Topic: Need Advice - Vertical Oscillation issue

[jpswapmohn]

Hey folks,
I recently started getting an up & down oscillation that comes through the handle bars. At 35mph, my hands are probably moving up & down 1/4 to 1/2" It feels "regular" as in the interval seems to remain same at given speed, changes w/speed.  No horizontal vibration, just vertical.

I noticed this about 2 weeks ago, was fine before that.  Took it to a shop in KC that works older bikes. They checked front wheel balance. Mechanic said it was not really out of balance and "a little out of true but not enough to make a difference".  He says he rode it and didn't feel anything.  I don't know how far or fast he rode it..  but I definitely still feel it.

What I got:  Front = cyclex tubes with progressive springs, dual disk conversion
                   Rear = progressive '78 spring-overs (1" longer than stock 77)
No indication of oil leaks in the forks.
No flat spots found on the tires
No indication of either brake rubbing
Been about 3 years since suspension was rebuilt but not a lot of miles on it since then

Any ideas what I should be checking? Thinking a fork oil change couldn't hurt but really doubt it will address this.

Thanks!
Bryan

[seanbarney41]

Be aware that problems in the back can and do telescope to the front causing symptoms similar to what you describe...how's your chain?

[kerryb]

When you have "a little"  out of round,"a little" out of balance, added to new springs on a fork that moves well, I think you have a recipe for a harmonic imbalance that only occurs at certain speeds.  Change one of those factors and the problem will show up at a different speed.  When I was chasing a similar issue, I had the local shop (LOCK CITY CYCLE, they're great) balance the wheel, check the trueness.  That reduced the problem to a minimum.  When I told them it wasn't gone completely, they said "remember it IS 34 year old technology"  So I figure this is what it rode like when it was new. 
If it were my bike, I'd get the wheel very balanced, very true, and go find a real smooth road to test it on.
Keep in mind I'm no engineer or machinist, just been there before you were.

just for fun...
ps while composing this post seanbarney beat me to it with a very good point!

[jpswapmohn]

Thanks guys. I will look to find someone to true the front rim and maybe get the back one as well. The one place I know of in the KC / Leavenworth area has a 4+ week backlog..

Chain and sprockets look to be fine but I will try to go link-by-link on the chain this weekend just to be sure.

Anything else I should be looking at/for?

I did take it to a few various surfaces (cement interstate, asphalt country road, a rather newly resurfaced road). I can pick it up on all of them.

Thanks again,

[scottly]

Chain and sprockets look to be fine but I will try to go link-by-link on the chain this weekend just to be sure.

Anything else I should be looking at/for?

Make sure the chain isn't too tight. It should be checked with weight on the bike, with the chain rotated in several locations, as they can be unevenly worn.

[scottly]

When I was chasing a similar issue, I had the local shop balance the wheel, check the trueness.  That reduced the problem to a minimum.  When I told them it wasn't gone completely, they said "remember it IS 34 year old technology"  So I figure this is what it rode like when it was new. 

That is not an acceptable answer, IMHO.

[Retro Rocket]

When I was chasing a similar issue, I had the local shop balance the wheel, check the trueness.  That reduced the problem to a minimum.  When I told them it wasn't gone completely, they said "remember it IS 34 year old technology"  So I figure this is what it rode like when it was new. 

That is not an acceptable answer, IMHO.

Agreed, thats a "I can't fix it and i have thrown in the towel" type answer....

[Rgconner]

Agreed, it is not 35 year old tech, a wheel is 5000 year old tech and they can be balanced perfectly if not damaged.

I bet a bicycle shop could do a better job than those jokers.

[Prospect]

Thanks guys. I will look to find someone to true the front rim and maybe get the back one as well. The one place I know of in the KC / Leavenworth area has a 4+ week backlog..

Chain and sprockets look to be fine but I will try to go link-by-link on the chain this weekend just to be sure.

Anything else I should be looking at/for?

I did take it to a few various surfaces (cement interstate, asphalt country road, a rather newly resurfaced road). I can pick it up on all of them.

Thanks again,

I have the same issue on my k1.  It's exactly at 35 mph.  I (almost) fully restored the bike and have only put about 100 miles on it so I'm thinking the wheel is out of balanced combined with slightly out of true for the spokes/hub.  Everything is new in there including bearings/seals/oil/springs. 

What can happen with the rear and front sprocket is that they can develop and oval shape and thus you can never tighten the chain to correct standard.  Even cheap new sprockets can be oval instead of round. The chain will go from loose to tight as it rotates due to the oval shape and I'm wondering if that has something to do with it.  I think the varying tightness/looseness can cause a slight jerking causing the front to oscillate vertically.  Just a theory. 

As of yet I haven't been able to find a definite solution.  Before the restoration the problem was much worse. 

[liPPy]

Following this one as I have the exact same problem and like Prospect only at a speed of around 35mph - a little faster or a little slower and it goes away. Quite clearly a harmonic effect.

I have new tires on freshly balanced wheels with new bearings and a new, properly tensioned chain. The only thing I didn't change was the sprockets as they were in pretty good nick.

It's such a mild & gentle oscillation it doesn't concern me that much, especially as it only happens at a specific speed.

Nonetheless, I'm curious to learn if anyone successfully identifies a solution. Likewise, should I resolve the issue I'll be sure to post the particulars

[lucky]

A major issue was left out by the "mechanic".

"wheel almost true" is very sloppy words or workmanship.

USE a 6mm wrench.

You can find out your self.

Take the wheel off and put in a trueing stand or
if you have an extra swing arm stand that up in the vise.
If you do not have either one then clamp a rod or heavy wire onto the rear swing arm of the motorcycle and bend it so that it just touches the rim on the side. turn the wheel slowly and see if the metal rod touches all the way around. THEN move that rod so that the end of it is pointed at the inside of the rim and just barely touches .
Turn the wheel and make sure it touches all the way around. For concentric check.

IF the wheel rim does not touch the rod all the way around you will need to tighten the spokes (OR loosen one) if needed to get the wheel to touch all the way around.
Do not count a small dent in the rim. You won't be able to get those out.

When you tighten a spoke make sure it is one that will pull the rim the way that you want. Only a 1/4 turn will often correct the deviation.

Spread out the corrective adjustment over 3 spokes if needed.
Make sure if you make an adjustment one one side of the wheel  toe turn the wheel 180º and work on that side.

If the wheel is off just a tiny bit, thickness of a playing card, just a 1/4 turn of a spoke usually corrects the problem. When Honda wheels come from the factory they are within .008 of being true. Of course I have not had time to check to see if that is true.




THEN

[lucky]

Rear shocks can be worn out and just bouncing if the dampening is not working.

[MCRider]

A few points: 35 yr old tech is BS. No reason it shouldn't run true and smooth. IF it was true and smooth before, the rim won't go out of true without an event, imo. Ditch that mechanic.

If it wasn't doing it before, and there wasn't an event, then something transgressed into the condition. Fork oil deteriorated, or I'm liking the rear end. You said its been 3 years. And the forward tilt your longer shocks puts on your front end may exagerate the condition. So I'd check for wear in the rear, chain, swingarm, and/or change your fork oil.

As to the tightsie loosie chain phenomenon. IMO this does not occur from sprocket wear. It is an indication of uneven chain wear. What happens is the chain is lubricated many many times. Over time (transgression) certain sections of the chain wear faster than others, from uneven lubrication. The word "stretch" is improperly used to describe the condition. What is really happening is the pin of the chain link passes thru a bushing of its mating link. That bushing hole wears into an oval, causing the chain to elongate. The sprockets are fine other than tooth wear.

I speak from first hand knowledge.

So part of the chain becomes longer than other parts and when you spin it, it gets tight and loose. The test of this is to simply replace the chain on the same sprockets and the tightsie loosie goes away. Proof its not the sprockets. Now you may want to replace the sprockets as well, as the worn teeth will accelerate the wear on the chain. But that's a different issue.

Back to the bounce, if the chain is bad replace it and see about your bounce.

[jpswapmohn]

Got a rear stand and checked a few things today.

I did not identify any obvious issues with the chain/sprockets. There are a little over 3000 miles on the 530 o-ring chain and sprocket conversion. That is based on what the PO told me and the miles I have put on it.

My rear wheel is definitely out of true. I set a straight edge across the rear shocks and rotated the rear wheel by hand. There is what looks like a bit over 1/4" variation. Doesn't seem good to me..

Next question: Is there anyone around Kansas City that does spoke wheels?  I honestly don't have time to try it myself.