How can I tell if my shock/springs are worn out?

The bike is an 82 Kawie KZ550 - C3, and I'm contemplating some
suspension work. The obvious work would include the installation of
new spring/shocks and rebuilding the forks.

Before I begin I am wondering if the repairs are really needed at this
time. Are there specific, objective tests of these components that
say "go" or "no go"?

Or are decisions made by "If it feels worn out it is"?

I do have a toolbox, a Clymer manual, and a positive mental attitude.
So tell me, Fount of All Knowledge, what are the objective means or
methods to test these components?

Thanks in advance,

Biker Dude.

 

Objective testing would require all sorts of measuring apparatus and
kit.

You'd need to measure the springs against factory length as new, measure
the spring rate against factory spec, etc etc ad infinitum.

Just assume that on a bike that's nearly 30 years old, and which was
built with crude suspension in the first place, that the shocks are
knackered and the forks probably worn out too.

Mileage helps here - under, say, 20k miles, you might be tempted to
leave things alone and only replace if you can feel (for example) a
bouncy rear end and soggy forks.

Over 30k miles and still on the OE shocks? Throw them away and take it
as read the front will need attention too.

Rear shocks are dead easy to sort - unbolt old units, throw away, bolt
on any decent branded pattern that fits.

Forks: I'd start with some quality pattern springs, a fork oil change -
the manual will give the right viscosity - and maybe new seals. All
pretty simple stuff, and cheap too.

Remember that, like I said, you're dealing with an old bike with a very
old-style chassis. There's not much you can do to make it handle like
something more modern. But a simple rear shock change and a fork rebuild
will definitely help. I wouldn't bother getting more ambitious than
that.

 

From the shop manuals I've seen, usually the only spring check is
length. That's pretty easy. Rear shocks wobble and bounce when they
are shot, especially on turns, that's pretty easy to check too.
Standing on the pegs and leaning on the front shocks is pretty easy as
well, just compare with how a new showroom bike feels. Some old-style
forks need a special bit to undo, not sure about Kawasaki, but with some
filing you can make the square tip for many Suzukis from a larger hex
socket bit. Putting new front seals in isn't hard but needs care and
gentleness to put them in square and there's no point if there are a lot
of scratches or corrosion. One or two little scratches usually don't
matter. Pretty important to make sure both have the same amount of fork
oil Straightening front forks isn't hard but it's best done with an
H-press and a true table, maybe even a dial gauge. However a straight
edge is good enough for making sure they aren't bent more than 1/8" or
so over two or three feet.


Any little grit can work its way into rubber and ruin fork stems. I
know quite a few riders who clean chains religiously but never wipe down
their fork tubes!

 

paul c wrote:
....

Forgot to mention one trick I've seen but is not mentioned in all shop
manuals - before removing front stems, try to loosen the bottom bolt on
traditional forks, ie. before unclamping from the tree, might save
having to put them in a vice or using a impact wrench or driver to get
those old bolts undone.

 

Everything might go well as it has a few times for me, except that a
couple of times I forgot to have a pan and some rags handy when I
unfastened the tube, pointing down and spilled oil on the floor. Even a
few hundred ml's of fork oil makes a nasty mess.

 

Sorry for all the posts, I keep remembering things from a few years ago
- it's really important to make sure you either have a very good memory
or take photos or have a good parts explosion diagram, because there are
some little parts, round on one dimension but asymmetrical on another,
inside the front fork assemblies, whose orientation can be very easy to
get wrong when re-assembling. A casual glance might suggest washers or
whatever they're called are the same from two different manufacturers,
but they really aren't.

 

paul c wrote:
....

Eg., A friend had a tech school rebuild his shocks. One leaked, so I
put new seals in it but when dis-assembling thought something wasn't
right, looker closer but couldn't figure out whether one of the inside
bits was upside-down or not. Looked at the other shock and it was
reversed. The microfiche at the dealer was no help, the resolution just
wasn't good enough. Half a dozen mechanics looked at it and couldn't
decide either. That's when I decided it was just as well to do my own
work. I still don't know if I got them put in right, just made sure
both forks were the same and haven't heard of any problems since, and
there were no more leaks. In that case (CB750) I sandpapered a short
piece of ABS plastic drain pipe to press the seals in with. Coated the
seals with oil to make that smoother.

 

paul c wrote:
....

Another one about paying attention during dis-assembly, some springs are
graduated, usually but I'm not sure if always, there are more turns per
length at the top end. The upper parts are meant to handle the smaller
bumps. I've seen more than one shop mechanic put springs on upside
down, likewise putting drain holes on turn signals point up into the
downcoming rain. In part, I like two-wheelers because they are so much
simpler than other kinds, it's still amazing how many people can screw
them up.

 

It's hard to tell if the springs are sacked out without a lot of
diasembly and measurement, but there are ways that experienced riders
use to tell if the springs are strong enough to do their job.

Find out what the stroke of the front forks is so you'll have an idea
of how saggy the front springs are.

Place a ty-wrap (zip tie) around the steel leg and take as much weight
as posible off the front end with one hand and push the ty-wrap all
the way down onto the dust seal.

Then gently sit down on the bike and get off and measure how far the
ty-wrap moved. If it moved more than around 50% of the stroke, the
springs are too weak *for your weight."

You can do the same test on the rear springs, which have adjustable
preload.

You should use up about 33% of the stroke just sitting down on the
seat. If you use more than that, the springs are either too weak *for
your weight*, or they are
sacked out.

So far as the rebound damping of the shocks and forks is concerned, do
the wheels chatter when you go across bumps?

That means the rebound damping is inadequate, possibly because the oil
in the dampers is too thin or too old or there just isn't enough oil
there.

And, if you are going around a fast curve with the motorcycle leaned
over to 40~45 degrees and the chassis starts misbehaving and the
motorcycle starts heading over the center line, that's a pretty good
indication that you don't have enough rebound damping, for one of the
reasons in the previous paragraph.

 

Here's another oddball one - use a magic marker to to note where the
tube and stem line up before you take them apart. I met some mechanics
who do the same when undoing axle nuts and claim that avoids a torque
wrench on re-assembly, but I don't know if they're right about that.

 

Odd...you just said exaclty what Neil and Paul said only not as well.

 

No, neither one said what I said.

But, how could you read anybody's messages with Neil Murray's dick in
your mouth?

 

s'matter too stupid or too lazy to read their posts...you just said
what they did only after a judicious re-write, you plagerizing hack.

 

Try sobering up and re-reading my message and comparing it to the
other messages.

Then, if you still have a divergent opininion, stick your finger down
your throat and
call out Ralph's name while kneeling before the porcelin throne.

 

Bit of both. Some are objective, some subjective.

First off, the front end. The fluid will be quite nasty by now, so count on
replacing it. The springs may have taken a set. Measure them. If they have
taken a set of a few mm, big deal. I used to use 2p coins as preload
adjusters. Washers have the same effect.

Budget for new seals. Not expensive and easy to do.

Your forks may have bushing in them. Just check for excessive wear. Check
also for wear and pitting in the stanchions.

Alternatively, go to the racetech site and buy some new springs and oil, or,
if you want a more comfortable ride, get some progressive springs.

As you've now got pretty much all the front end off, it is worth checking
and replacing/greasing the steering bearings.

At the back, if they are the original units, just check for leaks and
pitting on the pushrod. They will probably have lost any semblance of
damping by now, so budget for a replacement set.

You can get some cheap and nasty, you can get cheap and tolerable, you can
get inexpensive and quite good, or you can get very expensive, flash
looking, very good.

Personally, I use a UK company called Hagon, which fall in to the
inexpensive and quite good category. Unless you want bling, you don't need
the very expensive stuff that may have umlauts in the name for road riding.

I don't doubt you'll have a Hagon equivalent. I once had some Koni dial-a-
rides on a similar bike. They were quite good.

The three things you really need.

 

Race Tech has a spring rate calculator that's very helpful, but most
American riders have no idea of how to convert kilograms force per
millimeter of compression into a pounds per inch spring rate.

I've posted the conversion factor to various NG's several times, but I
haven't heard even the sound of crickets chirping for all my efforts.

A rider who follows that advice should be aware that progressive
springs take up more space in the fork stanchion tube and the amount
of fork oil should be decreased accordingly.

The biggest supplier of progressive springs to the motorcycle
aftermarket in the USA is Progressive Suspension who fabricate generic
progressive springs that fit many applications.

Since PS have not actually installed their springs in all the
motorcycles which the springs fit in, PS *cannot* tell customers
precisely what level of fork oil will do the job without hydraulically
locking the fork before it uses up all travel.

Having a front fork hydraulic lock when hitting a sudden bump whilst
leaned over in a corner will cause the front tire to have less
traction and the motorcycle won't follow the intended line, with
possibly fatal results.

 

That's what search engines are for

Last time I bought Progressive rather than Hagon, the package contained
quite detailed instructions on setting the air gap.

It really isn't difficult to work out the relative displacements of the
springs. Think Archimedes.

A hydro lock caused by a bump mid corner would have to have been one mother
of a bump as the relative bump displacement is vertical, not along the line
of the forks. In terms of bump absorption, the greater the lean angle, the
stiffer the effective rate of the springs appears to be. At 45deg lean, the
suspension is very stiff, or appears to be, with regard to bumps.

 

Well, it's good to hear that PS are improving their product.

One of my great grand uncles was named Pythagoras and another was
named Byron, but neither one helped me academically.

There is a definite dearth of good basic technical information in the
American motorcycle press. Since Gordon Jennings, a degreed engineer
with a passion for motorcycles died, only Kevin Cameron is left.

And what can one editorial column per month do to educate the American
rider in
a magazine that basically exists to peddle aftermarket products?

The rider thinks he can buy bolt-on improvement without understanding
what the product does or that he needs to know the basics of physics.

Once he owns the product, he cannot deny that he has wasted his time
and money on a product that doesn't achieve what he expected.

That's true, but Americans riding street bikes through canyons
following creeks
usually don't get leaned over much more than about 30 degrees.

And any decent motorcycle race track is going to need billiard table
smooth pavement if the riders are going to get to 45+ degrees of lean
angle...

 

Ikon shocks. They're basically Konis, but they don't have the rights to
the name, so they moved the 'i' to the front of the name. Supposed to be
good, though I've never tried them.

 

actually you hack I did...and once again your pathetic plagerizing
shone through. you loser.