Welcome back folks,
In this installment of how not to turn your already working motorcycle into a pile of scrap, we attempt to change the back end of the bike. I have written a post previously about fitting a pre-made cafe racer loop to the back of my XS750 project. For this current bike, I wanted to do something a little different.
I had initially planned on sourcing a tubing bender and doing it myself, but staring at the frame, it already had nice big curves from the factory (mmmmm) that I wanted for the back of this bike. I didn’t fancy going for a fully round cafe-racer style loop like before as I didn’t think this would match the style I was going for.
The aim of this bike is to keep it looking like it could have rolled off the factory (via a custom shop armed with blind apprenctice craftsmen) so I wanted to reuse as much of the original frame as possible. Also the tank that I bought to fit the bike (a future post) has a squarish profile. This meant, for lack of a better term, doing a cut & shut on the frame. As it stood, the end of the frame extended back over the rear wheel. For the standard bike, this was fine as it held the large rear mudguard. The back of my bike was going to be neatened up a little. I wanted to shorten the back end slightly. I took some reference points off other inspirational bikes and noticed a lot of the seats finished at the rear axle.
To begin, I attached a heavy nut to a length of string which was my pikey version of a plumb line. This was used to give me a vertical line. This was held alongside the rear axle and a point was marked on the frame on both sides. Using a square I confirmed they were at the same.
This then left me the with below which was where I wanted the end of my frame to be.
I then had to pick a point on the frame that I wanted to recycle….re[motor]cycle….GET IT?! The frame has a slight kick up towards the end (seen above) which a) I wanted to reuse as it had the curves and b) wanted to remove the kick up as this would be too much of an incline and ruin the look of the bike a bit.
I measured how much I had to cut to be able to get the end of the frame at the point marked by the plumb line…make sense? Then fired up old grindy mc grinderson and got to work chopping this frame to bits.
Shit, I measured the wrong place!! Just kidding…but I did measure and remeasure a good few times before I was happy with this. Learning perhaps….?
I now had a U shaped section on my workbench that required some massaging with a grinder. I chopped the angle out of this so that when it mated back to the original frame the end matched the profile of the rest of the frame. See below pictures for more detail.
I noticed that when I cut this loop off initially, the frame had a tendency to spring out, so before fitting again, I had to use a clamp to pull the frame back into line. This springing of the frame maybe isn’t hugely important for a seat loop, as there isn’t a huge amount of critical areas on the bike this may impact. but for larger frame alterations i.e moving suspension mounts, or more intensive cutting, I would look to building some kind of jig which would keep the frame true and square.
When I fitted the last cafe racer loop, it came with the metal slugs that fit inside the frame. These are used to help hold the frame together during welding. This time I didn’t have any metal slugs, so I made my own out of the excess parts of the frame.
The slug simply needs to be able to fit inside the Inner Diameter (ID) if the frame. This was a bit of trial and error cutting sections out of the slug, shaping it to be round in the vice and testing in the frame. the two slugs were good to go and reassembly could start.
Reassembly was fairly straight forward…now that I knew how to weld (kind of). I would use a combination of a butt weld and plug weld (dirty minds stay with me…who am I kidding hehehe butt plug) to reattach this loop. The plug weld adds rigidity and more strength to the joint. To do a plug weld, you drill a hole in the parts you are joining together, then place the mastercrafted slugs in. You weld through the hole, mating the slug to the frame. This is repeated on both sides….as always, see the short video below to explain…
The butt weld is then used to weld the two ends that butt up against each other together. I found it quite tough getting underneath the loop to weld and clean the welds up, as the bike is still intact. I will re-examine everything is OK when I strip the bike apart for powder coating
In total, this loop is held in place at two points, the butt weld and the plug weld. The whole thing is then ground down to within an inch of its life to make it look like the whole thing never happened and it came out of the factory that way.
The finished article I am happy with. I have left the original mudguard mount on because I think I will use this to mount the number plate. I still need to think whether I will run a mudguard on the back. Although this will be a scrambler and I may take it on some dusty tracks, I think this will end up being a fair weather bike…if it goes back together properly.
This job was done over a couple of nights but could probably have been done in an afternoon if you have the time. Having learned how to weld last year has made this job much less of a fear. I actually really enjoyed the process of reusing the original frame.
Next time we will look at the process for fitting an old rusty tank in place of the well-engineered plastic factory model, all in the name of looking cool ;).
To be continued,