in the mill if I really wanted to be serious, or buy a side facing cutter (another $15) but I don't think even the Park tool facer/reamer is that good.

So, waiting on reamer. I also have to braze back in the water bottle boss on the bottom of the downtube (the bottom lug point was partially covering this hole) and re-run the internal wire I burned up. Then toss some linseed oil in the frame and we'll be good to go!
I'd love to try this kind of stuff out one day. It all seems really up my alley. For now, I really appreciate your posts (and @Doug Fattic and @gugie 's) that help me live vicariously!
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Old 01-08-22, 02:02 PM
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@scarlson,

Thanks for posting this! Pretty straightforward. Make me want to try this some day.
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Old 01-09-22, 02:11 PM
  #68  
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Originally Posted by coolkat View Post
Really interesting post, love the pictures of the HT replacement process.

What I find interesting is that this is at least the third time we've seen documented issues with "handmade era" Trek frames, including the Ishiwata fork crown failures and numerous examples of poor brazing at the rear brake bridge. Hardly a pattern that should make Trek riders nervous, especially given the low numbers, but still, funny that things keep popping up.
Ha, well my fork failed too, so that could be the thread you've seen. It may just be me. I have broken two other Trek and one Holdsworthy frame as well. Also Phil BBs, Campy Record hubs, Mavic MA3 rims, Blackburn racks, you name it. I do have a feeling the chainstays will fail next on this bike...

Originally Posted by gugie View Post
Thanks for posting this! Pretty straightforward. Make me want to try this some day.
Yeah, fairly easy! I was pleased with how in-plane the frame stayed when I cut it apart. I didn't have to massage it much to keep everything nice and straight even with no jig. Ron Cooper also brazed freehand, after all. It was a good exercise to get my feet wet, as well. I was able to stick a soldering pick inside my vent holes and feel around for internal shorelines, and I am pretty sure I've got 'em, so another indicator that I achieved decent penetration and fill. It's worth throwing extra silver at the joint, even though it's expensive and may just be running down the inside of the tube, to insure against future failure.

Interestingly, I weighed the headtube scraps I cut and peeled off, and weighed the new tube (Columbus SL) and the lugs, and the new stuff was only 10g lighter!! That's without facing and reaming, but also sans 3/4 Troy of filler, and granted I'd lost some metal to sawing but the old headtube still had the headbage, so probably close to the final equation.
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Old 01-12-22, 09:58 PM
  #69  
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Here's the final step: reaming!

I bought a shell reamer off ebay for $15. It was advertised as 5 thou undersize 1-3/16". It turned out not to be undersized at all! So, I carefully hand-stoned it down to approximately 30.1mm, or just 3 thou under size. Fun times! Basically rotated the reamer against an oil stone until I got it. Then sharpened the cutting edges. In the process, I discovered why it had been so cheap: it was cracked. But no matter, this is light duty. It made it through with no trouble! And I learned something! You can see my lathe setup in the photos below. Again, not a lot of material taken off, so we don't need to be crazy careful about our setup. It just needs to be true and on-center, so I'm actually using the improper chuck jaws which don't grip the reamer that securely. It's OK. I took it easy and nothing slipped. You can see the result at the bottom.





Not bad, eh? Headset cups are a nice tight press fit.
I will make a handle to hold this shell reamer from a 2' piece of 5/8" threaded rod. I'll turn it to diameter and put a roll pin through it to keep the reamer from spinning. A little bit of machining will get me a decent piloting cone. An old BMW valve spring will provide the feed-pressure on the cone. That's the park tool, in essence. What sells for $500, I can make myself for $35. Sure sure, it's not quite "shop quality". But it's good enough for a homegamer like me!

Now I assemble the bike and get back on the road! Phew, I cannot wait.
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