Here is a big project I have been working on. Starting with a stock 1982 Yamaha XV920R
Pretty nice bike, but outdated in ride quality, and braking. This means two major elements have to be changed, the bias ply tires need to be upgraded to radials and the brakes replaced with something that stops. Combining better brakes with radial size rims meant a suspension upgrade was also in order... Before all that I tried some racing brake lines to see if that would help. It did make the front brake firm but the stopping did not improve!!! Still getting close up views of bodywork on cars and having to corner harder (riding on the edge) to make some turns...
I started by measuring the chassis and all the the suspension angles, travel, etc. to see what would easily retrofit. which brought me to the conclusion that major changes were required to fit radial tires and make the bike handle better. Looks are one thing, but crashing is not part of the plan. The measurements also revealed a huge weight bias towards the rear. To fix that I can either make a longer swingarm or shorten the front. Shortening the front was the way to go for better handling so I took that route.
The bike got stripped down and work started. First I unbolted the the rear lower frame (that holds the swingarm pivot) and sent it to Leon Eddins who helped adapt it to the Honda F2 swingarm I decided to fit. A lot of cutting and aligning was required for it to work. In retrospect, I should have made a swingarm from scratch because so much was changed or adapted.
I started with a CBR600F2 swingarm. One of the reasons for choosing this swingarm is that the length was right (based on target weight bias) and the F3 rear wheel (4.50x17) fits right in.
The pivot on the Honda arm is solid and goes from one side to the other. It had to be cut out and centerlines matched up. The Honda swingarm was hard to align because the pivot on the XV920 frame is offset to one side more than the other. Spacers were fabricated to align it. After that I had some seal cups machined to hold oil seals so that water doesn't get into the bearings that were now exposed on the inside. The XV920 pivot width on the stock frame is 145mm
Now that the swingarm pivot was sorted, I cut out all the shock mounts, then I carved the space between the swingarm pivot and as far back into the bridge that links the left to the right side. The distance for that cut was determined by the location on the bottom of the swingarm for a Yamaha YZF600 suspension pivot for the stock Yamaha "dog-bones". This was welded in place using the standard geometry from the YZF600 (i think 94-96 model). A jig was necessary for this operation and I made one from a thick piece of steel with threaded rods installed at the correct locations duplicating the stock geometry. Then spacers were used to hold the parts in the exact locations for welding to the modified Honda swingarm. The shock link is from the same YZF600.
For the geometry to work there were certain dimensions to respect and it was not easy to find existing components to fit. Settled on Honda CBR600F3 wheels because the rear fits the swingarm for the same and has the right length. It would also line up with the offset 520 countershaft sprocket. Lining up also required machining the sprocket carrier to bring the sprocket in, and there was some room left without having the chain rub the tire. The studs that hold the sprocket were cut down too.
A created with a new mount on the main frame had to be created too. That's when my good friend Vic Fasola suggested I speak to the best freehand torch welder around, Mr. Terry Stogget.