It all started with a comment from Ralf that he fitted an XS1100 swingarm and final drive into his XS750 sidecar. To be fair I had the same idea a while ago, but it always only came back to mind, when I really needed the old girl to be working and doing her thing on a daily basis.
The hard facts: approx. 7 percent shorter gearing, which should fix the issue with a slightly long first gear, when pulling a sidecar and as an added bonus 30mm more wheelbase due to a longer swingarm and being quite a bit sturdier than wouldn't do harm either.
It's rather apparent that not only the XS1100 swingarm (on the left) is beefier than its 750 counterpart, but also quite a bit wider.
19mm wider to be precise. Luckily due to the way the swingarm mountin is arranged on these bikes the odd millimeter up or down wouldn't make a differents as the swingarm runs on adjustable pins.
With the in mind, only way to do this - get the angle grinder out and hack that swingarm to bits. Sounds dramatic, but I knew that the outer bearing cup was originally only welded on (for those who want to do the same, the lip is about 5mm deep), so cutting it off sufficiently far away from the cup made the rest a rather simple job.
Clocking it up in the lathe using the original bearing cup of the swingarm bearing as a reference was a tad nerve wrecking, but I got it within 0.02mm between high and low spots.
Then turned it down to a nice press fit inside the swingarm tube
A final sanity check with the cup pressed in and it ended up spot on in terms of the width. Same 281mm as my stock swingarm.
An old 17mm rear axle out of a XV750 had to sacrifice it's thickened part, where it normally is clamped in the swingarm to act as a draw bar and alignment tool for the swingarm.
I admit, my TIG weld looks nicer than the stock MIG weld that was there before. It's probably also a lot stronger. (There were some penetration issues in the original weld that became apparent, when I shortened the swingarm.)
Fitting the swingarm was a royal pain as it is rather heavy and obviously imbalanced and there's not a huge deal of room to wiggle it in. Also some idiot forgot to put the rubber boot on.
Swingarm out again - aside from the width, the indent on the right and the brake brace mounting point had to be modified.
Next stop was the splash guard on the rear wheel. Turns out with it installed the rear wheel doesn't clear the final drive housing.
The bolts dig into the housing and if you were to replace them with countersunk bolts the studs of the final drive housing eat into the shroud.
Once you look at both the triple and the 1100 units, it becomes rather apparent why it won't work as the 1100 unit is more or less flat and the triple inner cover has got the wheel coupling sitting a notable bit further out, giving plenty of room for the shroud.
In the end it all aligned rather nicely.
Let's waste no more time and tackle the elephant in the room: Was it worth it? Oh hell yeah. First gear is now short enough that I can take off without touching the throttle on level ground. First and second gear as soon as the engine gets into the power band makes the rear wheel light up and me grin like an idiot. And in the end, ain't that what it's all about?
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