Front Suspension cleaning

[Kodackamera]

Hey Forum,

What do any of you use for cleaning the internals of forks? At college we were taught to simply use some new, spare, fork oil, pump it around and then flush it out to be replaced with new fork oil.

However, I have been working on a 2 stroke, with upside down forks, relatively primitive as in the damper is of a simple type just using passages, it is a sealed unit type of damper, built into the lower leg and cannot be disassembled much.

I believe I am the second person to ever have worked on the forks, the bike is from 1997, it is in great physical condition but simply dirty.

I drained the fork oil, absolute filth. I then used some petrol (strained through a folded t shirt) just a small amount and let it sit in the lower leg for 20-30 minutes, then I pumped it around by stroking the damper rod, left it for another 10 minutes. The sludge that came out was fantastic! I then used a little spare fork oil to pump around and remove any lingering petrol/residue/sludge and drained again.

Some people have scolded me for using petrol, however, the filth inside was immense and I believe really needed it, plus I used some spare fork oil to wash away what i could before residues could form much.

What do the professional race teams use within motorcycle racing? Again, at college we were simply taught to flush with spare fork oil...but what if there is extreme filth and the bike has 10+ years of grime, or for racing purposes must be surgically cleaned?

My dad said that paraffin and civilian (non fuel grade) kerosene should not be used because they contain "grit", he is from the 60's, a time of 4 cylinder disc valve 125's, have paraffin or kerosene improved? Some people claim paraffin will leave no residue, however, I would not want to introduce grit into a working area if it could accelerate wear of components needlessly.

[scotty dog]

I aso got told when i was at TAFE, not to use petrol as it is too harsh. We used to use Kerosene but that was to clean automotive engine parts etc.
Im sure theres something around that has the same result as petrol but without doing the damage petrol can.

[Kodackamera]

What about methylated spirits? Can it clean gunk, not leave too bad a residue and still not contain grit and be quite pure?

Come on forum, pour out thy wisdom! 

[TMKIWI]

Ive always used parts cleaner.

[eprovenzano]

I had to admit this, but I used gas (petrol) for years when cleaning parts. 

As far as the OP, I don't see a problem with your technique, especially since you "used a little spare fork oil to pump around and remove any lingering petrol/residue/sludge and drained again."

Based on that statemet I feel you did tyhe proper thing.  With oil being added and then drained, I feel you removed and lingering fuel, and the internals are now clean, and ready for fresh oil.
 

[juliend]

Cheap ATF is pretty good for cleaning .

[VintageBlueSmoke]

Professional race teams don't use old parts. They don't need such a scowering.

Petrol is harsh but is shouldn't be to bad on the fork internals if there is no plastic or rubber.

ATF is great stuff. SAE did a test awhile comparing penetrating oils such as wd-40, kroil, etc and found that kroil was best...but ATF was even better! They recommended using 50% ATF and kerosine...and it did't matter if it was used as long as it was clean! We often used it as fork oil (it's about 15 wt equivelent) back in the day and still sometimes use it for the Vintage bikes. Again, you can cut it with kerosine to thin it out.

I use Safety Kleen solvent (parts cleaner) on all mine, if only because that is in my shop.