FORK SPRING PRELOAD - TWIN-CHAMBER
Internal Top-Out Spring

 

Twin-chamber Fork Spring Preload is a little tricky. It cannot be measured directly, it must be calculated from two reference measurements. Here goes...

 

►ClickHere for Twin-Chamber rebuild instructions.

FA14- Slide the spring onto the cartridge and insert the assembly into the fork tube. At this point do not bolt in the cartridge.
Make sure the Outer Fork Tube is bottomed out against the Fork Bottom.

FA15- Gently rest the cartridge on the spring. Bottom-out the outer fork tube.
Make a reference measurement between the end of the bottomed-out fork tube and any easliy identified edge on the cartridge (any reference point will do). This measurement will shrink when the bottom bolt is installed.
In this case the reference number reads 88.4mm.

FA16- Compress the spring and insert the clip tool.
You can't see it in this picture but he is pushing on the cap end of the cartridge with his left hand.

FA18- Tighten the jam nut.

FA19- Compress the fork and remove the clip tool.

FA21- Tighten the adjuster bolt with a torque wrench to manufacturer's spec. No air tools.

FA22- Now that the cartridge is installed, the spring is compressed to its set length. Make sure the outer fork tube is bottomed-out. Measure the reference distance again. In this case it now reads 80.2mm.

 

The difference between the two measurements is the Preload. In this example 88.4 - 80.2 = 8.2mm preload. (FYI - 8.2 is too much for most dirt bikes.)

 

If you need to increase preload washers can be added below the spring.

 

Decreasing preload can be a bit trickier. This would include shortening the spring perch.