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Discussion Starter #1
After all these years they are still using a ball race head stem bearing..... Does anyone have the bearing part numbers for tapered thrust bearings. 2004 10r as I can't locate an after market supplier that handle them. Thanks
 

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Nothing worng with ball race Thrill, a lot of the time they have less surface contact than taper rollers and you dont have to preload them as much.
 

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Discussion Starter #3
Personally I believe there is. Ball races are really not suited to a static type situation, ie cruising down the highway where the balls are hardly rolling. The vibrations cause the balls and the race to become bruised resulting in a notchy feel in the headstem. I realise that tapered thrust bearings are not perfect either, however you at least have a fighting chance. Technically the pressure at each ball is through the roof given only a single point of support at each ball, (pressure = total load/area this is a divide by 0 situation as there really is no area of contact)
 

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The problem is the preload with tapered bearings like I said , you would have to have an inner spacer accurately machined to get the required amount of torque, the ball bearings and seat arrangement allow the top and bottom bearings to share the load.

You are also relying on a bigger and larger diameter outer/top race so to speak, with a tapered roller you would have all the load on the inner race allowing too much mechanical advantage to try and offset the bearing under braking, to counter this you would have to tighten the bearing and then you wouldnt be able to turn it so easily.

The ball race headsteam takes the loadings vertically and shares it with the 4 bearing surfaces, the taper relies on 2 mating surfaces and relies on thrust to keep it together.
 

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Discussion Starter #5
The frametube itself is machined and spaces the outer races (exactly the same as a car wheel bearing setup ... the hub spaces the outer races). This setup works extremely well and definitely does not affect your turn in. Have been doing it for years, on track and road bikes. Under most riding situations load is taken on the lower race, and lateral movement controlled by both. These bearings are capable of significantly higher loads and I can honestly say outlast open ball races about 3 to 1. If they were a problem as you suggest, they would not be used as wheel bearings in cars. With open headstem ball races the load is taken along the fork line as you say, however the bearings do not share the load ... the lower races are forced toward each other while the upper races are forced apart, except of course during wheelies
 

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I see what you are saying, but wheel bearings are used to take huge rotational loads and a lot of friction.

Ideally you would want 2 standard ball race bearings on the spindle for rotation and stability and then torrington bearings top and bottom (flat needle roller bearings).
 

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Discussion Starter #8
not a bad idea. of course the tapered thrust bearings are not a perfect answer to the problem, but they are a good compromise. What I have found in the past though, is that normally no bearing company make a standard tap' thrust race that match the headstems inner & outer diameter requirements, and all the performance bike part shops around used to import special kit bearings for them which are made up from 2 different bearings (inner from one set outer from the other) or they would supply a bush if they couldn't match the inner to the stem. None of these performance shops seem to carry that sort of thing anymore, propably because there are so many models now they cant keep up. Don't get me wrong though, I only started using the thrust bearings because they were easier than the ball type to install, and quite a bit cheaper, because in the days of my Mach 4 & Z900 riding, you had to go genuine for the standard race, but I quickly found (especially on the track, with the Mach 4) that the tap' thrust sets cut out near all of the front end chatter
 

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I tell you one thing that occured frequently years back,more by accident than intentionally, you would reassemble the headstock and lose a bearing or two and from that day on the chatter went away and the bikes turned easier, I guess the balls had more room to move and wouldnt stay in the same position for too long , relieving the bearing of having dents worn in it.

They have applied that to modern free running ball races and now there is a larger gap between each ball.

The thing that bothered me about the taper bearings is getting the preload just right and once they had bedded in the only way to adjust them was to machine or shim the spacer tube , if you are 0.001" out of tolerance they are as loose as hell or too tight.

If you get them just right then they will do a good job, its getting them just right which is a pain.
 

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Discussion Starter #10
This is not how they are set up. There is no spacer. The outer race of each bearing are fitted into the top and bottom of the frame neck exactly the same as the open ball race part (into a factory machined recess. You then fit one of the inner races to the base of the stem (at the bottom triple clamp) exactly as you do with the ball race. you slide the headtem up into the frame and your lower bearing is done. Next step you slide the other inner race over the stem from the top... fit the top clamp and tension it down. All exactly as you would a stock ball set. Its a piece of cake to do and you never lose any bearings. When I do mine I will post the pics. The tensioning is the same as a front stub axle type car bearing ... the outers are spaced by the hub, or in the bike case they are spaced by the frame head. This really does work a treat... never fails and no problems.
 

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Thrill, I am not doubting you at all , I am just saying that to get preload correct there should be a positive stop to stop the bearings getting buried in the outer race.

All the tapered bearings on our race cars and any other application I have worked on have a spacer between the two inner races to control the thrust, same as the inner wheel spacer on the bikes front and rear wheels.

I am just being a little picky , if you are going to take the time and effort to improve the steering by doing this you will still be reliant on how much preload you get dependant on how tight you do up the nut, if you had a correct size spacer then the bearing would act like your rear wheel bearing, no matter how tight you do up the nut the bearings are always loaded the same ,as the inner tube holds the inner races in the correct amount of preload (until you squish the tube of course).
 

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Discussion Starter #12
I see your point. However the spacer that you mention should then also be used in standard headset bearing setups. Also in passenger car wheel bearings, which take a lot more abuse than bike head stems. When u set them up the lower bearing is already preloaded when the weight of the bike is on it. all that is required then is to remove any play at the top.... exactly the same as adjusting a car wheel bearing. Personally, I have never seen spacers used between tapered thrust bearings, only between ball bearings (as you mentioned the front & rear bearings on bikes). Thrust bearings are designed to take thrust, and spacers between them could possibly not allow them to function properly.
 

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We use Timken taper rollers in all our uprights and preload them with spacers , it also shares the load between the 2 inner races so when you have an uneven load , i.e sideloadings on wheels under 2 g ,the thrust is still equalised so the outer bearing doesnt get buried , it would work the same way on the headstock, the inner races keep the dimension of the assembly without overloading any particular side and the spacer takes all the weight.
 

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Discussion Starter #14
this does not work in headstems as the thrust bearings are axially opposed to each other. Only one bearing at a time deals with axial load... ie top race during wheelstands, bottom race under normal loading (weight). The system you are used to must have the tapers running in the same direction for loadsharing to work
 

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No they are opposing , but if you imagine the upper and lower triple clamp themselves take the load through the inner races and the spacer tube as they are fixed entities .

The wheel bearings work a little different but the principle is the same.

I will dig out a drawing it may help explain my poor description of what happens.
 
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