Instability

[Barry]

If we analyze a wobble we need:-

A system that will oscillate - that's whole steering asembly (and sometimes the whole bike)

A positive feedback source of input energy into the system - that's the tire.  No question that tires are the source of wobbles in this respect.

The interaction between the tire and the road surface is the energy source for a wobble and that input is always there at a very low level. If we remove all sources of damping by taking our hands off the bars then under "certain conditions" the wobble can increase in magnitude so that with each cycle providing more positive feedback the wobble develops to tank slapper proportions.  

It's the "certain conditions" that we need to address and that can be one or more of the things that have been mentioned like tire condition, tire pressure, head, wheel or swinging arm bearings or even weight distribution.  So I don't think you can always put a finger on one specific source of a wobble but what you can do is provide the best circumstances for it not to develop by having some damping in the system to absorb the energy. That's why the steering head bearings were designed by BMW to have sufficient pre-load to provide that damping effect.

[georgesgiralt]

I've checked the tires. No "Radial" marking on the Lasertec so it seems to be diagonal.
But, both tires where made in Brazil. So the source of the Salsa is definitively the tires    8-)

[georgesgiralt]

I just read the BMW maintenance manual for the R45/R65 I bought 30 years ago.
On chapter 31 they explain how you change the bearings on the steering columns,
and at the beginning of chapter 32 they give you the torque value for pre-load :
In 1978 there is no value given. then at the first update, in 5/80 they give 35 N.cm +/- 20 and at the second update, in 8/82 they give "no play" ....
So this seems to be a very controversial figure ;-)
Nowhere they explain how to measure the torque and or adjust the play/pre-load... Unless I've lost some pages on the loose sheet binder ;-)
Maybe it's something they taught at the school for all bikes and that the value was specified then.

[Barry]

My BMW manual has the method but not the torque figure. I got the 2.6 ftlb from snowbum.

Got to say I'm surprised that they reverted to a no play setting. This is a safety critical item and if a little pre-load is safer without impacting on steering response (and it doesn't) why would they opt for a less safe setting.  The other issue is a "no play" setting is near impossible to set precisely especially with the weight of the forks and wheel on the bearings.  It's almost inevitable you will end up with a little play or a little pre-load. Better to aim for the pre-load.  

I suppose it's possible that 81 on models with the slightly longer wheel base were judged to be more stable and therefore not in need of any steering damping. Can't think of any other logic for the change. On the other hand the 81- on riders manual still talks of having the correct pre-load set.  

It doesn't add up. Maybe it's a translation error.

[steve hawkins]

I am not aware that the post 81 wheel base is any longer than the 79.  There are no changes in the forks /frame/shocks or swing arm?

Just because I am unaware, does not mean it isn't true.  Just never seen any numbers...

Changes in procedure for servicing and policy can happen for a multitude of reasons, not all technical.  

It amazes me how policy and procedures change even for things like medical and First Aid?  Over the years with the various jobs and hobbies I have had, it has been necessary for me to take first aider courses at various time - it is amazing how the Human body has evolved over the last 30 years, as the courses, have changed a heck of a lot!  No more mouth to mouth, I am surprised they have not changed the recovery position.....I digress.....Sorry

Rev. Light

[Barry]

We are talking just a few mm but there is a small difference in wheelbase. The figures I have from the riders handbook are 1390mm (54.7") for the early model and 1400mm (55.1") for the later model. The subframe swinging arm and drive shaft are all different part numbers.  I doubt it makes much practical difference to stability though. I was just clutching at straws trying to think why they would relax the pre-load requirement.

[Dave 2]

I just finished retightening my steering head bearings after my restoration because after several hundred miles it developed the high speed wobble. At the time of the restoration I thought I had the bearings as tight as I could get them even though the side to side "falling" of the front end was too quick and hit the stop too hard. I also had a clunking sound over some bumps. I used pliers similar to what Monte mentioned and was able to really get a grip on the large ring to the point that it was too tight. As previously mentioned when you re-torque the top two triple clamp bolts and the center bolt your bearings will be further compressed. It took me about a dozen tries to get it to what I believe is right. Good luck, Dave 2

[georgesgiralt]

So, I've modified a bit the pre load. Have to test ride the bike, though.
I used a very large falt screw driver and a rubber mallet to turn the big round nut. At first, after tightening the centre nut, the steering was very stiff. So I slackened the centre nut and did it again.

I could not turn the nut with my plumber's tool. too small. So I decided to go the screwdriver way. Doing it gently and lightly I did not mar the nut.
Will report back when I've ridden the bike.

[georgesgiralt]

I'm an happy rider !
Same place as before, same speed and same conditions : the bike runs strait. No wobbles !
On the highway if I leave the handlebar leave it's life, the bike also runs strait...
And no oscillations when running right.  So the pre load is not so bad.

The steering falls easily on the right side, but not so easily on the left side (I think my electrical harness is not routed correctly, and if someone can provide a couple of pictures as per the correct routing, it would be perfect)

I'm happy !    8-)

[EGRG]

Also check the engine to frame mount nuts. I had a disturbing low frequency wobble in fast curves that was corrected after adjusting the front engine bolts and nuts that where a little loose.

[montmil]

Victor! Where have you been? After hanging out with you at the MotoGP in Austin, I thought you dropped off the edge of the earth. Glad you're still above the grass.  

[EGRG]

Hi Monte:
Lot of work and just plain lazy.
But it nice to be back

I'm truly enjoying my bikes.
The K1100 is a dream to ride in Mexico that has few and far between highway patrols.
I let it loose and just grin.
But the R65 is my daily ride pride and joy.
The carbs are perfectly balanced and it just purrs along accelerating at its nice predictably strong pace. The valves play their music when cold and just enjoy the sound of the engine when it's at its proper temperature.
It's still the only airhead in town and maybe the state. All my friends are just amazed that it's that old and still going strong.
Looking for a R80GS but need to catch my wife off guards.