I guess I've been tensioning my chain wrong

I've always measured the 25-30 mm from slack up to where its tightish. 5 years later (well maybe only 4 since I changed belt to chain)
I have re-evaluated the diagram in the manual and its pretty clear I should have been measuring it from a pressed-down to a pressed-up position. IOW my chain has been twice as loose as it should have been.

This is why I hate icons and diagrams, They could have easily stated in plain English "Press the chain down and press the chain up, measuring the difference between the two" and it would have been clear as a summer day from the start. Instead the say "masure the vertical movement" which can be interpreted more than one way, and they give a diagram that only becomes clear 5 years later if you're an idiot.

For what it's worth, much better to be twice as loose as twice as tight!!
Nothing other then zero lube, destroys a chain and sprockets faster then way over tension.

I'm so used to that now it seems too tight. :ohmy:

By the way, the tightest spot is "also" when the swingarm pivot pin/bolt, rear axle and the front counter shaft sprocket center are in a perfectly straight, and aligned line.
I have someone sit on the bike to compress and bounce the rear shocks and use a tie down strap to hold it there from tail piece frame to swingarm/shock mount.

I always run it looser than the manual. This is especially important if you set the shocks taller. As Mission points out, the chain is tightest when there is weight compressing the suspension and making the sprockets and swingarm pivot come into alignment. If you raise the rear end with preload etc, it will make the chain looser when parked, but if you set the chain tension there, and hit a big bump, the chain will become tighter than recommended when you hit the bump.

I think the manual should have been written so that you set the tension when the rear shocks are removed, and the sprockets and swingarm pivot are in alignment. That way, it can only get slackened when the suspension moves.

Also, due to uneven wear etc. you might already be aware, that there will be tight spots when you rotate the wheel. You should find the tightest spot before setting the chain tension.

Great avatar, by the way.

82KZ305Belt wrote: I've always measured the 25-30 mm from slack up to where its tightish . . .
I have re-evaluated the diagram in the manual and its pretty clear I should have been measuring it from a pressed-down to a pressed-up position.

Yes. Measure chain slack between pressed up and pressed down position mid-way along the bottom run.

In my experience, both the Owner's Manual and FSM have diagrams similar to the following:




The original Z1 Owner's Manual says check chain slack with bike resting on center stand, with chain in its tightest position, and that ideal slack is 1¼" (30-35mm) mid-way along bottom run of chain. And to adjust if slack is less than 1" (25mm) or more than 1½" (40mm).

The KZ900B-1 LTD FSM Supplement (stock bike has no center stand) says measure slack mid-way along bottom run of chain:
On side stand 25-30mm
Rear Wheel Suspended 30-35mm (same as Z1 on center stand)

In practice, I generally roll the bike forward in gear until the top chain run is slightly taut, and then measure chain slack mid-way along the bottom run.

Good Fortune!

I've never noticed any difference in tension no matter where the wheel is. I've always been and still am baffled by the comment that it should be tighter at some point. The manual for my 305 doesn't specify whether to measure the top or bottom run. Since the muffler interferes with a clear view of the bottom run I've always measure the top. But I also don't see signficant difference in tension between runs, as far as I can measure it. I guess once again I could have interpreted the diagram to mean I must measure the bottom run, but I'll again gripe that if that's what they mean they should SAY THAT!

I also don't understand the business about putting weight on it, and since my manual doesn't say I should I'm wary of doing it any other way. I will continue to ride around never quite knowing if I'm doing it right I guess. 5 years and I'm not dead yet, though I suppose that could always change.

Too tight you can wipe out the chain and sprockets.
Steve

82KZ305Belt wrote: I've never noticed any difference in tension no matter where the wheel is. I've always been and still am baffled by the comment that it should be tighter at some point. The manual for my 305 doesn't specify whether to measure the top or bottom run. Since the muffler interferes with a clear view of the bottom run I've always measure the top. But I also don't see signficant difference in tension between runs, as far as I can measure it. I guess once again I could have interpreted the diagram to mean I must measure the bottom run, but I'll again gripe that if that's what they mean they should SAY THAT!

I also don't understand the business about putting weight on it, and since my manual doesn't say I should I'm wary of doing it any other way. I will continue to ride around never quite knowing if I'm doing it right I guess. 5 years and I'm not dead yet, though I suppose that could always change.

OK. Then you have the unobtainable, perfect wearing chain and sprockets.
And you'll always be measuring it wrong because you don't understand the mechanics of it all. LOL

82KZ305Belt wrote: I've never noticed any difference in tension no matter where the wheel is. I've always been and still am baffled by the comment that it should be tighter at some point. The manual for my 305 doesn't specify whether to measure the top or bottom run. Since the muffler interferes with a clear view of the bottom run I've always measure the top. But I also don't see signficant difference in tension between runs, as far as I can measure it. I guess once again I could have interpreted the diagram to mean I must measure the bottom run, but I'll again gripe that if that's what they mean they should SAY THAT!

I also don't understand the business about putting weight on it, and since my manual doesn't say I should I'm wary of doing it any other way. I will continue to ride around never quite knowing if I'm doing it right I guess. 5 years and I'm not dead yet, though I suppose that could always change.

The manual likely mentions that "the chain wears unevenly," which uneven wear may produce less slack at different rear wheel positions. Perhaps uneven chain wear is more evident in heavier higher horsepower models that produce more pulling force on the chain. I would expect a perfectly maintained high quality drive chain on a KZ305 to remain serviceable for a very long time.

The manuals with which I'm familiar call for lubing the chain before measuring slack, and include diagrams showing slack being measured in the bottom run. Sometimes there's accompanying text specifying the bottom run. Sometimes not.

Nevertheless, I believe measuring the top run is okay, and should produce equivalent results where the bottom run is being held slightly taut.

And chain "alignment" is also very important.



The manual may provide the means for measuring chain stretch, and how much stretch is acceptable.
For example, the original Z1 chain was measured by hanging a 20 lb weight at the end and measuring the length of 20 links, with replacement needed if the distance from the center of the first pin to the center of the 21st pin exceeded 15 5/16ths inches (389mm).

Or simply the amount pf pullaway from the rear sprocket.




In any event, it's better to be conscientious about chain care and maintenance, rather that oblivious or neglectful until experiencing chain noise, kinks, snatch, slapping from excess slack, excessive premature wear, etc.

Good Fortune!

The layout of the sprocket centers and the swingarm pivot are called the anti-squat geometry. You can google "anti-squat geometry" for more details.

Notice those 3 points are not in line with each other at all times. They form a triangle. As the wheel moves upward, they become more into alignment. When that happens, the geometry forces the sprockets to get further apart. Obviously that will tension the chain (or take up the slack). This happens every time you hit a bump. If the suspension has been altered, the position where the chain is adjusted needs to be altered accordingly, or the actual tension needs to be adjusted accordingly.

If the manual specifies the wheel position while on the centerstand, the wheel's position will be different if the shocks are longer or shorter. Thus the range of chain tension will be different from what the manual is expecting.

It's not a critically precise adjustment, so a little extra slop is safer than too tight.


So why "anti-squat"?
A bike tends to squat down when you accelerate.
When the rear squats, the chain tension increases as described earlier.
Now notice what happens if we increase the chain tension by trying to accelerate the bike. The engine pulls on the top section of chain. This has the effect of trying to pull the sprockets closer together. When this happens, the rear wheel tries to move down, jacking up the rear of the bike. This works against the squatting, thus it is called "anti-squat".

Getting a good launch, without wheelieing, and without spinning the tire, depends a lot on how much antisquat you have to start with. The more jacked up the rear end is while sitting at rest, the more it will tend to wheelie. With less antisquat, it will tend to spin the tire more.

Some bikes are designed with minimal antisquat. If you make the swingarm pivot concentric with the front sprocket, there is zero anti-squat effect. The bike would then rely entirely on the suspension to maintain the rear-end height during a launch.

Since your bike was originally a belt drive, which is designed to run with no slack, they may have designed it for minimal anti-squat in order to minimize the stresses from stretching and releasing the belt. That way the belt might last longer.

Standard chains have a nasty habit of developing kinks and tight spots. When you adjust it, you have to turn the wheel and watch the chain being sure there is slack all the way around. Best to lube the chain hot then check the adjustment.
Steve