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Shaking / Vibration starting at about 35 mph  

paul peterson
(@r80pete)
Eminent Member Expired Membership

This is strange to me: I finally have my 1983 R80 RT (fairing is off) engine running well with a new bottom end. Even just got new tires (the old ones were over 20 years old, but I don't recall any shaking).  Stating to take short rides, but when I get up to 35 or 40mph, there is a shaking/vibration, felt over the whole bike.  It is speed dependent, not RPM dependent.  Since the handle bars are also shaking, I had the front wheel re-balanced, but the shaking is still evident.  Any ideas on the possible cause(s) would be appreciated.

 

Quote
Topic starter Posted : 09/23/2020 10:39
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @r80pete

This is strange to me: I finally have my 1983 R80 RT engine running well with a new bottom end. Even just got new tires (the old ones were over 20 years old, but I don't recall any shaking).  

 

Those new tires is where we have to start. First thing to do is chock up both wheels off the ground, either singly or together. Here's some tests you can do to keep you out of the pool halls...

► Cup your hand around the road surface of the tire and spin the wheel fairly fast. The tire should feel super smooth, without any detectable surface irregularities, like bumps and bulges. 

► The look at the where the tire's "bead" meets the rim. There is a mold feature on most tires about 1/8" away from the rim. Follow that feature (on BOTH sides of BOTH tires) and make sure it remains the exact same distance from the rim all the way around. Some times an improperly mounted tire will not "pop out" and thereby fail to seat correctly on the rim. That feature must not "duck under" the bead of the rim.

► If the tire has a straight, central grove or is a classic "Rib" design, then the central feature MUST run perfectly straight. Otherwise the feature ends up steering the motorcycle, much as you describe. Brace a pencil firmly against the fender and set the point about 1mm away from the tire and slowly spin the tire. This will help you see it. 

► From the side of the wheel (especially the front wheel), grab the tire at 6 and 12 o'clock. Then do a manly push-pull. You should not detect any bearing play. You should not hear any clicking or popping noises. 

► Sitting directly in front of the bike, do the muscular push-pull thing on the bottom of the forks at the axle. You should not detect any bearing play. You should not hear any clicking or popping noises.

► Lastly, still sitting in front of the bike, steer the forks Left to Right from the front axle. You should not detect any roughness in the rotation indicating grit in, or damage to the head post bearings. Nor should the head post bearings "hunt", and jump from position to position. The forks should move with the lightest of commands over the full arc of steering movement. ANY form of resistance is unacceptable. 

 

One of those tests is going to keep you off the road for another week or so !!  😋 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 09/23/2020 14:17
paul peterson
(@r80pete)
Eminent Member Expired Membership

@wobbly

Thank you Mr. Wobbly Sir!  The tire beads are not properly fitting into the rims, and the rims were damaged during the tire removal / replacement process.  I have contacted the shop.  Hopefully they will offer a fair solution to this.  I am wondering if cast wheels can be repaired, or do I need replacements ?

 

 

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Topic starter Posted : 09/24/2020 17:28
Richard Whatley
(@wobbly)
Member Moderator

@r80pete There is definitely an issue with placing modern tubeless tires on the older snowflake wheels. The older tires did not touch the bottom of the rim's bead, but the newer tubeless tires make the air seal there. If you'll look at the inside of a cast snowflake wheel you'll see they were never machined at those points. The newer tires are counting on a precision machined surface of 18 or 19 inches, but the snowflakes offer an "as cast" surface that is often a larger diameter than the nominal.

That means the tires struggle to "pop out", even with copious amounts of lube. I know this because I've been mounting tires by hand since the mid-1960's, and these snowflakes are the MOST obstinate customers I've ever encountered. Even with super rubber lubricant generously applied to the tire and rim, it's often necessary to inflate the tire to 65+ psi to achieve the correct fitting. In short, you're taking your life in your hands to get the tire correctly fitted. No "tire boy" making $12/hr wants to take that risk. 

I also piddle with machine tools, and I've been racking my head to come up with a way to machine that surface without buying a $2000 gap bed lathe. So far nothing, but it's the elephant in the room. 

So you can explain the issue to your tire shop. If they are an Airhead shop then they should have known and worked out a solution in the last 30 years. If they are a generic motorcycle shop, then this will be news to them.

Either way, checking the seating of a tire is the responsibility of the installer. It's part of their job, just as much as putting air in, or making sure the rotation arrows are pointed the correct direction. 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 09/25/2020 06:16
paul peterson
(@r80pete)
Eminent Member Expired Membership

@wobbly

The work was done at a reputable Airhead shop, so I did not even think that the tire replacement might have gone wrong.  He did mention when I picked the bike up that his old tire machine had broken while he was replacing the tires.

I am wondering if the rims were damaged while getting the 20 year old tires off.  Many years ago someone told me they cut tires off when they are that old, because they don't stretch.

What is a good solution to this problem?  Can the wheels be repaired, or do I need another set?  The rims now have sections that are not true.  Your idea of spinning the wheels on the bike using a pencil as a fixed pointer was great.

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Topic starter Posted : 09/25/2020 07:37
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @r80pete

@wobbly

1. The work was done at a reputable Airhead shop, so I did not even think that the tire replacement might have gone wrong.  He did mention when I picked the bike up that his old tire machine had broken while he was replacing the tires.

2. I am wondering if the rims were damaged while getting the 20 year old tires off.  Many years ago someone told me they cut tires off when they are that old, because they don't stretch.

3. What is a good solution to this problem?  Can the wheels be repaired, or do I need another set?  The rims now have sections that are not true.  Your idea of spinning the wheels on the bike using a pencil as a fixed pointer was great.

1. Tire machine or not, the tires are not popped out. End of story. Poor workmanship. Period. Could have gotten you killed !! I'd keep a civil tone, but I would not put up with any excuses.

2a. You would need to work overtime to hurt a snowflake mag by simply changing a tire.

2b. False ! Old and new tires have a steel cable inside the bead of the tire to keep them on the rim at speed. Any tire, regardless of age, can be hard to remove if you don't know what you're doing.

3. A "good solution" (really, the ONLY acceptable solution) would be to take the wheel(s) back to the mechanic and show him how the bead is not popped out. Then tell him to fix it. Tubeless tires have been around for 25 years. Surely he's had had an opportunity to mount new tires on a snowflake in all that time. If he hasn't, then he's no Airhead mechanic.

How this helps.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 09/28/2020 18:15
john stirling
(@arni)
Trusted Member Expired Membership

if the wheel is bent Woody's Wheel Works in Denver can straiten it. But I'm with wobley. If the bead wasn't right they couldn't even balance them.

 

https://woodyswheelworks.com/

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Posted : 09/30/2020 02:29
paul peterson
(@r80pete)
Eminent Member Expired Membership

Does anybody have an opinion as to whether it is the beads not sitting in the rims that is mostly causing the vibration, or is it mostly due to the slight bend in a section of each rim ?

ReplyQuote
Topic starter Posted : 10/19/2020 07:37
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @r80pete

Does anybody have an opinion as to whether it is the beads not sitting in the rims that is mostly causing the vibration, or is it mostly due to the slight bend in a section of each rim ?

The problem is not up for "opinions", this is science. The rim is either bent or it's not. The tire is either fully "popped out" or it's not. The problem can be fully and accurate analyzed by placing the bike on the center-stand, a fat chick on the pillion seat, and then manually  spinning the front wheel while closely observing the intersection of the tire and rim. 

Here's what I see: The bike had no problems. New tires were fitted to the bike. All of a sudden the bike has issues. Connect the dots.

It's been a whole month since all this was laid out for you. Maybe it's time to spin the wheel !! 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 10/20/2020 13:58
paul peterson
(@r80pete)
Eminent Member Expired Membership

Yes, the issues have been identified.  Now the question is "will fitting the tires correctly solve the vibration problem?", or do the rims also need straightening?   Refitting the tires costs about $40.  Straightening the wheels will cost over $500.

 

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Topic starter Posted : 10/23/2020 08:26
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @r80pete

Yes, the issues have been identified.  Now the question is "will fitting the tires correctly solve the vibration problem?", or do the rims also need straightening?   Refitting the tires costs about $40.  Straightening the wheels will cost over $500.

 

► Sorry, but I do not concur. The issue has not been identified because you have not spun the front wheel while holding a pointer against something stable, like the front fender. 

► Refitting the tires does not cost $40 if they were initially fitted incorrectly. It's called "poor workmanship" and it has to be redone for free. In the repair trade it's called a "comeback". 

► If your rim got bent while the tires were being changed, then the mechanic is at fault and he should fix that too. But again, the chances of bending a wheel are nil and this hypothesis could be quickly eliminated if you simply took the time to spin the wheel. 

 

Hope this helps.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

ReplyQuote
Posted : 10/23/2020 15:12
James Strickland
(@8053)
Honorable Member Expired Membership

I simple possibility is the rear sub frame. The gusset under the seat has a propensity to suffer a cracked weld on the side opposite the seat lock assembly. 

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Posted : 11/01/2020 07:26

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