Those of us who fool around with four stroke
Zundapps will eventually run into the dreaded kick start “lock up”. It
is easily recognized. You put your foot on the kick start lever and
attempt to kick it down and it refuses to budge. You try it again. If
the result is the same then we have a jam or “lock up”.
What causes this?
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The main business of the kick start mechanism is
accomplished by interaction of the large sector gear, connected to the
kick starter through bevel gears, and the small ratchet gear connected
to the transmission main shaft. The ‘lock up” occurs when these two
gears fail to mesh smoothly. This is generally due to inadequate
lubrication and/or misalignment between the two gears. Lubrication is
essential for these gears to function properly. The two gears need to be
greased very thoroughly. When it jams our tendency is to keep kicking at
the lever. The gears become deformed and chipped and the problem just
gets worse. I have proved the value of lubrication to myself. I put a
transmission on the workbench and assembled the kick starter with
perfectly good gears and NO lubrication. I then depressed the lever 30
times and got 15 jams! I disassembled it, greased the gears and again
cycled the lever 30 times and I got NO jams. I was amazed it made that
much difference.
Some other things that can contribute to the
jamming problem are; Wear between the small gear and trans main shaft,
wear at the trans shaft ball bearing, wear at the bushing bearings that
position the large sector gear, missing alignment dowels between trans
and kick start housing and, of course, loose bolts.
How does it work?
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The small gear has ratchet teeth on the side next
to the transmission main shaft. This rotates the transmission main
shaft, clutch and engine crankshaft when the kick start lever is
depressed. The ratchet also allows the engine to start and run free of
the kick starter while the lever is being returned to the top.
The large gear has an
open space or sector with about 6 teeth missing. This allows the two
gears to be completely disengaged when the kick starter lever is at rest
at the top of its travel. The first tooth of the large gear is only half
as tall as the rest of the teeth on that gear. Its job is to bring the
teeth of the small gear into proper mesh with the large gear. I have
found this half high tooth missing on some kick starters .This was most
likely done by someone who was having a problem with the kick starter,
disassembled it and thought the half high tooth was a damaged full high
tooth and decided to grind it off to get it out of the way. Of course
that only makes the problem worse.
What can we do about this?
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We know that the problem occurs when teeth of the
two gears meet. We don’t always get a jam because the kick starter teeth
don’t always meet the small gear at the same place. There may only be
one tooth that’s damaged or they may hit directly on the pointed edge of
a tooth from each gear.
When a “lock up” or jam does occur the first thing
to try is pulling in the clutch lever and put some pressure on the kick
start lever. If the problem isn’t too bad the gears will go ahead and
mesh with the load from the engine removed. We can then release the
clutch lever and proceed with our kicking. If repeated kicking is
necessary only allow the kick lever to come up three fourths of the way.
This will keep the gears engaged and avoid the mesh process and the
possibility of another jam.
If clutching doesn’t clear the jam the next step
will be to shift into 2nd gear and roll the bike, with the
clutch engaged, forward or backward enough to cause the transmission
main shaft to rotate a little. This will reposition the small gear. We
can now shift back to neutral and try kicking again. I think the best
way to perform this process is to move the lever until you feel the two
gears make contact then apply only enough pressure till you know the
gears are meshed and you don’t have a jam, then kick it down the rest of
the way. This will prevent further damage to the gear teeth.
If jams are occurring frequently you will want to
fix it. This will most likely require replacing the two gears. Michael
Aichner, in Germany, can provide these parts. You should give him the
model, year and part number, and even the serial number of your machine.
I believe all the small gears are the same but there are at least two
different large sector gears. I refer to them as “early” and “late”
type. The “early” has the rivet stop placed 180 degrees opposite the
open sector. The “late” type has the rivet stop 90 degrees above the
open sector. They are not interchangeable. Replacing these parts is not
a hard job but you will have to remove the rear wheel and fender to get
the kick start housing off.
I will be happy to discuss this with anyone who
wants to.
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Darrel Spinosi
(If you want to talk to Darrel about this
article please e-mail me and I will put you in touch. n2deep@zundappfool.com)
