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Advice on new chainset/crank after pedal falls out

by spaceford
Thu, Jul 26, 2018 08:32
11

Hello, 

Have to admit to not having much bike tech knowledge. Can anyone advise me on replacing a chainset? 

My son's pedal has totally consumed the thread of the right side crank of the chainset. I thought, no problem, I'll just replace the crank, only to discover that you can't do this, you have to replace the entire chainset! 

The bike is an older red b'twin Triban 3 junior size. The crank is 170 and the cogs are 50/39/30. Decathlon don't stock a replacement anymore and equaivalent sets seem quite pricey. 

Firstly, has anyone used those Park Tool things that bore a new thread into the crank and then you insert a ring into it to hold the original pedal? 

Secondly, should I be trying to match the original cog sizes exactly, or will another size chainset work (although with slightly different pedal action) ? 

many thanks,

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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11 comments

Avatar
spaceford | 5 years ago
0 likes

Hi kil0ran, 

There doesn't seem to be an option here for direct messaging. 

Could you shoot me an email to matthewblandford [at] yahoo.co.uk and I'll give you my contact details and sort you out for postage. 

many thanks, 

Avatar
kil0ran replied to spaceford | 5 years ago
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spaceford wrote:

Hi kil0ran, 

There doesn't seem to be an option here for direct messaging. 

Could you shoot me an email to matthewblandford [at] yahoo.co.uk and I'll give you my contact details and sort you out for postage. 

many thanks, 

YHM

Avatar
Dnnnnnn | 5 years ago
0 likes

"BB" = bottom bracket

Avatar
spaceford | 5 years ago
0 likes

Thanks for all your comments. 

The crank arm is definitely the right side ie. the one connected to the cogs. 

The arm is 170mm.

I will probably look into fitting a helicoil, but

kiloran - that's a very kind offer. Yes, it is an Ounce brand chainset.  I'm not quite sure what you mean by the "BB". What kind of difference would it make if your crank arm is a few mm longer than my original? 

 

Avatar
Dicklexic replied to spaceford | 5 years ago
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spaceford wrote:

What kind of difference would it make if your crank arm is a few mm longer than my original? 

 

To be honest your son is highly unlikely to notice the difference of a 2.5mm increase in length, and it certainly won't cause any harm. But I would suggest that if you have the one from Kil0ran that you replace both crank arms, not just the drive side so that at least both sides are the same length.

Avatar
kil0ran replied to spaceford | 5 years ago
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spaceford wrote:

Thanks for all your comments. 

The crank arm is definitely the right side ie. the one connected to the cogs. 

The arm is 170mm.

I will probably look into fitting a helicoil, but

kiloran - that's a very kind offer. Yes, it is an Ounce brand chainset.  I'm not quite sure what you mean by the "BB". What kind of difference would it make if your crank arm is a few mm longer than my original? 

 

Probably very little difference, young bodies are more flexible. I've just checked, mine are 175mm. Might just need a tiny drop of the saddle. If you can reply with your contact details I can get it in the post to you ASAP

Avatar
kil0ran | 5 years ago
2 likes

The crankset on the Triban 3 was usually a B'Twin own-brand Ounce model.

I've got a used one in the shed you can have for the cost of postage. It's probably a 172.5 as it came off a large bike, might be 175.

Something like this will do the trick:

https://www.spacycles.co.uk/m2b0s109p2000/SPA-CYCLES-XD-2-Touring-Triple...

Word of caution - stick with square taper rather than trying to remove the BB from the Triban. The cups for that BB are plastic and you are absolutely guaranteed to round them off trying to get it out. I ended up having to dremel mine out.

Avatar
srchar | 5 years ago
3 likes

Take the crank and pedal to an engineering shop and ask them to put a helicoil in.  Take cash and tell them you're not in a rush.  It'll cost somewhere between ten and twenty quid.

Avatar
Dnnnnnn | 5 years ago
0 likes

You say it's the right hand crank - do you mean the one with the chainrings bolted on?

I ask because the other side (for the rider's left foot) has a reverse thread and is often damaged by people who don't realise that.

In contrast to Canyon48, I'd wager your chainset is a [what kil0ran said]. But it doesn't matter as they're usually interchangeable. As noted, you can replace it with another 50/39/30 (what would be known as 'road triple' sizes) square taper unit, or a 48-38-28 (sometimes called 'touring' or 'trekking' sizes). You may be able to find just the 'spider', i.e. the right crank arm cheaply on eBay - if so, you'd need to be sure it had the same bolt spacing for the chainrings (probably 110mm BCD) and check your chainrings are actually removable - they probably are but some really cheap units aren't.

You might need to move the front derailleur down a fraction (and adjust its cable tension) to maintain good shifting.

Finally, as kil0ran notes, the cranks come in different lengths. It's usually stamped somewhere on the back and is often 170, 172.5 or 175. Being the small Triban, it's possible it's shorter - 165mm is unusual but possible (it should be more common on smaller bikes). It would be nice to have the exact same size each side but 2.5mm is unlikely to be noticeable. 175mm on one side and 165mm on the other maybe more so... (although I don't know!)

Avatar
StraelGuy | 5 years ago
0 likes

I think you're referring to a helicoil. Might be worth giving a couple of small, local engineering firms a bell before you look at replacement.

Avatar
Canyon48 | 5 years ago
0 likes

I imagine the cranks are either suntour or shimano, it should say on the side somewhere. You can only replace a triple with a triple (3 chainrings). You can replace the crankset with a similar one but with a different number of teeth.

Lots on ebay https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313....

It probably has a square taper spindle, this is really easy to remove and install using a crank arm puller https://www.youtube.com/watch?v=cPQyQnNdews

Depending on the price (maybe up to £50), it might be more economical to buy a new bike.

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