Ninja 250 Race Bike fork work part 2.

I got pretty far down the path of disassembling the Ninja's forks the other day. I was stymied by the stuck damper rod bolts which is a usual issue when trying to service this type of fork. Damper rod forks are the most common type of fork used on bikes, especially older ones. Getting the damper rod bolt from the bottom of the forks is enough of a pain that there are plenty of YouTube videos out there with tips and tricks to get them undone. I took a break from the shop, had some dinner and a brew and watched a few videos to come up with ideas. Take a look at how the rest of the work went below.

I broke the left legs damper bolt free pretty quickly once I had a chance to think about it. I used my drill press vise to clamp the brake mounts of the fork leg and fired up my electric impact gun to break the bolt free. The other leg didn't have brake mounts so I had to reinstall the fork spring and cap to put tension on the damper rod. That kept the damper rod from spinning enough that the electric impact gun did its magic. The damper rod bolt washer was stuck in the recess so I had to break out the heat gun to warm things up. A few swift smacks and I was free to start the clean up process.

To clean things up I got some brake cleaner and set about spraying and wiping everything down. I had some gunk at the bottom of the fork legs that required shoving a rag down into the bottom a few times to remove. I worked like a surgeon with clean gloves and clean rags to ensure my fork internals were spotless. After doing all of this work I didn't want something to cause the seal to prematurely fail or to have some leaks while out on the track.

While I was spraying and wiping the big parts, I threw all of the internal small parts in the ultrasonic cleaner. They came out spotless after two or three cycles. I did one fork's worth of parts at a time and didn't mix the two sets of parts. It probably isn't that important, but on many type of mechanical parts, mixing parts from left to right or vice versa can lead to leaks of fitment problems. The parts have lived their lives in one spot and have worn into their places. When you switch them around there are microscopic differences that can manifest themselves in small leaks or too tight/loose fitting. Its best to avoid all of that annoyance straight from the start.

Two days after ordering, the Race Tech suspension parts arrived on my doorstep. I went with a full rebuild kit and got inner and outer fork bushings, new dust and oil seals, fork oil and a new set of springs more appropriately sized for my weight. I also picked up new crush washers for the damper rod bolts and fork oil drains. I went with Race Tech as I could get all the parts from one supplier. It isn't the cheapest option, but I have heard that their phone tech support is outstanding in case I need that later on. They threw in a ton of stickers so a few went onto my track tool box.

Here is the new spring on the left and the old spring on the right. I am measuring for the length of the new preload spacer in this pic. Race Tech includes a length of 3/4", schedule 40 PVC pipe to cut down into spacers. You are supposed to set the preload to what it was from the factory. They also included some 1mm washers so that I could fine tune the preload after the forks are fully assembled if needed. I bought another 5' length of PVC in case I wanted to experiment with different preload settings. Each one is about 5 1/4" in length so I have plenty of PVC to get the settings just right by making a few sets of different length spacers.

Here are the spacers I cut and another tool I made from the run to the hardware store. I needed a fork seal driver to drive in the outer bushings and oil seals into the fork leg. These specialty tools are around $100 for a well a made set. I spent $2.59 plus tax to make my adjustable fork seal driver from a 2' length of 1 1/2" ABS sewer pipe. I cut some slots in the end so that I could put a hose clamp around it and tighten the diameter as needed. This worked perfectly. I drove the bushings and seals perfectly flat into the fork recess with just a few firm smacks. This was another YouTube trick I learned while getting ready to do this project.

The reassembly went smoothly. I followed the instructions found in my Race Tech Suspension Bible that was a Christmas gift from the dear wife. I had to consult my Ninja 250 owners manual to ensure I had the parts in the right order. The pictures I took for the blog also helped as I referenced them during the process. When I did the disassembly, I laid the parts out in the order they came out of the fork. Between the manual and the pictures, I had no issues getting the legs back together and back on the bike. The syringe tool you see in this pick is one I picked up from Cycle Gear. I can set the height of the fork oil with the tool to be sure I get the precise amount of fork oil in each leg. Later on I can add or remove oil to tune the fork settings. For now I set everything to OEM specs so I can get a good comparison between the old springs and the new.

In the next post I will go into detail on how I check the sag settings and what they mean to your ride's performance. I will also hopefully have a new rear shock to get the back end of the bike in order. Once the suspension is set I will be going over the bike front to back to get it ready for my track day. I want to rebalance the wheels, change the oil, redo some safety wiring and give the bike a bath so that my tech inspection goes off without issue.

Stay tuned for more,

Blue