Instability on C5

[r80rt]

Who are you, who are so wise in the ways of science?

[gashousegorilla]

I am Arthur, King of the Brittons .Oh Geez,too funny. we better stop before they kick us off.

[ScooterBob]

Yes bob I have. up down and in the middle.I am not with the bike right now, but presently I believe it's set at center. Fork legs are now filled with 20 wt fork oil,(also have tried 10 and 15wt) to the volume in the service manual, again I don't have it with me, but if memory serves me, 200 ml's each? When I drained the stock fork oil , did not measure the volume, but they appeared full, by the amount that came out.
 Not to get off this train of thought, but while I'm thinking of it.My c-5 was one of the earlier ones over here. I believe you guys worked on it, due to the problem with the trans gears. Did not go to recall,you guys picked it up before the bikes went out.Did a good job it appears by all of the fastener paint. Is it possible that these motors have shims, or a motor plate missing or misaligned?Throttle responce is also a factor with this oscillation, or can induce it. And, no I'm not finger tipping the bars on the highway.Just trying to rule all out.
Thanks bob, Dan.

Dan - Interesting that you should mention the motor ..... As a stressed member of the frame, it must be able to absorb (dampen) any resonant vibrations in the frame. The frame, likewise, takes a bit of shake out of the motor by dissipating it in the frame. That being said - have you loosened the mounts so they'll just move and started the bike - or even ridden it a little bit to allow frame stresses to normalise in the bike? Re-tighten the bolts with someone sitting on the bike, holding it up level. We took all the engines out of the bikes with them firmly bolted down by the suspension to eliminate ALL the problems that would normally be caused by the frame flexing and moving around with the biggest single stressed member removed. This does not, however, preclude ALL movement of the "bits and pieces" as sometimes, from the Factory, they were under a bit of stress. There is nothing to align or shim at all - the assemble is brutally, wonderfully simple - but - if the frame has a slight torsional stress on it - it COULD, conceivably, create an oscillation at speeds in trying to "find center" again. The frames on these bikes are amazingly springy - they are probably made from some serious good steel. IF there was some stress in the frame (usually manifests itself as some hella handlebar vibration ....) it WOULD be trying to spring back - and may get you wobblin' ...... Just a thought.

[r80rt]

That little trick will sure smooth out a 500 BSA!

[gashousegorilla]

That little trick will sure smooth out a 500 BSA!

Ya know as i was reading bobs reply, that thought popped into my head, the old bsa trick. Sh@! it's wortha try! Bob no I have not tried it,but will now. I will let you know.

[Ducati Scotty]

I've never done it but it was standard practice with British bikes in the old days.  Break the engine in a little, loosen, sit, tighten.  Forgot all about that!  I want to do it just for giggles now.

Scott

[singhg5]

Ya know as i was reading bobs reply, that thought popped into my head, the old bsa trick. Sh@! it's wortha try! Bob no I have not tried it,but will now.

Yes bob I have. up down and in the middle.I am not with the bike right now, but presently I believe it's set at center.  

Fork legs are now filled with 20 wt fork oil,(also have tried 10 and 15wt) to the volume in the service manual..

Is it possible that these motors have shims, or a motor plate missing or misaligned?

Throttle responce is also a factor with this oscillation, or can induce it. And, no I'm not finger tipping the bars on the highway.Just trying to rule all out.
Thanks bob, Dan.

Dan:

Looks like the thread is moving forward in a positive direction.  To help it along, how about if you list the things you have tried and what was the result.  Also list the ideas  or any thought that you  have not tried yet.

Based upon what I have read in the thread I have compiled the list below.  By eliminating one by one, you may find the source of problem.  Add more as you keep up with your search.

1. Rear shock adjustment - Tried, but no improvement.

2.  Wheels balanced - Tried, but no improvment.

3.  Fork oil replaced with different weight - Tried, but no improvement.

4. Old BSA trick -  Not tried yet.

5.  Throttle can induce vibrations -  If old BSA trick does not fix it, then the interior of the engine may need further investigation.  

6.  Just to rule out - wheel alignment and typre pressure ??

7.  Swing arm bush ?

8.  Steering Head bearings ??

[SSR]

Things I have tried with no effect on improvement;

Rear shock adjustment
Wheel balancing
Old BSA trick which had effect only on vibrations and reduced it around 60% But no effect on instability. Which makes me think its not the vibrations but the swing arm/suspension related.

When it improved
 
Reducing rear tyre pressure to 27-28 Psi
Rear wheel alignment
Placing a shim between the hub and brake assembly

Things I have planned to try;

Changing rear shock absorbers to oil filled ones or some other make gas shocks.
Changing the swing arm plastic bushes to the rubber/iron bushes from CI bullet.
Strengthening the swing arm at the pivot joint and a bit further downwards

[BRADEY]

I am meeting the company's engineer tomorrow to get this issue of instability out of my life. Guys I only know how to ride a motorcycle, but have little or no experience setting one up correctly. Could you please suggest the areas I should ask him to look into. Please respond at the earliest.

cheers.

[ScooterBob]

Ya know as i was reading bobs reply, that thought popped into my head, the old bsa trick. Sh@! it's wortha try! Bob no I have not tried it,but will now. I will let you know.

Keep in mind that this is not necessarily to quell the high frequency, fourth order engine vibration - although it WILL - this is to remove any potential "spring" (kinetic) energy from the frame that would manifest itself at say - 4 to 8Hz - the frequency of the wobble. Remember that the frames are of GOOD steel on these and they WANT to be straight ... a little stress about the engine could store the needed energy to make 'er shake. Let me know, eh?

[ScooterBob]

I am meeting the company's engineer tomorrow to get this issue of instability out of my life. Guys I only know how to ride a motorcycle, but have little or no experience setting one up correctly. Could you please suggest the areas I should ask him to look into. Please respond at the earliest.

cheers.

Check wheel alignment, tyre pressure, suspension pre-loading and forl oil viscosity and level for YOUR weight. Check also the frame stress as previously posted - and do set the bars as low as they will go without banging the tank. Be sure that the engineers check the VERTICAL alignment of the wheels as well - especially the rer one. Let us know what they find.

[gashousegorilla]

Dan:

Looks like the thread is moving forward in a positive direction.  To help it along, how about if you list the things you have tried and what was the result.  Also list the ideas  or any thought that you  have not tried yet.

Based upon what I have read in the thread I have compiled the list below.  By eliminating one by one, you may find the source of problem.  Add more as you keep up with your search.

1. Rear shock adjustment - Tried, but no improvement.

2.  Wheels balanced - Tried, but no improvment.

3.  Fork oil replaced with different weight - Tried, but no improvement.

4. Old BSA trick -  Not tried yet.

5.  Throttle can induce vibrations -  If old BSA trick does not fix it, then the interior of the engine may need further investigation.  

6.  Just to rule out - wheel alignment and typre pressure ??

7.  Swing arm bush ?

8.  Steering Head bearings ??

Yes Sing, all tried, except BSA trick, tonight though. Add wheel truing, bearing inspection, Braced swing arm, 19" front wheel, Steering stabilizer and caged fork brace under front fender.Check my other threads, I know it's a bit of a tangent. And let me add, the swing arm bushing are not bad on these bikes, there is no excess movement in the pivot area.I think that putting rubber bushings would only add to the flex in the very long and unsupported C-5 swing arm. I do believe that the G-5 has a shorter swing arm.

[gashousegorilla]

Sing, sorry but also add wider handle bars,33", in an attempt to reigh in the bike at speed. I'll let you know about Labor day.
Thanks Dan.

[gashousegorilla]

Bradey, check out our findings under my thread, steering damper for C-5. See what the engineer thinks about the loading and unloading of the rear chassis.
Dan.

[csbdr]

You've gotten more erudite suggestions than I could give, but I was thinking going to the 19" front hoop might improve stability as well. Change the steering geometry.

FWIW, my C5 has had no problems.  I am routinely up to 70, and have gone higher. I can MAKE it oscillate, but it doesn't do it of it's own accord. Got to be something off in the setup.  Good luck!