Thompson-Gazelle and the 'Kurse of Kinex'...

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Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 14 Aug 2016, 9:02am

There are a fair number of bikes out there, (notably Gazelles, but there are others too, mostly hailing from the Netherlands or from Germany, nearly always of a 'sit-up and beg' flavour ) which use a Thompson-style BB shell into which a special bottom bracket is pressed.

Originally I think this frame design was meant to accept Ashtabula style steel cups, but with a three-piece crank/BB spindle, either cottered or square taper. Typically the RH 'cone' is part of the BB spindle and the LH cone is threaded onto the axle with a tab washer and locknut (again similar to Ashtabula). Like this (in which picture the left and right sides are swapped I think);

Image

For a low-cost adjustable bearing, this gives in a decent enough result. However the screw thread, the groove for the tab washer etc in the BB spindle often makes for a spindle that has a poor fatigue life.

On these machines the BB shell is traditionally a plain bore if the frame is steel, but if the frame is aluminium, only the ends of the BB shell are machined to the nominal diameter; the centre of the BB shell may be about 8mm smaller diameter.

There are several 'standard diameters' for the press-fit cups; I have seen 35mm, 38mm, 40mm, and at least one larger size yet (around 43 or 44 mm). Possibly there are many different shell widths too, but even without that there are bound to be variations simply because these machines are usually fitted with a chaincase, and the mountings for that are part of the BB assembly; typically there is a pressed steel bracket that is sandwiched between the RH press-fit part and the frame, or the mountings are actually integrated into the RH cup assembly. Either way there can be special parts involved.

Now, 'Trapas' is the Dutch word for 'bottom bracket'; you can get an idea of what you might be in for, if you do an image search for 'gazelle trapas' eg

http://www.bing.com/images/search?q=gazelle%20trapas&qs=n&form=QBIR&pq=gazelle%20trapas&sc=0-0&sp=-1&sk=

which shows you that there are very many types, few of them similar looking to others.

In more recent times the traditional adjustable cup and cone bearing design has been replaced by various styles of cartridge bearing unit, usually mounted in plastic cups. Now, when I saw this, I thought 'great, that way there can be a standard diameter/length for the BB cartridge within the cups and provided you have the correct spindle length, it may be possible to use the old cups with a new centre cartridge'. Indeed, I have managed to do this a few times.

However there are problems; the cartridge is often located by lips on the cup which engage with a groove in the cartridge unit. Once the cartridge unit is knocked out of the cups, the lips are lost/damaged and the location is compromised. I guess you can overcome this by using some adhesive/bonding agent but it is hardly ideal.

For the last year or two my utility bike (a Gazelle which has this style of BB) has been grumbling in a way that suggests that a new bottom bracket was definitely in it's future. I wasn't overly stressed by this prospect because it appeared to be 38mm dia and a style that is used on many Gazelle models. When there was just a small amount of play in the bearings, the bike rode normally enough.

I tried to stave off the inevitable by adding lube from time to time too, but I realised there was a fundamental problem; there is no drain hole in the BB shell, and water was finding its way into the frame somehow. I didn't realise how bad this was until one day when I went to ride the bike and it did what I can only describe as 'a generous but rusty wee' on my feet as I unlocked it. It seemed clear that the bearings would be swimming in water and that this would hasten their demise.

Eventually the bearings started to knock loudly in use and then I didn't want to ride it much; the bike sat unused (whilst I rode around on others), with weeds growing through the spokes, waiting for me to gather up enough enthusiasm to fix it.

I finally set to the other way; everything went swimmingly to start with; the cranks came off OK, the chaincase came off OK. Then I noticed that the RH plastic cup had integrated chaincase mounts for the Hesling chaincase; in this case two M5 threaded bosses that accept stainless steel screws. 'Oh... that'll be awkward...'

Mine looked (almost, but not quite, obviously... :roll: ) like this;
Image

Actually removing the BB unit is simple enough; the usual method is to support the frame (eg using blocks of wood) each side of the BB shell (choose carefully, you might damage it) and then getting the big hammer out. This may seem brutal but AFAIK (although there is one for installation, which you don't really need if you have some big sockets or similar), there is no 'special tool' available for this extraction job. I guess one cup could be broken up, cut away or melted out, but I don't advise that; the reason being that if hammering works, the cups come out in one piece and you might need to re-use the cups if they are a weird size. In this case I definitely wanted to re-use the RH cup because it had the chaincase mounts built into it. [Note that you cannot remove the BB unit without the hammer loads passing through the bearings themselves; between this and the changes in the press-fit, it isn't a good idea to remove these bearing units with the aim of re-using them.]

Once the BB was out found what I expected to find; a 'Kinex' cartridge unit. These don't have separate cartridge bearings per se; they usually have an outer race ground into the cartridge shell, and similarly there are grooves in the spindle in which the ball bearings run. There are usually seven or eight balls of about 3/16" or 7/32" size in each bearing, often spaced using an acetal spacer. With care, you can sometimes remove the spacer, disassemble the bearings and replace the balls etc. However this is pretty much always a waste of time; the most likely thing is that the spindle is worn and once this starts there is no stopping it.

Now, I'm lucky enough to live not far away from several LBSs that keep some stocks of these bottom brackets, and have suppliers that can supply more of them. So I wasn't all that worried as I set out to find a replacement; sure, the cups were weird but I'd expect to find a centre cartridge that'd fit my cups, like I had done previously...?. Several hours later, I was a little wiser; I'd examined many, many, such press fit BB units without finding an identical replacement. As well as the expected variations in axle length, axle type, press-fit diameter, chaincase mountings etc I found that the centre cartridge also varies in diameter and length, even from the same manufacturer (Kinex, Thun, Sun Race etc). I found centre diameters of 28, 29, 30, 31mm, with multiple cartridge body lengths for each.

So for now, I'm a bit snookered. I've got a couple of worn units of the correct type (which can't be rebuilt) and I don't want to fit those if I can avoid it, because that will soon knacker the cups, which I'm even less likely to be able to replace. If I was sure that I'd be able to (say) get a 30mm dia cartridge in the future, I guess I could machine the cups out to accept that size, but even that is uncertain.

I suppose I could (in this case) machine up a BSC-threaded sleeve and weld or bond it into the frame, because it has a plain bore. [NB This approach is not readily possible with aluminium frames, because they generally don't have a plain bore.] But even that isn't going to be a smooth ride because the chaincase mountings will need to be remade.

Gah.

BTW in case you are wondering how it is that the phrase 'Thompson-Gazelle' seems strangely familiar, it is because there is such a thing as a 'Thomson's Gazelle';

Image

It occurs to me that there is about as much chance of one of those being of some use for my bike as the average bottom bracket.... :roll: :lol:

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

slowster
Posts: 589
Joined: 7 Jul 2017, 10:37am

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby slowster » 18 Oct 2018, 11:04pm

Brucey wrote:...Then I noticed that the RH plastic cup had integrated chaincase mounts for the Hesling chaincase; in this case two M5 threaded bosses that accept stainless steel screws. 'Oh... that'll be awkward...'
...

In this case I definitely wanted to re-use the RH cup because it had the chaincase mounts built into it.

Brucey, I've taken the chaincase off my own Gazelle utility bike in the course of examining the chainset to see if I could change the chainring from 38t to 33t (no such luck, so I'm going to try fitting a larger sprocket instead), and found that it has this particular model of bottom bracket:

https://hollandbikeshop.com/en-gb/branded-bicycle-parts/gazelle-bicycle-parts/gazelle-bottom-bracket/gazelle-bottom-bracket-complete/gazelle-bottom-bracket-128mm-press-fit-with-bracket-wing/

Curiosity about its design prompted me to google 'Gazelle bottom bracket', and that resulted in my finding this thread as well as the link above.

In the unlikely event that you have not already come up with a solution to your BB woes, and the Gazelle BB linked above might be suitable, if you would like I can take the chainset off and measure the distance between the two screwholes on the 'wing' of my BB to see if they might be the right distance apart for your Hesling chaincase, albeit that they are not M5 threaded.

Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 18 Oct 2018, 11:23pm

the bike in question got stolen whilst it was pending repair (despite being securely locked etc). I was incandescent with fury; I'd put a lot of work into that bike.

Thanks for the link; I did find that BB before (at that site I think) but I couldn't find it for sale from any of the vendors that I normally use. Internally similar BB units usually cost about ten quid; all I wanted was to find one that had the same size centre part and to re-use the cups which I already had and I knew fitted the chaincase properly.

Mind you if some swine was going to nick it anyway I'd have felt doubly gutted if I'd just spent £32.40 on a new BB..... :roll:

BTW a larger sprocket is nearly always a better idea than a much smaller chainring; you can buy chainsets with a smaller chainring but they don't always fit inside the chaincase....

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

brynpoeth
Posts: 9541
Joined: 30 Nov 2013, 11:26am

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby brynpoeth » 19 Oct 2018, 8:55am

Why would a smaller chainring not fit?
Entertainer, juvenile, curmudgeon
Cycling-of course, but it is far better on a Gillott

Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 19 Oct 2018, 9:14am

every chaincase will accommodate a range of chainring sizes. Obviously a chainring that is too big won't go in the hole, but rather less obviously the tunnels will obstruct or rattle on a chainring that is too small, too. For example a Hesling excelle is designed for a 38T chainring and 33T is (IIRC) about the minimum that will fit.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

slowster
Posts: 589
Joined: 7 Jul 2017, 10:37am

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby slowster » 19 Oct 2018, 10:28am

I did not think this would interest anyone, but since the question has been asked and the information might just possibly be of interest to other Gazelle owners...

The plastic cover/disc on the Gazelle chainset is 92mm in diameter (it's this chainset https://hollandbikeshop.com/en-gb/branded-bicycle-parts/gazelle-bicycle-parts/gazelle-crank/gazelle-crankset/gazelle-crankset-38-tooth-alu-black/). The discs on these types of chainsets are designed to minimise the gap between the chainset and chaincase, and so stop rainwater and road spray getting inside the chaincase.

Most similar chainsets, such as the Shimano Nexus version, have a 95mm disc. I don't think the opening in the Gazelle branded chaincase would be large enough for a 95mm disc, so I decided to dismantle the chaincase in order to investigate more fully.

The chainring is not replaceable, and the plastic disc is secured to the chainring by 5 screws. To transfer the disc to another brand chainset, that chainset would need to have the same or smaller inner diameter where the disc goes over it, and screw holes at the same centre diameter, which I imagine may be unlikely.

I suppose I could replace the Gazelle chaincase with a Hesling one which would accept the wider range of other chainsets with 95mm discs, but that would be expensive, and a different brand chainset might result in the chainline being altered, possibly excessively so.

So a larger sprocket is evidently not only the best solution, it's probably the only practical solution.

The only reason why I did not simply order a larger sprocket to begin with, was because I was unsure how much larger a sprocket could fit inside the chaincase. Having now opened the chaincase up and had a good look, I'm fairly sure a 21t sprocket isn't going to be a problem. I do occasionally get a bit of rattle as a result of the chain coming into contact with the inside of the chaincase, and a larger sprocket might make that worse, so I might have to see if I can tension the chain a bit more with the larger sprocket to reduce the slack.

brynpoeth
Posts: 9541
Joined: 30 Nov 2013, 11:26am

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby brynpoeth » 19 Oct 2018, 10:54am

Interesting, +1

I thought chaincases/chaingliders were good, but if one cannae get the gear one wants.. :?
Entertainer, juvenile, curmudgeon
Cycling-of course, but it is far better on a Gillott

Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 19 Oct 2018, 1:06pm

IIRC Hesling make most (or all?) chaincases for Gazelle and most Hesling chaincases with a large centre opening will accept the standard 95mm disc. If not the chaincase is easily opened up.

The 95mm disc on a shimano Nexus NX75 chainset is 'on for good'; I think the only way it is coming off is if you break it. If you were to break it I think the base of the crank would be a funny shape.
Image
There is also another Nexus chainset FC-C6000 (the current model I think)
Image
which is more likely to work ok if you remove the disc because the crank is a more conventional shape.

There is a potted description of the two most common types of chaincase here;

https://www.dutchbikebits.com/chainguards


The type with the small centre hole will accommodate a 46T chainring I think.

It is normal for chaincases to accommodate a 24T sprocket, simply because that was a common size that was used with a lot of 5s/7s Sach/Sram hub gears. You can buy sprockets that fit most conventional IGHs from 13T to 24T. If you confine yourself to these sprockets and 33 or 38T chainsets you can have input gears into an IGH with a 700C wheel of about 37" to 80"

http://ritzelrechner.de/?GR=DERS&KB=33,38&RZ=19,17,15,13,14,16,18,21,24,20,22,23&UF=2185&TF=90&SL=2.6&UN=MPH&DV=gearInches

I recommend that you choose a combination that uses a large chainring and sprocket to give the right gear because it will run smoother and last longer. The only caveat to this is that the 24T size is specific to SRAM and they are no longer making IGH stuff, so you may not be able to easily buy that size in years to come.

The two common types (in their various versions) cover the vast majority of chaincase-equipped bikes out there, but there are some oddball chaincases (Gazelle and Batavus) which included an enclosed detailleur gear and/or a spring loaded tensioner. If these need replacing you have to go to the bike manufacturer.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

slowster
Posts: 589
Joined: 7 Jul 2017, 10:37am

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby slowster » 19 Oct 2018, 5:45pm

Brucey wrote:IIRC Hesling make most (or all?) chaincases for Gazelle and most Hesling chaincases with a large centre opening will accept the standard 95mm disc.

I've just measured the chaincase, and the opening measures 95.2mm. The cover on the chainset measures 92.3mm. I suspect that a 95mm cover would simply be too large for my chaincase: the manufacturing tolerances are just not going to be anywhere near good enough for the cover not to jam against the inside of the chaincase opening. I would have expected therefore that the standard Hesling chaincases sized to accept 95mm covers would have a slightly larger opening than mine to provide enough clearance.

Brucey wrote:It is normal for chaincases to accommodate a 24T sprocket, simply because that was a common size that was used with a lot of 5s/7s Sach/Sram hub gears.

That's very useful to know. I had assumed that the occasional chain rattle in the chaincase of my bike was because the sprocket and chainset might already be the largest sizes which the chaincase could accommodate, and so thought that might mean I would have to fit a smaller chainring to reduce the gearing. I'm going to fit a 21t sprocket for now and see how that feels: it will reduce the lowest gear from 44 inches to 38 inches (http://www.ritzelrechner.de/?GR=SNI3&KB ... 1&UF2=2280). The possibility of going lower does appeal, but I am wary of deviating too far from the general recommendation/warranty requirement not to use a chainring/sprocket ratio smaller than 2:1 to limit the torque on the hub. 38t/21t will give a 1.8:1 ratio, which I think should be OK from the comments I have read about the robustness of the Nexus 3 speed hub. 24t would give a 1.6:1 ratio, which I suspect might be asking for trouble, much as the prospect of the resulting 33 inch bottom gear strongly appeals to me.

Brucey wrote: The only caveat to this is that the 24T size is specific to SRAM and they are no longer making IGH stuff, so you may not be able to easily buy that size in years to come.

I presume that is only for 3/32", since I've bought a 21t Sturmey Archer 1/8" sprocket and SJS also selling Sturmey Archer 24t 1/8" sprockets? I know you've often recommended the fully bushed KMC B1 chain, so that is what I have bought to fit with the new sprocket in place of the KMC 410 1/8" chain originally fitted (interestingly the B1 chain has no factory applied grease on it, which I guess is how KMC are able to keep the cost of that particular chain so low).

Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 19 Oct 2018, 6:22pm

you are right, the opening on your chaincase is too small for a 95mm centre. Shimano centres are 95mm on the nose, so you would need to open up the hole to fit one into your chaincase.

The SA 24T sprocket is a new thing, as in new within the last few months; for years they didn't do one larger than 22T.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

JDTrickyTree
Posts: 2
Joined: 3 Feb 2019, 8:45pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby JDTrickyTree » 3 Feb 2019, 8:56pm

Hi all,

I've signed-up to the forum for just this topic. I'm a British expat living in Budapest. I've picked up an old East German frame with a press-fit style BB that needs replacing. After some 'hammerage' I managed to get ye olde cottered cranks off and tap out the old bearing cups. Now I've measured the shell (4 times over) and it's coming out at 39mm.

As metioned above, the suitable press-fit BBs (e.g. Sunrace BBS-08) come in 35, 38, or 40mm cup sizes. My question is: given that my shell is 39mm, should I go for 38 or 40mm cups? I guess 38 is going to have too much play; I could make some kind of shim but feel this is a bit of a bodge. If I try to press a 40mm is there any chance I could damage (warp / crack) the steel BB shell? I suppose I could file down the polymer cups, but again, this is too much 'bodgery' for my liking.

Any advice is much appreciated.

Kind regards,
James

Brucey
Posts: 33525
Joined: 4 Jan 2012, 6:25pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby Brucey » 3 Feb 2019, 9:30pm

the choice is really

a) machining down some 40mm cups (they won't go in without some adjustment if the entry diameter is really 39mm)

b) shims (and industrial adhesive) with 38mm cups

c) 39mm cups

BTW the old cups (if pressed steel) may be a generous spring fit, so may measure up to about 0.5mm oversize.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

JDTrickyTree
Posts: 2
Joined: 3 Feb 2019, 8:45pm

Re: Thompson-Gazelle and the 'Kurse of Kinex'...

Postby JDTrickyTree » 3 Feb 2019, 9:42pm

Cheers Brucey.

Will have a professional measure the shell, hopefully I'm just not able to be accurate enough with my limited tools. I've never seen 39mm cups, but will search again. If all else fails, I prefer option A, have someone machine down the 40mm. Can't be too difficult with a proper lathe. Will let you know how I get on.

FYI - brand is 'Komet Markenrad'. Someone might have the same issue and end up here. There isn't an awful lot of info about the brand on the interweb.

Keep up the excellent forum!
Thanks again, James