Round 7, FOAK: 1982 Kawie KZ550 C3 LTD Restoration Options

I am about to replace the chain and sprockets on this noble beast and
so begins the Quest for the Unknowable Right Answer:

Should I change the gearing, or in this case, the sprocketing?

It's a cute little in-town cruiser and bar hopper but it wasn't made
for sustained
highway riding. It's too rev-vy for that:

It redlines at 20 mph in first gear, I rarely take it up to 70 mph. I
know a few less revs at highway speed in 6th gear would be a bit more
pleasant.

Should I give it taller gears? Would I regret reducing the crusing
revs by about 8 or 10 percent with a corresponding loss of low gear
grunt?

What say ye, oh Fount of All Knowledge? <ducking for cover>

Biker Dude

 

It's up to you. The only way most people are satisfied with the answer
to the gearing question is experiencing what happens when they do it.

You can install a front sprocket with one tooth more (if you can find
one that fits in the space available, or install a rear sprocket with
three teeth less, and you will
usually achieve a gearing situation where sixth gear feels like it's
halfway between
sixth and an imaginary seventh gear.

If you live in flat country and you don't have to fight head winds,
you just might
like such an arrangement.

Oh, get real. I was talking to a guy at a motorcycle hangout and he
said that he and his "partner" frequently rode to San Francisco and
back together on his KZ550 (about 800 miles round trip) and the
biggest issue was that there was no way to carry souvenirs or
antiques ;-) home because the machine was so small.

Believe it or not, the engineers at Kawasaki *knew what they were
doing* when they selected the transmission gearing and the final drive
ratios.

A modern 4-stroke inline-four has a very short stroke in order to
reduce piston ring flutter at high RPM. Kawasaki designed their engine
in order to save wear and tear on the piston rings, so, if you're
cruising along at 5500 to 6000 RPM in sixth gear, you're NOT hurting
the engine.

If you're out on the road on a long trip and you're riding close to
the red zone on your tach for long periods, be sure to check your oil
level every day.

A 7.5% change in final drive ratio will generally put you right
between 6th and 7th
gears, in terms of cruising RPM.

Like i said, it depends on whether you have hils to climb or have to
battle head winds or carry a passenger. If you find that you have to
downshift two gears instead of one gear to pass a truck on a hill,
you've over-geared your final drive.

 

Sounds to me like someone has changed the gearing already.

It's more than 20 years since I rode a 550 Ltd but back then I was happy
to run it at a steady (indicated) 100mph. I've ridden a vanilla Z550 & a
GPz550 since then & they were both happy enough around 100mph.

[]

I'd second that - check the gearing & if it's not standard I'd change to
standard.

 

Utter nonsense.

 

If you want. I wouldn't.

That's a 550 Kawasaki for you. They're all like that. I've owned a
couple and ridden many more.

I'd leave it stock. There isn't that much bottom end in those engines
anyway. Not much mid-range either, come to that.

And now, I will see what KrustyUS advocates. I'll expect a ream of
superfluous info about gearing.

<Checks>

Yup, thought so. At least he tells you to retain the stock gearing, so
that's three or four votes in favour and none against.

 

Make that 5-0

 

Compared to a twin cylinder engine of equal displacement, inline-fours
*do* have a very short stroke, so they can rev up to higher RPM than
the twin, thus producing about 40% more power.

A few KZ550 specs:

Bore x Stroke: 58mm x 52.4mm

Power: 53 @ 8500
Torque: 35 @ 7000
Top Speed: n/a
RPM @ 60: 4902

Piston speed (in feet per minute) = .166 X 2.06 inches X 8500 RPM =
2913 fpm

At 7000 RPM, the piston speed is 2399 feet per minute.

At 60 mph, the engine is only turning 4902 RPM.

Piston speed is only 1700 fpm at such a relaxed cruising speed.

Now, compare what racing speed tuners say is a reasonable piston speed
for production based engines.

4500 feet per minute.

You would have to rev the KZ550 (or any engine with the same stroke)
over 13,000 RPM to reach the theoretical piston speed where piston
ring engineers started running into trouble with ring flutter. (1)

Nowadays, racing engines (like Ducati Corsa engines) are routinely
reaching piston speeds of 5000 feet per minute and consequently have
very short useful lives due to piston ring flutter exacerbated by the
low friction slipper pistons rocking in their bores.

The Norton V-8 protype engines of a decade ago were reaching piston
speeds of 5500 feet per minute...

(1) Back in the mid-1980's, Suzuki was racing their prototype
GSXR-750's in European endurance racing. They had to rev the engines
up to 13,000 RPM to get the 130 horsepower they wanted.

American roadracers drooled at the thought of getting their hands on
an engine that revved up that high and produced so much horsepower.

But the racing GSXR's had special Carillo I-beam connecting rods that
cost $1000 a set.

The production GSXR-750's that we got only had about 90 horsepower and
were RPM-limited to only about 11000 RPM because they used cheap
production connecting rods.

 

Quite right. Never said they didn't.

Short strokes equal higher revs, greater valve area, less tall engine,
and lower piston speed. Rocking of pistons in bores is nothing to do
with it.

To say that ring flutter is the reason why people use short strokes is
just daft.

<snip a raft of the usual irrelevaqnt technical stuff designed to
obscure your initial bollocks>

 

Nope. Yup. Maybe.

Kawasaki knew what they were doing when they came up with the gearing. It is
your bike though, so do what you want. If it makes the bike better for you,
if it makes you a happier rider, why not?

Even after all these years of riding Japanese middleweight fours, I am still
in awe of the engine speeds and reliability they obtain.

If the low first gear is a pain, set off in second.

You -may- regret it. OTOH, sprockets aren't vastly expensive.

Providing it fits, try going up one tooth on the front. Ride around for a
bit. Does the bike still pull without having to drop a gear?. Next, drop
two teeth off the back.

One thing to be aware of though is you may end up at, say, 4000RPM in 3rd,
where previously you'd be at 3750RPM in 4th. Just an example, no need to
hit me with maths...

You won't kill the bike. You may make it better for you, you may make it
worse. If you lose instant throttle response, or find yourself flicking
twixt 5th + 6th at motorway/highway speeds, it is a minor task to restore
the gearing.

If the revs bother you, mask your rev counter

 

Looks that way.

They're lovely little engines, those 550s. I lost my licence on a 1984
GPz550, the first ZX model. "In excess of 118mph" it said on the
summons. The police who nicked me observed that I was actually pulling
away from them at the time, but the police car would go no faster, so
118 was the figure. The bike was indicating just under 130 at the
time.

I also took a GT550 (the shaft-driven one: did you ever get that in
the US) around France once. That had what was basically the engine
from the first GPz550H1 in it, so very whizzy but not as peaky as the
ZX. Still needed winding up, though. That would easily indicate 120mph
solo. Comfy, too: they sold zillions of the things here to despatch
riders.

The LTD is a rare beast in the UK. Generally, we don't do the cruser
thing, and those who do tend to buy ones designed as cruisers from the
ground up, rather than the bastardised roadsters that predominated in
the late 1970s/early 1980s.

 

If you don't know the *basics* of high performance ICE's, you should
just STFU.

The engineers at Honda became intimately aware of the problems of
piston ring flutter back in the early 1960's when they developed 0.5
millimeter thick piston rings for their GP racers. (1)


And Ducati has stuck with their antiquated 90 degree V-twin because of
its popularity amongst wealthy aficionados, despite the problem with
piston ring flutter exacerbated by piston rocking.

You just aren't a technically informed as you think you are. Do try
and keep up,
M'kay?

(1) When Wiseco made pistons that could be fitted with those thin
rings back in the mid-1960's, I installed a set of them in my Yamaha
250cc cafe racer. However, street riding didn't require really high
RPM performance, so thinner rings just didn't make any difference for
my application.

 

OTOH, the OP may just be noticing that his transmission has a rather
"low" first gear, compared to the other five gears.

 

Yebbut the rear sprocket must be the size of a dinnerplate to drop it -that-
much. I suspect the OP may just not be used to how much these little fours
rev.

I rather liked the UniTrak GPz550. A good looking, sweet handling bike for
the time. ISTR it thrived on revs. Really came alive in the upper 3rd of
the rev range.

Our works pool bike for despatching was a GT750. Wretched looking thing, but
would run flat out on Motorways day in, day out, screaming the 'nads off it
without complaint. As it was the pool bike, it was subjected to the sort of
outright abuse that we wouldn't mete out to our own precious steeds.
Thrashing them when they've warmed up doesn't kill them. Lack of oil
changes and thrashing from cold probably would. No matter what we did, it
steadfastly refused to die.
We treated it to a can of beer when it reached 100,000 miles. Well, we
poured a can of beer over it. It was 18 months old, so it was kind of its
18th birthday too!

 

Looking at that, a couple of things come to mind. Firstly, what a good
looking bike it was, and still is.
Secondly, it looks 'together', and finally, my ( rather crap ) arbiter. When
I park a bike up and walk away from it, do I turn and look at it again?.

My current Bandit?, yes, every time. My XJ650?, yes, every time ( ged, I
miss that bike ). My SD900?, hell, I'll park that and just stare at it!. My
old TransAlp?, sometimes. When I had an ER-5, or an XJ750 or the ZG1000
Concours?. Can't say I ever did.

That GPz would always get a second glance as I walked away.

 

I do. You don't. Ring flutter is *not a problem* in anything but the
most highly tuned engines. And a 550 Kawasaki LTD (maybe 50bhp) isn't
that. Sure, ring flutter exists, but the reason for going to wider
bores just isn't for ring flutter. It's a by-product advantage on
super-tuned engines, I suppose, but hardly any road engines (until
perhaps the last few years) have been able to get to the speed where
it becomes a problem.

For engines, the advantages are, as I've said: lower piston speed,
yes, which just reduces wear on the bores and the rings too, I
suppose. The ability to increase the valve area. It makes the engine
shorter (less tall) although the trade-off is, I suppose, that makes
it wider. It also allows the use of a shorter camchain which in theory
reduces the inertial loads.

Now, about Ducatis. I'm not wealthy and I have one, and it has covered
30k miles without any ring flutter or rocking pistons that I'm aware
of. In fact, it's the most reliable bike I've ever owned. If you're
talking super-tuned bikes, see comments above.

Finally, I have a bike whose engine is capable of piston speeds of
around 5000fpm and it doesn't appear unreliable.

<snip usual irrelevance about antique bikes>

 

And how the phuque do you suppose that the engine evolved to such
capability, you daft ****?

It's not because there were a lot of ebayers trying to make a living
off of selling
NOS Honda side reflectors, yannow.

It's because the engineers were aware of the various mechanical
problems as they arose and they solved them so the racing department
could race reliable motorcycles on Sunday and the sales department
could sell a cheaper production version on Monday.

The sequence of problems was high piston speed (actually high
acceleration and deceleration causing ring flutter and valve train
problems.)

This was solved by thinner piston rings. Every high speed engine you
look into is going to have 0.5 mm thick rings these days.

As peak RPM increased, the engines ran into problems with connecting
rod stress.

This problem was solved by better quality rods.

Nowadays the problem is with piston cracking around the wrist pin
area.

However, Ducati V-twins are still stuck with a design that is
susceptible to piston ring flutter caused by excessively high piston
speed/acceleration/deceleration in their efforts to make an antiquated
engine competitive with I-4's...

And all this crap between you and me evolves out of my attempt to tell
some poor
rider "don't worry, be happy."

What is it about you that makes you think that your point of view is
the last word on any given subject?

 

And piston speeds on anything mother than full race-type bikes are
nowhere *near* enough to cause flutter. It isn't an issue. And road
engines couldn';t attain the sort of speeds where flutter was an issue
*anyway*.

And old Kawasai 550s don't need to worry about it either.

Mine isn't.

 

BullMurray!

Just because you've never revved your Eurofag Duck up to 12,000 RPM
doesn't mean the piston rings won't flutter when you do try it.

 

Well, thanks for proving my point. It's an irrelevance.

And how my Ducati 750SS (and you've *never* ridden one, nor indeed that
many bikes) would reach 12k rpm when the redline is at 9k I shudder to
think.

 

Thank you. He reads techie stuff, you know, but doesn't understand it
properly. And he simply hasn't the experience anyway. I remember him
banging off a while back about how the Japanese didn't use roller
bearings for their cams, a while back.