Type 2-10 Yamaha KYB 34-38 1976-78

 Dirt and Street - KYB

  • 34mm RD400 1976-78
  • 36mm TT/XT500 1977-78
  • 38mm YZ250-400 1977-78
This is the stock damping rod head. It is threaded on and held in place with a roll pin. It does not have to be removed from the damping rod to modify it.

As shown, the head has outlet ports exiting the sides.

This is a side view. The top of the head must be machined off down to the bottom of the outlet holes.
The damping rod head must be machined off flat just below the outlet holes. This is best done on a lathe but can be done with a hack saw and a file if you are REALLY careful (don't blame me if you mess it up).
This is a cross section of the completed damping rod head. If you look closely near the top, you will notice there is still a lip from the head covering the end of the damping rod tube.
Here is another angle. Leave the roll pin in place.
Enlarge the original compression holes depending upon size of damping rod:

  • Smaller than 17mm diameter - 6mm (1/4")
  • Larger than 17mm diameter - 8mm (5/16")

Add one more set above (left in the picture) at 90 degrees to the last set for total of 6 compression holes. Deburr inside and out.

DIRT WITH AIR-ASSIST ONLY

The original long, soft Top-out Springs are on the bottom of this picture. These soft springs require the use of additional air pressure which makes them harsh. These are found in some 36 and 38mm Dirt forks.

RT has new Top-Out Springs (FRST K3801) for 38mm forks. These are shown on the damping rod. They allow the use of modern rate springs and increase travel by 7mm.

Street forks have standard Top-Out Springs.

EMULATOR ADAPTER

The adapter is a sleeve with a piston band, that goes between the damping rod and the Emulator.

Some Adapters are recessed on one side. If your Adapter is recessed that side goes up, towards the Emulator. You will see it only fits well one way.

Notice the Emulator Adapter has a piston ring even though the stock damping rod has one. The stockers seal poorly.

The main spring holds it all together.

 

Here is the completed assembly from the YZ. Notice the new Top-out Springs. Street has standard top-out springs.

See also Standard Emulator Installation Instructions.