Topic: CB550K1 - correct amount of fork oil?

[david 750f]

Another complication is that there is no standard for fork oil. Various brands can be different viscosity at the same rated weight.

[caluser2000]

Another complication is that there is no standard for fork oil. Various brands can be different viscosity at the same rated weight.

When I got bthe R80s forks done they use a 50/50 mixter of Motul 10w40 and ATF.

[flatlander]

Sorry, I don't agree there, the size of the air chamber in a front fork is very important, I use more, but lighter oil in those CBR's to keep the damping light enough to cope with my (light) weight, and prevent slamming through the forks while braking hard. And a CBR1000F has been my main means of transport for 30+ years, I think I know them inside and out

exactly.
while the oil takes care of damping, the the spring and air together make up the overall spring rate of the fork. compressed air tries to expand - just like a compressed coil. reduce the air chamber and you effectively increase the spring rate of the fork, or vice versa. in order to understand how to tune your (damper rod) fork you need to know the height of the air chamber.

[dave500]

the forks are stiff anyway,ive just used atf forever suits me,its cheap and works fine,even in dirt bikes i just run atf.

[robvangulik]

+1, and it keeps the seals soft!

[Deltarider]

Yep, these simple legs are quite spartan. I have always used ATF until there was a discount offer: Shell Advance Fork 7,5. I didn't throw in more than 140cc. Good for the next ten years.
https://prodepc.blob.core.windows.net/epcblobstorage/GPCDOC_X_cbe_24855_key_140002262025_1A0F.pdf

[Erny]

Yep, these simple legs are quite spartan. I have always used ATF until there was a discount offer: Shell Advance Fork 7,5. I didn't throw in more than 140cc. Good for the next ten years.
https://prodepc.blob.core.windows.net/epcblobstorage/GPCDOC_X_cbe_24855_key_140002262025_1A0F.pdf

10 years w/o change?

True is that CBfour forks from 70's are primitive construction compare to modern ones, but still even after 1 year oil is black, smells bad. I change it every year or 2.

[dave500]

lotta modern bikes dont have a drain plug,ya gotta remove the forks,great for the dealers workshops,in time theyll get neglected?

[PeWe]

160mm from top without springs and fork fully collapsed was recommended by the German  progressive springs I gave my CB750 a few years ago.

American Progressive wrote 140mm from top as max oil level as a general note for all bikes.

[flatlander]

per, were your german springs also made by wilbers?
between your sources and mine, it sounds like 150mm from top is a reasonable rule of thumb. beyond that it would be up to personal preference.

[PeWe]

Wirth, bought on eBay.de

I added washer on top of spring this winter for more pretension and less sag.
Almost 5mm thick which filled tube with fork fully stretched.

[caluser2000]

I change my CB550 Fork oilat every third oil/filter change (12,000kms). No issues at oil. I generally just use ATF. May try something different every now and again but the bike handles superbly with ATF. I like the fact the forks are so simple on these machines.

I've an old Clymer manual hare which says to replace ATF with Tarco20 weight fork oil for slightly improved damping. Also mentions put a 1 inch spacer under the fork cap for preloading the springs.  I guess that spacer can be reduced depending or the riders preferences.I wouldn't use more than a 1 in spacer though. These suggest were in the Performance Improvement section at the back of the manual.It can be quite difficult to put the cap on do the spring pressure.A small spring on top can also do the job. I'm currently playing around with preload options  just out of interest sake.

That could be a topic for another thread possibly.