Modifying the FZ600 Swingarm to fit the RZ350 frame
I'd like to say this was my own idea but I got the idea and instruction from this site. I had quite a few questions that I had to figure out on my own so I thought I'd build on the original site and try and document the work at each step.
Above is a 1986 Yamaha FZ600 swingarm which differed from the RZ350 in quite a few ways. First it is aluminum so it weighs significantly less. Second it is much more robust, and lastly and the main reason for this conversion is that it is wider at the axle end to allow for different wheels and more modern tires.
While it is close to a bolt in situation in terms of the wheel base and shock linkage, the main stumbling block for a basic mechanic such as myself is that the pivot point is wider than the pivot point on the original RZ350 frame. With the dust caps and spacers in place the total width of the pivot area is 220mm. With the dust caps and spacers removed the actual aluminum width (and internal steel sleeve) is 215mm. The easiest way to slim this down is remove equal amounts of metal from either side of the pivot point.
First remove the two dust caps from either side. I plan to replace these as they are a pain to install if the swingarm is in the bike, but cheap and easy to do now. These parts are shared between the FZ600 and RZ350
With the dust cap off you can see the bearing and the edge of the pivot sleeve.
Be sure to either save or replace the spacer inside the dust cover which is hard to see when covered in grease. I decided to re-use mine since I couldn't really see any wear on them.
Then push out the pivot sleeve. This should easily push out with not much force at all. Also note how there is a slightly recessed area that the dust seal lip covers. This will have to be remachined further on to the pivot area once metal has been removed.
The pivot bar is also 220mm long. Since we can use the existing RZ350 pivot bar this can be removed and sold or used as a paperweight.
Since this swing arm came off a bike that had been siting for quite some time I also decided to remove the relay arms and check the bushings and oil seal where it pivots inside the swingarm. The relay arms are bolted together with a single bolt, and once removed they can be separated and removed from the swing arm hole.
I then cleaned up the swingarm and took some initial measurements. Please note these measurements are as accurate as I can make them with a metric tape measure and I have rounded off to the nearest millimeter. The axle area is 218mm and the pivot width is 215mm.
In order to machine the pivot point the existing bearings need to be removed. The easiest way to do this is to use a wooden dowel of a slightly smaller diameter and hammer them out from the inside. If they are very stubborn, you can heat the aluminum with a blow torch (which will expand faster) which should release a little pressure on the bearing.
Usually the bearings are destroyed in the process, but I planned to replace mine with new ones anyway since it will be a while before I have the swingarm off again.
The bearings are each 28mm deep, and should be installed flush with the pivot point face when new ones are installed.
The next step is to get it ready for the machinist to reduce the pivot point width to around 205.5mm. This measurement is taken from the Haynes manual (page 119) which shows the length of the RZ350 sleeve to be between 205.2 and 205.5mm. The easiest thing to do is remove the RZ sleeve and take it along to the machinist and ask him to take an equal amount off each side of the swingarm pivot ends in order to match the width of the sleeve. You will also need a lip for the pivot end cap which is 10mm deep and a diameter 1mm less than the outside diameter of the pivot tube, or 39mm. One lucky thing is that the pivot bearings are only 28mm deep but the factory machined depth in the swingarm pivot point is 36mm so I will be able to remove +/- 5mm on either side and the new bearings will still be flush with the pivot face!