I have been saving a new pair of Suzuki GT750 J/K style fork tubes (or stanchions if you prefer) for many years in anticipation of using them on a restoration, and the time finally had arrived. When I first looked at the old ones on the current project that I refer to as ‘Big Blue’ (see more on my web site at this link) the chrome in the areas that the seal contact actually looked quite good and there was no pitting to speak of that I could see. This is obviously a credit to the rubber fork boots that had slightly survived all those years of sitting outside in all weathers. However, upon closer inspection, I discovered that one tube was slightly bent. While it could be straightened I decided to take advantage of the fact I had replacements and got to work. After all, replacing fork tubes is a simple job so how long could it take ? Quite a while as it turned out ….
I bought these tubes from CruzinImage in Japan via eBay, and while most of the time I’m really happy with both the quality and the value of their products, this was one of those instances where it didn’t quite hit the mark. As a matter of interest, I note that CruzinImage hasn’t offered fork tubes for the J/K for quite some time which probably should have been a clue. There is a lower piston or valve that has to slide over the bottom of the tube (part number 51112-31030) and I found that the tube was just fractionally too big in diameter. As the tube is chromed, and as chromium plating is hard, my options were either to grind the surface of the tube down, or hone the inside diameter of the valve to make it bigger. My toy lathe has a very small through hole in the head stock, so I removed the tail stock and set the tube up using a steady rest with one end held in a chuck to see whether or not it would run true enough that I could use an oil stone to grind down the chromium plating. The reason for doing so is that replacement pistons/valves are hard to find, and so I didn’t really want to modify any good ones that I had. In the end, it worked well enough. And then I ran into another problem.
As the tube was ever so slightly too big, the circlip that the piston/valve butts up against prevented the valve from moving far enough up the tube to allow it to fully seat home. As a result, I found that the lower snap ring that secures the piston/valve would not seat into its groove. I seriously considered going back to the old tubes at this point, but then decided to go ahead and shave just a hair off the inside step of the piston/valve. Once this was done, it all fit together as intended.
My plan is to keep the old tubes and at some point I may look at trying to straighten them. In other places on the globe you can get tubes re-chromed and then ground back to the original size, but here in Canada there are not a lot of options. I do have the name of a place in Toronto, but the cost appears to be more than buying a new set from a place like Frank’s Fork (previously called Forking by Frank) in the USA or from Tarozzi in Italy. I have previously bought fork tubes from Frank’s and the fit was exact and the price was reasonable, so if I were to do this over again, that would be my first option.
And so the build continues !