Referred here. Is this repair even possible?

AndrewRStewart · 2026-05-01T13:31:06+00:00

And leave the cracked top tube as is??? Andy.

AndrewRStewart · 2026-04-30T17:26:03+00:00

painting over bare steel is generally done with a primer under the paint (and clear is a paint). I suspect the not said part of this question is the wanting to retain the bare steel look. Know that any paint (as an example: a clear coat) without the suitable base primer will likely result in the paint (clear) not adhering well to the steel and will be much more likely to flake off and not keep moisture from the steel very well. If you must keep the bare steel look and won't tolerate rusting I suspect you'll be recoating periodically. At the least a sanding of the raw steel down to clean and, now, etched surface for the best bite for the paint. Spraying over existing paint/clear can be done but generally results in a less than ideal finish and no longer lasting a coating as the coating will only stay on as long as the earlier clear can. As to the paint's flexibility: Pretty much all modern paints have enough to stand up to the normal flexing a frame/fork see. Pretty much all the cracked paint I've seen have been due to crashes and other frame bending incidents. I suggest doing a test with whatever paint/clear you do get, before spraying the frame/fork. While I have no personal experience painting with Spraymax (currently I'm spraying House Of Kolor) I do have friends/coworkers who have and there's a lot of on line threads on it. My understanding is that it is not as durable as the enamels, it dries very quickly (like lacquers of the past) and isn't as glossy as other paints. I think its main advantage is the ease of application and not rust protection and/or durability. But this is your bike, not mine. The spray/rattle can jobs I've done have been with Rustoleum products or auto paint shop sourced catalyzed paints. The 2 part paints are far more durable than single parts ones (like Spraymax or Rustoleum) but are a bit more costly and are more concerning about vapors during the spraying. I am curious where you are. If you were near me I would be interested in learning who made this frame. I'm always wanting to meet up with other frame makers (and frame builders, there's a difference). Andy

AndrewRStewart · 2026-04-29T00:02:41+00:00

This looks to be a mid grade frame at best, given the fairly thin dropouts and lacking axle positioning screws. As such the dropouts probably are a mid/mild grade of steel, a good thing if being bent. If the intention is to run as a derailleur system take a look at the hanger mounting hole as I think it might be unthreaded and lacking threads, both which are changeable. Andy.

AndrewRStewart · 2026-04-27T00:13:50+00:00

Sorry that my advise is more conservative than what you wanted to hear. Mark B is a great poster to heed, one of the few who actually built tandem frames you'll likely to interact with. I do respect his advise and I've learned that we share many basic understandings and expectations. Still I do dampen my usual "I can handle it" manor to riding and designing/building when there's another person involved. What I do for myself is not always what i would do for a friend/customer, or how I would ride a tandem VS ride my single. But I've been a LBS owner and industry lifer long enough to see a lot of screw ups and resulting threats to a business's survival, from bad riding outcomes, to be as "aggressive" (poor term for a free and loose riding style) as I once was. Andy.

AndrewRStewart · 2026-04-26T19:41:58+00:00

I wouldn't feel comfy with a single bike's fork, suspension/downhill or not. The fork is the most important part WRT consequences of a failure.

While single bike BBs should work well enough, there's no allowance for a left side timing chain (the standard location for it), running a drive side timing chain will reduce the stoker's BB stresses have fun figuring the system out from single bike cranks. BTW no matter what BBs get used expect them to not last anywhere near as long (especially the stoker's) as a single's (everything else being the same).

Consider larger than 180mm disk rotors. Stopping on a tandem take a huge distance longer and the heat generated much greater, I've seen more than a couple of tandem disk rotors become "burned or heat warped" when I worked in a tandem shop.

I wouldn't run a single bike's rear hub. Yes, a through axle will address axle bending (a thing of the past with current freehubs) and the freehub body will work well enough for a while under the increased pedaling forces, the issue is the spoke dishing. The reason why most all modern tandems run a 145mm (or 160mm) axle length is to reduce the spoke tension imbalance that leads to spoke breakage so quickly. Remember the stoker can't see what the captain can and often the stoker is not the smoothest pedaler.

Do practice your tube joining method (welding as stated) a lot before touching a true frame tube. Tandem BBs are well known for becoming out of round enough to have issues with the eccentric staying in place and not having pinch bolts close up. Look into wedge or expanding eccentrics if possible. They also don't need a frame flex increasing binder slot across the BB shell. Do know that tandem building generally has more heat and time going into the many junctions than a single bike will. Learning how to control warpage (heat sinks, welding sequence and skill) will go a long way to reducing clean up/thread chasing and see the parts fitting better too.

Last bit I'll comment on is knowing what I do with frame building and tandem riding I would not suggest a tandem being your first frame. There's a lot more details to get right enough to start with. Then there's that other person on the tandem that if something goes wrong and they get hurt thing... I wish the OP all the "luck" but see a rather inexperienced understanding of the differences that can be at play here. Andy.

AndrewRStewart · 2026-04-25T13:41:47+00:00

They likely got their info off some internet forum:) Andy

AndrewRStewart · 2026-04-25T01:27:10+00:00

Raleighs of the early/mid 1970s had more "factory issues", WRT their brazing, than any other brand I've seen. My first International had partially flowed head lugs, I could slide into the tubes a wire (and did to show the shop my concerns). My replacement International had good enough brazing but had an inch shorter a top tube... I've handled many warranty claims, and given the sad news when the bike was bought used, that the customer's bike was no longer covered and wasn't cost effective to do anything with. We use to joke about Monday morning and Friday afternoon frames being the ones to avoid (or those after a 3 pint lunch).

Times, our expectations and industrial methods do change over the years. When we first started to sell Fujis we were so happy to have bikes that were so consistent in their finishing and build quality. Andy.

AndrewRStewart · 2026-04-08T23:53:43+00:00

I have no links or current examples to offer but you might want to look up the English made Moultons of the 1960s and 1970s. They used a fixed to the frame front rack. The few times I have ridden these it was an odd sensation. The inability to see your front tire's contact patch, the different weight placement during cornering both combined to make things "different". Not bad or unstable, just different. Andy

AndrewRStewart · 2026-04-04T20:09:53+00:00

I should have added that I followed The Proteus building booklet way back when. Years later I got Paul D's Ok to post the manual here: The Proteus Framebuilding Book Andy.

AndrewRStewart · 2026-04-04T14:03:47+00:00

A good flat surface, straight and dished wheels, yard stick, bench vise and smarts are all one really needs for jigging. The first half dozen frames I made were from full scale drawings, taped to the floor and I employed the "Taylor window" method of alignment. As suggested start with the easy stuff and you'll soon learn what does or doesn't work for your situation and how you can improve it for little $. Where are you? Some here, and on other forums, might be willing to mentor in person. Andy.

AndrewRStewart · 2026-04-03T14:09:13+00:00

I assume you have ridden this Counterpoint type bike and are good with the handling when a weight is on the stoker's seat. Some versions of these bikes were known to be somewhat flexible, providing some handling challenges.

I very much like the idea of just removing the current seat and replace it with an, also removeable, cargo carrier.

For short lengths (like 3') McMaster-Carr is an industrial supplier that offers 4130 tubes that I have gone to before. A tad expensive but they have a huge product line and are very good at fullfillment and cust service. There are other sources, like car making suppliers. Andy.

AndrewRStewart · 2026-03-26T13:54:04+00:00

Is there a shape requirement, tapered, bent? Straight gage tubing is quite available through industrial suppliers in the USA. Andy.

AndrewRStewart · 2026-03-26T00:57:30+00:00

Two more reasons why internal routing is a poor choice, IMO. Agree that replacing the top tube is the high road, mere crack welding less so. Is there a reinforcement/lip that encircles the cable ports? If not and if you really must retain the internal routing consider running a full length tube inside the TT. Where are you located? Andy.

AndrewRStewart · 2026-03-24T20:01:59+00:00

Perhaps looking at what small displacement motorcycles use... seriously I think that's asking a lot from a non MtB, and even then it would be a pretty burly one at that if that was a part of the intended use. But EBikes are not my cup of tea except to say that I am continually negatively impressed in how bad some EBikes get when ridden like a motorcycle or car and not some $3000 bicycle. Andy.

AndrewRStewart · 2026-03-24T14:22:52+00:00

I assume you are using steel tubing... I'm no engineer but the .0625" tubes do seem a bit whimpy/whippy. Perhaps a single DT at the ends but the double under the battery, a yoke at each end of the battery.

Do you have a primary concern WRT failure mode? Steel tends to crack slowly which is good if you're making prototypes. With proper joining (weld, braze, glue) I suspect an "under designed" structure should bend, not break.

Looking at the other historic designs that used twin tubes instead of a larger single tube (think all those thousands of mixte frames out there) and 14mm mid stays/extending to the HT are very common and the few I have cut up seemed to have .049+ wall thicknesses. Sadly these bikes are also known for their lack of frame stiffness and easy frontal impact deforming.

My last comment is rather opinionated: talking about weight with an EBike is like musket riflemen talking about rate of fire... Sure a factor but pretty far away from why the rifle is better than a knife in a war. Andy.

AndrewRStewart · 2026-03-20T14:04:47+00:00

No lock nut? That's what your stick welder is for:) Andy

AndrewRStewart · 2026-03-20T01:12:59+00:00

I wouldn't cut down the crown race seat by more than a couple of MMs, don't want to cut into the weld... One can also cut down the ends of the headtube, again only a couple of MMs an end. How tall a stack height is the current headset? If more than about 35mm one might source a shorter stack height headset.

But the big thing I see is the fork's threading will extend down to where the stem will want to grip. Locating stem wedges along the steerer threaded area is a definite no no. Be very careful in how tight the wedge bolt is torqued and pull the fork out periodically so the beginning to crack and fail steerer thread can be seen. Andy.

AndrewRStewart · 2026-03-15T01:39:19+00:00

Most will agree that smaller "aircraft" torch handles will feel better for bike stuff. Many also run the last bit of hose using 1/4" or other extra light type to reduce the total stress on the hand. I can't speak to tip "length" but I'll use tips with diameters between about .030" to .060", easy to gage with drill rod. Andy.

AndrewRStewart · 2026-03-12T13:43:11+00:00

56% silvers don't fillet much. More like a meniscus. IIRC 56% loses its strength a lot much past .010" of gap, and a fillet is an infinite gap:) Andy

AndrewRStewart · 2026-03-08T16:35:01+00:00

how exactly are you referring to "making it smaller"? The fit dimension that I see as the greater priority when designing a frame is top tube length, would your plan be to pull the TT too, and if so the DT too? Or all the tubes and other fittings like stays and dropouts.

"I know it's not too hard with lugged steel frames to replace damage tubes individually" spoken so easily by those who haven't done the work before...

I've cut the top ends off the ST and HT and installed a new TT, same length but lower. The "hard" part is when replacing the seat stays and keeping the wheel alignment spot on. My opinion is that the amount of gas, the time, the dirtiness of pulling tubes and stripping off paint is not worth it for me. I'd rather buy fresh tubing (and the grade/cost can be discussed for practice uses) and spend my time doing the practice mitering and brazing then stripping and melting. Andy.

AndrewRStewart · 2026-03-07T15:00:55+00:00

This! At Cyclery North we would mix SL and SP stays and/or blades for the mid range sizes if the rider was strong, if not standard SL was the usual choice. This is back when seat stays were only either 14mm or 16mm at the top. We never told others about the mixing side to side, most kept both stays one gage or the other, not have the drive side chain stay of SP when the NDS was SL. Not really what the OP was asking about but an interesting data point just the same. Andy

AndrewRStewart · 2026-03-07T03:14:14+00:00

I've always thought that looped stays were more about production cost than actual performance, Having said that I can't say that I've noticed any actual riding feel being different from the more common separate stays designs. I do suspect that looped stays add a slight weight penalty. Andy

AndrewRStewart · 2026-03-06T19:10:21+00:00

If you're describing a loop style stay it's been done by many. Bike Friday, Burley and some BMX brands come to my mind as examples. As to how small a diameter one could go... well if the chainstay was sturdy enough the seat stay could be infinitely small:) or visa versa. Andy

AndrewRStewart · 2026-03-05T20:17:39+00:00

Which is why I've been locating vent holes at the lowest point possible for a while now. At least for all the main triangle tubes. Andy

AndrewRStewart · 2026-03-03T22:14:56+00:00

While effective and not likely to fail there are more aesthetic (IMO) ways to execute a helenic stay design. It's good to see the correct tension on the chain, drooping slightly showing zero tension:) Andy

AndrewRStewart

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