I don't know if Im going to get shouted at for posting this here, but I can't post it in the market place because I don't have a premium membership, so I thought this would be the next best place.

I have had my Triumph Cyclone for almost half a year now, and some time ago I posted a thread on here about how the crank arm kept coming loose. I tightened it as much as possible, and it was ok for a few months, but recently it has really started to loosen up all the time.

The guys in my local bike shop said that I should by a new crank arm, but they don't stock the right size for my bike, which currently has 165mm cranks, with a square taper. Does anyone know firstly if there is a website, or company that stocks older parts for bikes that could sell me a crank, or if it would just be better to replace the whole crankset? For example I found a crank on a website, but it has been made some 20 years later than the rest of my bike! Will this mean that it may not fit? For example are there measurements for the square taper as well as the length of the crank, or do they all have the same size slot?

https://www.cyclex.co.uk/product/cycl...and/cwc10.html (thats a link for the crank I found on the website)

Also what happens if you have different sized cranks on either side? There is one going on ebay at the moment for £2 which is 170mm, this doesn't sound like a massive difference in size to me... but say I bought that would it make my pedling unbalanced and feel weird???

Thanks

So order the correct size from them.

so it won't matter that its a much more modern crank? The guy in the bike shop made it seem that companies didn't make parts that would fit my bike any more...

Well you didn't say that. I'm only suggesting that since you are unfamiliar with these parts, you should rely on the expertise in the shop. You said you've had the bike a few months without anymention that it was a very old bike. Any competent bike shop should be able to order the correct part for you. If they are no longer made, you may have to replace the whole crank set but that should be available too.

Square taper cranks are not all the same size, not even close. You will need to match the crank to the bottom bracket spindle or you run the risk of having the crank arms too close or too far from the frame. The surest way to get something to work would be to buy a crankset and bottom bracket that are made to work together. Or you can measure you current bottom bracket spindle length and get a crankset that works with that spindle but for older parts this often degrades to trial and error.

sorry for the confusion, although I did say that the bike would be 20 years older than the new crank, my bike shop don't stock the right size cranks but can get me a new crank set.

Sounds like I could save myself money by just buying a new crankset cause the shop assistent said it would only cost £30. He was a bit hesitant about selling me a new crank set though. I can't remember exactly what he said, but it was something about the chain, off the top of my head I remember him mentioning something about how the chain might have bitten to the crankset? and might not work well with a new one... which would be more money again I suppose!

I assume the non drive side arm is the issue. If this is the case, there is less of an issue with getting a replacement as chainline will not be effected. You want to stay with 165mm length (having two different lengths wouldn't be a huge problem but why go there?) and get the right square taper interface (see here for the different standards: https://sheldonbrown.com/bbtaper.html ). Then just make sure it is installed properly so you don't have the same issue again in a few months.

If my assumption is wrong and it is the drive side, I would consider replacing the crankset and bottom bracket as a set.

Chainrings are probably showing wear which means your chain is probably stretched and ready for replacement. Which could also point to issues with the rear cog(s). Maybe a picture of the drive train to let us see what we are all guessing about?

Sorry for the long reply, been trying to sort lots of things for uni!

These are some photos of my crank arm, and the chain. Forgive me but I didn't want to remove the crank arm, because its loosening again and I want to be able to cycle down to the bike shop when I need to get a new one!

I might just ring up the bike shop and ask them to replace the whole crankset, do you think this might be best, seeing that they are professionals and having a new crankset isn't the worse thing in the world!

if the chain is at the end of it's rope, you're going to want to replace the chain and probably cassette at the same time. Going to be a little pricey, but probably the right thing to do at this point.

I'd look at velo-orange as they have BB/Square taper cranks that go nicely with classic/vintage bike setups.

Is the cassette the group of sprockets on the back wheel? Sorry for my ignorance!

thanks for the idea, they look like lovely parts... but alas as a student a bit pricey at the moment

Oh... finding a crank! I was going to say something about how after riding a while the old belly may get a little smaller and make such things easier.

$13 and up on Ebay. Plenty of square tapers to choose from.
https://www.ebay.com/itm/BIKE-BICYCLE...item43a9d0e2e4