Possible headstock bearings issue?

So, I've noticed that recently if I'm going at a medium speed (I haven't fully tested what speeds yet, but so far I've noticed it between about 35-55mph) the handlebars will vibrate left and right pretty fast. I say vibrate because it's faster than a mere wobble. I'd say about 5-15 degrees in both directions if I let go of the handlebars. I don't notice it trying to do this when I'm even so much as lightly holding on to a single side of the handlebars, but once I let go wobwobwobwobwob left and right. The bike still goes straight but it's unnerving.

I thought maybe it was the roads... I ride on some really terrible roads... So, I took it to a road that had just been repaved and steamrolled down to be nice and smooth the previous day. There were no grooves in the road, they didn't have any trucks or anything making permanent tire marks in it while it's still soft like some of the slack jawed yokel contractors around here will do... Just smooth as glass. It still does it there even.

If I'm going at interstate speeds, like 65-80mph, it doesn't seem to do it, and going on residential roads, 20-35mph, it doesn't do it, though it does kind of sway a little bit at 15-25mph.

This is kind of unnerving. I just did a simple check of my headstock bearings by putting the bike on the center stand while pointed up hill a little bit to help tilt the rear back and lift the front wheel up. Then I gently turned the handlebars left and right. It felt smooth as silk except when it's pointed straight forward. I don't know if there's SUPPOSED to be an indent there or what, but it feels like an indent, and it's not perfectly center, just slightly off center.

Is there supposed to be an indent or should I start looking into having the bearings serviced? Sadly this is one thing I can't really service myself because I don't have a proper jack for the frame or anything.

There's one other thing I can think of that might be causing this... the front right fork has been slowly leaking oil ever since late November... I haven't replaced the seals because I've been waiting on these salvaged forks that are seized up but have no corrosion or pitting, so I've been wanting to replace what I've got with those once they're unseized and have been restored.

The indent suggests the bearings are knackered.

Put a block of wood under the engine to hold up the front end and then take the forks off. Getting the old bearing races out is the hard part. You can use PCV pipe to put the new bearings in.

That indent you describe is a common problem. It is the result of damage known as "brinelling" see en.wikipedia.org/wiki/Brinelling .

There is no repair for the problem other than replacing the bearings. You should replace the steering stem bearings with tapered roller bearings. The folks at www.allballsracing.com should be able to tell you exactly which ones you need for your bike. I installed their tapered roller bearings in my KZ650-C1 years ago and have found them to be vastly superior to the original ball bearings that came in my bike's steering stem.

Brinelling is the result of the balls making impressions in the races when the bike hits a bump or by the bearing pressure squeezing the balls against the races. If it is somewhat severe it can cause notchiness in the steering and sometimes you can feel the front end tend to seek being pointed straight ahead. This is sometimes referred to as "indexed steering." When these conditions occur the front can develop a bit of a low speed wobble (at least this was the case on my KZ650).

Tapered roller bearings give much more bearing surface area than loose ball bearings. Think of the bearing contact area of a tapered roller as a "stripe" for each roller that goes from one end of the roller to the other where the roller contacts the races. Then consider the bearing contact area of a ball as a small "spot" for each ball where the ball contacts the races. The total contact area of the roller bearing "stripes" is much greater than that of the ball bearing "spots." This additional contact area spreads the load reducing the pounds per square inch of pressure at the contact area and eliminates the "dimpling" that is common on ball bearing steering stem races. This reduced pressure also makes tapered roller bearings last longer than ball bearings mainly because the races are much less affected. The reason is easy to visualize when you consider the roller bearings making contact with the full width of the bearing races compared to the ball bearings running in a single line near the center of the races.

That may or may not be the total cause of the wandering, but you should not ignore it. If you have time, a torque wrench, and some other common tools and follow the instructions in the Kawasaki Service Manual you can replace the steering stem bearings yourself.

Here's how I did mine several years ago:

To do this work I had to remove the front forks. I did the work in my basement during the winter. I laid a 4’ x 8’ sheet of 7/8” hardboard on the floor and parked the bike on it. This was to protect the basement carpet from possible stains, and it also enabled me to very securely anchor the rear of the bike while the front forks were removed. With the bike on the center stand, I put a small bottle jack under the front of the engine with a piece of wood between the jack piston and the oil pan to protect the oil pan (image below). I jacked up the front of the bike until the rear wheel came in contact with the hardboard. Then I ran a cargo strap through the swing arm, attached the “S” hooks on the ends of the strap to the edge of the hardboard, and took the slack out of the strap. That strap made the bike very secure. You may want to use this same method if you remove your forks.
Ed

So what size bearings should I get for an '82 KZ750-LTD?

I've also noticed the handle bars will point left a lot easier than they'll point right. So I assume it needs some tightening... I put it on the service stand and grab the forks and try to shake it and it doesn't feel loose, so I'm not sure it's a bearings being shot issue (the shaking that is), Though I won't argue about the brinelling problem. I definitely believe you about that... Is brinelling be possible without the bearings being loose like shot wheel bearings are?

Problem is I don't have a wrench big enough for tightening the steering bearings.

Ball bearings are shot. Look up All Balls Racing. They should a have tapered kit for your bike.Channel locks will worn on the spanner nut.
Steve

I just got back from a local Kawi dealer and they were able to order some new tapered bearings and races, and it wasn't terribly expensive.

Soon I'll be putting this saga behind me... I probably should look into rear wheel and swing arm bearings, but I'm not having any issues out of those so I'll leave it alone for this month. I have a very limited monthly budget.

Was definitely the steering head bearings. I replaced them with tapered bearings as suggested and the head shake has gone away entirely. Also, steering is way more responsive now. I didn't have the proper tools for the job, but I was able to jerry rig some solutions that did the job without damaging or warping anything.

Here's hoping I don't need to do this again for a long time because that was six hours of hard labor... Part of the problem was getting the race off the bottom of the steering stem. It was being held on by just 35 years of neglect.

the handlebars will vibrate left and right pretty fast.

Hopefully it was a head bearing issue - if it doesn't fix it then find the problem urgently.

Oscillation through the bars can cause lethal 'tankslappers' sometimes from a mismatched / worn back front tyre combination. Sometimes happens at and above a certain speed and builds up like a swinging pendelum. Really scary, happened once to me at 70 mph.

The technical term is 'castoring' like a supermarket trolley wheel , complex engineering to understand.

Tyrell Corp wrote: the handlebars will vibrate left and right pretty fast.

Hopefully it was a head bearing issue - if it doesn't fix it then find the problem urgently.

Yeah replacing the head bearings fixed the problem. Steering is now liquid smooth and I can let go of the bars at any speed and the bike just move straight with no oscillation of the handlebars... The new bearings are sealed tapered roller bearings as opposed to the unsealed, loose ball bearings the bike came with.

Setton wrote:

Tyrell Corp wrote: the handlebars will vibrate left and right pretty fast.

Hopefully it was a head bearing issue - if it doesn't fix it then find the problem urgently.

Yeah replacing the head bearings fixed the problem. Steering is now liquid smooth and I can let go of the bars at any speed and the bike just move straight with no oscillation of the handlebars... The new bearings are sealed tapered roller bearings as opposed to the unsealed, loose ball bearings the bike came with.

I did the neck bearings on my GPZ with an allballs set when I did my forks last month. It's like a brand new bike, isn't it? One of those jobs that's a bit of a pain but the rewards make it worthwhile.