SBDU Ilkeston Special 753 Dynaflite SB4409 1981 (Reynolds 753 Fillet Brazed with Ovoid Tubing)

Wow, there are some rare frames, and then there is this one. The overwhelming reaction from most people is “Never seen one of those before…”

This is an SBDU Dynaflite frame made from Reynolds 753 Oval tubing and I’m thrilled to be able to add this to my collection. A version of the Dynaflite is shown in this extract from Raleigh’s 1982 Brochure. That Dynaflite differs to my frame because it has a braze on fitting for a front derailleur. If you look closely, you can see that the circular ‘TI’ logo transfer at the base of the seat tube has been fitted to the side of the oval tube. In the brochure, Raleigh describe the frame as “Dynaflite Ovoid Tubing”.

Apart from the image in that Raleigh brochure, I’ve only seen one other picture of a Dynaflite, that was in the article below. I’ve also heard recently from Mike Mullett, a former workshop manager at the SBDU, who mentioned a Dynaflite that was built for the Chairman of Raleigh, together with 2 others that he recalled. In the article written for Cycling Plus in January 2007 by Hilary Stone, he mentioned that there may have been no more than 25 Dynaflite frames built – that isn’t many! Adding together the Raleigh brochure image to the Dynaflite in Hilary’s article, the 3 mentioned by Mike, and mine, that is 6 frames that I know of.

The Dynaflite was a technically challenging frame to build. For decades, a standard frame was an assembly of tubes which were cut and mitred to different angles and held together with lugs; a filler material, typically brass, was heated and flowed into the tiny gap between the tube and lug forming a solid joint. As long as the tubes were not overheated then steel such as Reynolds 531 was not affected by the temperature required to melt the brass.

Before Reynolds 753 was introduced to the public at the end of 1975, the SBDU had been working with the Reynolds Tube Company to define the specification for 753. Tube gauges and brazing methods were all tested and specified. The SBDU perfected the technique of joining the heat treated tubes into a lugged frame. Low heat and soft flames were vital and Silver Solder was used as it had a lower melting point to Brass. If too much heat was applied to 753, the strength of the heat treated tube was lost. A new certification process was introduced before anyone could build with Reynolds 753, frame builders had to build a sample for evaluation and receive that coveted certification.

Reynolds 753 required much closer tolerances, not just at the mitred joint, but also between tube and lug. This meant that preparation was very important. The heat treated tubes could not be ‘cold set’ after building in the same way as 531; therefore 753 frames had to be built true. Silver was also more expensive than Brass. The SBDU actually changed their frame features for their 753 frames. Different fork crowns, lugs and bottom brackets were used. Lugs had cut out sections to reduce the heat required to form the joint. Bottom bracket shells were typically Cast which had a better fit, and seat stay caps were much simpler. All these features were changed from their 531 frames to create better tube fit and reduce the heat required during the frame build process.

Frame builders who had 753 certification and could build a lugged frame with Reynolds 753 were very highly skilled craftsmen. But a Dynaflite was on another level, the tubes were not round and there were no lugs, mitres were more complicated and had to be perfect. The joints required 2 different types of Silver, with 2 different melting points, and the builder really needed to know how to use a torch. Hilary’s article details the process that many people thought could not be done, that is fillet brazing 753 with Silver Solder. Here is the same description in Mike Mullett’s words…

“The tubes were mitred accurately and a ring of the normal Silver Flo 66 was bent to shape, very free flowing used for the lugged frames, and placed INSIDE the tube. It was then “teased” out with the torch until a sparkle of the silver solder appeared on the outside. After the joint had cooled, ArgoFlo was used which was a very pasty LOWER TEMPERATURE silver solder. As the name implies it had an element of gold in its make up. It was then possible to build up the significant fillet without melting the initial Silver Flo 66. Yes 753 could be fillet brazed by a builder with enough torch talent.”

This is probably why the Dynaflite model was not listed as standard frame in the same way as the 753 Road or Time Trial Special – they were listed under ‘Specials’. The details of this frame are something that I don’t think I’ll ever get tired of looking at, they are so different to other frames.

The Dynaflite forks are standard SBDU 753 forks. The forks for SB4409 are fitted with a Cinelli SC crown. To say that they are standard forks is under rating them a bit, they are still beautifully built and detailed forks.

The bottom bracket has no sockets to accept tubes and chain stays like a traditional lugged bottom bracket, it is a simple threaded tube, all the frame tubes are mitred to fit perfectly against the outer surface of the shell.

The seat stays are a huge feature of the Dynaflite. They are almost flat and very narrow, which you can see at the base where they join the rear ends.

These seat stays actually form a very early incarnation of a ‘Fast Back’ arrangement. The SBDU didn’t bring the Fast Back into normal production until the latter part of 1982 when the new Double Taper seat stays were introduced by Reynolds, but the Dynaflite was there ahead of time!

The stays are cut to form a join with the threaded bosses forming the seat fastening. As the seat tube has no lug, the Dynaflite has some small reinforcements placed between the seat fastening and the tube.

The head tube has a small reinforcement ring around the base of the tube to prevent the bottom of the tube from stretching. The seat tube is standard round section tube at the top to allow for vertical adjustment of a seat pin and then changes dramatically to the Dynaflite oval section.

It’s difficult to capture the oval shape of the frame tubes with a camera so I’ve tried to hold a metal rule to the rear rim and tyre and the seat tube. The seat tube is the same diameter as the Mavic SSC rim and Clement Seta tub fitted to these wheels.

As soon as I get a headset fitted, I’ll do some geometry measurements. But at first glance, the frame has some tight clearances. I’ve done a quick check on fork rake and that measured 36 mm, which is a typical SBDU Time Trial fork rake. This frame has been built with a single gear lever boss and one groove under the BB shell for a single gear cable. There is also no front derailleur braze on fitting so this frame was definately designed for a single chain ring set up. The frame doesn’t even have the luxury of being able to hold a water bottle as there are no bottle bosses.

Small reinforcement gussets have been fitted below the top tube/head tube, down tube/head tube and down tube/BB joints.

The more I look at this frame, the more I’m liking the colour. The paintwork is in excellent condition. The transfers are not original and the paint is probably not original either, although I can’t see any trace at all of an original colour. If this isn’t original and is actually a repaint then it has been done very well as it is a lovely finish, with an even, thin coverage of paint. It only has a few small chips around the drop outs and the top of the seat tube.

I’ll be keeping the colour and replacing the transfers with the originals – the original style can be seen in the Raleigh brochure. The transfers are very similar to the standard Raleigh SBDU Time Trial Specials with one exception, the top tube simply says “Special” – I can’t think of a better word to use!