FM350 wrote:Personally I have yet to see any Spanish frame that is that great! Poor design using cheap materials never tends to work that well, but in terms of function the earlier Spanish frames made out of heavy gauge gas pipe, seemed a lot less prone to breakages? With better basic design though there is no good reason why cheap materials shouldnt work fine for trials use, and frame breakages on bikes like Fantic, Honda, Yamaha are very rare, even though these bikes are also made using cheap ERW tubes.
Yes it is true that It is the design that is most important, and less important if the tubing is ERW or seamless, but I think you should study up a bit on Spanish bikes, because you are dropping quite a few clangers with your generalisations.
My Bultaco tubing is also seamless, definitely not welded but extruded. Bultacos also came with a small sticker on the bike that stated they were made from chromoly. Also not to sure why you cant weld it with a MIG welder? I had a brand new 159 325 back in 1975 that I rode A grade on for two years without any frame issues at all, no bending, buckling or cracking. Like David said.
Modern air hardening high tensile steel tube can be joined using MIG welding. Chrom-moly of the type available in the 70s would have needed to be welded either using oxy-fuel or TIG as outlined here: http://www.weldcraft.com/2007/08/tig-we ... oly-steel/
All the Spanish frames I have seen were ERW, but I guess some may have been CDS, which would explain the lack of any seam. I guess some of the works bikes probably had chrom-moly frames, but as having these on production bikes would very likely have doubled the unit cost of the frame, this would explain the lack of any TIG or bronze welded customer machines.
Bultaco used chrome-moly tube from about 1973 onwards, The frames were as light as you could build in that period given the materials and production techniques available. There was quite a lot of publicity given to the fact that they were the first production trials bike to use chrome - moly tube.Bultaco in the 70's were in a lot of respects the innovators, they were the first to introduce a conical front hub [this made the front wheel the lightest production wheel at the time] the first to introduce a larger engine, the first to introduce plastic tanks. They won 5 world championships on the trot with three different riders.
sherpa wrote: They won 5 world championships on the trot with three different riders.
Not to mention 4 European Championships the predecessor to the World Championship, 7 Scottish Six Days,11 Spanish Championships and 10 English Championships
It is easy to look back at these bikes and say they should have been made this way or they should have done this or that, but they were the best bikes available at the time and incorporated the best available technology. The smaller European firms did and still do introduce upgrades during the model runs and you basically got what the factory riders had the previous year and I dont believe this has ever been the case with the Japanese firms
This is the reply from an email I sent to a mate, who is a metalurgist and has been since the 70's
Greg, The general consensus among our welding experts is that they were probably TIG welded. It was possible that oxy was used as well. The Chrome Moly referred to is made as tubes in AISI 4130 steel. This indicates that the steel has 0.30% carbon. Because of the thin wall section preheat is not necessary. The steel tubes are supplied in the US to military specs for aircraft use and they are either normalised & tempered (Tensile strength about 655MPa and yield strength about 500MPa) or quenched & tempered (Tensile strength of 860-1240MPa and yield strength of 690-1140MPa). Reynolds in UK still supply tubes for bikes (both motor and push). They quote tensile strengths of 700-900MPa (varied by the amount of cold work by drawing) and I think they also supply quenched and tempered tube. Again the material is 4130.
MIG would have caused too many lack of fusion problems back then before flux cored wire was available. Send me a photograph of some welds.
What a lot of fuss about a cracked frame!! May as well through in my 2 cents worth. I have worked with localy sourced CrM tube in the manufacture of speedway car chassis and a couple of motorcycle sidecar frames. I can tell you that the tube that I have used which I think came out of the USA is different to the stuff in the Spanish , German and Jap bikes(claimed to be CrM) that I have done frame repairs and mods on over the last 30 years or so. The production motorcycle frames seem to be much softer and bend easier than the tube that was sold to me as CrM 4130. All I can assume is the motorcycle tube is not 4130 or it is some form of annealed tube that they used. There are quite a few grades of tube that are generaly taged as being Chrome moly. AS far as welding goes, the US 4130 tube that I have used in manufacturing was TIG welded and every motorcycle frame that I have ever repaired was done with stick until I got a MIG about 25 years ago. I have also seen quite a few frames repaired by brazing that didn't last very long in service,probable because of overheating the metal while doing the repair. I would only braze together a frame it was to be a replica English frame. When TIG welding CrM you use ER70 filler rod, this has no Cr or Moly in it and the deposited weld ends up being a little lower in tenstile strength than the parent metal. This is done to keep the weld a little flexible to help stop cracking. Most general perpose MIG wire is ER70 as well so the use of MIG on CrM tube is normaly not recomended because the weld fillet ends up way bigger than that of TIG creating a large inflexable weld. I have been told that with carefull grinding down of the weld fillet a reasonble joint will result. This last bit of info came from the buisness on the Goldcoast that makes a large percentage of the Sprintcar chassis in Australia, they TIG weld everything but told me that if you are stuck just use the MIG but keep the weld fillet small and never quench it.
I agree they look like MIG welds to me as well, anyway I have just got another email from the metalurgist after sending him some photos
Greg, The welding gurus now say it is MIG after looking at your photographs. This is because the welds look a bit ugly. Regards,
I think the Spanish would have used chromoly with the lowest amount of Carbon content as possible so that they would avoid many of the issues associated with the welding of high carbon alloy steels cheers Greg
Anyway ... I used one turnbuckle and chain on the rear engine mount and one on the front and brought it all nicely together - these even straightened out the slight bend in the middle (under seat) tube. So now I just need to get time to take it down to Coffs Harbour to have it tigged
