Fork oil question

Guys, I'll be soon replacing my fork seals in 4 bikes. Two KZs and two GPz's. My question is - will heavier fork oil help stiffen up the old worn front ends? Riding my 84 GPz is a bit scary when I apply the front brake. It noses down pretty far. The seals are shot and fork oil has leaked out. I'm assuming the fork springs would be a bit weak for as old of bikes as they are. So basically, will a heavier fork oil stiffen up the forks?

You need to change fork oil on a regular schedule. I replace mine every 2 years. However, if your fork seals are leaking you should go ahead and replace them, clean all the goo out of the forks if they have not been properly maintained, and then fill them to the CORRECT level with a quality fork oil. I have been using Bel Ray 15w Fork Oil since my bike was new and have never had a problem. And yes, the fork oil is what provides the damping when you hit the brakes or a bump, so with bad or inadequate fork oil the front end will be a double pogo stick. Ed

Do you Guys know why some fork oils, gear lube type fluids etc. smells terrible when you drain it?
The cheap stuff is made with partial animal fat! Yes! Fat. :ohmy:

When I was working, I used to order 250 - 500 gallon bulk shipments of 90 weight gear oil and hydraulic fluid to my receiving dock for a big closed printing manufacturing plant. "F U!" Quad Graphics! Over the years, they all were cheap bastards and purchased the cheapest fluids they could.

I just drained some 76 KZ900 tubes the other day to rebuild for an ebay sale. Stuff smelled terrible.

Thats why when you drain your forks or auto gearbox or differential, the stuff stinks.

heavier oil will make the front end stiffer.


leon

You can try changing the oil/seals first. If you're riding the bike at any sort of high level you should look into heavier springs and a set of emulators. The emulators will help with dive.

Just rebuilt mine a month or so back also. Replaced seals and both tubes(with OEM) and some BelRay fork oil as well.Works great.

All you need is non-detergent oil SAE 15 or 20. If you can find it anymore.
Your springs shot?
Throw a harbor frieght short 1/2" drive 3/4"socket in for a spacer.
$10 bucks and your good to go. "Old Man Engineering"

For a time during the KZ era air assist forks were all the rage. The fork springs themselves were soft, with the expectation that you would add air assist to firm up the ride. Problem was the air added seal stiction and often leaked out. For air assist type forks one of the best purchases you can make is a set of Progressive springs so you can ditch the air. If money is tight you can stiffen up the front end by chopping off a few inches of spring and replacing the lost length with PVC pipe. This will increase the spring rate which is more effective than just adding a spacer which increased ride height, but doesn't change the stiffness in the same way.

Of course you should keep fresh oil in the front end but that of itself doesn't increase the stiffness, just damping. 10W is speced in the 750 models, but 15W will firm the ride some. 20W is pretty jarring, but to each their own.

I believe I have this problem of "stiction". I have a 82 GPz 750 R1. I rebuilt the forks and alas they are leaking. The only other reason I can see for the leaks are that I bought seals that were not genuine Kawasaki. My reasoning is that this is 2014 and maybe the materials are better today than they were in the 80's, also I didn't want seals that had sat on the shelf for 30 years.
So my choices are reseal with OEM seals, or get some new springs. Can you give me specifics for which springs to buy. It has been awhile since and the forks apart but I believe replacing the fork springs would be easier than replacing the seals.

Unless you are using air forks and pumping in too much pressure to compensate for damaged springs, I don't understand how replacing the springs will stop faulty seals from leaking. Ed

If you go to the Progressive Suspension website there is an application program which will direct you to the springs you need. Regarding the seals, I'd get OEM. There is no new technology in seals that I'm aware of. Parts like fork seals move off the parts shelf fairly quickly so no worry about receiving 30 year old parts.

New seals & bushings need to break in. Quick way to check if it's the seals is to spray WD40 on the fork leg and push down on the front end. Should move freely, not notchy. I'm not familiar with your bike but see what the service manual says about front wheel installation. If it's still notchy (stiction) try removing the front wheel completely and resting the forks on a piece of wood and push down on the front end. Try to have the bike at normal ride height, if you have the front end too low the extra weight can give you false readings. If there's no stiction, you have an axle or fork alignment issue.