Showa forks oil replacemet

[george K75s]

Hi!
Servicing my front suspention,I noticed that previous quantity was 360ml !!! So I wonder how much should I refill . Would also like to know your opinion about putting Eni fork oil 15W.
Thaks,George

[Martin]

I weigh 65 kilos ride a 92 k75s with Showa forks.I found that after a lot of experimentation that 350 ml of 7.5 ,works the best for my riding style.The Haynes manual says 280cc + or - 10 cc. There was to much dive with standard levels.You can vary the levels but don't add too much as you could blow the seals.More oil firms up less oil softens it up. I also think 15 w may be to heavy, I only ever went as high as 10w.I am in no way suggesting that you do this I am just stating what worked for me.
Regards Martin.

[Laitch]

My references state Showas on a K75s get 410cc for replacement or 420cc for a rebuild. Of course, that amount can be adjusted for personal preference. Pre-1992 manuals—like the workshop manual available on this site—only have the 280cc figure for the pre-Showa forks, so it's not surprising that you were getting a lot of dive, Martin, until you adjusted the level upwards. It's important to have a manual that covers data for your year of bike, George. If it  really has Showa forks, 410cc and 420cc are the numbers, then you can adjust them downward for handling response. Whether 7.5, 10, 15w or something else will work for you is something only you can determine.

Before I serviced my bike's forks, its suspension had the rebound response of a bicycle floor pump. When I took my forks apart for seal replacement, I refilled with 420cc of 7.5. Response now is pretty quick, let's say.

[Scud]

I'm going to install Progressive springs in mine soon. The guy I spoke with at Max's BMW recommended that I use 12.5 or 15 fork oil to slow the compression and rebound.

As I understand it, the weight of the fork oil affects movement most during the early part of the stroke (when the oil is being forced through little holes). The amount of oil (and technically, the remaining air gap) affects movement most during the later part of the stroke (when the air pressure provides additional resistance).

[Gio]

+1 re Laitch's reference - my Haynes indicates 410/420 cc for '93 on K75/S/RT w Showa forks (not done yet so can not confirm)

I did also find a reference from ibmwr.org/ketch/fork-oil which indicated 410cc for K75 Showa and 280 cc for K75 Sport (w "s" stamped on plug) ?

Gio

[Scud]

My Clymer manual shows the following oil quantities in the Quick Reference section:

K75s (1986-1991)
    Standard:  320-330cc
    Sport:  270-290cc

K75s (all models 1992-on):  410cc

It seems there may be three different forks on various K75 models. Does somebody know the differences between the three forks? Is one type more desirable than the others?  I am especially interested in the difference between the 1990 Sport and the 1992 (as I have both sets and need to decide which ones to keep).

[george K75s]

Hi and thanks to all of you!
Well,as said,I replaced with SAE15(420ml) by ENI my forks.
Much better now and easily can steer with +10-15 kph in each turn.Feels safer!Though, it is very stiff and kind of loses contact in continious bumps(mal-rebounding).Not to mention that my fairings are now clanging over bumps!
I guess if roads here were as they should, I 'd have been more satisfied.
Previously 360ml of SAE5 was fitted,resulting extreme dive and unsufficient:my bike felt like dancing on the road when steering.

A friend of mine told me afterwards that Honda recommends SAE 7,5 in its Showa forks,so I am willing to try it soon and let you all know results.
Searching and asking all this time I found that in k's are three types of forks were fitted:a standard(filled with 360ml),a sport by Fichtler and Sachs,known as "s"(280ml if I am correct) and after 93 Showa were fitted and filled with 410ml(or 420 when rebuilt) fork oil.

Here is a link I found interesting and very helpfull:  http://www.ibmwr.org/ktech/fork-oil.shtml .

Wishing you enjoyable rides , George

[Gio]

Hi George,

Sounds like good progress and good info to add to the collective knowledge - I think you found the same ibmwr link that I referred to also.

15w might be too heavy an oil from what you describe ... roads here in Canada can be less than smooth also! It is difficult to compare one manufacturers weight of oil with another directly ... ENI is a good brand (and recommended for Moto Guzzi) but not readily available here ... I am planning on refilling the K75s forks with 10w Lucas over the winter (same weight I use on the MG).

Wishing you enjoyable rides also - we had snow today so not much of that going here!

Gio

[rbm]

I'm going to install Progressive springs in mine soon. The guy I spoke with at Max's BMW recommended that I use 12.5 or 15 fork oil to slow the compression and rebound.

Read these Good articles on suspension tuneup at Sport Rider magazine.

Oil viscosity is one factor that will affect compression and rebound damping in the forks and rear shock.  If the Max BMW advice giver didn't specify from which manufacturer you should select the 12W or 15W oil, then already you're in troubled waters, because oil viscosity ratings are ranges and one manufacturer's 12W will be different than another, and might even react like another manufacturer's 7W oil.  You can't tell without comparison testing.  Furthermore, adding too much oil can blow the seals on rebound as there is insufficient air gap at the top of the fork to absorb the shock of landing, or it can cause oil stacking whereby the fork progressively locks up on bumpy roads since it can't recover on rebound from the previous bump before encountering the next bump.

If you use too thick an oil, your compression and rebound damping characteristics could cause twitchiness and instability in corners and on bumps as the suspension will not be able to react quick enough to the changing road conditions.  Too much compression damping will give a harshness through the handlebars on sharp angle bumps, instability at low velocities on bumpy roads, and instability in bumpy corners as the rebound damping will allow the wheel to loose contact with the road (oil stacking).

I use Bel-Ray 5W fork oil in my K1100 Marzocchi forks.

Someone correct me if I'm wrong. I think the Showas have compression valving in one leg and rebound valving in the other.  I know that is true with the K1100 Marzocchi's.  Using different oils in each leg can give different rebound and compression characteristics.  The best you can do is:

• eliminate friction and stiction in the front forks,
• then adjust rider sag by playing with the preload spacers,
• then start to play with oil viscosity.

 
If you want to understand fully how to tune your suspension, get Paul Thede's and Lee Park's book "Race Tech's Motorcycle Suspension Bible".  It is a thorough treatise on  motorcycle suspension systems.

[Scud]

Thanks. I have Lee Park's second edition of Total Control that has a great chapter on suspension setup. Getting the sag right is, of course, a prerequisite to the finer adjustments, including oil selection.

The advice-giver at Max's didn't specify a brand, and didn't have oil for sale (although SUPER-helpful with everything else I wanted). The manual has a long list of acceptable oils, I'll just take that into a shop and try to pick something close to the BMW recommendations - and adjust from there if desired.