I am considering buying an Alan Super Record aluminium frame, but there is a hairline crack in the lug on the bottom of the headtube. Is this a big problem, and would it be unsafe to ride it?
Is there any easy way to fix it, or it is a sign of a more serious problem? I have no access to welding or advanced repair machinery.
Answering your questions in the wrong order, it isn't a sign of "something more serious", it is though a serious defect in the frame.
At best, the bottom cup will be a loose fit, and the crack will slowly propogate upwards if ridden until the lug is split and the bonding to the headtube is compromised somewhere on the scale from "completely" to "significantly."
It is probably repairable by an experienced aluminium welder. I do not know if these old frames/lugs were heat treated, but if you did go for repair, you would lose alot of the fancy scrollwork, the repair would always be obvious to some extent and the headtube would need reaming back into spec to take headset cups as the heat of welding will distort it as well as the extra material being there to form the repair. It is possible that after a few years, under stress, the repair would fail again, or some of the adjacent material as a result of the heat used for the repair.
I would suggest that it's perfect for "Display Only" but don't feel too downheartened: I've heard from enough people that these ALAN frames are very flexy and not to everyone's taste. They do not have the best reliability reputation either, though many people love them and the price has spiralled up over the last 10 years since I'd considered getting one.
Questions of "Is X safe?" generally class as Opinions and tend to attract both YES and NO answers.
Ultimately it comes down to your personal risk tolerance and the severity of the consequences. If a head tube failed suddenly while you were riding, you could be mudsucking before realising something was wrong.
Conversely, a torn saddle (for example) has low consequences, perhaps just staining your trousers.
Personally I would not ride that frame - there are plenty more bikes out there, just keep your eyes open.
This would be a high-consequence failure if it let go quickly. If it gave-way slowly you'd hopefully notice and cease riding before complete failure.
I lost a nice Ghost All Mountain Range MTB to a similar hairline crack.
While nobody can predict when or if it will break completely, the logical argument is this: there was a reason why the hairline crack appeared in the first place. This reason must, with a chance of 99.999...% be something that is not an individual event, but the systemic and constant wear and tear (material fatigue) caused by frame geometry and the dynamic forces acting at that spot. This material is, after all, not glass, where a single pebble impact can easily create hairline splits.
Assuming that it is so leads to the conclusion that the split will indeed get larger over time - no matter how long it takes. As the split has already weakened the area, it can be further assumed that the rate of growth will be at least as fast as before, maybe faster.
Aside of the technical/objective aspects, there is the statistical thinking - no matter how small the chance that the spot fails during a ride in a catastrophic way: the possible damage to the rider is very high, possibly fatal. Think about going OTB at high speed or in dangerous traffic, or over the side of a steep mountain ledge. So the expectancy value of the damage (probability multiplied by damage) can possibly be very high indeed.
Your conclusion depends on your character and risk aversity. I personally went and bought a much nicer new bike - it was a welcome excuse for that. ;)
There are several red flags:
old Aluminium alloys are often very susceptible to stress crack corrosion
old frame that saw many load cycles and is susceptible to fatigue
this is a very long crack, it is certainly longer than what is visible
cracks grow when loaded, even in modern alloys without fatigue or corrosion promoting it
With those red flags in mind, always assume it will fail next time you ride the bike. On failure the lower headset bearing will be lose and the fork would have no lateral stability. In everyday riding there are frequently conditions where an uncontrolled fall cannot be avoided.
Is that acceptable risk to you?
I had a similar crack on an Apollo. I used a lathe and old piston to make a tight collar which fit over the bottom then refit the cup. 70 mm x 12 mm by correct ID. Probably not what you're looking for aesthetically, but works fine.
I would not ride without fixing but welding will create more problems and deface the Alan so a sleeve is stronger and covers part of the Alan design at bottom of headtube.
I have found some information that those Alan frames are screwed and glued together. Probably both at the same time. I doubt heating the lugs with welding would do the glue bond any good.
I'd hang it on a wall.
Not an Alan frame (whatever that is lol) but on a similar note, I like late 90s to mid 2k Specialized Rockhopper and Hard Rock Sport small frames. I'm 5'7" and they fit me well. I can not afford a modern Specialized or any other top brand that is "fit" to me as most of them are well into the thousands and beyond to 5 figures. I'm a low paid construction worker so I am really only able to spend a few hundred at the most on a bike so I find older ones on Facebook marketplace, Craigslist, local listings, ebay, etc for between $50 and $150 or so and put all new inexpensive Shimano Altus or Alivio parts on them and whatever else they need such as seat, tires, bars, etc, etc.
Those frames I mentioned above are the most comfortable for me to set up and ride. I do a lot of riding for both commuting and fun. It's best if I have 2, which I do now. 1 is a hardtail with cargo rack, pannier bags, and a full set of creature comforts that I use as a commuter bike and then I have a FS lightweight that is stripped down of anything that isn't necessary to ride it. I picked it up for $60 from Facebook and I had been looking for one for awhile so I was excited for the project however I made the mistake of ordering all the parts for it before tearing it down and fully inspecting it and while doing so, as I was taking the headset out I found a hairline crack in the head tube which starts at the very bottom and goes about halfway up before disappearing so I was quite devastated. I contacted the seller and of course he said he hadn't noticed it and that it was an as is sale so "sorry".
It's only $60 and most of the parts that were on it are worth at least that and still usable such as the wheels and tires, brakes, saddle and post, pretty much everything besides the headset and bottom bracket. It's a 3x8 24 speed and the derailleurs are still useable as well as the shift and brake levers, bars, and both the RockShox suspension fork and the rear suspension shock and spring combo. the parts I ordered for it are; bottom bracket, headset, new shift/brake combo levers, front and rear derailleurs, brake cables, wheel set for disk brakes, tires, rotors, cable pull calipers, crankset with chainrings, cassette, chain, saddle and suspension post, handlebars, "gooseneck", grease, and oil for the fork overhaul.
I went on a search for possible options for repairing the frame and saw solutions for; a full professional "proper" job involving removing the tube completely, welding a new one on and having the frame heat treated, quenched, baked, and straightened which also includes grinding or otherwise removing any excess welding material and any other work to have the frame fully ready for assembly @ $300+, or using some type of device to keep the thing together, which another site has instructions for using shaft collars or something equivalent to keep the tube from having a catastrophic failure.
The guy that made the video said he was "over" engineering it but the bike meant a lot to him. This one's only valuable to me in a in the sense that these frames can be hard to come by as they weren't worth a lot to begin with and aren't very sought after today so most of them either went to the junk pile or are sitting in an obscure hard to notice spot in someone's garage, basement, shed, etc. and most likely will be for a long time to come.
While searching for shaft collars, as I wasn't aware of what they were actually called so I typed "pipe clamp" into Google, I saw, among many non viable things, 1-5/8" muffler clamps so I am going to get 2, one for the top and one for the bottom, and follow the rest of the procedure from this guy's video which includes; drilling a small hole at the end of the crack to hopefully stop it from going further up the tube. I think that the muffler clamps will be plenty strong enough to hold it together. if not, and i crash and die, well I won't be able to come back in here and tell you how things worked out but if I'm just injured and am able to come back and post results, I will as well as if nothing happens and the repair stays put which is what I'm expecting. I found grade 8 hardened stainless steel clamps for less than $10 each and to hide the ghetto look of muffler clamps on the head tube of my bike in going to take a piece of stainless steel sheet metal or aluminum if I can find some and put some kind of cool graphic on it.
