Front end time...

Hi guys,

It's amazing....Once you start working on the bike it seems it never stops...there is always something else asking for service...
This time i'm turning to the fork oil.
I went through some threads in the forum and I learned that it should be 420-450ml/leg and, as recomended by Pete and Mark, 5W.
But I also saw someone saying the the oil weight for the same spec., 5W for example, will be different from brand to brand...Is this confirmed?
If that is the case, which brand are you using Pete and Mark?
The specification on the manual also puzzles me....5W or 20W ?
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Also, I saw the routine to take as much oil as possible out (pouring/pumping), but there is always the chance that some of it remains inside. Will it be better to use the same oil (chances are it will be AGIP ENI) or there are no major concerns mixing brands/types?



Thanks in advance for your inputs

I went investigating on the net and what I understood is that a good reference to select the fork oil will be the viscosity at 40ºC.
In a quick search I found out that the ENI 5W has a viscosity of 21 mm2/s, while the Motul 5W has 18mm2/s and Motul 7.5W has 24.6 mm2/s.
I might go with the Motul 7.5W, considering I weight 92 kg...
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:ong & short answer is you can drive a bus through fork oil specs and the actual viscosities may vary a lot because the specs are so loose as applied to just 'fork oil use' . e.g SAE W uses only KV100C as a spec (actually also uses CCS viscosity for crankability & MRVTP-1 viscosity for pumpability but these are for cold sump/engine conditions only) & your forks don't get that hot !


The KV100 viscosity spec for 0W is the same as 5W & AFAIK there is no such thing as SAE 7.5W but it's a 'marketing game' to create a made up grade for viscosities between 5W & 10W. In example you quote the 7.5W oil actually meets 10W KV100C viscosity !

Because the fork oil is more likely to live at around 40C; the KV40 is a better indicator (doesn't exist in the SAE W specs) to compare different fork oils & decide lighter vz heavier options.

I don't think your weight has a big effect on oil grade selection (that's more spring rate) given you will already be onboard by the time the suspension gets bounced around by road surface - it's more to impact the speed of fluid flowing through the valving ie lighter oil gives less damping

BTW mixing should be fine but viscosity may be impacted if you leave a lot of different grade oil.

Thanks Paul.
Do you understand MG specification of "5W or 20W"? 20W would be rock hard...

Just use 5W of any quality brand.

^^^^^^^ That

...and I went with the Motorex 5W.

The lower end of my fork legs is starting to show some pitting... Can you recommend any recipe to deal with this?
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Don't worry too much it is below the area swept by the seal edge (and may be below the area swept by the dust cover)

All chrome on steel is micro-porous to the steel below and rust can come throught the pores rub it off with oiled fine wire wool and wipe the area with oil every now and again - e.g. ACF anti corrosion oil

Thanks lcjohnny.