Topic: Shake and Hop in 3 second intervals wtf

[KingCustomCycles.com]

Good afternoon all,  I have a problem that I can't figure out and was wondering if anyone had experienced it before with a solution.  A couple of my Honda SOHC 750 Bobbers (76 and 73) have vibrated in a similar fashion.  They are smooth for 2 seconds, shake for 3 seconds, and then are smooth again.  I have adjusted the steering tree tension (new grease) replaced the front tire, shortened the forks 2 inches, and installed a fork brace on one.  All this helped but I can still feel the hop, shake, or vibration in steady intervals.  It seems worse at 60 mph and it stops below about 45 and when accelerating hard.  The frames are stretched 4 inches and rigid with stock rake and trail.  Thanks!

[bwaller]

I'd shake too if my arse was locked up solid.   

[WFO]

tire balance?

[TwoTired]

Tire/wheel balance.

 Or, perhaps "Slime" in the tubes?

Maybe hose Skull and Dice dust caps put on the schrader valve stem after balancing?

[KingCustomCycles.com]

I'll have my tire balancing guy flogged.

[WFO]

Tire/wheel balance.

 Or, perhaps "Slime" in the tubes?

Maybe hose Skull and Dice dust caps put on the schrader valve stem after balancing?

I have ran into that before also have had tires with factory defects cause vibration.

[TwoTired]

It can be a problem mounting tubless tires on tube type rims.  Check that the tire is seated properly on the rim.  There is usually a line cast in the tire near the bead seat.  Spin the whell and watch that line to be sure it is equidistant from the rim for the circumference on the wheel on both sides.

At the same time, you can check the wheel runout side to side and radially.  Then make sure the tire is also round, too.

Cheers,

[754]

Check the tire balance yourself..

[MCRider]

Good afternoon all,  I have a problem that I can't figure out and was wondering if anyone had experienced it before with a solution.  A couple of my Honda SOHC 750 Bobbers (76 and 73) have vibrated in a similar fashion.  They are smooth for 2 seconds, shake for 3 seconds, and then are smooth again.  I have adjusted the steering tree tension (new grease) replaced the front tire, shortened the forks 2 inches, and installed a fork brace on one.  All this helped but I can still feel the hop, shake, or vibration in steady intervals.  It seems worse at 60 mph and it stops below about 45 and when accelerating hard.  The frames are stretched 4 inches and rigid with stock rake and trail.  Thanks!

Its a frame thing and not an engine thing? Got all your motor mounts in place and tight?

If the frame is a little overextended it may be flexing in a "natural frequency" and need some stiffening. 

(This is amazing and worth the wait, action starts at about 1/3 of the way through.) 

[KingCustomCycles.com]

I had considered a frame geometry issue since it has happened on 2 of the bikes.  They also share the same cheap chin Shin tires. I had ruled out the frame because of the modest stretch.  Extended swing arms of much longer length are common with no problems.  Those usually have springs/shocks with the associated dampening effect, however.  The resonant frequency idea has some real merit. If that is the case, I know it is about moving the frequency response point out of the normally encountered range.  That is about all I know.  I am open to ideas on how to move that response point short of welding in more tubes. I do know rigidity vs. flexing is not as important as changing when and how much it flexes.   In the mean time, I will experiment with the tire balance by adding weight and riding to gage the effect.  I guess that would be considered "dynamic" balancing :-)

[Jonesy]

It can be a problem mounting tubless tires on tube type rims.  Check that the tire is seated properly on the rim.  There is usually a line cast in the tire near the bead seat.  Spin the wheel and watch that line to be sure it is equidistant from the rim for the circumference on the wheel on both sides.

At the same time, you can check the wheel runout side to side and radially.  Then make sure the tire is also round, too.

Cheers,

That's what happened to me recently with my new front tire. I was getting the same thing, and I took it back and had it rebalanced. The front still felt shaky at 45+ MPH. Side-to-side runout was OK, but the tire looked to have a high spot on it. I chalk marked the beginning and end points of the high spot, and coincidentally, the valve stem was right between the marks... Hmm....

When I deflated the tire, I found the problem. Some of the inner tube was folded up and caught under the tire bead, so when the tire was inflated the trapped part of the tube would jack the bead up away from the rim, making a high spot on the tire. This was likely caused by threading the nut on the valve stem on too far when initially mounting the tire. I was able to carefully work the tube down into the tire and re-inflate after lubing the beads and rotating the wheel while smacking it with a mallet to seat the beads fully on the rim. It now rides nice and smooth...

They also share the same cheap chin Shin tires.

I've had problems with Cheng tires being out-of round. I installed one on a relative's bike and he complained of a shaky front wheel. After trying a bunch of stuff, we finally replaced it with a Continental RB2 and that solved the problem.

[754]

Before you experiment with the tire balance, check it first..

Are your fork sliders wore out??

[tonycb650]

I have chin sheng hi-max tires on 2 bikes and havent had a problem fwiw.

[KingCustomCycles.com]

I jacked up 3 bikes in the shop and checked for front tire out of round, flat spots, etc..The used Continental was dead round, 2 brand new Chin Hi Maxes had obvious flat spots and bulges.  If this is the problem, this would make the 4th. tire I have gotten that was defective.  I'll call JC Whitney tomorrow and deal a new Continental trade or at least get something round.  My wheel weight experiment resulted in no improvement.

[MCRider]

ISNIP  I am open to ideas on how to move that response point short of welding in more tubes. I do know rigidity vs. flexing is not as important as changing when and how much it flexes.   SNIP

Agreed. Just some clamp on bracing might interrupt the natural frequency.  But now I see from later posts you may have a tire problem.

[KingCustomCycles.com]

Follow up that solved the problem.  Cheng Shin Hi Max tires are junk.  I replaced with their Barracuda version and the problem is solved.  Smooth, and just begs to be run hard and fast. That would make 4 Hi Max tires that were defective from JC Whitney.  Buyer Beware.