1980 KZ750 engine not siezed but hard to turn over

Hi all -- I have a 1980 Kawasaki KZ750 G1, the LTD twin model. 14,000
miles on the clock.

I rode the bike about 80 miles on the highway and when I pulled into the
parking lot, the back tire locked up and and the engine died. Now when I
try to start the bike, it turns over, but very slowly and sounds very weak.

The bike has a kickstarter too, and its almost impossible to turn it
over even with my entire body weight. Here's what i've deduced:

-Not the gearbox, or anything rearward of the gearbox, as it kicks over
easily when the clutch is pulled in.
-Not stuck valves, as I pulled the plugs on both cylinders and tried
again; still turned over slowly but I could see the intake and exhaust
valves moving.
-Not a siezed piston, as I can see the piston move when I try and crank it.

Any ideas? I'm guessing its something on the bottom end of the engine.

Thanks all

 

Jammed up starter clutch? It's probably a ramp and roller centrifugal
over-running clutch.

If the starter clutch is jammed, you're trying to backdrive the starter
when you kick the level. The starter doesn't like to be backdriven.

 

Thanks for the reply.

The starter clutch actually has been giving me problems, its been
slipping some when i've tried to start it. but never anything like this.

Luckily I have a spare one because I was going to replace it at some
point anyway. I will try this.

 

I had lots of trouble with the Frankenstein-designed starter clutches
on my GT and GS-series Suzukis. The starter clutch actually seized up
while I was riding at freeway speed and that instantly slowed me down
to 45 mph as the starter was destroyed from being backdriven.

The second time the starter clutch jammed, I had to push the motorbike
home about a mile. It was uphill, and I couldn't get the transmission
out of gear, so I was pushing with the clutch pulled in.

If you're going to work on the starter clutch, you might as well take
the starter apart and grease the bushing on the brush end, if it has a
bushing.

And check to see if the brushes aren't worn out.

 

Love to see the pics of the tranny damage, if you could post the link!

Ben

 

Looking at the starter parts diagram, I get the impression that you
cannot kickstart your engine while the transmission is in gear with the
clutch lever pulled in.

Is that true? Do you have to find neutral to kickstart the engine?

The design looks like the older style Yamahas of the mid-1960's that
had a ratcheting device that engaged with first gear to start the
engine.

Later designs were called "primary kick starting", because I could
quickly start the engine by pulling the clutch lever and kicking. I
didn't have to find neutral before kick starting if i stalled the
engine at a stop light.

Primary kickstarting wasn't without its problems though. It meant that
there had to be an idler gear that was mounted on the end of the
transmission countershaft.

Yamaha went through about three designs before they came up with a
solid bronze idler gear that could survive sitting stationary on the
end of the spinning countershaft...

I had to split a steel idler gear that seized onto the countershaft
with a cold chisel before I could split the crankcases to replace the
ruined countershaft...

Your motorbike doesn't seem to have an idler gear, as it has a primary
chain going to the clutch...

 

Ouch! Looks nasty.. the kind of thing we all hope will never happen!

 

Do the math. Calculate the starter armature rpms when cranking the engine
at 50 rpm. Now multiply by 100 for 5000 RPM. I have seen staters spun so
fast that the commutator bars fly off and the windings eject from the
armature.

 

Yes, I did the math about 25 years ago when my GT-750's starter
self-destructed from being turned about 36,000 RPM. Fortunately, I had
access to a free starter that came off a street bike that my friends
and I were stripping to make into a road racer.

The typical electric starter used on a motorcycle engine will have
anywhere from 3:1 to 10:1 gear reduction and may be capable of cranking
an inline four up to about 1000 RPM or more with the spark plugs
removed.

 

Yeah, you're correct in your assumption...if I try to kick it while
pulling in the clutch, the kicker will just freespin and do nothing.

 

I would tend to suspect the starter clutch screwing up or the electric
starter then.

Another possibility might be some problem with the chain-driven
counterbalancers.

 

It'll be this. it happened to a Honda CB500T of my acquaintance, and
yes, the rollers had jammed. Easy to strip and fix, luckily.

Hmmm... nah, not really. When these go wrong, it's invariably the chain
wearing out so the damn things get slightly out of phase.

 

You may not recall that the OP was asking about how much his engine
should vibrate when he first posted about this particular motorbike two
or three years ago.

It's hard to imagine how badly mechanical devices can go wrong until
the train wreck...

 

In that case, I will bid a dollar three eighty on the KZ-750 basket
case, sight unseen.

Do I hear a buck and a half from TOG?

 

I'm actually trying to sell the bike, if either of you are at all serious.

 

I haven't worked on the bike yet, it's 80 miles away and I currently
have no truck to get it home to fix it. So the final story is still up
in the air, I guess.

I do however have a spare starter clutch that, when I can get the bike
back, I'm going to install.

I'm in Georgia. how much would you be willing to offer?