Fork Oil Capacity

[Tony Mac]

G'day, my Haynes Cook Book says 446cc as the Fork Oil capacity for my 1992 FJ1200d
Would this amount be for each fork or both forks combined?
If it's for a single fork, why can't I simply add 450cc ?
Just ask'n
Thanks in advance.

Be Good.
Tony

[X-Ray]

It's for each leg Tony. Actually I think when I first did my fork oil change, I couldn't be bothered measuring out 446cc of fluid and just put in 450 each leg. No problems at all.

A few owners actually recommend using 10w40 engine oil instead of basic fork oil, cheaper and has as much, if not more resistance to breakdown in the forks. Makes sense to me, [but not if you have RPM valves etc ]

[FJ1100mjk]

Yes, each leg like X-ray says. I would also check the volume stated with a measurement of the oil level from the top of the fork with it perpendicular to the ground, spring removed, and fully-compressed. I have found that the values sometime differ, and I err on the side of the oil level height, and not stated volume.

Decreasing the level (try 6mm at a time, and probably not more than 12mm total) softens the fork as it compresses fully when the bike is ridden, and increasing the level has the opposite effect.

Fork oil brands (even the usage of motor oil), weights, volumes/levels, seem to vary by personal opinions and experiences. I don't think that you can go wrong whatsoever, by just replacing the old tired oil, with fresh oil at the correct capacity, and maybe a fresh set of springs too, that are configured to your weight and riding style.

I'm sure others will chime in regarding the above too.

[Mark Olson]

With springs out and forks compressed , your level will be between 120mm and 130mm from the top of leg . work the forks up and down so the fluid settles .

the 120mm will be a stiffer ride.
the 130mm will be softer ride.

Depending on oil used , with this baseline you are able to pull some out with a turkey baster if needed . Also put some back in when needed .
there have been times a fork has leaked some fluid and I just need to get it back to specs for a short time before changing seals. 

[Pat Conlon]

Yeppers, I agree with the fork oil level being more important/accurate than the volume..

I use this:



Available from Randy @ RPM
http://www.rpmracingca.com/proddetail.asp?prod=tools%3AForkLevel

Very simple to use.
1) Set the desired fluid level on the tool
2) Fill your fork to a little over (higher) what you need
3) Draw back on the syringe to remove the excess oil and your level will be dead nuts accurate.

Good tools are a wise investment.

[Burns]

I use a yard stick marked at 5".  Get 'er done.

[Mark Olson]

I use a yard stick marked at 5".  Get 'er done.

5" yard stick will get you approximately  128mm.

[Firehawk068]

This is what I use. It's a super-thin ruler that i got from Fel-Pro years ago.
It has a handy hook on the end, so I can just place it in the fork tube and rest it on the top.



I have Racetech springs, and Gold Cartridge emulator valves.
Racetech states anywhere from 100mm to 180mm for fork oil level, and to tune in 10mm increments.(as long as the fluid is well above the valve)
I settled on 150mm this time. I believe I used 130mm the previous time.

Yamaha Factory Service Manual says 169mm for '89-'90 forks.

[Burns]

yep (5" is near the top of the range), and "approximately" is where you always start.  
There is no magic number.
Add/Subtact to fork oil level is like putting salt and pepper on mash potatoes (season to taste).

You can take that RPM doo-hickey and put your level "exactly" on the mark only to discover you'd like things a little stiffer or softer.

Only use I can figure for that piece of kit  (other than the joy of RPM patronage) would be for dialing a racer in on track day when you are logging ALL the info.

The perfect level at 60 degrees ambient temperature at one track might not be the perfect level for 110 degrees at another.

For street riding, just get it where you like it.

[Burns]

This is what I use. It's a super-thin ruler that i got from Fel-Pro years ago.
It has a handy hook on the end, so I can just place it in the fork tube and rest it on the top.



I have Racetech springs, and Gold Cartridge emulator valves.
Racetech states anywhere from 100mm to 180mm for fork oil level, and to tune in 10mm increments.(as long as the fluid is well above the valve)
I settled on 150mm this time. I believe I used 130mm the previous time.

Yamaha Factory Service Manual says 169 mm for '89-'90 forks.

==============
that "tune in 10 MM increments" speaks volumes on the precision issue.

I'm wondering how much you weigh and what spring rate are you using. I'm thinkin' the spring might be a tad light.

Reducing the volume of air (raising the oil level) increases the progressive resistance since each increment of travel compresses a greater percentage of the air in the chamber, (e.g. 1 inch is 1/3 of 3 inches but only 1/5 of 5).  As I recall, pressure increases are exponential to compression increases.

Seems to me the smallish air chamber you are running would probably be a bit harsh for most folks, and a stiffer spring/lower level might be an improvement.

Of course, if you have it where you like it that is all that matters

[Firehawk068]

I'm a fairly heavy dude, and I am using 1.05kg straight-rate springs currently.
I lowered my fork oil height this time to get a slightly softer feel on max compression.
I ride pretty aggressively sometimes, and I'm happy with the spring rate.

[FJ1100mjk]

I ride pretty aggressively sometimes

Me too, and I think there's a lot of people here that do that too.

[Burns]

It's like tuning a guitar. Sometimes I like the "g" string a little on the flat side; sometimes not. Depends on what I'm playin'.  Extend metaphor to taste.

[Mark Olson]

season to taste , that's funny . 

A lot of good advice has been given and hopefully not been too confusing . nice pics Alan . I have one of those rulers too.

So measure in the factory recommendation and then see how far the oil is from the top of fork for reference guide. If you have stock forks with no valves (emulators) your level will be lower down the tubes.

ATF fluid can be used in place of fork oil . Each brand is a different weight .

When using old stock springs you can add a spacer (pvc pipe) on top of spring to get back to specs for sag and then mess around with oil weights for your desired flavor.

[Firehawk068]

ATF fluid can be used in place of fork oil . Each brand is a different weight .

Yup!  I'm pretty sure that's what I used in mine.. 



It is cleverly disguised as Honda (Showa) 10wt Fork Oil, and about 3-times the price of ATF.



Don't confuse the bottles when servicing your forks.