All dirt bike forks are only operating well if you service them often. Do the first service on a new fork after 10 hours with a change of oil and bushes.
For all forks it is absolutely necessary to change oil, bushes, piston rings and check the internal valves every 50hrs!
I can't say that loud enough. Fork service is often only done when the oil is all over the garage floor. It is totally accepted that you need to do a motor service after certain intervals. The oil goes off due to heat and pressure.
Well, it's the same with your suspension. The high pressure in the suspension often causes pitting on the piston surfaces. Bushes and piston rings wear out and shims can get bent permanently. Damping is lost.
How come most riders don't realise that loss of performance? It happens slowly. You don't feel the difference from one ride to the next. But if you get on a new bike then you realise that your forks feel bad.
Here is the service interval sum up:
If your outride takes 5 hrs that means every 10th outride your suspension needs a service. If you ride every weekend you should change bushes and seals every 3 months.
In the average fork there is around 500ml of oil. The oil is forced with enormous pressures through valves to create the damping. It is converting the bike and rider movements via damping into heat energy. Shock oil can reach temperatures up to 120 C ͦ. The fork does not reach the same temperatures, but it operates at speeds 2-3 times the speed of the shock. Forks also move over greater distances and wear can be considerable.
The oil must also lubricate all the moving parts within the suspension and at the same time reduce friction and wear. Not only the oil suffers. Piston surfaces, bushes, seals, piston rings and shims wear out.
The fork oil is black after around 15hrs of hard riding. Much of this is coming from the spring rubbing inside the inner tube. This black residue is what remains in the suspension after chroming or manufacturing. Mostly it is carbon based residue. It contains microscopic particles that contaminate the oil, clog up bushes and so causes unwanted friction.
Harsh suspension is 80% caused by friction and unserviced suspension. Especially suspension that is serviced without changing bushes and seals! It does not matter how often you change oil, if you use aftermarket seals, cheap oil and do not change bushes then you will always have harsh suspension.
Microscopic particles in the oil clog up the bushes. This is hard to see with the naked eye if you don't know what you are looking for. So even if the bush "looks good" they should be changed with every service.
Friction is the enemy number one in your dirt bike fork. If you would like to read more on how to minimise friction then click here to go to fork seal maintenance.
The Dirt Bike Garage Manual
HOW TO GUIDE for "do it yourself" riders