Topic: CB500 Steering Issue

[jaytee-nz]

I've just finished (or I thought I had) the restoration of my 73 CB500.
On the first test ride I noticed a wobble in the handlebars at around 70 kph (40 mph). If I took one hand off the bars it was quite noticeable. The bike has new wheel bearings front and rear.
Since then I have carried out the following work:
- Checked the front and rear wheel alignment - small adjustment made.
- Fitted new tapered roller bearings in the steering head.
- Balanced the front tyre (new).
- Checked the swingarm bearings again (did this during the rebuild) - no play or movement.
- Checked all the fork and wheel related bolts and re-torqued to the Honda spec.
After all this, it still has the wobble.
It's fine up to about 50 kph / 30 mph and above 90 kph / 55 mph.
I did check the rear wheel balance when I fitted the new tyre and it was good - maybe I need to check it again, otherwise I'm out of ideas !

[HondaMan]

A couple of thoughts:
1. What is the condition of the rear tire? These bikes will self-wobble when a big flat spot runs around the rear tire (this was mostly a USA problem, though, with our thousands of miles of straight interstate hiways...).
2. How is the in-line alignment of the 2 wheels? Could the rear wheel be cocked relative to the front wheel?
3. What is the condition of the drive chain and sprockets? Many chains tend to wear into tight-loose-tight sort of running appearance, with slack over one-half revolution of the chain and tightness over the other half. This can actually twist the frame (if tight) at hiway speeds. This can be checked with the bike on centerstand: just gently roll the rear wheel and see if the lower part of the chain rises and falls. If it does, it can cause wobble at speed. The immediate 'fix' is to make sure the chain is slack 3/4" at the tightest point, no less: this can also make the chain hit the centerstand when decelerating.

[jaytee-nz]

Thanks Hondaman.
Responses are as follows:
1. Both front and rear tyres are new.
2. I have aligned the wheels using a straight edge. It did result in the chain adjusters being at slightly different swingarm marks which worried me a little as contrary to some others, I have always found the marks to be accurate.
3. Both sprockets and the chain are new and the chain is adjusted correctly.
The only thing I can think of now is to re-check the rear wheel balance.

[HondaMan]

Hmm...from your response toe #2 above, another thought:
have you tried to rotate one of the front forks in the triple trees, to see if one of them (or both?) might be slightly bent? If they were run into something hard in the past one day, they would be ever-so-slightly bent backward, and this is hard to detect. I test for it by turning just one of them in its loosened clamps to see if it rotates 360 degrees without binding the fork lower's travel. If it does bind, they might be slightly bent. This isn't terrible, so long as the bend is adjusted either straight forward or backward on both forks: the forks will still work OK - they just need to be 'paired' in their arcs for that to happen.

Reason I ask: once in a pit crash (1972, involved a bikini and a long-haired 18-year-old brunette in the pits), a Suzuki (X-6 Hustler) slightly bent its forks. All was fine until 85+ MPH when it started wobbling a bit a few races later: they had "discovered" the wheels were not in line and offset the rear wheel to make them so during between-race maintenance. The real issue was that they had rotated one of the front [bent] forks with front brake work, which then offset the front wheel a bit. Realigning the front forks together, and with the slight bend backward on both legs together, returned the handling to normal (if they did lose a few mm of trail in the process). That was one fast little twin!

Her name was Barbara, if it matters...

[jaytee-nz]

Haha - Barbara did some damage alright.
The fork tubes are new as well and they slid nicely into both the triple clamps as well.

[bryanj]

Head races too tight or too loose will do that, also what make of tyre did you fit?

[jaytee-nz]

Bryan - I've just checked the new bearings again today and they are firm but not tight or loose. I've also tested for any movement by holding the bottom of the forks and rocking them back forth (front to back) - no movement at all.
The tyres are Shinko's which aren't top quality but I've used several before and had no issues.

[Oddjob]

What size are the tyres?

For what it’s worth I’ve fitted loads of head bearings, most were ball bearing type but in later years these tended to be taper rollers. Out of the two I’d prefer to go with tapers but they do have there little quirks. The last ones I fitted were to my CB1300 and whilst I’d normally just glance at the workshop manual for torque figures etc in this instance I read the section for head races completely. It specified what I seem to remember being called preloading, you tighten the special nut, the 4 prong fitting, down to specified torque, no forks fitted, just bare yokes, you then use a balance weight to pull the yokes straight ahead, from a full lock position, it should take around 2-3lbs of force to do this. You slacken or tighten the nut until you get this reading. Seemed simple enough so I decided to do it. The result was far in excess of the feeling I’d normally accept as tight enough when moving the bars from side to side, far too tight I thought. However when all the forks and the wheel are fitted it feels perfect. No weaving, no tram lining, no wobbles. The reason I wrote all that was to point out that even though there may feel no play it may have enough to allow the wobble to develop. Maybe give the Honda method a try and see if it cures the problem?

[newday777]

Bryan - I've just checked the new bearings again today and they are firm but not tight or loose.

My thought from your words, you didn't torque the steering bearings with a torque wrench?
I learned some time ago from a suspension specialist of goldwings that the stem nut must be torqued properly with a castlenut socket and torque wrench to the correct torque. Trying to do it without properly torqued gives you your results.
The steering neck bearings are usually the cause of the 35-50 mph deceleration wobble, especially if you let go of the bars.

[seanbarney41]

Been chasing a very similar issue on one of my long term riders.  This malady can be caused by a nearly infinite amount of chassis problems...incorrect spring rates, spring pre load, tire size, brake problems...all in addition to what's already been mentioned.  95 percent of the time it comes down to steering head bearings  t's the other 5 percent of the time that can be a real bear to track down.

[scottly]

The amount of preload on the steering head bearings is only .7-1.4 ft/lbs. Besides, the problem started before the bearings were changed.
It has been said before that if you feel the issue in the front of the bike, the problem is actually in the rear, and vice versa. I would take a close look at the rear wheel and it's bearings, and also make sure the spokes are all evenly tight.

[Oddjob]

Where are you getting the preload figures from? AFAIK they have never been published for such old bikes.

[Deltarider]

[...] It has been said before that if you feel the issue in the front of the bike, the problem is actually in the rear,...

True, it often is.

... and vice versa

I didn't know that.

[jaytee-nz]

Ok, took the rear wheel off and may have found the "smoking gun". The tyre (tire) is perfectly balanced, however the left side wall has a distinct wobble to it. It's seated evenly all round so the tyre is concentric, its just that it wobbles a bit as if the rim is bent (not that it is).
I'm sure that movement will transfer to the front end causing my issue.
As its new I have asked for a replacement tyre.
As I'm rebuilding a CB550 I already have a set of tyres for that, so in the meantime time I'll fit that one and see if my theory is correct.

[HondaMan]

Ok, took the rear wheel off and may have found the "smoking gun". The tyre (tire) is perfectly balanced, however the left side wall has a distinct wobble to it. It's seated evenly all round so the tyre is concentric, its just that it wobbles a bit as if the rim is bent (not that it is).
I'm sure that movement will transfer to the front end causing my issue.
As its new I have asked for a replacement tyre.
As I'm rebuilding a CB550 I already have a set of tyres for that, so in the meantime time I'll fit that one and see if my theory is correct.

That would surely make it wiggle!

[Deltarider]

As far as the rear, realise that the design of the CB500/550 hub and its parts concerned is far from perfect and makes a true dynamic balancing practically impossible. I've witnessed more than once mechanics in the tyre workshop couldn't get it quite right and after attempts settled for some sort of compromise. IIRC it had to do with the rubbers in there.

[bryanj]

550 to 500 rear wheel swap is best done as complete wheel as some 550 have different hub, brake plate and spacers

[jaytee-nz]

Ok, just want to confirm that the issue was indeed the rear tyre.
When I spun it on my balancing stand, the left side wall had a distinct wobble to it as if the rim was bent. The right side wall was dead straight.
By the way, the rim is dead nuts straight run out wise and ovality wise.
The tyre shop I purchased it from replaced the faulty tyre with a BT46 this time for no extra charge, and the shake / wobble at the handlebars has gone.

[HondaMan]

Yeow! A bad tire...that's actually pretty rare, in my experience?
Not unknown...just rare.

[newday777]

Good to hear you got it sorted out!
I have had a bad tire like that. Bought it from Chaparral in Riverside CA. They wouldn't believe it was outta round, I had to take my wheel off and bring it over to their shop 60 miles away in my van for them to check it on their stand. They replaced the tire right there.

[MauiK3]

Good to find the problem
I was about to wonder out loud if the tires are both vertical at the same time (vertical alignment). Not sure how to check but if they weren't in the same plane that would indicate a bent frame or swing arm or similar problem

[Stev-o]

A bad tire...that's actually pretty rare, in my experience?
Not unknown...just rare.

I've seen it a couple times, good reason to steer clear of the china tires.   

Where are those Shinko's made?

[jaytee-nz]

Shinko's are made in Korea. I've used them many times before so wouldn't condemn them.
Member "Terry from Australia" has used them a lot and always has positive feedback.