The Key to Disassembling the Upright Fork is to Prevent the Damper Rod from Spinning Around.

There are two types of upright front forks, the basic damper rod type and the cartridge type with an adjustment mechanism. When replacing the oil seal inserted into the outer tube, the damper rod bolted to the lower end of the outer tube must be removed, but this is not always easy to do, so be careful.

You want to loosen the damper rod bolts all at once, not "slowly".

You'll be lucky if you can loosen the damper rod bolts all at once with the torque and rotational force of the impact wrench. The key is to be able to keep the internal parts of the inner tube temporarily assembled and keep the tension on the damper rod. Once it starts spinning, it often won't loosen up anymore.

The principle of a front fork is that when the inner tube expands and contracts, the oil inside creates damping force by flowing through it. The type of upright fork where the damper rod (fork piston) is bolted to the lower part of the inner-outer tube is called a floating valve type.

Since the piston diameter at the top of the damper rod is larger than the diameter of the lower end of the inner tube, it is necessary to remove the damper rod bolt and remove the damper rod itself to replace the oil seal that has hardened over time or to remove the inner tube that has developed point rust.

This is a common task in upright fork maintenance, but in some cases, the damper rod bolts can be very difficult to loosen.

If you're always going to struggle with all types of motorcycles, you'll have to be prepared for it, but it's a tricky one that's not always the case. The damper rod, which is secured to the bottom of the outer tube by a bolt that attaches from the back of the outer tube, is held down by the fork spring inside the inner tube. So the spring's tension can be a deterrent to getting around and can be easily loosened with a hex wrench.

When performing front fork maintenance, once the fork assembly is removed from the trident, it is common practice to remove the top cap, drain the fork oil, and then loosen the damper rod bolt. If the damper rod itself turns when you loosen the bolts there, the technique of putting the spring or collar back on the inner tube and temporarily assembling the fork is described in the motorcycle manufacturer's service manual.

The damper rod bolt is a hexagon socketed bolt coated with a thread locker to prevent it from loosening and is turned with a hex wrench. If you try to turn the bolt with weak force while the thread-locking agent is in effect, it will often spin around with the damper rod bolt and get stuck in the ditch, so the key is to loosen it with a strong torque on the first shot.

If the fork spring is temporarily assembled, it can often be removed at once with an impact wrench, but if it is halfway loose and starts to spin around, it is a common pattern that it will not come off anymore.

If the bolts are not loose, fix the damper rod from the top of the inner tube.

The four edges of the square pyramid bite into the hollow holes of the damper rod to prevent it from turning around. It is very versatile, but not all damper rods can be fixed with this tool.

Insert the damper rod holder attached to the end of the extension bar from the top of the inner tube, and loosen the damper rod bolt from the bottom of the outer tube. This is often done with a vise between the brake caliper mounts.

If the damper rod bolts keep spinning halfway loose, or if the wrench to turn the bolts is responsive to the wrench but shows no signs of loosening at all, force the damper rod itself into place.

The tool called the damper rod holder is used for this purpose. The damper rod itself is hollow, as the inside of the body is an oil passageway, and the holder is inserted from the top of the inner tube and holds the damper rod directly in place to prevent it from spinning.

There are two types of damper rod holders: one is a special tool designed by the motorcycle manufacturer for each model, and the other is a special tool that is designed to be versatile enough to be used on other models. The specialized tools are developed by the motorcycle manufacturer and fit perfectly to the top of the damper rod, but if you have a number of motorcycles, they may not work with other models (although they may be compatible).

In contrast, the general-purpose damper rod holder inserts into the center of the hollow damper rod and fastens it in place. It has a square pyramid shape to accommodate as many different rod diameters as possible.

No matter if it is a special product or a general-purpose product, you need an extension bar that reaches to the end of the long inner tube to fix the damper rod at the bottom end of the outer tube. And because the damper rod is located at the end of the long inner tube tunnel, it is difficult to see the shape of the rod tip, which is a problem.

If your motorcycle has already been disassembled many times, you'll know how to fix the damper rod with any tool. However, if you are going to use a universal type of damper rod holder when you first disassemble your motorcycle, you must know the shape of the upper part of the damper rod.

As an example here, the inner diameter of the front fork for the 1980s Suzuki RG250 Gamma is too large for the size of the damper rod holder, and we were able to loosen the damper rod bolts by pushing it forcefully against the edge of the square pyramid in a bad way.

When I pulled out the damper rod, I found a 6 square x 2 = 12 point hole at the top. I thought it was difficult to get a special tool for this model, so I went to the hardware store and bought a steel bolt that fits the size of the 12 point hole./I made a damper rod holder for this model by welding a socket for the impactor that was leftover from an 8-inch socket. When I used this holder to hold the rod in place during assembly, it did not spin when I tightened the holder bolts.

As an aside, when tightening the holder bolts, instead of applying the prescribed torque from the beginning, it is better to apply a few strokes to the inner tube while it is temporarily assembled so that the damper rod and the oil lock piece do not touch each other, and then tighten the bolts to the prescribed torque.

This is the relationship between the outer tube and the length of the damper rod. The piston in the upper part of the damper rod is larger than the hole in the lower part of the inner tube, and it becomes a stopper when the inner tube is fully extended. This is why it is important to use the correct torque when tightening the damper rod bolts to prevent them from coming loose.

The tip of the damper rod on the 1980s Suzuki RG250 Gamma was machined with a 12-square tip, and I found that the two-sided 17mm wide bolts fit perfectly, so I made a special holder for it.

A deep socket is welded in to stop the damper rod from turning around so that the extension bar can be inserted. This greatly reduces the amount of work required to disassemble and assemble the front forks.

How do you fix the upper part of the damper rod without a hole?

The front fork damper rod for the Kawasaki KZ900LTD has a unique structure. So the square pyramid-shaped damper rod holder and normal sockets don't work. I had to forcefully remove the bolt with a nut twister.

Part of the round protrusion was cut out 12mm wide so that the 12mm deep socket opening could be cut out and held on two sides. Probably the specialized tools of the time were shaped like this.

There are some rare cases where the spring and collar in the inner tube cannot be loosened, whether you use an impact wrench or a universal damper rod holder.

When disassembling the front fork of the Kawasaki KZ900LTD, I didn't have a special tool, so I inserted the square pyramid damper rod holder into the inner tube, but there was no response at all.

When I illuminated the bottom of the inner tube with a flashlight, I could see that it was not a hole in the damper rod, but a convex shape, so I tried inserting several sockets, but none of them were spinning and there was no sign of a halfway loose bolt coming out.

So, as a last resort, I used a nut twister to loosen the nut and nut with a licked hexagon head, and finally, the damper rod was fixed and I was able to pull out the rod bolt.

Looking at the tip of the rod, I found that some of the round protrusions had been cut parallel to the end of the rod and were 12mm wide, so I sanded the opening of the 12mm deep socket to make a special rod holder.

I don't know why the top of the damper rod is capped, but the fork oil flowing through the rod can enter and exit through the side hole in the cap area, so it's probably not a problem in terms of the mechanism that generates the damping force.

This type of construction is rare in terms of damper rods, but keep in mind that there are many different types of damper rods for upright forks, and there are a number of ways to fix them when they are spinning.