shimano fc-c103 bike arm crank

[deathtokoalas]

my grandmother gave me this italian-built bicycle years ago, because it was just sitting in her apartment storage. i'm going to guess it's a 90s model, or earlier, but it was like a brand new bike when i got in 2011. i have ridden it to the brink the last few years and now have what i believe is labeled a "loose crank arm".

i bought a ratchet set to try to fix it, but i can't unloosen it, which is leading me to the conclusion that it isn't loose. i'm a thin/toned type (i have no upper body strength), but i'd imagine i could get the thing loosened if that was actually the problem, because it would be...loose....

i can't find any information about the model online, and what i'm learning from watching youtube videos is that the system is rare nowadays, but what i'm wondering is if the actual problem is not that the crank is loose but that the lock ring and cone, together, just somehow just fell off, or were perhaps vandalized. i'm also wondering if there isn't actually a bolt on the bracket at all.

i have some pictures:

does that look like parts are missing in the shaft? is it just the ring? the cone? both? more?

if just the ring falls off, is it typically loose? is it required to actually fix, or is it just annoying?

in a scenario like that, it may potentially be an inexpensive fix, if i just need to replace the $5.00 parts around the bracket, but if i understand correctly, i'd have to take both pedals off to do it, and that requires buying specialized tools. i didn't mind buying a ratchet set because i should have a ratchet set, anyways, and i thought i had no choice but to disassemble it. if it's actually too tight to take apart, i might not want to at all. how often are fixes like this actually successful?

it's a nice bike, in theory, but it's been ridden to death, and i'm trying to determine if trying to fix it is actually worth it. my budget is very small (i would replace it with a used bicycle that will certainly have a much shorter lifespan than this one). i will no doubt fix it eventually. i mean, i'm not going to landfill it.

j

 

[deathtokoalas]

maybe somebody could confirm, but i think it's just the lock ring, right? the lock ring....locks...the system so that it's not...loose. so, if it just corroded due to use and weather and whatever else, this would be the expected result - it would be loose, and the threads where the lock ring connects to would be exposed. right?

 

[Deleted member 1258]

It looks to me like a square taper bottom bracket, its difficult to tell from your photos, the whole unit might be knackered and need replacing.

 

[Ajax Bay]

As @dave r says, this is very likely a 'square taper' BB and crank. A picture from the side would likely confirm. There is a simple cap which screws off (bladed screwdriver normally). Or could be a hex keyed bolt. Remove.
If you'll see a nut. Tighten it. Hit crank with mallet (resist hit from other side) and tighten again if possible.
Check if better. If not:
There is a thread 'in' the crank. You need a crank puller tool (cheap) and can remove the crank. Clean check replace (minimal grease) and tighten on (see above).
If still loose, probably the cranks are f***ed (NB aluminium crank, steel spindle) and will need replacing (the square hole in the crank is too damaged).
See how you get on and report back.

 

[deathtokoalas]

the system is certainly a square taper, but the bolt is not loose. my question was whether it looks like the lock ring is missing or not.

 

[Ajax Bay]

There is no lock ring - what do you think a lock ring would 'lock'? The crank slips on to the BB square taper spindle and is tightened on to the tapered square end by a bolt. You can see from the 20-spline end that the BB is a cartridge version like a UN-55 or similar.
You've said that you "now have what I believe is labeled a "loose crank arm" and:

i can't unloosen it, which is leading me to the conclusion that it isn't loose. . . . I imagine if I could get the thing loosened if that was actually the problem, because it would be...loose....

'Fraid your conclusion is ill-founded. The bolt can be well tight but the crank/BB spindle (square) interface can be damaged resulting in movement (which will get progressively worse). In fact the bolt is probably super tight because a bit of crank looseness has been remedied by serial tightening of the bolt as the crank deteriorates. You imply you are the one who's ridden this bike since 'like new' so you'll know whether this is the case.
I take it you don't threaten the lives of bears from Peru?

 

[T4tomo]

have what i believe is labeled a "loose crank arm".

but the bolt is not loose

so which is it?

my question was whether it looks like the lock ring is missing or not.

if you are asking is the gap here normal?

the answer is yes.

there should be a bolt on the end that screws into the BB spindal that "holds"* everything in place, but you need a crank puller to rmeove the crank *as its really the square taper that holds the crank on so removing the bolt wont release the crank.

 

[Ajax Bay]

so which is it?

I suggest this is a false dichotomy

 

[deathtokoalas]

the bolt connects the pedal to the axle, it doesn't connect it the frame. it is the lock ring that connects the axle to the frame and prevents it from moving. the axle and the pedals are now locked together as one system, but that system is disconnected from the frame. that is why the crank arm is loose and the bolt is not.

i believe it is true that you could disconnect the bolt once you've locked the pedal in place, but only if the lock ring remains in place to connect the entire system to the frame.

i was able to answer my question via my own research.

these posters are not well informed.

 

[deathtokoalas]

for the benefit of any other readers, note that the following video explains the system quite well, and goes through the locking process as well:

 

[Deleted member 1258]

the bolt connects the pedal to the axle, it doesn't connect it the frame. it is the lock ring that connects the axle to the frame and prevents it from moving. the axle and the pedals are now locked together as one system, but that system is disconnected from the frame. that is why the crank arm is loose and the bolt is not.

i believe it is true that you could disconnect the bolt once you've locked the pedal in place, but only if the lock ring remains in place to connect the entire system to the frame.

i was able to answer my question via my own research.

these posters are not well informed.

There is no lock ring on a square taper bottom bracket, I've got one on my fixed, and have used square taper since the 1990's, the most likely reason for your crank to be moving is that the bearings in the cartridge are knackered and it needs a new cartridge.

Square taper bottom bracket.

 

[Deleted member 1258]

these posters are not well informed.

The posters that replied are knowledgeable people and know what they are talking about.

 

[deathtokoalas]

i may have been imprecise in my description. i do not have the square taper you're suggesting and i should have looked it up before agreeing with you. the type of bottom bracket here is called a Bayliss Wiley Unit Bottom Bracket.

 

[deathtokoalas]

i don't really know how old this bike is. as mentioned, i think it was built in italy. it was sitting in storage for a long time.

 

[deathtokoalas]

i asked the forum because i didn't know. i have a reputation for being snarky, but this was an honest question, as this is something i don't have any experience with. i like to ride my bike, and i can change a tire or adjust some brakes, but i don't know how to disassemble and reassemble it and my time spent in the physics department was solving differential equations, not reverse engineering vehicles. i was looking for an experienced poster to quickly look at the bracket and say "yup, that's a ..."

i am sure that there has to be a lock ring because the connection is threaded. the gap is normal on many different spindle types, but the existence of a threaded surface gives it away - something is supposed to be there, and has apparently rusted away or been otherwise ridden down and fallen off.

i believe this type of bottom bracket went out of style in the 60s, but the bicycle might have been built from spare parts in the 70s or 80s. i don't know.