Remove crank arms?

Richard.S

Hi,
I have popped off the plastic caps which were on the end of each crack arm, and then unscrewed both hexagonal bolts, but neither crank arm will pull off?

Is it possible that there is also something else inside which needs unscrewing, or do they simply need to be hammered off?

The frame was provided to me, so I do not know who It is made by, but I was told it has a BSA 68 bottom bracket.

I thought the crank arms would slide off after I removed the bolts, but evidently not :shock:

Thank you all in advance.

whyamihere

You need one of these: https://www.wiggle.co.uk/x-tools-crank-extractor-1

The crank arms fit onto the BB spindle, which is slightly tapered. This makes them a solid fit, even with the bolts removed. The extractor screws into the threads you'll see inside the crank arms, then pushes against the spindle to pull the crank arm off.

EDIT: Alternatively, if you don't want the crank arms, just ride it round the block a few times with the bolts out and they'll likely fall off. They'll never stay tight again though...

Richard.S

Luckily I purchased one of those in advance, when I knew I was going to be changing most of the parts

Still having trouble turning the wrench hard enough, to actually push out the crank arm.
Should it still be stiff, even with the crank puller gizmo, or do I just need to eat more spinach??

Thanks.

whyamihere

It can be hard to get some initial movement, especially if the cranks have been on a long time or were installed by a ham-fisted gorilla. Just make sure the puller is fully engaged in the crank threads and that the threads on the puller itself are lubricated, and then find an extension bar.

Richard.S

Thanks for the advice.

I seem to be having trouble screwing the crank puller completely into the threads, at the moment it is about half way screwed on.

Will try wearing my steel toe capped boots and stand on the wrench, to see if that helps

Richard.S

Success.

I used an a old handlebar to slide over the wrench, increasing the leverage - worked like a charm. I guess I now need to do the same on the drive side?

Sorry for the newbie questions, but have learnt a lot just from a few various questions

keef66

You need to ensure the inside bit of the puller is unwound fully before trying to screw the puller into the crank. You ideally need to engage it fully in the crank threads. I once tried with a puller only partly screwed into a crank and ended up ripping half the threads out of it.

The other thing you need to check is that you didn't leave any washers behind when you removed the bolts. Ask me how I know that too...

Richard.S

Ok, can’t resist - how do you know that too
Will check for washers now.

Thanks for all the help, it is much appreciated.

Richard.S

Both crank arms and the crankset are now off, thankfully (even though the crank extractor is now permanently stuck inside the drive side crank arm) :oops:

I now just have the square metal tapered spindle sticking out of each side.
If I now buy a nice new crankset, will it simply fit onto the spindle, or is there anything else I need to do / remove?

I am happy with the bottom bracket, I just want new cogs and crank arms, so I presume I can leave things as they are?

Also, just out of curiosity, surrounding each side of the spindle is a circular, what feels like plastic disc, which has small holes around the perimeter. How would I remove that if I ever needed to replace the bottom bracket?

Addendum: I have just measured the spindle length from end-to-end and it measures 119.7mm. Is this a standard size, and does the new crankset need to match this exactly, as most of the cranksets I have seen either do not show the spindle length, or are shorter.

Thanks in advance.

larkim

The plastic bit is part of the BB assembly - you need a special tool to unscrew that on both sides if you want to remove the BB completely. A square taper BB would be cheap to replace so just satisfy yourself that it is nice a smooth now as it might be timely to replace that anyway.

I've been in exactly your position a few years ago, having absolutely no idea about how cranksets and BB fitted together, and the pain of the effort required to remove the cranks so I can empathise!

Yes, a new square taper crankset should just slide onto the square splines, (maybe with some grease so that they are removeable at some point in the future), tighten up the bolts to seat the cranks and you're good to go.

Richard.S

Thanks.
It is the spindle length which is perplexing me.

Not sure if a crankset meant for a shorter spindle would be safe, or even fit on my 119.7mm spindle.

keef66

Assuming it's a square taper cartridge bottom bracket have a look at:

https://www.parktool.com/blog/repair-he ... ridge-type

I can't work out if the plastic rings you describe are in fact the notched cups you fit the BB tool into...

Regarding what chainset you can fit, have a read of this explanation of JIS and ISO square tapers:

https://www.sheldonbrown.com/bbtaper.html

It's best if you match the taper of the spindle and the cranks, but you can get away with mixing them.

keef66

Richard.S wrote:

Thanks.
It is the spindle length which is perplexing me.

Not sure if a crankset meant for a shorter spindle would be safe, or even fit on my 119.7mm spindle.

The spindle length effectively determines how far out the chainrings sit. So you need a short one for a single ring setup, slightly longer for a double and longest for a triple. Spa cycles list the following for the Shimano UN55 BB:

107mm English Thread
110mm English Thread
113mm English Thread
115mm English Thread
118mm English Thread
122.5mm English Thread
127mm English Thread

I'd say your 119 is meant for a double chainset. Frame geometry can also play a part; mount the chainset too far inboard and the inner ring can foul the chainstay. Too far out and the front mech may not reach the outer ring

Richard.S

Thank you for that explanation, I now understand it better.

So am I correct in presuming that just for example, if I put a single cog crankset onto my 119mm spindle, it would cause the cog to sit more inward, resulting in a potential chain-line problem with the rear smaller cogs?

cooldad

Cranksets will have a recommended BB length.

https://www.sheldonbrown.com/bbsize.html