Shortening Alu Cranks (for my kid)

[mountainfun]

Hi

My kid has long cranks on his bike (175) and I'm keen to shorten to 140-145.

Any suggestions whom to contact?

I previously posted on my carbon cranks needing shortening and can happily say that I've crossed over to shorter alu ones (RaceFace Atlas) and am super happy!  Thanks for all the comments on that thread, really appreciated the feedback.

Best

JL

[Jewbacca]

I did a set of Lyne 1st gen alu cranks. Measure, mark, measure, mark.... cut. Reduced them from 175 to 145.

You need a drill press and some one who has a pedal thread set, which will be a lot of bike shops and a grinder. 

You need to make sure you are using solid alu cranks, not shimano hollowtech II or other hollow cranksets for obvious reasons.

It's not a big job. If you have a local engineering shop, they could do the drilling for you in a matter of minutes but the pedal thread size and the reverse thread die in that size is even less common, so phone around your area for a theadset. 

If you do the shortening and the drilling, cutting the threads in the workshop will only take a few minutes, pay them for their time and tools use. 

If you want someone to do it for you, my advice would be to contact Kevin Wilkinson, used to be a bike tech at BMC, now has several engineering/fitting/turning containers with which he does on site work.

He is based daily at the airport industria. DM me and I can send you his number.

[DJR]

Agree on Kevin Wilkinson - 082 466 4565 (been a while since I needed him, but hopefully the number is still functional. Otherwise Google is your friend.) He's done all kinds of small precision engineering stuff for me on a number of bike builds. Always came out great. Nice guy too. 

Edited January 28 by DJR

[quade]

Following this thread 

 

Is there a rough guide on age/height and crank size ?

My 12 year old is riding 175's and was looking at shorter options 

Not sure how small they go off the shelf ?

[Jewbacca]

55 minutes ago, quade said:

Following this thread 

 

Is there a rough guide on age/height and crank size ?

My 12 year old is riding 175's and was looking at shorter options 

Not sure how small they go off the shelf ?

I don't think there is an age formula, more a height/inseam fitting that 'should' be considered by everyone on a bike.

Most people on 175s should be riding shorter cranks.

Thanks to E-bikes, anything from 150mm can be had off the shelf these days, but they are pricey. A set of 2nd hand shimano deore solid alu cranks can be shortened for relatively cheap

The Lyne or SRAM 3 bolt cranksets are also a really good option as you can fit a 28 tooth narrow wide DM chainring while a 30 is the smallest you can go with a 104mm spider.

 

[Kuys]

My kids (7 and 9) have these cranks on their bikes in 140mm

https://prevelo.com/products/heir-direct-mount-crank?variant=32105296167014

uses standard Shimano BB and has SRAM direct mnt interface so they can run 28t chainrings. 

 

 

[mrcg]

Sorry for the highjack. Have a set of carbon cranks (left crank) where the pedal insert has been stripped.

Would you guys recommend a helicoil insert? Needs to be reverse thread. Bike shop didn't find anybody who could provide a reverse thread helicoil. 

Any recommendations for who could assist?

Much appreciated

Edited January 28 by mrcg
Typo

[Prince Albert Cycles]

6 hours ago, mrcg said:

Sorry for the highjack. Have a set of carbon cranks (left crank) where the pedal insert has been stripped.

Would you guys recommend a helicoil insert? Needs to be reverse thread. Bike shop didn't find anybody who could provide a reverse thread helicoil. 

Any recommendations for who could assist?

Much appreciated

Try Nils at Woodstock Cycles

[DJR]

28 minutes ago, Prince Albert Cycles said:

Try Nils at Woodstock Cycles

Nooooooo, don't go near that place and don't talk to Nils and do not use words like Eroice, Classic or Tour of Ara! Every time I go there to buy something small, like bartape, I see something else that I MUST have. A frame for instance.........and then it starts another bike build. Or, if I really resist, I buy something innocent, like an old derailleur.......and then it starts another bike build. Even just buying a saddle inevitably leads to another bike build. I tell you, that is a dangerous place. My house is overflowing with bikes, I think if I get one more skelmpie, my wife is going to kick me and all my bikes out! 

Ps Y'all seen my tongue firmly in my cheek?

Edited January 29 by DJR

[Jewbacca]

8 hours ago, mrcg said:

Sorry for the highjack. Have a set of carbon cranks (left crank) where the pedal insert has been stripped.

Would you guys recommend a helicoil insert? Needs to be reverse thread. Bike shop didn't find anybody who could provide a reverse thread helicoil. 

Any recommendations for who could assist?

Much appreciated

Nils might still have a few inserts.

There is a kit you buy with standard and reverse thread sleeves that are also threaded on the outside.

So you drill the original hole out, tap with the supplied tap and then epoxy in the threaded insert.

New pedal threads in 10 minutes!

You can order the kit off E-bay for a few hundy too

[mountainfun]

Thanks, it's incredible how useful this community is!

Amazing!!

Now smiling!!

[bebnin]

can agree with all the above, I've shortened some al cranks doing exactly this (drill & tap with the right tap set) - if you're in woodstock often, let me know and I can help you out.

[quade]

13 hours ago, Jewbacca said:

I don't think there is an age formula, more a height/inseam fitting that 'should' be considered by everyone on a bike.

Most people on 175s should be riding shorter cranks.

Thanks to E-bikes, anything from 150mm can be had off the shelf these days, but they are pricey. A set of 2nd hand shimano deore solid alu cranks can be shortened for relatively cheap

The Lyne or SRAM 3 bolt cranksets are also a really good option as you can fit a 28 tooth narrow wide DM chainring while a 30 is the smallest you can go with a 104mm spider.

 

Thanks
This link seems to have some interesting info 
https://thebikedads.com/kids-cranks/

[mrcg]

15 hours ago, Jewbacca said:

Nils might still have a few inserts.

There is a kit you buy with standard and reverse thread sleeves that are also threaded on the outside.

So you drill the original hole out, tap with the supplied tap and then epoxy in the threaded insert.

New pedal threads in 10 minutes!

You can order the kit off E-bay for a few hundy too

Thanks for the details. Question: is the epoxy strong enough for such a high torque spot? Anyway, will hit up Nild and see what he says. Thanks again

[Jewbacca]

7 hours ago, mrcg said:

Thanks for the details. Question: is the epoxy strong enough for such a high torque spot? Anyway, will hit up Nild and see what he says. Thanks again

Bear in mind the epoxy is being used more as a thread lock than anything else.

No more torque on those threads than there are in your pedal spindle threads which you definitely don't epoxy in place......

I have done thousands of KM in one of these on my BMX, which is also home done shortened cranks, so it definitely works and is neater and more user friendly than a helicoil when you change pedals.

 

[DJR]

8 hours ago, mrcg said:

Thanks for the details. Question: is the epoxy strong enough for such a high torque spot? Anyway, will hit up Nild and see what he says. Thanks again

Locktite is just an epoxy. And remember that most modern airliners are held together with epoxy these days............enjoy your flying.