Steering head bearings (2013)

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Tintin said:
Dkt26 said:
Ouch!! Tintin, you need some ice for that burn???
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Burn? Which burn? You mean the most lame and oldest attempt of an insult known to any engineer? IMHO there is proper craftsmen, technicians and engineers on one side and bodgers on the other. TRBs with the original coarse thread nut and a tab washer is a bodge job. So how could I be insulted? :twisted:


Tim
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Put the knife down buddy. It was a joke to try and lighten the mood. A circuit breaker if you will. Looked like you two were gettin a bit testy. This is supposed to be a safe and friendly space.
Wasn't tryin to rile you up
 
LOL, I've busy and unable to add anything, but read it all. Good stuff.
The tapered roller bearings will be just fine with the original nut and tab washer. Just think about the millions of wheel bearings fit up with a course thread and cotter pin. The beauty of the steering neck and swingarm applications is that we can preload quite heavy because of the large contract area (and very little, low speed movement). This is usefull because we can snug up the steering as needed. NO inner race spacer is required, nor would it be practical in this instance.
The use of angular contact bearings in the steering neck is an acceptable mis-application of this type, again NO inner race spacer, preload to suit by FEEL. I replace these type bearings routinely as I refurbish the thrust/support bearings on ball screws used in precision machine tools. I measure and calculate the size of multiple bearings within 2 microns and custom grind the spacers and retainers to acheive the desired preload. That level of precision isn't needed, nor practical for this usage.

My original post posed the question whether the retrofitted TRB's had shown a better resistance to "the weave", based on behavior of other bikes with too little steering neck preload. My hypothesis was that, (gasp) the sealed ball bearing design was an inexpensive, easy to assemble (the inner spacer allows it to be SLAPPED TOGETHER, the nut tightened without having to worry about bearing preload, it's all set by the spacer, just the same as all modern motorcycle wheel bearings. Cheap, easy to replace and damned near idiot-proof) and replace design, however, it was flawed (GASP!) in that it provides too little to NO preload allowing the fork to flop to the lock.
My original post was gathering info, seeing if any improvements have been observed. That's all.

I truly have enjoyed all the contributors!
 
My only question to you is, can you not get preload too tight as well? Won't this induce a "Dutch Roll" in the steering?
 
MikeG said:
My only question to you is, can you not get preload too tight as well? Won't this induce a "Dutch Roll" in the steering?
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Of COURSE you can get it too tight... EVERYONE (over the age of 30) has driven an old bike with a friction steering damper and experimented by turning it TOO TIGHT. :roll: (again, read any motorcycle service manual, it will give examples of too tight symptoms) But too loose sucks almost as bad.
 
Norman White ex racer and frame and frame builder of some note converted my feather bed with TRB to the Commando BB Set up. All his race bikes use the Commando BB setup an he maintains it stop over tightening TRB which is what cause weave. He races on these round Isle of Man so that good enough for me. Also someone said near the start of all this the forks should not fall freely from side to side WRONG YES THEY SHOULD that is how the rake and trail allow the wheel to center. if they are stiff it starts to weave as the wheel cannot freely center. With the BB setup the steam nut just compresses the inner races and space between yokes so you can't over tightening them the torke figure is to stop the nut itself or stem heard being damaged as it is thin and so easily stripped. The only draw back with stock setup is once there is play the bearing must be replaced as there is no adjustment .
 
Hello Gents, I read through this topic and I remain a little perplexed. I just pulled the 2 steering head bearings from my 73 Cmdo and they read simply FAG 6205 RS, was this the incorrect bearing size? I have read at several places that it should be 6205 2RS. Which should I replace them with?
Thanks in advance, Dennis
 
NORBECER said:
I just pulled the 2 steering head bearings from my 73 Cmdo and they read simply FAG 6205 RS, was this the incorrect bearing size? I have read at several places that it should be 6205 2RS. Which should I replace them with?
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6205 is the actual bearing size and type (25 x 52 x 15mm single-row deep groove ball bearing).

"RS" usually just means 'rubber seal', although a bearing with a single seal is generally known as '1RS' and a fully sealed bearing is '2RS' so ask for 6205-2RS when ordering replacements.
 
L.A.B. said:
NORBECER said:
I just pulled the 2 steering head bearings from my 73 Cmdo and they read simply FAG 6205 RS, was this the incorrect bearing size? I have read at several places that it should be 6205 2RS. Which should I replace them with?
Click to expand...

6205 is the actual bearing size and type (25 x 52 x 15mm single-row deep groove ball bearing).

"RS" usually just means 'rubber seal', although a bearing with a single seal is generally known as '1RS' and a fully sealed bearing is '2RS' so ask for 6205-2RS when ordering replacements.
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Will do,thank you!
 
Interesting read. I'm rebuilding the front end of a 72 Interstate and just found that the PO had installed tapered roller bearings in the steering head. Based on reading this thread, I believe I understand the difference, but a question I did not see the answer to is: how do I know when the correct preload is applied to the bearings? Thanks in advance for any help.
 
Spacer tube is eliminated with tapered conversion. Set up is straight forward as you've described, tighten just until stiffness can be noted, then back off 1/8 turn.
 
concours said:
...this “Dutch roll” you speek of....
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"Dutch roll"=weave. A term my father used to use. Not sure of it's origin but considering he spent his life in the aviation field I assume it came from there. If his car needed an alignment or it wandered on the road he called that a dutch roll...or if I came in weaving on my feet from too much suds I'd get told I had it.
 
acadian said:
Spacer tube is eliminated with tapered conversion. Set up is straight forward as you've described, tighten just until stiffness can be noted, then back off 1/8 turn.
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Right, no spacer tube involved. I think I get it. Tighten till stiff, back off 1/8 turn. Bend the tab washer. Then ride it to be sure it is a stable setup. (no Dutch roll)
 
When I removed the stem and upper yoke from the steering head, the lower bearing and inner race dropped out but the upper bearing and inner race are still at the top of the stem. Both outer races are still in the steering head. With the dust cover and washer between the upper bearing and the yoke, I can't get at the topside of the inner race to push it off the stem. Is this normal? It may not be a problem since the bearing is ok and does not need to be replaced but this is not what I expected.
 
acadian said:
Spacer tube is eliminated with tapered conversion. Set up is straight forward as you've described, tighten just until stiffness can be noted, then back off 1/8 turn.
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I don't think I would be doing that personally as the lower triple clamp is not captivated by lock rings as on most applications.
There would be little to stop the lower triple moving upward besides the stanchion clamping.
Modifying the stock spacer tube would be easy, everything stays happily in place and it would mostly be more stable than a bike than came with tapered roller bearings.
I will see what I can buy bearing wise and add it to the long list of things to do even if they don't really need doing. :D
 
The early workshop manual says "Raising the front wheel off the ground as shown in Figure 34. Place the fingers of the left hand on the point where the handlebar lug meets the top part of the frame head lug"....... and continues on to adjust the bearing play so no movement is noticed at the left hand. That was for the early tapered roller bearings with no spacer. I used annular roller bearings in my 69/70, but that was what was in it when I got it.
 
Balls or tapered, no spacer tube installed: With the machine fully assembled and on the center stand have an assistant sit on the rear of the saddle such that the front wheel is off the ground. The steering head bearings are properly adjusted when a slight tap on the end of either bar end the front end should just fall to its stop, do this on both sides. Tighten or loosen, with pinch bolts loose, until both sides, with just a tad of encouragement, will just hit the stops. Tighten the pinch bolts and check again.

Take the motorcycle for a slow ride and be extremely conscience of any tendency to wander or vibrate. If the machine behaves slowly increase your speed, use the brakes, hit a few bumps; if the bearings are too tight the machine will wander or weave, if too loose the machine generate vibrations between the frame and the front end you can feel this best by putting your left hand between the upper fork yoke and the frame: readjust. If all is well bring the motorcycle back to the barn and check that the bars just fall to the stops, check again in 50 miles, but don't become complacent, it can easily kill you.

In my experience the easiest error, and the most dangerous, is not seating the bearings completely; a good hard bump may do this for you. If this happens you will be treated to a "tank slapper", if you survive the first thing on your to do list will be to change underwear, the EMTs may do this for you...

Check adjustment annually, don't ask me how I know this...

Best
 
I don't understand why any one with the later spacer tube type setup would want to change it for something else! The standard setup works great, requires no adjustment, lasts almost indefinitely. Maybe in pure engineering terms it's not ideal but in reality it works.

Taper rollers need maintenance and adjustment. The bottom nut thread is too course to make correct adjustment easy and there is no proper way to lock it in position, the tab washer is a crude way to do it. A locknut would be the better way but there isn't enough thread. I've never tried a Commando with taper rollers but I suspect they would slow the steering down. I've sampled a featherbed fitted with tapered rollers in place of the original ball races and it did slow the steering unpleasantly.

To me there are no benefits of using tapered roller bearings, only drawbacks. My 10 cents worth.

Ian
 
Nortoniggy said:
I don't understand why any one with the later spacer tube type setup would want to change it for something else! The standard setup works great, requires no adjustment, lasts almost indefinitely. Maybe in pure engineering terms it's not ideal but in reality it works.

Taper rollers need maintenance and adjustment. The bottom nut thread is too course to make correct adjustment easy and there is no proper way to lock it in position, the tab washer is a crude way to do it. A locknut would be the better way but there isn't enough thread. I've never tried a Commando with taper rollers but I suspect they would slow the steering down. I've sampled a featherbed fitted with tapered rollers in place of the original ball races and it did slow the steering unpleasantly.

To me there are no benefits of using tapered roller bearings, only drawbacks. My 10 cents worth.

Ian
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I am tending toward agreeing with you. My issue is that unbeknownst to me, this bike was fitted with what appear to me to be brand new tapered roller bearings marked 30205C STEYR AUSTRIA MA. I think previous owner believed this would bring higher performance. I don't know that the bike was ridden after being fitted with the TRB, as it sat for 20 years, partially assembled, before I purchased it. I am beginning to conclude that maybe I should bite the bullet and purchase the standard bearings and spacer and go back to the original setup.
 
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