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High Speed wobble (properly assembling steering stem, background info)
by: Tapper
I had an irritating high speed wobble. I fooled with it quite a while before finally discovering the problem. Turns out, the steering tension was heavy (not light).
Measuring the tension is done by taking a sping scale (I bought a good one at a machine shop graduated from 1 to 5 pounds in increments of tenths) and hooking it to the fork interference (the little nub of the fork itself sticking out of the upper triple tree. ) You measure by looping a pice of wire over the nub, and pulling it with the spring scale perpendicular to the fork and at right angles to the direction of fork movement.
A good reading is somewhere between 1 and 2.5 pounds, with 1.5-2.0 being just about right. Take note, that every stock stem tension I have measured (50 bikes or so) has been set light by Honda. The factory stem tension varies from .75-1.5 pounds or so (as measured by my scale).
During these tests, I ran into something that gave me trouble. The problem - while reassembling the neck, stem tension would shoot to 5 pounds or more when the top nut was torqued. Changing the bottom adjusting nut torque would not change this value in proportion to the torque applied to it (as it should).
The problem was caused, by a crushed "lock washer". Thing is, the lock washer isn't really a lock washer at all, it's a torque isolation spring. It has 4 little legs bent at a 45 degree angle around the inside edge which serve as springs. In the process of reassembly somewhere, those legs had gotten bent flat, and when this happens, the washer no longer serves as a spring to isolate the torque from the top nut (which should bear against the top adjusting nut) from the bottom adjusting nut. When the washer gets flattened out, it no longer isolates the top nuts torque from the bottom adjusting nut, and the whole assembly "stacks", transfering tension to your steering, and making it too heavy.
Heavy steering symptoms include a tendency to hunt or drift in lanes, and a distinct wobble. Normally, when the steering is set properly, the velocity of the bike will tend to drive the steering stem straight again when it is deflected by a change in direction of the front wheel (like hitting a rock, changing lanes, changing the weight distribution on the bike, etc.) If the steering stem isn't set light enough, the bike wobbles, because the stem doesn't return to center easily. If set too light, it overcompensates and overshoots the center.
Normally you can tell the difference by the speed of the wobble. A very fast wobble usually means too light tension, and a slow distinct wobble means too heavy. Both can be caused by the crushed lock washer (in the light case, the bottom adjusting nut was set so loose to compensate for the top nuts torque, that the stem isn't really fully seated and imitates a bad bearing).
To properly assemble the steering stem, you should:
1. Load upper and lower bearings with a good moly grease. Smear grease on inner bearing races, and smear some into the dust cups to make a good seal.
2. Take lower triple tree, with bearing attached, and insert it into steering head. Insert the upper bearing into stem.
3. Smear threads on steering stem with motor oil.
4. install lower adjusting nut. Tighten to 30 ft-lbs with a good torque wrench.
5. Move the triple tree back and forth, from stop to stop, 8 or 10 times.
6. Loosen bottom adjusting nut, and re-tighten to 100 inch-lbs. move the tree from stop to stop 10 times, and re-torque the lower adjusting nut. Repeat this a few times, until the nut no longer moves between tries.
7. Place a brand new stem washer on the adjusting nut, so that the pre-bent tabs go in the slots on the nut. Screw on the top adjusting nut slightly finger tight, then carefully tighten using your fingers only, until the tabs on the washer line up with the slots on the top adjusting nut. Bend the tabs up. Install the forks, now according to the manual, but do not install the top nut. Leave the lower pinch bolts tightened, and remove the upper triple tree.
8. Using a spring scale graduated from 1lb to 5lbs, and a string - hook the string around the top of the fork tube, and pull at a right angle to fork. It should read about 1.25 - 2.5 pounds. If it is less, then tighten the lower adjusting nut a bit. If it is more, then loosen and re-tighten the adjusting nut. It is best to use a torque wrench for this, and increase or decrease by five inch-pounds each try, until you get it perfect. BE VERY CAREFUL NOT TO OVER_TIGHTEN THE TOP ADJUSTING NUT, or you'll have to get another tabbed washer in order to get the stem right. Finger tight only!
9. install the upper triple tree. Check that the forks line up to right height, and tighten the upper pinch bolts to 41 ft-lbs.
10. install and tighten the top nut to 74 ft-lbs.
11. Test the tension, using the same method as above. It should read just barely higher, than it did before you installed the triple tree. If it reads a lot higher, by say a pound or more, congrats, go buy a new tabbed washer, and repeat the process.
Last update: 2008-08-22 00:57
Author: Tapper
by: Tapper
I had an irritating high speed wobble. I fooled with it quite a while before finally discovering the problem. Turns out, the steering tension was heavy (not light).
Measuring the tension is done by taking a sping scale (I bought a good one at a machine shop graduated from 1 to 5 pounds in increments of tenths) and hooking it to the fork interference (the little nub of the fork itself sticking out of the upper triple tree. ) You measure by looping a pice of wire over the nub, and pulling it with the spring scale perpendicular to the fork and at right angles to the direction of fork movement.
A good reading is somewhere between 1 and 2.5 pounds, with 1.5-2.0 being just about right. Take note, that every stock stem tension I have measured (50 bikes or so) has been set light by Honda. The factory stem tension varies from .75-1.5 pounds or so (as measured by my scale).
During these tests, I ran into something that gave me trouble. The problem - while reassembling the neck, stem tension would shoot to 5 pounds or more when the top nut was torqued. Changing the bottom adjusting nut torque would not change this value in proportion to the torque applied to it (as it should).
The problem was caused, by a crushed "lock washer". Thing is, the lock washer isn't really a lock washer at all, it's a torque isolation spring. It has 4 little legs bent at a 45 degree angle around the inside edge which serve as springs. In the process of reassembly somewhere, those legs had gotten bent flat, and when this happens, the washer no longer serves as a spring to isolate the torque from the top nut (which should bear against the top adjusting nut) from the bottom adjusting nut. When the washer gets flattened out, it no longer isolates the top nuts torque from the bottom adjusting nut, and the whole assembly "stacks", transfering tension to your steering, and making it too heavy.
Heavy steering symptoms include a tendency to hunt or drift in lanes, and a distinct wobble. Normally, when the steering is set properly, the velocity of the bike will tend to drive the steering stem straight again when it is deflected by a change in direction of the front wheel (like hitting a rock, changing lanes, changing the weight distribution on the bike, etc.) If the steering stem isn't set light enough, the bike wobbles, because the stem doesn't return to center easily. If set too light, it overcompensates and overshoots the center.
Normally you can tell the difference by the speed of the wobble. A very fast wobble usually means too light tension, and a slow distinct wobble means too heavy. Both can be caused by the crushed lock washer (in the light case, the bottom adjusting nut was set so loose to compensate for the top nuts torque, that the stem isn't really fully seated and imitates a bad bearing).
To properly assemble the steering stem, you should:
1. Load upper and lower bearings with a good moly grease. Smear grease on inner bearing races, and smear some into the dust cups to make a good seal.
2. Take lower triple tree, with bearing attached, and insert it into steering head. Insert the upper bearing into stem.
3. Smear threads on steering stem with motor oil.
4. install lower adjusting nut. Tighten to 30 ft-lbs with a good torque wrench.
5. Move the triple tree back and forth, from stop to stop, 8 or 10 times.
6. Loosen bottom adjusting nut, and re-tighten to 100 inch-lbs. move the tree from stop to stop 10 times, and re-torque the lower adjusting nut. Repeat this a few times, until the nut no longer moves between tries.
7. Place a brand new stem washer on the adjusting nut, so that the pre-bent tabs go in the slots on the nut. Screw on the top adjusting nut slightly finger tight, then carefully tighten using your fingers only, until the tabs on the washer line up with the slots on the top adjusting nut. Bend the tabs up. Install the forks, now according to the manual, but do not install the top nut. Leave the lower pinch bolts tightened, and remove the upper triple tree.
8. Using a spring scale graduated from 1lb to 5lbs, and a string - hook the string around the top of the fork tube, and pull at a right angle to fork. It should read about 1.25 - 2.5 pounds. If it is less, then tighten the lower adjusting nut a bit. If it is more, then loosen and re-tighten the adjusting nut. It is best to use a torque wrench for this, and increase or decrease by five inch-pounds each try, until you get it perfect. BE VERY CAREFUL NOT TO OVER_TIGHTEN THE TOP ADJUSTING NUT, or you'll have to get another tabbed washer in order to get the stem right. Finger tight only!
9. install the upper triple tree. Check that the forks line up to right height, and tighten the upper pinch bolts to 41 ft-lbs.
10. install and tighten the top nut to 74 ft-lbs.
11. Test the tension, using the same method as above. It should read just barely higher, than it did before you installed the triple tree. If it reads a lot higher, by say a pound or more, congrats, go buy a new tabbed washer, and repeat the process.
Last update: 2008-08-22 00:57
Author: Tapper
