- Joined
- Sep 26, 2009
- Messages
- 2,210
The importance of fork oil change's.
Ok, you have filled your forks with fresh oil,and thats it for many years to come?. well many of us have pulled apart a set of forks to find the internal's red rusty and parts pitted... said oil as emulsified, its become a water based sludge.
Bmwbob [forum member] and Lansdowne fork kit user asked me what differance 20cc of oil less would make to the kit?
So i connected a pressure gauge to a fork assembly to observe the pressure readings.
The first "pump" increased the air pressure to 30 psi which then dropped just as quickly back to zero when the stanchion returned..But! and here is the interesting part of this test;
Repeated pumps decrease the readings! Yes you read this right...pumping the fork's decrease's the pressure.
here is why this happens;
The effect ; You are riding down the road and brake firmly,your forks compress the air in the leg,simply because the slider take's up the extra space.thus decreasing the air gap....and yes most people know that :shock:
But here is the BIG BUT :!: when this happens the compressed air escapes past the seal slightly reducing the pressure,so when the fork extends back we now have a slight neg pressure, as this repeats several times the fork starts to equalize [negitive-possitive] a single lipped seal will suck air easly,because the lip faces towards the oil.
When the bike comes to a stop the fork is under a slight negitive pressure condition...But this slight vacuum is short lived .and air [fresh and moisture laiden ]is "sucked" back in via the seal.
This constant refreshing emulsifie's your oil to produce a sludgy rust promoting goo, that many have see dribbling from the drain hole!!
So put a fork oil change on the "the winter lay up" tasks...
I would guess new double lipped leak proof seals will help. But again its the air getting in...not the oil getting out thats important for good operation,and long life.
Best wish's John Lansdowne Eng
Ok, you have filled your forks with fresh oil,and thats it for many years to come?. well many of us have pulled apart a set of forks to find the internal's red rusty and parts pitted... said oil as emulsified, its become a water based sludge.
Bmwbob [forum member] and Lansdowne fork kit user asked me what differance 20cc of oil less would make to the kit?
So i connected a pressure gauge to a fork assembly to observe the pressure readings.
The first "pump" increased the air pressure to 30 psi which then dropped just as quickly back to zero when the stanchion returned..But! and here is the interesting part of this test;
Repeated pumps decrease the readings! Yes you read this right...pumping the fork's decrease's the pressure.
here is why this happens;
The effect ; You are riding down the road and brake firmly,your forks compress the air in the leg,simply because the slider take's up the extra space.thus decreasing the air gap....and yes most people know that :shock:
But here is the BIG BUT :!: when this happens the compressed air escapes past the seal slightly reducing the pressure,so when the fork extends back we now have a slight neg pressure, as this repeats several times the fork starts to equalize [negitive-possitive] a single lipped seal will suck air easly,because the lip faces towards the oil.
When the bike comes to a stop the fork is under a slight negitive pressure condition...But this slight vacuum is short lived .and air [fresh and moisture laiden ]is "sucked" back in via the seal.
This constant refreshing emulsifie's your oil to produce a sludgy rust promoting goo, that many have see dribbling from the drain hole!!
So put a fork oil change on the "the winter lay up" tasks...
I would guess new double lipped leak proof seals will help. But again its the air getting in...not the oil getting out thats important for good operation,and long life.
Best wish's John Lansdowne Eng