Using a square mount kick start on an XS650
My current project is an XS650 and I am using a lot of brass accents on the bike. I had this Kickstarter lying around with a brass pedal that is perfect for the bike, but it has a square mount point. I considered hacking the square mount off and welding it to the stock Yamaha kickstart, but after more thought, I decided that milling the stock Kickstarter shaft to fit the square mount point is the right way to do it. While I have access to a Bridgeport mill, trying to set that up in the days of Covid was going to be a hassle, and besides, I only need to remove about 50 thousands from each side of the kicker shaft. I was discussing this with my shop mate who is about 20 years my senior and he said “Why don't you just use a hand file?”. While a mill is not necessarily considered modern technology, we often overlook the most basic of tools in our shop in favor of something more automated. I cracked open a Miller Light and got to work!
The first rule of any machining operation is “…if you can’t hold it, you can’t machine it.” So step one is getting the kicker shaft in your vice. Notice I’m using a couple of spacers on one side of the jaws to get a nice even grip across the length of the shaft. Be careful not to gouge up the worm gears on the shaft. You can use some leather or brass spacers to ere on the side of caution, but I was just careful about how much I tightened down the vice and it was fine.
Next, start filing! This operation is really about getting a much metal off as quickly as possible, so the bigger and courser your file the better. Nice long even strokes are best and most efficient and try and stay as level as possible. I was worried that I would not be able to keep my strokes flat, but with this sort of work you taking off such a small amount with each stroke that it really does even itself out over time.
While we are not using a mill to do this operation, you should do calculations just as if you were using a mill. So measure the inner diameter of the square kicker mount and the outer diameter of the Yamaha shaft and do the requisite math. In my case the ID of kicker is about 400" and the OD of the XS650 shaft is 600". So the total I need to remove is 200", or 100 from each side. So I start filing and keep my dial caliper handy to take a measurement a few minutes.
Once I have removed the right about from one side, I then flip the shaft around to do the opposite side. To get the shaft “square” I am putting a level on the flat portion of the shaft that I just filed. Once its level I can start filing again on the opposite side. Again, keeping my caliper handy to take measurements as I go.
You will repeat the same process above for the adjacent sides until you have your square. The nice thing about using a file for an operation like this is that you don’t have to worry about taking off too much and you can easily “sneek up” on the correct measurement. Once you are square you can use a L carpenters shaped square to check for squareness and adjust as needed. You can err on the side of a little bigger and begin test fitting the kicker once you are close, then take off more until you get the fit you want. Once mine was square I could hammer it on the shaft, but it took a few more passes all the way around to get it so you could slide the kicker onto the with little effort.
Using a hand file like this is not going to give you the accuracy of a mill, but you have to consider the application. In this case, the mount point is square so you have quite a bit of leeway in how accurate you are. Also, having the through-bolt takes up the slop in the fit you might have.
Hope you enjoyed this. It was a reminder to me of how effective a hand file can be for milling operations like this and that you don’t need expensive tools to do some pretty cool work in your garage.
Happy wrenching!
