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The Swingarm

Hi, I have tried to keep this as condensed as possible while explaining my process with this restoration/modification. It was all new to me but I found it very rewarding and a nice little learning curve. Here goes...

As have said in an earlier post, shot blasting metalwork reveals all the hidden areas of rust hiding behind years of grease, dirt, paint and old powdercoat. I had the frame and swingarm shot blasted right after strip down to see what I was dealing with. The frame was not too bad considering the time the bike had spent in that (presumably damp) barn but the swing arm was in a right old state.

The underside of the box gusset had rusted right through and the wall nearest the brake stop too. The tubing was all very pitted but salvageable. I could have gone a number of ways here. There are aftermarket replacements available from china but you are never sure of the build quality of such things. I could also have taken a punt on a used one from a breakers but again, there is no guarantee you are going to get a solid one and the thing is, I am not keen on the stock swingarm anyway. It's the same with the CG's. The pressed steel box gusset is a only a 1mm wall and I find them a poorly shaped, messy design. I decided that having a go at redesigning and restoring it was only really going to cost me my time. I now have all the equipment I need to complete the job so why not?

I knew that all the patching and welding in the world would not save the box gusset. So, I started by carefully removing it with the angle grinder making sure I did not cut into the tubes. I then took some measurements from the centre of the side and joining swingarm tubes and plotted the shape out on card. One aesthetic thing I don't like about the stock part is the lop sided arc. This is put in because contrary to first impressions. The swingarm is far from symmetrical. if I wanted to make this arc true, while keeping the same wheel clearance, I would have to mirror the deepest point in the arc ensuring there is more clearance, not less. I ordered in some 2mm, mild steel plate and transferred my templates. One thing I am yet to acquire for the workshop is a good band saw. So, I had to again use the angle grinder to cut the plates.

After cutting out the top and bottom plates, I tack welded them on the inside, making sure to get good, penetrative, tacks. It was then a case of welding a first run down each side on the outside faces. I would eventually make three passes down each side as I planned to blend the welds and it's vital that these are strong. After building up all the welds considerably, I did a first run with the flappy discs and it started taking shape. I carefully cut out the gusset wall out of the same 2mm steel and the curve was created by hammering it out, with a rubber mallet, over an old piece of iron drain pipe. This was then fitted and welded in place.

Once I had the basic form, I turned my attention to the brake stop. I carefully removed the stock one from the old box gusset and traced the shape of one side on card. I then mirrored the shape with a 10mm gap between them to accommodate the bend. After transferring the template to 2mm steel, I cut it out and used a piece of bar in the vice to fold it into shape. I then used the bench grinder to ensure it was all perfectly symmetrical. To ensure that the stop holes were perfectly in line, I had decided to drill them out in one hit. This meant that I needed to insert a piece of wood between the two sides of the brake stop to prevent it closing up under pressure while drilling. I took stock measurements and drilled out the 8mm holes. after removing the wooden filler piece and giving it a clean up it looked pretty good. It is vital that this piece is correctly welded in exactly the right place and that it is as strong as possible. It took some time to mark it up and again, I decided to do several passes with the MIG, building it up at the sides.

After fabricating the brake stop and knowing it was all structurally sound, it was all about getting the whole job right cosmetically. I wanted all the lines and angles right. So, I spent a lot of time with the MIG and grinder filling, blending and shaping the whole piece. I am very pleased with this fabrication. It already looked so much cleaner than the stock part and I knew it was a lot stronger. Time to get it to Dan at K&M Powder for a coat of satin black. Dan did his usual, awesome, job and it came back looking like a brand new piece.

I had ordered some solid bronze bushings to replace the composite stock ones. It's always necessary to replace these bushings as they can get damaged during removal and they never really fit properly a second time. These bronze ones were a nice little upgrade though. To fit these, they needed to be pressed onto the swingarm tube. I said in a post that my 10 tone press is one of those tools that sits around the workshop for 99% of the time gathering dust. For the 1% you actually need it though, it's worth its weight in gold. Now, there is an order to this little manoeuvre. You need to press one bushing onto the pipe first. That then gets pressed into the swingarm and the final bushing is pressed into and onto both, last. You can view the time-lapse of this below.

The swingarm, now complete, looks really good and I'm confident is a big upgrade to the stock piece. The design is a great deal cleaner, the hardware has been replaced and upgraded and I'm very happy with it. It has taken a great deal of time and it is true that it would have been easier to go and buy a new part but this is now a bespoke piece and it is the way I wanted it to be.

I'll be adding a new post soon to conclude the frame modification. I've been a little distracted recently by all the shiny parts arriving to complete the build. If you follow me on Instagram, you will understand why. See you next time.

Jonathan Hull

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1 comentário

auld isle cycles
auld isle cycles
21 de dez. de 2021

Great post Jonathan, really enjoying reading about a bike build as it happens rather than watching it for once, looking forward to many more! Gary 😎🙏🏴󠁧󠁢󠁳󠁣󠁴󠁿

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