Cartridge bottom bracket with lockring on one side only NB There is an edit to this post added 06.02.2017

I need to replace the 68/118 BB on my Giant Rock (made around 2000 I think). It has a locking ring on one side only as shown in the photos. The problem is I can't find one like this online. The nearest I've found was on Sheldon Brown's website but I can only post two links/photos with my reputation so you'd need to google "Cartridges with a lockring on each end" if you're interested.

I want to order the right spares and tools the first time round (to avoid paying for two deliveries) so my questions are:


Do I need to get any special tools other than the obvious: BB tool and lockring tool?
What replacement part do I need? Can I use a BB without lockrings, a BB with two lockrings, or does it have to be a BB with just one? Specific model recommendations would be welcome but not essential - it's the type I need to figure out.


If it helps, the thread on the chainside crank (used to attach the crank remover) had some wear on it, so there may have been some work done on this setup in the past, but I don't know how to tell if there used to be a locking ring on both sides. Please do let me know if further info is needed to answer the questions.

bottom bracket right end (nearest to the chain)


bottom bracket left end (furthest from the chain)


Edit on Tue 06.02.2017

Hello, I have browsed the web for a bit longer, and came across some info which I'd like to share here. Hopefully it helps someone make a more specific judgment of what the crack is with my bike.

There are some shops and ebay listings offering a "semi sealed" bottom bracket:
http://www.ebay.co.uk/itm/BICYCLE-BOTTOM-BRACKET-VINTAGE-BALL-BEARINGS-STYLE-118mm-or-126mm-IN-BLACK-ONLY/331915747544

http://www.ebay.co.uk/itm/Raleigh-Bikes-Bottom-Bracket-Set-Semi-Sealed-Axle-118mm-Black-/141399887346

There is also this youtube video which I gave its 76th view and which leaves more questions than answers:

                
            

The sales listings quoted above don't seem to explain clearly what the difference is between an average cartridge bottom bracket
 (like a shimano bb un55) and a "semi-sealed" unit. In fact, most results I get on google for  >>"semi sealed" bottom bracket&lt;&lt; are from ebay and shops. The main point however is the fact that there is indeed a locking ring on one side only on these.

Now then, I can get a NECO B910 sold with the BB tool for £12, whereas a semi-sealed unit and a BB tool have to be bought separate and add up to at least £16. So the cheapest semi sealed is a few GBP more than the cheapest model without the single locking rings, and I'm not totally clear if I can use either, or only the semi sealed. I don't have the budget for error, so I would really do with some hints here. It seems I have four options really:


Buy a BB tool on its own, get my BB out and take it from there - I might do that if I don't get a definite response on here in a few days, but this will cost more if it turns out I could have bought the £12 BB combo in the first place
If someone is able to positively identify that the unit I've got can only be replaced with a semi-sealed BB, I will buy one of those from a source where it's cheapest to buy the part and a BB tool (with delivery)
Ebay listing 331915747544 linked above seems to suggest this type can be taken apart and bearings can be replaced while keeping the rest of the assembly - if someone can confirm that
, I will probably end up buying just a BB tool first to identify bearing size etc, but at least I will have a reason for it.
If someone is able to positively identify that the unit I've got can be replaced with that NECO B910 or another similar BB without a lockring on one side, I will get that £12 set. This could in effect be what CardMechanic says (thanks for your response), but he hasn't mentioned "semi-sealed", so I'm not sure he considered the option that one of these might be required.


Thanks in advance for any input!
Your standard cartridge and "loose bearing" bottom brackets have two threaded "cups".

Usually the right (drive) side cup has a lip on it, so it will only screw so far into the bottom bracket housing.  There is no adjustment, and no need for one, since the distance that the shaft should project outward is determined by the design of the parts.  And if the bottom bracket is a cartridge one often the right side cup is permanently attached to the cartridge.

However, nothing is perfect.  If the cups do not tightly restrain a cartridge unit it will move about and make annoying clicks.  And if the cups are loose in a loose bearing style unit the axle will wobble around in the bearings.

So one side (at least) is made adjustable, without the lip on the cup, but instead with the threads extending a few mm outward beyond the expected distance it should be screwed into the BB shell.  This adjustable cup is then screwed in "tight enough" to achieve the desired pressure on the bearings.  But "tight enough" is not generally so tight as to cause the cup to "lock" in place like a regular bolt, so the lock ring is added to allow the cup position to be preserved, in spite of the various mechanical pressures that would attempt to turn it.

Note that this "adjustable cup" is generally on the left side, allowing the adjustment to be accessed without interference from the chainrings.

The vast majority of "3-piece" BB setups, at least on lower-end bikes, are of this variety, with one "fixed cup" and one "adjustable cup".  For the most part these units are interchangeable, so long as the style of the axle end matches (and there are 3.5 different styles).  There will be a modest variation in the length of the right-side shaft, between 2-ring and 3-ring fronts, but most 3-ring bearing assemblies will fit 2-ring bikes, and likely a fair number the other way.

A few bottom bracket bearing assemblies have adjustable cups on both sides.  This allows for various things, such as a BB shell that is wider or narrower than normal, or desire to adjust the "chainline", moving the sprockets closer to the frame or farther away.  It also allows a single BB bearing assembly to fit several (slightly) different setups.