Tricky fork spring/oil question for the gurus!

The Bike - a 1987 XJ900N NON ANTI DIVE model.

The proposal - to fit new aftermarket fork springs purchased from XJ Forever.

The problem - Finding out the correct fork oil amount for my bike and whether spacers are required?

Len Chacal has done his best (see below) although having read it several times I'm still not clear on how many cc's to put in each leg? Note - I suspect the newer springs have a different coil thickness...

I am also not sure whether I need spacers or not? (Len reckons the newer springs are longer so why is he recommending spacers?).

I look forward to hearing from some clear thinkers!



In regards to the forks springs, we have the progressive springs that are listed by the manufacturer as fitting all 1983-1994 XJ900 models. However, we note from the factory
parts manuals, service manuals, etc. that original springs differed quite a bit in their specs. We know that the 1983-84 900RK/RL models accept the aftermarket springs and perform properly (since we've used them ourselves, but I'm not real sure how they are going to perform in the other 900 models. That being said, here is the info that
we have:


Inner Tube Fork Springs:

NOTE: the following springs are correct for the XJ900RK and RL models, and will also fit the XJ900 N, FN, and F model fork tubes, but we do not have the information for the non anti-dive forks in regards to spring spacers or oil fluid capacities required. Original non anti-dive fork springs (XJ900N, FN, and F models) are 5mm shorter than anti-dive springs, so it is same to assume that a 5mm (or greater) spacer may be needed, and the oil level adjusted to achieve a 168mm height.


HCP9439 Aftermarket front suspension COIL SPRINGS, one pair does both forks. For all XJ900RK, XJ900RL, and XJ1100 models. No spring spacer is needed when using these springs on the XJ900RK and RL models. NOTE: due to the difference in size of this spring versus stock springs, you will need to use approximately 31 cc's less[ fork oil (for a total of 255cc's per tube) when installing these springs, or adjust to a 164mm oil level.

 

clear thinker i 'm not, but.
a 5mm spacer isn't enough to worry about, use it or not i doubt it will make much difference.
then read this for the oil level

 

My book says 276cc of 5WT oil, put that in with no spacers & see how it rides, you can soon let some oil out or add a spacer if the ride is not to your liking.

 

Mmmmm thanks Mr Wiz but methinks that is too much remembering the new springs are thicker diameter coil than original. As for letting oil out easily wellllll I'd love for you to show me how me how you release equal amounts on each side 8)

BTW when you say "your book" what model are you referring to?

 

1985 XJ900 non anti dive .
Undo screw 2 turns, count to 3 & tighten, repeat on other side.

 

Are these springs from Progressive Suspension?

Looking up a 1987 XJ900 on the Progressive site it indicates that the non-Seca model does not require a spacer. Says nothing about oil.

The springs should be tight against the spring seats when the forks are fully extended. If they aren't flush or higher than the top of the inner tube I'd put spacers in to bring them up to 3-6 mm above the top.

I'd also reduce the oil volume by 31cc.

 

I'd use Wiz's method, but instead of counting to three I'd let it dribble slowly into the very same dedicated graduated plastic baby bottle I used to measure the fork oil to begin with, and just remove equally measured amounts.

 

this is what to use, then make yourself a dipstick and adjust away

 

Thanks Gentlemen! Good useful replies! 8)

 

I'm running Progressive springs from Chacal, but mines an 84 with anti-dive so can't help much but say they made a big difference to my front end.

 

Thanks Peter...I'll report back once mine are fitted

 

I put progressive springs in to my 87 forks with 276cc of 20w fork oil and a 1inch preload... I've now done this to 3 or 4 sets of forks and never had a problem... Except for people pulling out in front of me and ending up with bent forks...

Handling is superb.

 

Check out this site: http://www.ntnoa.org/suspension_preload.htm

 

Thanks for that.

ALive, why the 1 inch preload?