Front Forks Re-Build Question - How Much Oil To Use?

[DarkSideR]

I am getting ready to rebuild the front forks (each has leaked), and upgrade to the Progressive Springs.

In my research however I cannot find a good answer to what amount of fork oil needs to replaced because the Progressive Springs are shorter than the stock springs. Thus replacing the fork oil by a measured amount of fluid ounces wouldn't be possible.

If you got all that here is my question. I have access to a graduated cylinder. I can find the difference in volume between the OEM & Progressive Springs. Could I then simply add/subtract the difference to the amount of fork oil?

Example;
 - New fork oil 26.2oz (suggested by the manual).
 - Progressive Springs
  + Are 2.5oz (by volume) smaller than the EOM Springs.
 - New amount of fork oil to be used - 26.2 + 2.5 = 28.7oz

Could it be that simple or am I missing something?

[WintrSol]

Easier to put in a little more than needed, then use a brass tube and a suction device to lower it to the height shown in the manual. Just get a thin brass tube from a hardware store, and mark it at 142mm for the left fork, and 135mm for the right, then lower the tube to the correct mark and suck the excess fluid out; you will get the 'soda straw slurp' when it is done.

BTW, 26.2 Imperial ounces is for the left fork only; that is 25.2 US ounces. For the right fork, it is 23.6 Imperial ounces, or 22.7 US ounces. Both are for the standard or Tourer, different numbers for the Interstate.

From what I've read, Progressive doesn't recommend a differing amount of fluid for the Valk; they do for my VS800, though. If the springs really displace less oil, you may want to contact Progressive on this.

[WintrSol]

I just looked it up, and both the stock and Progressive springs are longer than the oil is deep, so the amount of oil should not need changing, if the instructions don't call for it. The amount changed for my VS800 because the stock springs were a continuous pitch between coils throughout. The stock springs are a progressive wind, increasing in pitch as you go from the bottom to the top; since the Progressive springs have a similar wind, they probably displace the same amount of oil, or the difference is very small.

[hubcapsc]

I used the amount specified in the manual, using the measured-from-the-top/springs-out
method instead of the by-volume method when I rebuilt and put in progressives. I think
it worked out perfect...

-Mike

[DarkSideR]

Perfect, thank you for your responses. That will make the rebuild easier.

[TJ]

I've rebuilt about 40 sets and when I replace the springs with progressives , I use 1oz less then the manual calls for... Never had any bad remarks and everyone is happy with them...

[big poppa pump]

I've rebuilt about 40 sets and when I replace the springs with progressives , I use 1oz less then the manual calls for... Never had any bad remarks and everyone is happy with them...

^^^^^What he said. I rebuilt the forks on both my bikes and used the volume method minus 1 oz.

[DarkSideR]

Why less 1 oz? I am guessing it is because the progressive springs are stiffer, and less 1 oz. slightly softens the ride?

[hubcapsc]

Why less 1 oz? I am guessing it is because the progressive springs are stiffer, and less 1 oz. slightly softens the ride?

Here's fork oil spraying all over my deflectors on the way to Inzane a
few years ago:



I hated having oil all over my bike, and eventually on the lens of
my goPro... but it didn't make my bike feel any different.

I don't think an ounce here or an ounce there matters. Using the amount
specified in the manual is a good and easy way to do the job without
over thinking it  ...

-Mike

[Jess from VA]

Years back, I had mine done by a dealer with a mechanic who had been a wing specialist (so they said).

New 10wt and progressive springs.  Afterwords, my front end was very hard and unforgiving and holes/bumps would almost jerk the bars from my hands.  It was expensive work, I complained, and they wanted more money, so I lived with it.  After a year or so, it got better (with no leaking).  I have heard others with the same experience.  If I ever have this done again, I am absolutely going to go with at least 1- 1 1/2 oz less fluid than called for on each side.  I don't think the Progressives are much stiffer than OE, except maybe at maximum compression (or displace any more oil), but too much oil (whatever too much is) is not good.  All I can say is if you err, err on the low side, not the high side (of fork oil).

My other IS has had an intermittent small leak for several years (fixed temporarily with the seal mate several times).  However much I've lost, the bike continues to ride OK.  

[longrider]

The posts above about using less oil with progressives are correct.  I installed progressives in a new to me 2000 (my third valk)  I used the correct amount of oil in each and now have a harsh ride exactly like Jess.  I will be removing an ounce or so when I get home from Arizona