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  (#1)
Spike
 
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July 1, 2005, 11:17 AM

Without actually riding the bike, how can I tell if front forks are bent? Is there any way of doing this without tools??


RIP Greg Walker, I will never forget you

If everybody thought before they spoke, the silence would be deafening
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July 1, 2005, 11:25 AM

If it's not obvious, then you'll need to remove them to check. That will require tools.


'08 MARRC Expert Racer of the Year
2009 #3 Combined Overall Championship

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July 1, 2005, 11:30 AM

Here are some pointers from a BMW forum:

http://faq.f650.com/FAQs/SteeringFAQ.htm

Quote:
Steering FAQ
compiled & edited by Kristian #562
updates edited by PDuffy#1244, Kristian #562

General Questions & Solutions

Check the Fork Brace

Forks twisted with respect to the Fork Clamps.

General Questions & Solutions



Q. I dropped my bike onto itís side and the bars seem crooked. Anyone know a sure-fire way to check for bent bars? Or is it just if it looks right, it is right?

A1. It could be bent bars, but most likely the handlebar mounts just moved in their little rubber damping sockets. There are rubber mounts in between the handlebars and the top triple-clamp that can shift or move. It could also be the fork brace or finally the forks have moved with respect to the Triple Tree.

Q. Does anyone have a good tip on how to fix a bent handlebar? I dropped my CS and the RHS of the handlebar was slightly bent upward. BP316

A1. Get a long piece of pipe put it over the end of the bar and crank it (preferably with all the levers, grips, etc. off or you MIGHT damage them. Make sure you do it against the steering stops and someone else holds the bike. Don't over do it. Only for slightly bent bars. Kristian#562

A2. I am not sure about the new models, but the 1997-2000 bikes handlebar clamps are rubber mounted and relative loosely bolted to the upper triple clamp. When the bars are hit the clamps will move and they can just be twisted back into alignment. You should not have to tighten them, unless you start to hear or feel a click when stopping or moving the bike around with the handlebars. It can sound and feel like loose steering head bearings, but is usually just loose bar clamps. If you feel this click, then the clamps need to be tightened slightly. This is done by loosening the jam nut that holds the tension nut for the clamps in position and tightening the nut above it. They are located under the triple clamp, where the sun don't shine. Tighten the tension bolt no more than on turn, re-tighten the jam nut and the clicking should disappear.




Checking if the Bars themselves are bent or they just moved.

Line up the triple clamps (Marked Yellow) as square as you can. Maybe get a piece of string and ensure equal distances from some known center point.
Then, also using a string compare distances from bar ends to some other known center point. There's also a possibility the entire triple clamp/fork assembly has twisted a little, though I would think the bars are the weak link and would bend first.
Before you dig out the tool kit to loosen the pinch bolts and wiggle everything back into place, just try sitting up on the seat and pulling the bars to the direction which would straighten them, by hand, and pushing the opposite way your foot. Yes, the actual BAR mounts move a bit. You can actually reef the bars quite a bit to the left and right after the front end reaches full lock - but this is NOT a twisting of the front end proper, but just movement of the risers in the (top) triple clamp. It's good in a way for an Enduro bike, but a bit of a surprise when you first witness it.
So try just move them back by twisting the bars, while holding the front wheel straight. Sometimes these clamps can get a little loose and cause a "clunk" when coming to a stop or pushing the bike around with the engine off. Look under the upper triple clamp for the bolt, nut and jam nut holding the bar clamps to the upper triple clamp.
In a slow speed fall, the bars will nearly always twist in the rubber mounts and not bend. If you're trying to straighten the bars by yourself, turn the handle bars as far as you can against the stop, then force the bars into position. this is a lot easier than trying to hold the front wheel straight, which usually takes two people.
or :
Take 4 good straight pieces of 2x4, clamp them together loosely on the forks, one set at the steering head, one by the tire, with 2 parallel string lines on the faces of the 2x's will tell you if your forks are tweaked. If they are loosen the 8mm Allen screws at the triple clamp and lower fork clamps, use 2 longer 2x's in opposition to restore the forks to their former glory. Bolboajeff.
Q. Does anyone have a good tip on how to fix a bent handlebar? I dropped my CS and the RHS of the handlebar was slightly bent upward.
A. Get a long piece of pipe put it over the end of the bar and crank it (preferably with all the levers, grips, etc. off or you MIGHT damage them. Make sure you do it against the steering stops and someone else holds the bike. Don't over do it. Only for slightly bent bars. Kristian#562.


Q. Why are my Handlebars loose/wobbly or a bit off?

Because on the Classic there are Rubber Dampers (Part #4 in gif below) which can get sloppy over time. To fix it, undo the lock nut underneath the Triple Tree (One of the TWO #8's), do up the higher one, then redo the lock not. Do NOT over tighten, you are just tightening against the rubber!

Q. The strange thing for me to understand is that there are 2 nuts, that just screw on together for each shaft. You have to access then from underneath. Why are there 2 nuts per shaft?
You are talking about this, Parts 3 through 8 incl.

There are TWO #8 Nuts (Not Shown) because one is a lock Nut. The first nut should just be SNUG and then holding the first with a Spanner, you Lock the Second nut onto the first, to stop both undoing. The reason for this system is that as I noted earlier, the first nut should just be SNUG, because you are tightening a Rubber Connection and if you go cranking Nm's of Torque into rubber, you'll just compress the rubber.
Q. What do I torque those nuts back to when tightening? Do I have to put them on a special way? Is one supposed to go on first, face a certain direction? And what is that shaft called that connects the handlebar mounts to the triple clamp?
The Torque table gives those nuts as:
- Nuts to handlebar mount 10Nm,
- Locknuts to handlebar mount 50Nm but the second seems VERY high Check the Manual.
- Normally what happens is that Rubber gets a bit loose over time/with dropping. Undo the Lock nut (lower of Two, do up the Upper one a little until SNUG, then holding the Upper one, tighten the lower one (the Lock Nut), onto the Upper one.
For the Classic ONLY, (the GS does not have rubber dampers, so (a) the vibration feels like it is more and B, the Classic ones can go out of whack more easily.).



Check the Fork Brace.


Problem: Everything looks straight, goes together smoothly...but the bars are askew. If you turn the bars in their mounts so they pointed the same way wa the tire, they are clearly not aligned with the triple clamp.

Possibly a minor incident a long while back bent the black metal "fork brace" that holds the fender. You may have bent it just slightly. A new brace can fix your problem. cost: $19.
The only way to see if it is bent is to take it off completely, and look at it from the bottom. That way you can see that the sides don't line up just right.
Forks twisted with respect to the Fork Clamps.



Highly unlikely but you will need to get at the Fork Clamps (Upper, Lower), undo them (one at a time) and realign the forks with respect to the wheel, triple tree and handlebars.



Unless you have really bent the main frame, try this:

Remove the front wheel.
Loosen the fasteners holding the fork tubes in the triple clamps.
If you are really serious, remove the fork caps and fork springs.
Compress the forks completely and re-tighten the triple clamp bolts.
Re-install the front wheel.
Re-install the fork springs and caps.
If your twisted forks is slightly less serious (and this should work for 85% of the cases) just remove the front wheel, loosen the triple clamp fasteners, re-install and re-tighten, everything.



Note! Stroking the forks up and down prior to tightening the front wheel!

Most of the "mis-alignment" from a low speed dump is just "twisting" of straight components. By loosening all of the fasteners, these parts are allowed to "relax" and assume their proper alignment.

I would even recommend this procedure to anyone who rides a good bit "off-road" for any length of time. These parts aren't welded on. They move. Give them a chance to "move back".

Damaged Front Suspension FAQ
BradG#1002 & Kristian#562

This simple FAQ provides some tips and suggestions for what to do if you think your front suspension may be damaged.
Refer also the Steering FAQ and Suspension Tuning FAQ.

Q: After a recent crash I seem to have tweaked the forks. Any tips on checking them out?
A: If the crash was minor or you think the affect on the forks was small then it may just be that the front suspension assembly is just temporarily "pushed" out of alignment. There is some flexibility in the assembly and the fork to triple clamp connection can twist and stick out of alignment. The trick is to support the bike on a stand and loosen up the triple clamp to fork connections. This will allow the assembly to come back to it's normal un-flexed state. You can loosen the fork brace and axle as well but most of the problem is going to be in the triple clamps area. By loosen we don't mean so much so that everything falls off the bike, just enough to allow for some movement. You can loosen just one side to help prevent the forks from sliding down. Gently working the assembly by moving the handlebars back and forth while someone restrains the front wheel can help. Tighten up (make sure the forks have not slid down out of the triple clamps) just he upper triple clamp and make the front wheel secure then sit on the bike and work the forks up and down. Now tighten up the lower triple clamp and check the alignment. Hopefully your problem is solved. If things still look wrong and you're using the handlebars as a reference it may be the handlebars are bent.

If you are still concerned you have a problem then one of the forks could be bent. This is going to require that you do a bit more. One easy check is to remove the front wheel, fork brace and fork cap to allow you to freely slide the fork tubes up and down independently (with no spring resistance). If you feel any binding as you move the lower slider up and down (do it slowly if you have oil in them) then something is bent and you'll want to have your dealer or other professional take over. Tubes can be straightened but you may want to check the costs of repair versus replace to be sure it is worth the effort. The Official BMW manual describes the process of how to measure a fork tube for straightness. It requires some tools you may not have. If you have a large flat surface (like a thick marble or granite table) you can try rolling the tube to look for bends.

NOTE: This is a fairly simple but involved process and it deals with a major structure on the bike. The information provided here is meant only as a general guide in the absence of a full FAQ text.

One company that can provide assistance is Forks by Frank.

Another is http://www.motorcycleframeman.com/. The Frame Man in Sacramento straightened both fork tubes, the top clamp and the triple tree for $148 including return shipping for a '97 Classic. Flash #412 (CO)

If the stressed parts (ed. fork tubes) are Magnifluxed (tm), any subsurface hairline cracks in them will show up. Any good speed shop should know where to get this done in your area. - Flash #412

If you remove both fork legs and measure the distance between the tubes while they're in the yoke, it should be the same at any point between the yoke and the bottom. Now rotate one tube 90 degrees and repeat. Repeat until you have rotated that tube all the way around. Repeat for the other tube. If they measure straight, they're straight enough. It is quite possible to bend a fork brace with a twisting motion that is within the elastic capabilities of the tubes themselves. - Flash #412

Here is a Check List for inspecting a damaged front end. Provided by mtiberio

With the wheel still mounted, spin the wheel. is it bent? yes, have rim straightened if not too bad, or replaced. not bent? with the wheel removed, stick your fingers in the bearings and turn, is there roughness in the bearings? yes, replace them. no? go to step 2

Remove the front axel. using a large straight edge (level, vernier calliper, etc), and/or possibly a piece of glass, and any other means at your disposal determine if its bent. yes? straighten or replace, now go on.

Remove forks from triple clamps (after removing calliper, fender, etc). Holding the fork slider fast, and using a run out gauge (dial indicator or eyeball), turn the tube inside the slider, and look for any run out at the far end from the axel (top). if you have more than 5 or 10 thou, think about straightening/replacing. you can straighten bent tubes if they are just bent, and not kinked, creased, wrinkled, etc.

Turn the triple clamp in the steering head and feel for roughness or notchiness. If any replace the lower bearing at the least.

Find a straight section of the tubes if possible (if you pull them from the sliders, the section that was originally down in the slider is usually straight cause you were probably braking and close to bottomed at the moment of impact), and try and re-insert it into the triple clamp, do the same for the other side. If the tubes go up with no binding, then the clamps are probably straight, but check for parallelism between the upper and lower by eye as well. if not straighten or replace.
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  (#4)
Spike
 
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July 1, 2005, 11:33 AM

Thanks guys, much appreciated!


RIP Greg Walker, I will never forget you

If everybody thought before they spoke, the silence would be deafening
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