Front end "wobble"

[RandyN]

My new to me 86 R65 develops a front end side to side wobble around 80 kmh. It is very noticeable but easily rectified with a firm grip on the handlebars. I have tried removing the windshield but no change. The front tire is an Avon. the PO was a bigger rider and when I got it, tire pressures front and back were low. The back tire seems to have an odd wear pattern where the tread blocks are higher on the outer leading edges. The front tire looks okay but is about 1/16 radial runout. it is also 7 years old and starting to weather check, so it will be replaced. The static balance seems okay. The front springs are aftermarket progressives and the steering head seems to have no free play but seems slightly looser toward the end of travel on both sides.
Any ideas on the causes of the wobble before  I start to tackle it?
Thanks
Randy

[Tony Smith]

Ideas as to what is causing the wobble.


Everything you mention could cause a wobble. Address them and see if it is gone.

Also check steering head bearings  (while you are there check that the upper triple clamp is nice and snug) and wheel bearings.

The odd wear pattern on the rear is a bit of a worry, put someone one it and have a long careful look form front and back and make sure you aren't dealing with a bent frame or some other misalignment.

[montmil]

"...front springs are aftermarket progressives..."
Not really likely to cause wobbles but will definitely harshen your ride depending on your ATGATT weight. You did mention a 'heavy' PO.

"...steering head seems to have no free play but seems slightly looser toward the end of travel on both sides."
Time to take a look. Properly adjusted, steering head bearings should provide a gentle movement to the stops when pushed off-center with the front tire clear of the ground. Check for old, hardened grease, brinneled outer races.

"The back tire seems to have an odd wear pattern where the tread blocks are higher on the outer leading edges."
Under inflation could cause that. Front end wobbles can also be caused by loose and/or worn out swing arm pivot bearings in the rear. Check 'em.

And as already mentioned, wheel bearings should be inspected, cleaned, greased and adjusted correctly.

[RandyN]

thanks for the confirmation and feedback so quickly. I will start with the front end and work my way back. Its going to take a bit but I will post back up once I am done.
Cheers
Randy

[thrang]

Not much to add to what's above, other than to check that all the engine mounts are correctly torqued, unlikely to cause a wobble, but worth a look. Another thing to have a look at is that the forks are in alignment. I'd also whip the tank off and have a good look at the frame head, for any fresh paint and/or odd looking welds just in case its had a front end prang and someone done a 'scaffold pole' frame straightening repair job. Finally and I'm not being insulting here because I've done it myself in the past, the tires are on the wheels the right way for direction of travel.

[Barry]

I might be tempted to start with the rear tire which when badly worn can cause problems even when everything on the front end is perfect.

The steering head bearings are worth checking and re-greasing. When setting them up the object is to lightly pre-load the bearings to provide a degree of drag and therefore damping. Often a clean and re-grease will be all that's needed.

BMW's spec for maximum lateral runout is 1.7mm which is just a tad over 1/16"  so that's probably not the cause. I just put on a new front tire which has a similar amount of runout although I haven't yet measured it accurately. It hasn't caused any perceptible problems.

I just re-read your post and it's radial runout that you have. The spec for that is surprisingly slightly bigger at 1.8mm so you are still OK.

[RandyN]

I pulled the steering head aprt today. The grease was old and very hard. This is the bottom bearing. The top was a bit better. While there was no perceptible freeplay, I was able to undo the adjuster nut with my fingers. New bearings being ordered on Monday.
I also checked the tires and they are mounted correctly for rotation. No insult taken, as I have made the same mistake also. I will be checking everything else that has been suggested
Cheers and thanks
Randy

[Barry]

I's a shame that the bearings are gone. Often with hard grease you get away with just a clean up but if there was no pre-load on the bearings you get brinelling like that and perhaps the lack of pre-load was the cause of your wobble.

[Tony Smith]

I am surprised that the headset did not give more indication of the horrors within.

That is a pretty buggered bearing in the photo. Out of curiosity, how did you remove the outer races?

[montmil]

Randy- I recently replaced the steering stem bearings on a friend's R100/7. They were really bad but yours get the trophy. With a too loose stem nut, you likely did not have the "notchy" steering as did my buddy. Both of you will appreciate much improved control and safety.

You've found the primary source of your DUI R65's behavior but with this evidence of zero PO maintenance, suggest you continue your stem-to-stern inspection.

Keep us posted. BTW, we all love photos!

[Semper Gumby]

Improperly tightened swing arm bearings can also cause wobbles.  The BMW manual gives a range for final torque for these bearing.  I use the top end of the range.  (It's not very much btw.)

PS what really cured my wobbles was replacing the front end with one of a 1988 K100RS.  That solved all kinds of problems.  

[RandyN]

I am surprised that the headset did not give more indication of the horrors within.

That is a pretty buggered bearing in the photo. Out of curiosity, how did you remove the outer races?

I used a small chisel and drove it in at the base of the race until the race moved enough that I could get a drift behind it. I had to modify a drift to get enough offset, but it worked well. Next time, if there is a next time, I would weld a bead around the inside of the race.
Cheers
Randy

[Tony Smith]

I am surprised that the headset did not give more indication of the horrors within.

That is a pretty buggered bearing in the photo. Out of curiosity, how did you remove the outer races?

I used a small chisel and drove it in at the base of the race until the race moved enough that I could get a drift behind it. I had to modify a drift to get enough offset, but it worked well. Next time, if there is a next time, I would weld a bead around the inside of the race.
Cheers
Randy

I use the welded bead method, but others here believe in buying expensive tools that do not always work and which strangely enough cost about the same as a cheap stick welder. More power to you for getting them out the way you did. Rev Light drilled holes and used a drift which impressed me, I am simply surprised that you way worked at all as I didn't think there would be enough room to get a strong engough chisel in there - well done anyway.

[RandyN]

I got the steering head back together today. The wobble is gone!! I still have a vibration in the front end that feel like it is coming from the tire. The wear pattern on both front and back looks suspect, so I am ordering 2 new tires. The tires were definitely run under inflated for a period of time.  The front well has 1 1/4 oz of weight for a static balance and the tire has about 1/16" of run out. I am thinking of Bridgestone Battlax tires.
Cheers
Randy

[Luca]

If the bike sat long enough the tires could have developed flat spots which will cause vibration.  Riding the bike will get the tires closer to round, though it sounds like you need new sneakers anyways.

Good advice here to go over the whole bike and make sure everything is up to snuff.  In addition to swingarm preload, you can also make sure the swingarm is centered, and make sure that your fork fluid levels are correct.

If you can, I'd also suggest only making one change at a time so you can see how each affects the handling.