Thorn Cycles Forum

Technical => Transmission => Topic started by: Moronic on November 08, 2021, 05:13:26 am

Title: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 08, 2021, 05:13:26 am
Note that this problem has been solved, as reported in reply 22. Over a further few hundred kilometres since then it has not rearisen. Reply 10 details the response from Thorn.

Hi to the owner custodians of Thorn mechanical knowledge.

Unfortunately my near New Mercury has developed the dreaded bottom bracket knock, otherwise known as click, which from a search of this forum seems to have no known cure.

Before I chase up Thorn mechanical support from the shop, is anyone aware of a cause and repair that has eluded my research or hasn't been posted?

My reading tells me that most replies on this topic suggest that the noise originates elsewhere. Believe me, this noise originates at the bottom bracket.

I suspected the pedals, one of which had a loose spindle. So I've replaced them with new Shimano XT.

With that cause ruled out, investigation led to successful static reproduction.

With the bike upside down, and the cranks vertical. I can generate the click by pressing down hard by hand on the lower pedal. That is, by generating torque that would rotate the crank spindle end to end.

Having done so, I can rotate the pedals 180 degrees and generate the same click by pressing down on the opposite pedal. It feels as though this returns a moving part to its former place.

Clearly there is movement available in the BB area. However, the movement is fine enough that it is not easy to observe.

Certainly: 1. It is not the eccentric moving in the frame. The securing bolts are well nipped up and if that were moving I believe I would see that movement.

2. It is not a loose spindle on worn or maladjusted bearings, as far as I can determine. I've not removed the cranks but the axle spins nicely with no discernible play. Plus BB bearing is all but new and hasn't been badly treated.

Hence, it appears movement is taking place between the bearing housing and the eccentric that holds it.

I reckon I can just about see this, but it's subtle enough that I wouldn't swear to it.

Does anyone understand the mechanicals well enough to see how this might be possible? And if so, what possinilities are there for a fix.

(Optional extra question: will damage occur or worsen if I continue to ride the bike? My intuition is that it will.)

Thanks in advance for helpful thoughts.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 08, 2021, 06:12:47 am
Okay a bit more research tells me my bottom bracket is one of these, which threads into a non-eccentric BB shell as shown in this slow but fairly clear video:

https://youtu.be/ewb8Miaksmw

Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 08, 2021, 06:27:28 am
And since a view from the bottom of the BB shows this:

(https://photos.smugmug.com/photos/i-dzpx9h3/0/05d9fb20/L/i-dzpx9h3-L.jpg)

I am going to hazard a guess that the plate between the BB eccentric and the chainwheel should be flush against the eccentric, and therefore that the BB housing on the drive side has been unscrewing itself from the eccentric.

In which case the appropriate response will be to purchase a crank puller and BB socket, pull the drive side crank, give the exposed threads a clean, and then tighten the BB housing.

Any chance I am on the right track here?

I'll talk to Thorn as it looks like a warranty issue. Not sure what they can do from the other side of the world.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: steve216c on November 08, 2021, 11:55:59 am
I think the technical term for this noise is bearing creak- but whatever you call it, it is annoying nonetheless  ;D

I don't have a Thorn, but the bottom bracket bearing creak can happen on any bike once those bearing stop working quite as they should do. I've replaced bottom bracket bearings on bikes with free sitting bearings sitting in a cup, with ball races and with sealed cartridge. The noise is the same when the bearing gremlins get to work. It is just a question of time before it happens. But it is NOT the end of the world and it is unlikely to be an issue with your eccentric. And you ruled out pedal bearing creak too, suggesting it can only be the BB.

If you can cope with the noise, then you may continue riding. If it is the bearings, the worst you can do is make the bearings and the associated noise worse. It will only damage that component more, which you are likely to need to replace anyhow.

Saying that- can you fix it?

I'm going to assume you have a Shimano UN-BB 55 bottom bracket or similar. Technically speaking, these have no user servicable parts being a 'sealed unit'.
When I purchased my 2nd hand Rohloff powered bike, there was some BB bearing creak. Not much but enough to irritate. As I did not know the size nor model of BB to order, I removed it. If memory serves, I have a Shimano UN-BB 61 which I could find nowhere as identical replacement, but I ordered 3 UN-BB 55s of same size to replace with. And I carefully cleaned the old BB to allow me to use the old BB till the new ones arrived.

Using a toothbrush, I carefully removed all the debris/dirt collected on the chainwheel side. Holding the BB at an angle where no liquids could get in, I then dipped the toothbrush in terps to thin and cleaned the area as best as I could so that no residual dirt could be seen. I then tried packing as much lithium grease (marine grease or alternative grease would probably work too) around the chainwheel side and  non chainwheel side where the axel meets the housing of the BB. I used the Shimano removal tool to try and push against the grease evenly in the hope that some would get into the sealed unit gaps or, at the very least, stop further ingress of additional debris.

After refitting the old BB, I carefully filled out additional grease where the tool at removed it when refitting.

And that BB creaking stopped for about another 3000km after 20-30km of riding must have drawn enough new grease into the sealed unit.

Very slowly, it did gradually develop a bit of play, not discernable at the time the noise first became apparent but eventually easy to spot. But when that noise did return, I just switched it for one of the UN-BB 55 brackets which had arrived soon after my experiment but which had been sitting for around 4 months while I continued to ride on the 'fixed' bracket.


There are youtube videos on alternative ways to open up a Shimano BB, but my method was pretty non invasive and worked for me. You may even be able to clean and repack crease without removal of the BB from bike just from the chain wheel side.

You've got nothing to lose by giving a clean and grease if you are going to have to replace it eventually anyway. I know the BB-UN 55 is hard to source in 'Thorn' size. Be wary of the entry level alternative replacements. I did that once on another bike, and it was worn out within 3-4000 km. There is the fabled Phil Wood BB, but a decent quality alternative that is not entry level might be enough to keep you creak free for a few more years.

Good luck!





Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: mickeg on November 08, 2021, 02:24:40 pm
Do not try to just tighten the bottom bracket from the drive side.

Before I remove a crank arm, I like to mark the crank arm and bottom bracket spindle so that I put the arm back on the spindle the same way as it was before.  This probably is not necessary these days with computer controlled manufacturing, but decades ago I had a spindle that the square taper was really rectangular, not square, and I had a problem re-fitting a crank arm that had deformed to fit the crank only one way.  If you do not want to mark them, skip this step.

Remove both crank arms. 

Loosen the non-drive side bottom bracket bushing.  One side is left hand thread, I do not recall which but it might be this side.  Probably does not need to be fully removed, but you might want to.  The point here is that if the non-drive side bushing is in too far, the drive side can't be fully tightened.

Then you can tighten the drive side, but if I was doing this I would first remove the drive side completely and try to figure out if it came unthreaded on its own, or was there some reason that it was not threaded all the way in the first place.  In other words, inspect the threads.  I usually grease my threads before I assemble.   I usually do not use a torque wrench on this, but if it really did loosed by itself, you might want to use a torque wrench.

Then install and tighten the non-drive side.

Then put on the crank arms.  When I do this at home where I have a torque wrench, I ususally use that.

And if the pedals were off, re-attach.

I am assuming you can re-use your bottom bracket.  If you need a different one, I am not sure if the Mercury is 68 or 73mm width.  My Thorn Nomad Mk II uses a 73mm width bottom bracket.  Before you order one, measure your old one to make sure you order the correct one.

I do not know if you have a crank puller or not.  And I do not know where you are located.  If you are in USA, I like the XLC crank puller for touring because it is small and most important it uses a 15mm open end wrench, thus a pedal wrench works with the XLC.
https://www.ebay.com/itm/223058360956
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 09, 2021, 08:07:06 am
Thanks for the responses, gents. The bottom bracket is a VC Components BC in 73mm, as in the video I posted a link to. One of these:

https://www.vitalmtb.com/product/guide/Bottom-Brackets,25/VP-Components/VP-BC73,14278

I wandered into a local bike shop today for a crank puller and BB tool, and was kindly given extensive and relevant advice. It appears the chain side BB carrier is indeed meant to be tightened against the BB - or in this case the eccentric - in which case mine has or is unwound significantly.

Hard to know how that would have happened. I seem to recall being surprised when the bike arrived that the carrier wasn't flush, but as I was ignorant of modern BB design thought it must have been set that way. OTOH it is hard to attribute such an oversight to the Thorn assemblers, given how neatly everthing else was prepared.

Having ascertained that likelihood, your replies make lots of sense to me and are helpful.

So it sounds like I pull the cranks, unwind the chain side carrier a few turns, give the threads a clean and regrease, unwind the off side carrier a few turns, wind in the chain side carrier until it is good and tight, then wind in the off side carrier until it snugs up against the internal housing. Replace the cranks and I should be good to go with no knock.

I'm surprised how little a replacement sealed bearing unit would cost - from memory under 20 pounds on the Thorn invoice and about $35 over here. The local shop pulled out a Shimano unit to demonstrate the componemts and even it was only $55. The Shimano unit came with Loctite or similar preapplied, so unwinding by implication is a common problem.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: JohnR on November 09, 2021, 08:54:35 am
Thorn used to use a Shimano UN55 bottom bracket but Shimano stopped making them so Thorn had to find other compatible parts and have got a range of compatible products (73mm length 107mm) listed at https://www.sjscycles.co.uk/square-tapered-other/ . Eventually they'll find out which is the best of the alternatives. Did you report your problem as it's clearly a black mark against the VP components product? When you do the maintenance check for threadlocker.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Andre Jute on November 09, 2021, 02:01:21 pm
Moronic says:
Quote
I'm surprised how little a replacement sealed bearing unit would cost

I think it is very likely that most bottom brackets owe all but a fraction of their retail price to branding and promotion rather than to development and materials and manufacturing cost.

Check out, for instance, the Stronglight JP400 sold by SJS for STG15:

https://www.sjscycles.co.uk/bottom-brackets/107-stronglight-jp400-plastic-cups-sealed-bearing-square-taper-bottom-bracket/?geoc=IE

They don't have it in your size but this mechanically superb bottom bracket is made by Kinex, bearing specialists in the Czech Republic, and branded for anyone who buys a big unit load, and sold around the world at surprising prices, low and high. It comes as a standard fitting on Eurobikes from the very top drawer, manufacturers who test every component compulsively. It's on permanent sale elsewhere in Britain for a tenner, and under other brand names than Stronglight has been under ten Euro on the Continent many times. It is made with a choice of plastic cups, as in the one SJS offers above, aluminium cups, or steel cups. The plastic cups aren't just for weight weenies: one manufacturer told me they fitted the plastic cups after their outside test engineer advised them that the small amount of movement the plastic cups permit is desirable for the longevity of the threads in the BB and for the exclusion of moisture because the fit is permanently tighter (presumably for the lifetime of the BB -- I didn't think to ask because these people don't sell anything you can't pass on to your grandchildren unless it is deliberately intended to be replaced at some specified interval). I was surprised to hear the high-buck, high-reputation names of some of the bottom brackets this single-euro (in wholesale bulk) BB beat out in a tough lab. I've had it on several bikes and it just soldiers on; I eventually went to the Shimano UN55 to get an axle length which suited a desired tread width, because Shimano stopped making the UN26, the previous Shimano value champ. A Kinex BB I took off and gave to someone else and fitted for him to ensure the job was done right is still working well after years of abuse like being parked outside in the rain for months.
(https://www.sjscycles.co.uk/images/products/medium/22940.jpg)
It's probably fair to say Kinex occupies the place Europe that Tange occupied for decades in the Far East, as the makers of everyone else's branded bottom brackets. The Tange BBs under their own brand that SJS stock in a fair size range are near the bottom of the page JohnR referenced.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: mickeg on November 09, 2021, 08:12:08 pm
...
So it sounds like I pull the cranks, unwind the chain side carrier a few turns, give the threads a clean and regrease, unwind the off side carrier a few turns, wind in the chain side carrier until it is good and tight, then wind in the off side carrier until it snugs up against the internal housing. Replace the cranks and I should be good to go with no knock.
...

Yup.  But, keep in mind that one side is left hand thread.  Unfortunately I do not recall which side, I always manage to figure it out so quick that I don't remember which.

I assume you have the tool that fits in the bottom bracket.  Those tools are cheap.  Mine fits on a half inch drive ratchet.

I think it was about five years ago, I had a clicking noise in the bottom bracket area.  Changed pedals, tried lots of other things, nothing fixed it.  So, decided to change bottom brackets, and that was when I discovered that my non-drive side bushing was tight, but not tight enough.  When I went to unthread it, it came loose much easier than it should have.  So, instead of replacing bottom brackets, I tried tightening up and reassembled.  And that fixed the clicking noise.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 10, 2021, 09:47:35 pm
Thanks again guys. Interesting background, Andre. John yes I emailed Thorn Monday. Haven't heard back so I'll likely phone them today. Don't really want to work on the bike till I've had a conversation with them.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 11, 2021, 10:57:38 pm
Had a an amiable chat with Robin Thorn. He apologised for what was likely not enough tightening by the assemblers. The fix is as above, although he suggested removing the drive side cup, cleaning it and the mating threads and applying some thread locker before reassembly. He observed that even if threads had been damaged through being ridden loose, on a Mercury the threads were in the eccentric rather than in the frame, and so could be wholly refreshed with just a new eccentric. Obvious but I hadn't thought of that.

Not sure what I think of the Loctite idea. That would mean tightening a big fine steel thread dry into aluminium, on a part of the bike that's exposed to splashes. Otoh lubing the threads invites a repeat loosening. I suppose if Shimano supplies its BB with threadlocker preapplied, thats the direction to take.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: JohnR on November 12, 2021, 08:21:49 am
Not sure what I think of the Loctite idea. That would mean tightening a big fine steel thread dry into aluminium, on a part of the bike that's exposed to splashes. Otoh lubing the threads invites a repeat loosening. I suppose if Shimano supplies its BB with threadlocker preapplied, thats the direction to take.
I use threadlocker as a matter of course on everything except the pedal spindles (which get grease) to reduce the risk of vibration causing things to work loose. It's possible that whoever assembled the bike was so used to using the Shimano UN55 with some pre-applied threadlocker that they omitted to apply some when using a different bottom bracket. There's a description of the different grades at https://www.henkel-adhesives.com/uk/en/insights/all-insights/blog/difference-between-threadlockers.html. Keep away from the red stuff and you'll have no problem with disassembly in the future.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: mickeg on November 12, 2021, 09:19:59 am
I am not sure which country you are in, if you are in USA, this is what I bought last time I bought some thread locker.
https://www.truevalue.com/6-ml-removable-blue-thread-locker-1

There are lots of brands, I wanted a small bottle that was cheap and that was what I saw at my local hardware store.

Note that it says removable.  I think blue is a common color code for removable, it says blue on the package even though the bottle is red.

Shake well before using.  The tip on the bottle can clog, I keep a paper clip attached to the bottle with a rubber band to use to unclog the tip.

After several occasions on tours where I met people that lost rack bolts or some other important fastener, I have started to carry a small bottle of that thread locker on tours.  But lately most of my tours were on my S&S coupled bike, so I was installing and removing racks at the start and end of the tour.  Thus, I primarily carried it to use on my own bike.

I use that thread locker on all rack bolts, bolts on cantilever brake posts, kickstand bolts, recently added shoe cleat bolts to that list too.  But use grease on water bottle cage bolts, seatpost bolts, stem bolts and just about everything else.  I usually have used grease if it was a steel and aluminum interface, such as an aluminum bottom bracket thread on a steel frame. 

Dave W, formerly of SJS had commented that dissimilar metal corrosion can be an issue with Rohloff drain screws, so I started adding thread locker on those.  Apparently I use the wrong thread locker as the one I use he says is soluble in oil, but I continue to use that thread locker on my Rohloff drain screws, which i continuously re-use.

Some bike shops do not even have a bottle of thread locker in the shop, they just tighten things way too tight, some mechanics use a lot of grease and some use too little.

Grease is a very viscous fluid, so it can also function to reduce the chance of a loose bolt from vibrating loose.  So, even though grease is a lubricant, it can help prevent loss of some fasteners.

Some times specifications say to use grease or threadlocker, but sometimes they say not too.  But I think most people working on a bike never bother to read any such specifications.

I am not saying that what I do is best, just describing what I have settled on doing after decades of wrenching on bikes, mostly my own but I also worked in a bike shop before I went to college.

If you have an interest in learning more than you ever wanted to know about greasing threads, an interesting discussion in part of this post on that topic.
https://www.velonews.com/gear/tech-wearables/technical-faq-velon-transponders-greasing-fastener-threads-and-warm-shoes/
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: PH on November 12, 2021, 10:14:51 am
Glad you got a response from Thorn,shame if it was an assembly error, but on one's perfect.
Shimano have pretty much relegated ST to the cheap end, they don't make any higher end ST chainsets so it's unsurprising they downgraded the BB as well, add to that the less common width and there isn't a lot of choice. I've been swapping to high end IRD when mine need replacing, 10 year guarantee and the bearings are replaceable, I'm hoping they'll be the last BB's I need.
Park Tools recommend  threadlock, or if you haven't got that, anti-seize paste, or if you haven't got that grease - Mainly they're telling you not put it in dry! it's a bit of an odd one, because they also tell you to tighten to the recommended torque, but that will vary depending on the thread treatment.
I use Copperslip and have never had a BB loosen or seize, but I also remove and re-apply on an annual strip down service.  I save threadlock for those things I don't intend to disturb, racks, bottle cages, light fittings.  I see no reason not to use threadlock on the BB, just for me it's easier to clean and re-apply Copperslip.
A BB in a EBB shell is better protected than one in a frame, it only has to deal with what's coming at it from the crank side not internally, I once removed one from another touring bike and a cup full of water poured out!
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: lewis noble on November 12, 2021, 10:47:07 am
Well done for getting it sorted, and Robin for giving clear advice.

Threadlock vs copperslick . . . . . I used to put threadlock on pretty well everything, cycling and non-cycling bolts - but found that some became too hard to undo if needed - too many rounded nuts and bolts.  Probably I used the wrong grade of threadlock.

So now, on all of my bikes,family bikes etc, I use copper slick / copper grease on pretty well everything, rack, guards, stem bolts etc., and nothing has ever worked loose, I suspect because the threads 'seat' better and over the whole of their surface.  No problem in undoing them however wet they get / exposed they are.

Not expensive, small tube in toolbox lasts for ages, usually starts leaking or gets squashed before it runs out.  And if repairs need doing on tour, no problem and no need to take the tube, as enough grease stays on the threads for 2 - 3 dismantlings at least. 

Lewis

Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: John Saxby on November 12, 2021, 02:48:18 pm
+1 on Loctite/Permatex/whatever blue

Elsewhere, I read a comment by Jan Heine, who recommends a light smear of beeswax plus correct torque settings.  Haven't tried beeswax yet -- still have tubes of Loctite blue -- but pure beeswax is not so easily found in my neighbourhood.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: mickeg on November 12, 2021, 05:59:29 pm
... but pure beeswax is not so easily found in my neighbourhood.

In my part of USA there often are what are called "farmers markets" where once a week people show up to sell stuff at a small stand.  Often includes bakers, organic vegetable growers, flower gardners, etc.  And at some of them you may have someone selling honey, and chunks of beeswax.  I got a chunk of beeswax at one of those, but never tried it on a bike.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Danneaux on November 12, 2021, 08:00:33 pm
I have been a longtime (40+ years) user of beeswax and found it worked well as a threadlocker, especially in bottom bracket cups (in steel frames), threaded steerers, and bottle cage machine screws.

The secret is to pre-knead the beeswax before application. Kneading it -- working it thoroughly between one's fingers, like pulling taffy -- changes the texture of the wax from dry and crumbly to more of a spreadable semi-solid. It is well worth the effort and I have found it to be a good barrier to the formation of rust in threads where it has been applied. It needn't be "pure" but I have found it best to get the filtered kind that does not include wings and legs and other large inclusions as it is easier to knead, more consistent to apply, and does a better job of filling gaps and the valleys between threads.

Best,

Dan.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: John Saxby on November 13, 2021, 04:12:37 pm
Quote
the filtered kind that does not include wings and legs and other large inclusions

Thanks, George and Dan.  I'll check out those options.  I regularly use beeswax as a hand & skin cream, but that usually includes additives such as olive oil & jojoba bean, I assume to keep it smooth & easily applied. (The best I've found in that respect is in 'Straya, though it's a bit far to go...)

Bees, including honey bees, are under siege in Ontario -- the provincial gvt has allowed farmers to use pesticides which include neonicotinoids, and although that's being contested, the policy remains in place.  :(

Cheers,  J.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: mickeg on November 14, 2021, 12:11:11 pm
Bees are having a tough time, just about everywhere.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Andre Jute on November 14, 2021, 05:06:02 pm
+1 on Loctite/Permatex/whatever blue

Elsewhere, I read a comment by Jan Heine, who recommends a light smear of beeswax plus correct torque settings.

I'm not surprised at Heine's recommendation.

Beeswax is well known to oil painters as a drying oil, a substance that hardens in contact with air to form an immovable but, for artists more to the point, an impenetrable layer on whatever it is applied to. My friend Marialena Sarris, a Greek watercolorist, applies beeswax (in an artists' formulation, very pricey) over her larger paintings which will hang in galleries to protect the surface without the interposition of glass, among other advantages. The grade of beeswax sold at art and craft stores as pellets is the one you want, and is pure enough; this is presumably what Dan describes using for 40 years in a post above.

The most common drying oil in the art world is linseed oil, available in many versions but the cheap plain version sold in art stores is the one cyclists want. Take care not to buy anything with resin in it to aid faster drying. Linseed is not a new recommendation: the late Jobst Brandt and Sheldon Brown also liked linseed oil for setting bicycle spoke nipples. I find linseed oil a bit slow setting for my oil painting, so I don't have any (except a special formulation which is water-miscible and -soluble that you absolutely do not want near bicycle threads you want to stay put!).

Don't use the cold or liquid wax sold in bicycle shops for chain maintenance; it has all kinds of cleaning chemicals in it which also makes it non-sticky to metal, so that it falls off, carrying impurities with it.

Here's an alternative recommendation from me: Walnut oil from the supermarket is a pure ingestible grade and cheap, a couple of sponduliks for 250ml which will last forever -- well, that's if your family doesn't grab your bicycle setting oil for salad dressings. Mine is particularly popular because it is smokey to make my bike smell good as well as look good, just like my paintings. Do not buy your walnut oil at an art store: it may have resin in it, which will set that thread so hard, you'll deform the frame trying to get it out. In any event, art store walnut oil is several multiples the price of the same oil at the supermarket. Walnut oil is also cleaner than linseed oil, in that it attracts less filth. Note that my recommendation of walnut oil, especially the smokey one, makes a thin, pale green-brown ring around the screw, so that if you can see the screw's open end, you can tell in what condition your locking agent is, which is useful on critical fasteners for those of us who don't do annual or biennial disassembly maintenance.

If cleanliness is your thing, a pale, very clean drying oil is poppyseed oil, used for setting white and light colour oil paints. It doesn't discolor (to yellow) like linseed oil, or show a base tint like walnut oil, and it isn't yellow-white like beeswax. However, it is the slowest of the main setting oils to set, so it may be a couple of months before your screw is truly locked.

For those of you who will now wander into art stores to see what else is useful for cyclists, the oil paint varnishes will also set your bike's screws -- forever. Stay away from them, even if the bottle or can doesn't list "shellac" among the ingredients. And it doesn't matter whether a resin is synthetic or "natural, rubbed on the thighs of African virgins", you don't want anything with resin near your bike except in the paint on it (where it is probably illegal these days).

All the recommended drying oils in this post are for threads you don't want to shift until you deliberately apply considerable loosening torque to them.

I don't even have a tube of general "blue" threadlock, or the Rolloff-friendly stuff Dave told us comes from the factory on the Rohloff service stud. However, these drying oils aren't so smart on the Rohloff stud because eventually bits of hardened drying oil will break off and fall into the gears. I reuse studs until the factory application has worn off, then start a new stud. No leaks on my Rohloff.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: John Saxby on November 14, 2021, 11:15:12 pm
Thanks for all this, Andre.  With winter about to set in, The Tweaking Season is near upon us.  Now the screw-fixing compounds have a très chic & helpful coloration index as well.  Before the snow really sets in, I'll wander the High Street of our part of Ottawa (that's Richmond Rd, named after the old route to the nearby village of the same name, in turn named after a dissolute English aristocrat who died of rabies 200 years ago, although rabies might've been explanatory cover to attract sympathy and deflect attention from a prolonged commitment to alcohol -- but I digress) checking sources for walnut oil and art-store beeswax pellets.  Both have a whole lot more je ne sais quoi than Loctite, that's for sure.  ;)

Cheers,  J.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on November 26, 2021, 12:23:19 pm
Thanks again for the wealth of info in the replies.

So I've bought the tools, pulled the cranks, loosened the non-drive cup, loosened and cleaned the drive cup, tightened the drive cup, tightened the non-drive cup, and test ridden over 50-odd km.

Everything works as it should. Im loving my new XT pedals.

What a bike!
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: RobertW on July 25, 2022, 01:13:09 pm
I too have experienced a knock/clonk from the drive train - which seemed to come from the bottom bracket area - this can be felt through the pedals.  This is a Mercury Mk 2 frame with mini EBB.  New in Feb 2022 and seemed to start within 1000 miles.  Pressing hard by hand on the leading pedal could get a distinct 'clonk', spin the cranks 180 degrees and press on the leading pedal again generated the clonk.  While riding for a while it could also occur once on back pedalling and also if spinning a light gear (presumably when chain was under variable tension).

There seemed to be no movement in the cranks/bottom bracket.  The EBB securing bolts all seemed tight.  The chain is hardly worn about 1mm 'stretch' over 10 whole links (254mm) and degree of slack in the acceptable range given in the Thorn user guide.

Following the discussion in this thread I have removed the cranks and bottom bracket, regreased with Copaslip and reassembled.  After a 50km ride the issue seems to have been resolved.  There might have been the slightest trace of movement in the fixed cup - though this might have been the tool slipping.  Otherwise everything seemed OK.  The EBB shell showed a witness mark from the fixed cup over part of the circumference and the bearing on the other wide showed marks over part of the circumference.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on July 27, 2022, 02:50:20 pm
I'm glad the thread was helpful, Robert.

You experience makes me wonder whether there is a systemic issue in the assembly process at Thorn. It sounds uncannily similar to mine.

How did you manage to purchase a Mk 2 Mercury new this year?
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: John Saxby on July 28, 2022, 05:56:53 pm
Guys, your resourceful and successful sleuthing merits my highest compliment:  this story could serve as an illuminating example to be inserted somewhere in the website of St Sheldon Brown! (Here FYI, in case you haven't come across it already: https://www.sheldonbrown.com/ (https://www.sheldonbrown.com/))

Cheers,  John
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Matt2matt2002 on July 28, 2022, 09:41:36 pm
Nice thread.
May I ask what you used to remove the cranks?

I can slide my Raven EBB out a little either side but not completely.

Best

Matt
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: UKTony on July 29, 2022, 07:30:06 am

How did you manage to purchase a Mk 2 Mercury new this year?

There are still predecessor frames to the mk3 for sale on the Thorn website albeit the sizes/colours available are limited. I wouldn’t be surprised if one of the reasons why the Mk 3 isn’t likely to be restocked for some time  (if it ever will be) is that they want to clear out more of the older model first. The discount on the older frames is only £50 at the moment.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: PH on July 29, 2022, 08:25:21 am
... the Mk 3 isn’t likely to be restocked for some time  (if it ever will be)
The idea of that is making me re-consider selling my "Spare" Mercury frame.  Though I have no reason not to think the current one will outlast me, you never know... I might bubble wrap it and pack it under the bed!
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Moronic on July 29, 2022, 02:52:08 pm
Nice thread.
May I ask what you used to remove the cranks?

I can slide my Raven EBB out a little either side but not completely.

Best

Matt

If that's a question for me, Matt, I went into a bicycle shop and asked for a crank pulling tool and a bottom bracket extraction tool.

The crank puller has an external thread which matches an internal thread on each crank arm. It also has an internal thread which carries a matching hreaded slug. You screw the tool into the crank arm, then wind in the slug. The slug presses on the outer face of the crankshaft and pushes the arm off its taper.

The bottom bracket extractor, a separate tool, has external teeth that engage with internal teeth on the bottom bracket housing.

PH, yes if I had a spare Mercury frame in my size I would be motivated to hold onto it. Especially if I had already crashed one and been lucky enough to bend only the fork. However, I've a suspicion Thorn has ordered a new batch of Mk 3s, simply because their recent advice on a little-used Mercury on their website said that for an equivalent new the wait time woukd be about 18 months.
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: UKTony on July 29, 2022, 03:57:17 pm
simply because their recent advice on a little-used Mercury on their website said that for an equivalent new the wait time woukd be about 18 months.
Well spotted! 🙂
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: Matt2matt2002 on July 29, 2022, 05:19:14 pm
If that's a question for me, Matt, I went into a bicycle shop and asked for a crank pulling tool and a bottom bracket extraction tool.

The crank puller has an external thread which matches an internal thread on each crank arm. It also has an internal thread which carries a matching hreaded slug. You screw the tool into the crank arm, then wind in the slug. The slug presses on the outer face of the crankshaft and pushes the arm off its taper.

Yes, it was & thanks for the reply.

I think I'll leave it to  LBS given my limited mechanical abilities.

Best

Matt
Title: Re: Thorn Mercury Mk3 bottom bracket click or knock - any solutions?
Post by: RobertW on August 20, 2022, 06:11:51 pm
I'm glad the thread was helpful, Robert.

You experience makes me wonder whether there is a systemic issue in the assembly process at Thorn. It sounds uncannily similar to mine.

How did you manage to purchase a Mk 2 Mercury new this year?

Apologies for delayed reply, I don't come here very often.  The Mk 2 was 'old stock' with a bit of discount - there was no stock in Mk 3 in my required 610L size and at best a very long wait before they had new frames.  The Stealth Black paint job has seemed very resilient so far.

The Thorn cranks came of the square taper BB quite easily with a Park CCP-2 tool.  The BB just needed a standard splined tool to fit and a big spanner (plus remembering which way each cup is threaded).  To put it back together just needed an additional long-handled 8mm allen key. I did not touch the EBB.

Probably done 200 miles since this fix and all still seems nice and 'clonk' free.

Robert