By Darrel Spinosi
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?
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?
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?
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.