So its been a little while since my last update but things have been happening in the background and I've been spending a lot of time on the lathe. And so its the lathe that makes an appearance for this fork update. My first attempt at the spring seat though functional was not pretty, I couldn't get that smooth finish that you normally see on machined parts and so was not happy. It took me 5 attempts to get it where I was happy and involved playing with the machine more, eventually I found the right speed 470rpm and the right setting on the auto feed (setting 3, 1/8th).
And so that is the finished spring seat. If you were wondering the seat is (and please remember these are +-0.5mm) 16mm diameter and 166mm from the base to the seat, the spring locator is a further 5.5mm on top and 9mm in diameter. In the picture above my spring seat is the top one.
The seat was then put into the right hand fork and oil added. I have filled both forks with 10wt oil and have a 146mm air gap measured with a compressed fork springless. So next is to fit the springs. I'm using the ones from the spare forks and as can be seen they are both the same length. The spring is installed with the smaller taper at the top so the larger end fits over the locator, both springs are installed in this orientation.
The next problem I had with the forks was the upper spring seat. This spacer that acts as preload was not in the spare set of forks and of course there was only one in the bike originally and Yamaha no longer supply them. My original idea was to make my own as I have a lathe now fairly simply its a M20x1.0mm thread so a die of the right size is easy to buy. The real problem is making the 8mm hex hole or to use the technical term, to broach a 8mm hex. If you want to blow your mind search youtube for a video on drilling a square hole, its the same principle for the hex, so all I need is a broaching tool. I did a little research and found a good tool at $1600, a little bit pricey for making one part. You can use a manual broach (again check it out on youtube) basically its a harderned tool that you press through the hole to cut the hex, again these are $500. You can make your own but I wasn't confident on this.
Thankfully eventually via the medium of eBay a secondhand original spring seat turned up. Unfortunately I've forgotten username from the YSR forum of the chap that supplied it to me, but if you're reading this thanks very much and thanks for the other part...
Upper spring seat in and fork caps on they are good to go. Once they go in the frame I can add the dust seals and the handlebars allowing me to tighten them up properly.
The next update will involve some more parts that I have made.