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Steering Stem Bearing Tension

kuksul08

kuksul08

Suh Dude
Joined
Mar 17, 2014
Location
Hoonville
Moto(s)
Whee!
This past week I replaced the bearings in my VStrom 650 (the greatest motorcycle ever produced). Upon preloading the bearings, I was faced with an interesting predicament. Due to the way the steering bearings are tensioned, using a lock-nut system, the tightness of these locknuts is critical. Too tight, and the bike will handle very strangely - tending to fall over in the turns and having generally scary handling. Too loose, and it will clunk. The difference between too tight and too loose is a mere few degrees of rotation on the preload nut. Further, due to backlash in between the nuts and steering tube threads, the tightness of the upper lock nut against the lower lock nut significantly changes the preload on the bearings. It takes a trained mechanic or lots of experience to get the right feel for the sweet spot. The service manual specifies a handlebar force that can be achieved through trial and error.

This got me thinking. What are your thought on introducing a belleville spring washer into the system between the upper bearing inner race and the lower lock nut? This way, it would allow for 1/4-1/2 turn of "spring" before bottoming out, and allow a tightness range rather than one correct tightness.

In the standard setup, the tension preloading the bearing comes from stretch in the threads of the steering tube, stretch in the nuts, and microscopic stretch in the steering tube itself. This "spring" is extremely stiff, so a few degrees of nut rotation can mean the difference between 5lbs of preload and 500lbs of preload. A belleville spring washer with the correct rate would allow a range of say, 20-50lbs across 180 degrees of nut rotation.

This is a common practice in thousands of industrial bearing applications, even in some high speed CNC spindle bearings that require very specific tension and high precision. Yet, motorcycles don't do it. Any ideas why?

Just like this:
SpindleCrossSection.jpg
 
STEERING HEAD BEARINGS
If your steering head bearings are too tight the bike will weave and
not seek it own center... if you're steering head bearings are loose
you'll notice a pronounce clunk during braking... I don't use torque
figures rather I raise the front wheel off the ground and tighten the
steering head bearings until the bars lock then I back off the nut
until the bars free wheel with a slight drag... with this method you
find that sweat spot and avoid over tightening and under tightening
even if you upgrade to taper roller bearings...
 
The general rule is that you tighten it such that the front end just barely falls over when you tap it to one side or the other. If you can achieve that level of resistance with a belleville, then there should be no difference. My guess is that you may have trouble finding the right belleville, but give it a shot. You might be able to take what is normally a very narrow window of torque and make it more forgiving, which would be awesome. Usually takes me a few tries to get it right and it's a little annoying, so I see at as a worthwhile effort.
 
byke said:
The general rule is that you tighten it such that the front end just barely falls over when you tap it to one side or the other. If you can achieve that level of resistance with a belleville, then there should be no difference. My guess is that you may have trouble finding the right belleville, but give it a shot. You might be able to take what is normally a very narrow window of torque and make it more forgiving, which would be awesome. Usually takes me a few tries to get it right and it's a little annoying, so I see at as a worthwhile effort.
Click to expand...

That's essentially the goal. Make it more forgiving. I just went through this and it took 5 times to get the tension just right. Kind of a pain.
 
That's one of the few torque figures that is actually an art, not a a science.
 
To answer the question, in motorcycle steering, it's not needed. CNC turns a complete 360 degrees and at a high rate of speed.......nothing close to what a motorcycle steering does, plus the load input to the bearings from the wheel going over a road surface is not experinced in CNC.

Proper application..........
 
I would NOT use Belleville washer or any other kind of spring. If it was that simple, bike manufacturers would have done that years ago.

And yes, it's a bit of an art. Here's what I do. After installing new bearings (always tapered rollers), I slowly tighten the nut while turning the stem back and forth, until the bearings are just at the point where they are too tight. You want to ease up to this point as you don't want to damage the bearings. (Tapered bearings are much harder to damage.) Usually this means the steering stem will not turn freely. Oh, and I ALWAYS do this with the wheel off.

With the nut in this position, make a reference mark on the nut and on some fixed part of the bike. The two marks should line up.

Now, back off on the nut and slowly tighten it again until play or slop from sideways forces on the fork tubes/steering stem just disappears. You are tightening the nut untill all excess play is gone but no further. Then make a second mark on the frame or other fixed reference.

You now have two marks, one where the adjustment only just removes bearing play and one where the adjustment is barely at the point where the adjustment is too tight. Now, using the reference marks you made, set the nut halfway between those two points , lock it down, and you're done.
 
ST Guy said:
I would NOT use Belleville washer or any other kind of spring. If it was that simple, bike manufacturers would have done that years ago.

And yes, it's a bit of an art. Here's what I do. After installing new bearings (always tapered rollers), I slowly tighten the nut while turning the stem back and forth, until the bearings are just at the point where they are too tight. You want to ease up to this point as you don't want to damage the bearings. (Tapered bearings are much harder to damage.) Usually this means the steering stem will not turn freely. Oh, and I ALWAYS do this with the wheel off.

With the nut in this position, make a reference mark on the nut and on some fixed part of the bike. The two marks should line up.

Now, back off on the nut and slowly tighten it again until play or slop from sideways forces on the fork tubes/steering stem just disappears. You are tightening the nut untill all excess play is gone but no further. Then make a second mark on the frame or other fixed reference.

You now have two marks, one where the adjustment only just removes bearing play and one where the adjustment is barely at the point where the adjustment is too tight. Now, using the reference marks you made, set the nut halfway between those two points , lock it down, and you're done.
Click to expand...

Elegant and correct.
 
I should add that any time the bearings are replaced, upgrade to tapered roller bearings. And for grease, first smear the races and rollers with high moly content paste. Burnish well into the metal surfaces. Then pack the bearings with high quality full synthetic wheel bearing grease with moly.
 
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