looks like a normal cottered set-up …
Though hardly a classic, there is one thing that I found thought provoking while disassembling this bicycle, and that is the mysterious bottom bracket. It’s a proprietary unit, I think, with standard BSA right hand threads on the non-drive left side cup, but the drive side is an extended cylinder that mates with the left cup to form a sealed unit that can be disassembled, complete with standard 1/4″ plain ball bearings and a cottered crank axle. The whole setup is wedged into a threadless oversized bottom bracket shell by tightening the assembly, fitting the wedged lock ring, first matching a keyway in the shell to a notch cast on the large cup, much the same way as some old seatpost pins and quill stem pinch-bolts slot in to stop them rotating. Rubber seals on the axle holes help stop outside entry of water and grit. Perhaps modern sealed BBs have evolved from this idea ?
until…
Why make such a big deal about an old non-standard BB ? Well, this is an old bike blog, so you won’t be seeing octalinks, hollowtech IIs, BB30, BB90, or that sort of newer thing, but this one made me take notice because the bearings and surfaces inside were in truly excellent condition considering the bike’s age and assumed usage. This is because the rust, grit and water build-up inside the frame remains outside the casing as you can see from the corroded exterior. Often this accumulated gritty gunk finds its way into the bearings and a completely new BB is required, but not here !
minus the standard cottered axle
As well as that, they are user serviceable unlike the modern sealed bearing square taper replacement BBs that are long term throwaways. And they need to be in this case because if this fixed cup had worn out 30 years later it would be very difficult to replace, perhaps then making the bike useless ! What else would one fit – with no threads ? Of course, that’s true only because this system didn’t become a standard arrangement…
I am going to experiment with converting it to a square taper axle, as I have said before I’m not a fan of cotter pins unless on a ‘valuable classic’ and even then that’s only for originality… if that works the bike can be modernised with a lighter chainset, with the hope that this bracket will stay put.
a new recyclist 
Velo Orange do a threadless bottom bracket that just might work here,if you can find a cotterless spindle. They come in various lengths and I used one on a Peugeot fold-up that had bung threads.
cheers,
Thanks for the tip – I’ll see how the original goes first, then check out the V.O.
That’s pretty nifty, seems like a good design. One encounters some interesting weirdness working on old bikes.
It took some head scratching to figure out at first !
Hi I have a 1982 Malvern Star Sportstar racing bike. It has the same type of bottom bracket. It also has a cotterless crank. My crank was very worn. My dad had been riding my bike to work for many years after I left home and it took it’s toll.
Apparently these bottom brackets and cranks are no longer available. My Father in law (a toolmaker now retired) made up a new crank for me and I got new bearings. It is still going ok after a few years of use.
I’ll be interested to see how you go with this as it is the achilees heel of the bike. I’m just about to order some new brakes to replace the originals and was trying to decide what I would do if the BB went again.
Good luck with it.
Tony.
Hi Tony,
The crank, bearings and left hand cup all seem standard items. The most important parts to preserve is the large drive side cup and left hand locknut wedge – the best way to make the original last will be good maintenance ( i.e. remove, clean and grease regularly ) and keeping it in proper adjustment.
Thanks for the feedback !
I just bought one of these bikes and I’m looking to restore it but I also want to put in a square taper. It looks like you had no trouble fitting one in. Was there any issues with size?
As long as the axle is the right length for the intended chainset and the cups aren’t worn I think it should be OK, James. Probably best to test-fit an axle first as I may have just been lucky.
I used the original cups as a standard BB cup won’t fit the larger diameter shell.
Also I haven’t completed this bike yet because of other projects but no problems with the BB.
Thanks Peter,
I’m having trouble getting the ‘shell’ part of the BB out of the frame. Does it just need a tap with a mallet or something?
Probably James, I’d put plenty of releasing agent on it first and don’t stress the bearings by hitting them hard. Can you see the slot on the bike and key on the BB cartridge that stops the BB turning around ? Mine needed a careful tap from memory.
Great. I’ll do that.
Mystified about the axle sizing. I’d like to buy a square taper one online but I’m worried it won’t fit. I’ve got some measurements by using a caliper. Looks to be about 16mm diameter at the cone holes. Online there is little reference to diameter for ebay axles for sale. Hmmmm.
The diameter shouldn’t be a problem. It’s more important that the width is right for your intended chain line i.e. for whatever crank, chain set and rear gears you are using. Be careful with the rubber seals in the cups and you can re-use them if they are in good nick. Generally I use a 107mm axle for single speed and maybe around 113mm for double chainset – as a rough guide only,
Hi Peter,
I picked up an old bike off Gumtree the other day and looking at your photos I think it must be a Malvern Sportstar. The previous owner converted it to a singlespeed but geared it 52/18 which is far too tall for me in my hilly area. I was wondering if you might be able to help me source the smaller chainring which comes with the original crankset as it would help with my gear ratio and chainline. I’d be happy to send you photos to confirm that it is the same model.
Many thanks,
Michael
Hi Michael,
Does it have the same threadless bottom bracket ? First thing I would do is make sure that’s in good shape otherwise it could be a waste of money going further. The small chainring (40 or 42T) still needs to sit onto the big one which will make it a very heavy ‘single speed’ chainset.
My plan was to fit a new axle of the appropriate width, upgraded to a square taper and with a lighter single speed chainset. What type of rear hub and sprocket is now fitted – i.e. fixed, freewheel or coaster etc. ?
Would it be easier to make it a 52 x 22T ?
Peter
I believe it does have the threadless BB though I haven’t had a chance to disassemble it to confirm. However, it seems to be operating smoothly.
I understand there’ll be some excess weight from running two chainrings but I bought the bike as a “let’s see if I actually do much riding before I invest in anything more expensive” thing. If it weren’t for the steep hills in my area I would just leave it as is.
It’s currently got a freewheel on the back. The 52 x 22T might be another option.
I’m pretty sure I’ve donated my crank set to the metal recyclers, and it won’t be easy to find the 3-bolt inner ring for it, so I think you might have to use the 52T unless you can find an old bike parts hoarder or repairer in your area.
I’m not actually sure if 22T freewheels are available or not – at any rate, I wouldn’t be spending too much unless it’s in really good condition.
Hope you can sort it though … if it has a cottered crank set I would recommend replacing that with a square taper 40T or 42T single speed – which means fitting a shorter axle too .. problem is, you can’t use a threaded cartridge BB which would normally be the easy way out !
Hey Peter,
I finished my Sportstar build a couple of months back. I really enjoyed the process. I actually love the bottom bracket design. It’s so unique and it is so well engineered. It’s also super firm so power transmission is great. I bought a beaut cottered crankset which looks fantastic on it. Here’s a photo of my bike on instagram: https://instagram.com/p/4dOSPsPItp/
Thanks for your advice on the bottom bracket a couple of months ago!
James
Wow, that looks fantastic, James. I wish my frame had been in that condition originally !
Hopefully Michael will be inspired too, seeing your bike.