Fork Oil for '80 KZ440 LTD D

Hello everyone! I want to replace the front fork oil on my 1980 KZ440 (D) LTD and the manual says to use SAE 5W-20 as the type of oil. Admittedly, I've never changed the fork oil and never really had a reason to look into it, but I'm not finding any 5w-20 oils specifically for motorcycle forks. All I can find is synthetic engine oils.

Probably a silly question, but it is safe to just use regular ole SAE 5W-20 fully synthetic motor oil in my fork, correct? I don't want to cause any damage by accident.

Multi-viscosity fork oil is pretty hard to find these days. Most folks go with a straight 5, 10, or 15. I prefer using a dedicated fork oil, but others will be along shortly to point out that I am full of s@!t, and that they have been using 40wt engine oil, atf, WD40, freshly squeezed squid, for 104 years, and it works fine.

ymmv

Yeah, I figured as much when I couldn't come across many results. Lol, freshly squeezed squid! :laugh: Would you have a personal recommendation as far as 5, 10, or 15?

Go squids!!

www.racetech.com/ProductSearch/12/Kawasaki/KZ440/1980-83
Looks like Race-Tech recommends 15w fork oil.

Well, to make your choice monumentally more difficult, fork oil wights are more about marketing than about the oil. A Motul 15 will be a different viscosity than a PJ1 15, which is different from a Bel Ray 15, et cetera. There are even differences between different lines of oil from the same manufacturers. A year or three ago, I posted a fairly extensive list of fork oils that compared tested viscosity numbers verses what is printed on the label.. It will make you bang your head on a table.
It also depends on how it feels to you.
I would grab a name brand, probably a 10 or 15, and give it a try. If after a couple hundred miles, you still love it, carve the exact name and weight into your workbench and ride with a smile.
If after the test miles, you decide the forks are too stiff, change down a weight or two IN EXACTLY THE SAME BRAND AND MODEL oil, and give it a ride.
If the initial test leaves you thinking that the forks are too squishy and bouncy, go up a weight or two.

Ah, that makes sense. I ended up buying a few quarts of 5WT Maxima fork oil because my original KZ service manual said the fork took SAE 5W-20, and I read somewhere else that the more important part was that the weights of the oil match or something like that. However, I noticed that my Clymer Manual for the bike says the front fork takes 10W-20... I'm not really sure if I should just use the 5WT Maxima fork oil now or try to take it back (I haven't opened them yet) and switch it out for the 10WT? I didn't think this would be a matter of preference. I've never changed that fork oil out (shame on me, I know) and I don't know what the last owner put into it before, so I don't have much to make a judgement on.

5w sounds awfully thin to me. I've always used Bel Ray 15w fork oil in my KZ650 forks, and it works extremely well. Ed

Me, too Ed. At least he did not go for 0 weight. Since the fsm calls for 5w-20, it seems to me that a 15 or 20 straight weight would be the ticket, especially in the summer.

yep
bel-ray 15w fork oil here as well.
change every year.
add the proper amount.

How much oil did you use? My '77-78 manual says 160cc per fork tube, which is like half as much as my old GS500. Does not seem like enough.

SpecialGreen wrote: How much oil did you use? My '77-78 manual says 160cc per fork tube, which is like half as much as my old GS500. Does not seem like enough.

Take another (closer) look at your Kawasaki Service Manual, and find the rest of the sections that talk about fork oil. You should see a description of the fork oil LEVEL, not just the amount of fork oil. The fork oil level rather than the amount of fork oil is what you need to use to ensure you have the correct amount of fork oil in the forks. Be sure to follow the instructions (springs out, front end elevated, etc.) carefully to do the job correctly. Ed