Front end bouncing Up and Down

[simac203]

Hello everyone,

I have a 1977 GL1000 with spoke rims.
This one is completely original and was partially restored about 4 years ago.
It rides very well with no problems.

Except when I had the tires changed in May 2023 from Metzeler Sportec Klassik to Bridgestone BT46s.
Since the change, the front of the bike (wheel, fork, handlebars) has been going up and down.

The phenomenon occurred between 60 and 85 km/h after 90, no more problems even a peak at 160 no problem either.
The bike's not dangerous at all, there's no handlebar climbing, just this up-and-down.

It happens when I'm stabilized, when I slow down (braking or not) and even when I'm in neutral (pulling the clutch lever).

I check the tightening of the wheels, the mounting of the tire on the rim, it's correct, you can see the line of the tire sidewall aligned with the rim.
I go back to the garage where I had the tires changed, and they check the balance (dynamic) and the tire, which is OK.
Well, nothing's changed.

With a friend who works at KTM, we check the rims' balance on a static balancer. It's not great, so we rebalance. We're having trouble with the front, which needs a weight of +- 12grams.
How bad is it?

It's much better, but still a jump between 70 and 85 km.

Finally, the mechanic orders a new front tire and changes it for me free of charge. I tell myself it's OK now. But no, same issue.

I take my front rim to Honda near the house.
I pick it up with a slight jump in correction. He tells me there's nothing wrong with the tire.
Conclusion: still the same problem.

I dropped the bike off at another garage.
The mechanic checked what I had already checked:
- Steering bearing => OK
- The fork was completely rebuilt 4 years ago.
- Rear shock absorbers are vintage Koni and seem to be in good condition.
- No free play in the swingarm.
- Front wheel bearing => New 2024 no play in the wheel.
- Rear wheel bearings => New from 2024 no play in the wheel.
However, the bearing on the disc side (where there's the big nut with the seal that locks the bearing in place) doesn't need an extractor to get out. It seems normal to me, but I'd rather ask.
And of course, same issue.

So, we tried another set of tires, we mount 2 new Avon Roadrider mk2.
And the issue persists between 60 and 75 km/h.

What I think to do now, is to remove the front fork and check everything like the bushings, remove the steering bearing and maybe the swingarm bearings (There is no free play).

if anyone has ever encountered this kind of problem can help me?

Thank you in advance for your response.

Sim

[Rambozo]

Have you checked all the spokes? I've had bikes that didn't like some brands of tires. Since you have tried two brands, that is less likely. But if it was fine with the Metzelers, maybe get another set of those?
Also, often a front-end issue can be caused by a rear end problem. Check the rear wheel bearings, swingarm bushings, shocks, rear tire, etc.

[simac203]

Hello Rambozo,

Thank you for your response.

Yes we have check all the spokes, the 2 rim have been inspected by the last mechanic. And seems good.

Unfortunately, Metzler didn't make this tires anymore... And for what I check is not possible to have the rear dimensions in Metzler for the GL1000....
For sure I have to check the rear more.

My father want to try the bike this weekend (He is mechnic for the old cars). I will check everything into the rear after that.

Regards,

[Sassy]

I didnt read that anything was tried with fork oil or tire air pressure.
Have you considered a different weight fork oil or a test ride with no oil?

[simac203]

Hello Sassy,

You are right about the fork oil. I've done all fork service there is 4 years ago. All internal parts and for the oil I'm not sure but I think it was 10w.
I have to check the fork again.

For the tire pressure I tried 2.5 for front and rear and nothing change so I came back to Honda pressure (2 and 2.25).

Thanks.

[cfairweather]

Since the problem started when the tires were changed, I suspect the tire is not fully seated on the rim. Look carefully at the tire ring line next to the rim edge and confirm the tire is fully seated on both sides, all the way around.

[remindme]

Sounds frustrating! You've checked a lot already. I second the suggestion to look at rear components too, sometimes front issues can be caused by problems in the back. Swingarm bushings and rear tire balance are good places to investigate further.

[Len_R]

I had the same issue with this tire. Trying to go double dark side. I went back to a regular front tire and that fixed it. Marked it up to a bad tire. Was the strangest thing. Not sure how many times I remounted that tire. All with the same bounce result.

[Dougrobinson]

Have you tried installing balancing beads in the tire? I use the on my bike and it gives a really smooth ride at all speeds.

[simac203]

@cfairweather yes we checked all set of tires (Bridgestone and Avon) and they seem properly installed .

@remindme sound good to check at the rear. But balance, hop and bent for the both wheels have been checked by two mechanics.

@Len_R yes but same result with two Brigdestone BT46 and one Avon, seems crazy What tire did you install finally ?

@Dougrobinson In Europe or more in Belgium is not very know by the garages. I've only read this on US forums. But I know we can buy this. So I will find out.

But my father had tried my GL this week-end (He is mechanic in the old cars) and for him the front suspension is not working properly. It seems not to absorb shocks correctly.
He find the steering too heavy.
I followed him with my car and you can see all the bike bouncing (Front and Rear).
It is so crazy.
I have to check front suspension and rear swingarm.

Thank you for all your replies. It is very appreciated.

I will try to respond everytime I check something to help maybe someone else

[WingAdmin]

Have you checked the level of oil in your forks and rear shocks?

[simac203]

Hello,

I work on the GL today.
I have disassembled the fork. The oil level seems good more and less 190-200cc.
Both spring seems good with a length of 515mm (Service limit is 495) .

Bottom pipe (Part number : 51430371003) and the ring (Changed 5 years ago) (51437371003) seems in good shape.

But for the left fork, the OIL LOCK (51432371003) has a very bad shape.
Maybe it was not tighten enough ?

Thank you for your help.

Next work, It will be to check the steering column (But there is no free play). And after that, all the rear.

[simac203]

Hello,

To complete my previous post.

Here, a picture of the fork bushing.
I will rebuild the fork with ATF oil instead of 10w fork oil to see if it change something.

They seems not in good shape on both sides. I don't know if it can do something on the driving?
But I know it is not possible to buy them...

So yesterday I remove the triple clamp.
Beerings (all balls) seems in good condition but I can see some marks on the rings.
What I can say it the the head top thread (53220286000) was easy to remove with hands.
But there was no free play in the triple clamp.

Thank you for your help.

[cfairweather]

Before and after you mount the tires, did you carefully verify the rim was true by putting it on a trueing stand? Checking the spokes is good, but you need to make sure the spokes are correctly tightened to make the rims true, all the way around. Sometimes after you mount the tires, the rim will no longer be perfectly true, so check it again after the tires are mounted. You can adjust the spokes after the tires are mounted. You can actually check the trueness after the wheels have been mounted on the motorcycle, but it is harder to do because you have the forks, fenders and swingarm in your way. When you have the front end apart, make sure that each side has the same number of damping holes in the fork tubes and the inner fork locks. Honda made some with different number of holes and a previous owner may have mismatched the fork tubes and inner components. I have seen this before and one side will respond differently than the other. Also, be aware that the front suspension is marginal on the GL1000 even when everything is perfect. So, you must polish the forks so they will have as little friction as possible on the metal surfaces and also on the seals. Also, I don't think the lower bearing ring is fully seated on the steering head. If you over tighten the triple tree nut, it will probably seat it for you, but then properly tighten the nut so the triple tree has no play, but freely turns without friction. In Europe, you can buy a product called Liquid Moly Fork Oil and I like it.