Forks

I fitted new seals a moth or so ago on my 86 VFR and I put a couple of hundred mm of fork oil in them and all is fine except when I enter or leave a driveway with any speed an it gives a clunk almost as if it is bottoming out. Any thoughts?

 

Not to sound like a wise ass but did you re-install the springs? If your forks are similar to my 5th gen forks then each tube should take about 250 cc of fluid. 100 cc seems really low.

 

They got 200mls in each leg and the springs did go in. I'm not sure how mls relates to cc's

 

They are the same.

 

Well not really the same but they seem to have same meaning here. cc = volume area. Your engine is measured in cc. ml = liquid measurement. A ml does not occupy a cc of volume. I have never neasured or even thought about that for that matter. Norm will understand that. Australia is metric I think.

 

cc=cubic centimeter same as 1 ml according to my metric converter on my iPhone!, but you are right one is volume and one is a liquid measurement. Nice part about the Metric system, everything is base 10. I remember when I was living in Toronto, they started sell gas by the liter, mainly to make it appear cheaper than an Imperial gallon.

We refer to our bikes as 800 cc's, but a VF1000 is referred to as a "liter" bike! Go figure.

 

Would be too hard to refer to an 800cc bike as a .8 liter bike or a 750 as a 3/4 liter bike

 

Do you mean mL rather than mm?

Is it bottoming out? If so, you may not have enough oil. Oil height is critical to the performance of the fork, as that sets the effective strength/progressiveness of the air spring, the volume of air trapped in the fork. Oil height is used as a tuning mechanism to alter the bottoming resistance, as well as mid- to full-stroke firmness.

Fork oil level height (mm down from the top of the compressed fork tubes, without springs installed) is the more accurate measure rather than adding a particular volume of oil (say 250 mL).

 

Thanks Colin, so do you know where this height measurement is taken and what air pressure is required in these forks?

 

The height is measured from the top surface of the fork tube down to the top of the oil, with the forks fully compressed. I don't have the specification for your bike, sorry.

Air pressure? Are your forks also air-adjustable?

 

Fork air gap is the way. No springs, fork leg compressed, fill with oil then slowly pump the fork up and down for 6 or so times to fill the whole fork and expel the trapped air. Buy a Racetec syringe that has an adjustable tube that is marked with mm. Stand the fork upright and draw out the oil until it starts to gurgle. Job done! e.g. '99 Fi X is 130mm

Er...no air pressure guys..just ambient. The trapped air acts as a rising rate spring.

 

Er sorry forgot all about this post, my forks are fine now, I made up a 30mm spacer to fit on top of the spring

 

Is that in addition to the stock spacer tube? Just a bit curious as to why you've added 30mm of preload to the springs

 

Haven't pulled mine apart yet to do the seals, but yes, I have an air chuck at the top of each tube and there is a warning sticker on the tank referring to recommended air pressure in the forks.

 

Adding air (2-4 psi) gives a nicer ride but usually forces oil past the fork seals.

 

Interesting. Once I get this thing running, I might just ride it a bit to see if the seals really leak, or if the PO had too much air in them.

 

Since there is already a thread about forks, I'll post another question for the gurus.

Is there anything to be gained by installing dual-rate (RaceTech) springs with the stock valving?