J
jim beam
Guest
* * Chas wrote:
> "peter" <[email protected]> wrote in message
> news:[email protected]...
>> * * Chas wrote:
>>
>>> It occurred to me that a slightly loose headset could cause
> premature
>>> damage to the bearing races. A well adjusted headset in an
> accurately
>>> set up frame with a slight bearing preload should distribute impact
>>> loads throughout all of the ball bearings preventing this kind of
>>> failure.
>>>
>>> A slightly loose headset will allow movement during normal road
>>> vibration and impact shock. This can easily lead to indentations in
> the
>>> bearing surfaces especially in the front of the lower headset and
> crown
>>> races.
>> My experience has been the exact opposite. The times that I've
>> encountered indexing of a headset it has been when tightened to the
>> point of having at least some preload. OTOH, I've ridden many
>> thousands of miles with a slight, but definitely noticeable, looseness
>> in the headset bearings and have never had these develop the
>> indentations that cause indexing.
>>
>> This appears to support Brandt's contention that the problem is due to
>> fretting rather than Brinelling. When adjusted with some preload and
>> ridden in a straight line the lubricant can be squeezed out of the
>> contact zone and result in fretting from vibration without significant
>> movement. In a loose headset there will be enough movement to
>> replenish the lubricant.
>>
>
> There is no indexing in this headset yet. It loosened after only an hour
> of riding and I was musing about the cause without tearing it apart.
>
> Headsets are thrust bearings and most thrust bearings require a preload.
>
> What no one seems to address here is effect the quality of the steel in
> the races and the type and degree of hardness has on indexing. I've
> caused indentations in the races of a newly installed cheap case
> hardened headset by overtightening when replacing them on a customer's
> bike.
>
> I've only run across a few damaged bearing surfaces in through hardened
> steel headset races over 55Rc hardness.
>
> I've seen damage in most case hardened headsets. The zone of hardness
> may be only .005" to .010" thick and less than 55Rc. The steel under
> the case can be 30-35Rc or less which would easily allow indentation to
> occur.
>
> My point being, most of this discussion has consisted of arguments about
> various failure modes when the real problem lies in the bearing material
> and hardness of headset races.
>
> In addition, the old reference to false brinelling in bearings of
> automobiles being transported doesn't take into consideration advances
> in lubrication technology. Oil and grease are both liquids that can be
> easily squeezed out between bearing surfaces. Modern lubricants contain
> extreme pressure additives that create solid molecular boundary layers
> to reduce or prevent metal to metal contact.
>
> Additives like molybdenum disulfide remain in place for long periods
> without breaking down and can work when almost dry.
>
> http://en.wikipedia.org/wiki/Molybdenum_disulfide
>
> Unless someone used a very low quality lubricant in their headset like
> Vaseline or KY, Jobst's argument about lubrication failure is pretty
> weak.
absolutely. that's why we haven't had motor vehicle transportation
bearing failure in 50 years. regarding materials, vacuum degassed
steels have also proven to be highly effective in this situation.
> "peter" <[email protected]> wrote in message
> news:[email protected]...
>> * * Chas wrote:
>>
>>> It occurred to me that a slightly loose headset could cause
> premature
>>> damage to the bearing races. A well adjusted headset in an
> accurately
>>> set up frame with a slight bearing preload should distribute impact
>>> loads throughout all of the ball bearings preventing this kind of
>>> failure.
>>>
>>> A slightly loose headset will allow movement during normal road
>>> vibration and impact shock. This can easily lead to indentations in
> the
>>> bearing surfaces especially in the front of the lower headset and
> crown
>>> races.
>> My experience has been the exact opposite. The times that I've
>> encountered indexing of a headset it has been when tightened to the
>> point of having at least some preload. OTOH, I've ridden many
>> thousands of miles with a slight, but definitely noticeable, looseness
>> in the headset bearings and have never had these develop the
>> indentations that cause indexing.
>>
>> This appears to support Brandt's contention that the problem is due to
>> fretting rather than Brinelling. When adjusted with some preload and
>> ridden in a straight line the lubricant can be squeezed out of the
>> contact zone and result in fretting from vibration without significant
>> movement. In a loose headset there will be enough movement to
>> replenish the lubricant.
>>
>
> There is no indexing in this headset yet. It loosened after only an hour
> of riding and I was musing about the cause without tearing it apart.
>
> Headsets are thrust bearings and most thrust bearings require a preload.
>
> What no one seems to address here is effect the quality of the steel in
> the races and the type and degree of hardness has on indexing. I've
> caused indentations in the races of a newly installed cheap case
> hardened headset by overtightening when replacing them on a customer's
> bike.
>
> I've only run across a few damaged bearing surfaces in through hardened
> steel headset races over 55Rc hardness.
>
> I've seen damage in most case hardened headsets. The zone of hardness
> may be only .005" to .010" thick and less than 55Rc. The steel under
> the case can be 30-35Rc or less which would easily allow indentation to
> occur.
>
> My point being, most of this discussion has consisted of arguments about
> various failure modes when the real problem lies in the bearing material
> and hardness of headset races.
>
> In addition, the old reference to false brinelling in bearings of
> automobiles being transported doesn't take into consideration advances
> in lubrication technology. Oil and grease are both liquids that can be
> easily squeezed out between bearing surfaces. Modern lubricants contain
> extreme pressure additives that create solid molecular boundary layers
> to reduce or prevent metal to metal contact.
>
> Additives like molybdenum disulfide remain in place for long periods
> without breaking down and can work when almost dry.
>
> http://en.wikipedia.org/wiki/Molybdenum_disulfide
>
> Unless someone used a very low quality lubricant in their headset like
> Vaseline or KY, Jobst's argument about lubrication failure is pretty
> weak.
absolutely. that's why we haven't had motor vehicle transportation
bearing failure in 50 years. regarding materials, vacuum degassed
steels have also proven to be highly effective in this situation.