Kawasaki KZ650 cafe-racer. Chassis. Part 1.

Now I am working on KZ650 chassis now , modifying some parts, and calculating, and drawing all adapters I have to order to be made: for Zephyr 550 swingarm, for shocks, and so on. This work needs  some concentration, and it’s result doesn’t looks impressive.  However, it has some interesting moments.  For example, I decided to check, if Zephyr 550 swingarm has symmetrically positioned shock mounts.  One may say: what might be easier, just put straight rod to shock mount and check if distance between rod and sleeve housing is similar on both sides. But nope, it wouldn’t work. The only parts that really must be straight and leveled in Zephyr 550 swingarm are: sleeve, its housing, and chain tension eccentrics.  Swingarm mounts might be completely in place, but slightly angled to longitude axle. And even one degree of deviation on length of swingarm would end up as 9.5mm of difference. So the best idea is to make measuring depending on things that are straight for sure. So as base for my measuring I used swingarm sleeve being pulled on some fixed distance from bearings.

And sure, I used laser tool instead of rod. I put it to sleeve and pull sleeve to the level where laser beam is aimed to center of left inner shock mount.

Then I measured distance from end of sleeve to sleeve housing and pulled sleeve from other side of housing on same distance. Beam of laser tool, that I put on sleeve, was aimed completely in same point of right shock mount.

This means that shock mount of Zephyr 550 swingarm positioned symmetrically to sleeve and its housing. To make sure that there was no mistake I put some leveled part (like wheel spacer) to sleeve housing and repeated measuring.

Result was the same, thus symmetrical position of shock mounts was confirmed.

Little illustration of fact that eccentric’ end and sleeve/housing’ ends are in parallel planes:

My next task was to check how shocks’ mounts on swingarm match shocks’ mounts on frame.  Here I had no choice, but use shock mounts on swingarm as base for laser tool.  To decrease influence of fact that mounts might be not strictly perpendicular to swingarm’ sleeve I decreased distance between upper and lower mounts:

Measuring itself looked like this:

It shows that the difference between right and left pairs of shock’ mounts is around 1.5mm. This means less than 1mm of deviance from potential center of motorcycle.  Really it’s nothing for frame made more than forty years ago. This even couldn’t be called an issue, as solution is built into shocks themselves: the rubbers that are placed in their lower and upper heads diminish effect of non-parallel shocks or some difference in width between upper and lower shock heads. Moreover, these rubbers could be moved to either side of shock’ head for a couple of millimeters, so position of both shocks might be adjusted to perfect.

To be continued.


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