Replacing Hollowtech II Bearings

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CyclingSi
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Re: Replacing Hollowtech II Bearings

Post by CyclingSi »

The Shimano bearings are made of cheese it would appear I have found little to last like the old UN72 units, if their hubs are anything to go by then there will be very little grease in the bearings which does not help. I can heartily recommend the Hope Stainless HT2 bottom bracket though, I have had one on my mountain bike for 2 years, still as smooth as the day I fitted it and the bearings can easily be replaced, I will be getting one for my commuter/tour bike when the stock one fails.
Brucey
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Re: Replacing Hollowtech II Bearings

Post by Brucey »

CyclingSi wrote:The Shimano bearings are made of cheese it would appear ...


The lack of grease as standard is not a help, hence the suggestion upthread.

It would surprise me greatly if your 'cheese-like' failed bearings didn't manifest clear signs of water ingress on close examination.

cheers
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byegad
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Re: Replacing Hollowtech II Bearings

Post by byegad »

My HollowtechII bearing failed on my Kettwiesel. Rarely used in the wet and the BB is above the frame mounted above the front wheel, which has a mudguard and under a fairing. 4500 miles and they were well shot. They are cheap enough and very easy to replace but that's shockingly poor durability.
"I thought of that while riding my bike." -Albert Einstein, on the Theory of Relativity

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Brucey
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Re: Replacing Hollowtech II Bearings

Post by Brucey »

well there are plenty of things that can kill them;

- poor alignment
- incorrect preload
- poor lubrication
- water ingress.

The last two can be deadly; one dose of water can be enough.

If anyone wants a second opinion on the likely cause of bearing failure please post some close-up photos of failed bearings that have been opened up.

cheers
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meic
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Re: Replacing Hollowtech II Bearings

Post by meic »

Brucey wrote:
robc02 wrote: .... then flooding the spacer tube with heavy oil or semi fluid grease would be a good idea. A good way to do it would be to push the axle about 2/3 way through, squirt in the oil/grease, and then push the axle the rest of the way through. It would keep a constant supply of lubricant to the bearings and seal lips, and would be easy to refill.


yes, exactly; and on shimano ones turning the bearings so that both seals are on the outside makes perfect sense for a scheme like this. If you lay the bike on its side when adding the lube, it should be possible to get loads of lube in there.

I think that if the right lube is used ( a semi-fluid grease I reckon) and there is usually a little leaking out, no water will get in, and even standard shimano bearings -once turned- may last for years like this.

cheers


Wouldnt this have to be done after wearing out the bearings and while replacing with new ones, as driving them out will ruin them?

I keep seeing reference to semi-fluid grease but I dont know which grease is semi-fluid, I havent seen it written on any tins, could you give some examples please?
Preferably cheap ones. :lol:
Yma o Hyd
Brucey
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Re: Replacing Hollowtech II Bearings

Post by Brucey »

I have removed bearings from shimano cups without damaging them. The trick is to use a drift that bears against the whole back of the bearing, so loading all the balls at once. If you warm the assembly (e.g. with boiling water) then the bearing will come out really easily; they are fitted to the cups with a soft bearing fitting compound.

Semi-fluid greases are rare wee beasties. The problem is that greases are usually rated for 'consistency' and the NLGI grades (or similar) are typically assigned by seeing how far a shaped weight will penetrate into freshly-worked grease. NLGI #0, #1, #2 are greases of increasing thickness and a #2 grease is mostly what you get in a tub from halfords. This rating system is OK but says nothing about how easily the greases will separate, or indeed how thixotropic the grease is. Thixotropy is useful because it means that you can have a grease that sits there and doesn't move when not in use, but is nice and fluid when it is being worked. Most greases are thixotropic to some extent but for bicycle use if the seals are OK there is almost no such thing as too much thixotropy.

A cheap option is the stuff that is used in land-rover swivels. However this wasn't what I wanted for some jobs and after failing to find anything that was just right I decided to make my own. So now I have some stuff now that has a consistency that is a bit like tomato ketchup, but is a super lubricant. So far everything I have lubed with it has stayed lovely for years at a time.

cheers
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MisterTea
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Re: Replacing Hollowtech II Bearings

Post by MisterTea »

Shimano hollowtech BBs are renowned as being made from cheese, and in the off road community here in the harsh gritstone peaks they last about 3 months of use before seizing.

The only hollowtech BB that seems to work and work well is that made by Hope. (Even blingbling Chris King units fail within 1year around here) Hope are fully serviceable with basic tools, well sealed and you can easily (carefully) flip the seals out to regrease. Takes me about 15 mins to service one. Hope sensibly design theirs with stainless bearings (or the expensive ceramics if wanted) and I have 3 of their units on bikes right now, the oldest has been running through the harshest winter off road riding for the past 5 years with never a problem. Just an annual top up of grease and bingo, smooth as butter. Extra bonus is that Hope bearing units are easily replaced if you ever need to replace a bearing.
freeflow
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Re: Replacing Hollowtech II Bearings

Post by freeflow »

Can I check if I've understood correctly some of the things I read here regarding lubrication. All of the Hollowtech II BB I have are fitted with a tube which goes between the two cups. This tube has gaskets at either end which I assume is to seal the inner side of the bearings from water ingress via the seat tube or the screw hole for the BB cable guide. The chainset axle goes down the center of this tube. My understanding is that if I add oil to the inside of the tube this will facilitate lubrication of the inner and outer seals and thus enhance the life of the bearings. I'm just about to install a Hope BB and Ultegra chainset on my winter bike so am thinking this would be a good idea as I have a bottle of Halfords chain oil which was a failed buy as its far too messy to actually use on the chain but could be ideal for BB lubrication.
Brucey
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Re: Replacing Hollowtech II Bearings

Post by Brucey »

Yes that is it more or less. But the chain oil will have to penetrate through the inner bearing seals on an unmodified bearing unit to get into the bearings and thence the outer seals.

In the event that the inner seal is effective and the outer seal wears first then the unit could still fail as normal.

In the event that the inner seal is a bit leaky the lube will penetrate the bearings and the assembly should last fairly well until all the lube leaks out (if it is always runny) or until it ceases to move freely inside the bearing unit (e.g. because the lube has 'set' which some chains lubes do). After a few months I'd suggest inspecting and adding more lube.

BTW the experience in industrial applications is that stainless steel bearings routinely outlast conventional (1% Cr steel) ones only in applications where corrosion is an unavoidable issue. If someone can confirm the manufacturer/model of the Hope bearings we can simply look up the ratings and compare them with the bearings that are used in other OBB units.

That the Hope stainless bearings do wear out is arguably either because the water still gets in (which still increases the wear rate in a stainless bearing, but not by x100 like a chrome steel one....) or because the bearing design (in any form) is genuinely a bit marginal for the application. In the latter instance a better grease, i.e. one which is designed specifically for very highly loaded bearings operated at low speeds (which probably isn't anything you can buy in a bike shop or Halfords BTW) will benefit the life of any bearing.

In very many failed OBB units I have seen the left bearing failed first (despite seeing a lower service load) and I think the reason is that the right bearing seal area got just an occasional dribble of chain lube by accident and perhaps just a little of the crud aimed at it hit the chainset instead, When such bearings are examined the left one has to date showed more signs of water getting inside it; I'd be interested to hear the experiences of others here.

cheers
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geomannie
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Re: Replacing Hollowtech II Bearings

Post by geomannie »

When such bearings are examined the left one has to date showed more signs of water getting inside it; I'd be interested to hear the experiences of others here.


Spot-on. The left bearing of my recently replaced BB was totally shot due to water ingress, the right still in very good order. I am not sure if the accidental lube of the right bearing from accidental spill of chain lube is the reason however. I have been using dry lube on the chain and have avoided spillage onto the bike/frame as it leaves white spots and is easily seen.
geomannie
freeflow
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Re: Replacing Hollowtech II Bearings

Post by freeflow »

Thanks for the confirmation Brucey. Seems like the oil will do no harm even if it doesn't do any good. To follow up on your comments about the LH bearing there is a distinct difference between Shimano double and triple road chainsets when you look at the Shimano technical docs. The triple road chainsets have a 3mm spacer that sits between the crank and the bearing cover. Its approximately the same diameter as the bearing with only a narrow gap between the spacer and the bearing cover. This spacer doesn't appear in the drawing for the double chainsets, nor does it appear on Shimano triple MTB chainsets. It would be interesting if there is data available to compare hollowtech II bearings on triple and double chainsets to see if this spacer provides any protection. From my perspective this discussion means I'll be dribbling oil into the gap on a regular basis for my winter bike.
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geomannie
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Re: Replacing Hollowtech II Bearings

Post by geomannie »

he triple road chainsets have a 3mm spacer that sits between the crank and the bearing cover.


Having just fitted a triple I can confirm that there is a spacer but I it has no obvious sealing potential. Good if it had.
geomannie
Brucey
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Re: Replacing Hollowtech II Bearings

Post by Brucey »

I'm not sure that the spacer itself provides any extra protection for the bearing per se but the chainring above it (on a road triple) might do. IIRC on an MTB triple the assembled bearing unit is a touch wider anyway, so again the RH bearing is kind of below the inside chainring and just slightly shielded by it.

cheers
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freeflow
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Re: Replacing Hollowtech II Bearings

Post by freeflow »

I didn't make myself clear. For a triple the spacer is on the left handside and essentially provides a screen for the bearing cover so it is more difficult for water/crud to get directly onto the bearing cover and from there into the bearings. The downside is that the gap is also narrow enough to allow water/crud to be sucked into it via capillary forces. However, rotational forces also expunge the water crud. So my view is that putting oil in the gap will lubricate the lip of the bearing cover and also help to prevent water getting in. Therefore it may be that for road triples, the LH bearing may last longer than on doubles.
MisterTea
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Replacing Hollowtech II Bearings

Post by MisterTea »

Not sure that pseudo scientific hypothesising as to why things might happen are very helpful, IMO they are a distraction from facts.

Facts are clear in my observations from the 220 members of my cycling club here in the peaks, that Shimano (and most others) BB bearings are like rusty cheese within a few months of installation, and that the only BB to last in these conditions are from Hope. Simples.
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