Crank arm fell off. [thm clavicula]

Discuss light weight issues concerning road bikes & parts.
eric01
Posts: 530
Joined: Mon Feb 06, 2006 1:06 am

by eric01

Design issue? Isn't that more or less same design as Shimano hollowtech? Slide the crank arm onto a splined spindle and then two perpendicular bolts tighten up?

Earlier poster suggested that modern bikes esp with weight weenie / boutique parts need to be inspected more often. I run mostly Dura Ace but even then I will do a quick bolt check about every 4-5 weeks to make sure nothing's wiggling loose. Takes less time than posting in internet forums! LOL
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jimaizumi
Posts: 711
Joined: Mon Jan 30, 2006 1:48 am

by jimaizumi

@eric01, its actually very similar to that of the Shimano Hollowtechs except that the process is reversed in which you insert non-drive crank arm onto the star-spindle first, clamp down the securing bolts, and then bolt down the preload cap. if you do the opposite, you wind up with a locked crank that doesn't spin. Pretty simple in nature and in installation but it only takes one small item that gets lost white riding and it totally ruins your day.
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by Weenie


leej88
Posts: 333
Joined: Mon Apr 05, 2010 4:22 am

by leej88

Image

This was what I was talking about.

Whatever the case is, I'm pretty sure a bit of loctite and two set screws would keep the crank arm from ever falling off.

For those who decide to buy their own set screws, the dimensions are: DIN 916 A2 M3x4

http://www.evt-schraubenshop.de/product/en/stainless-steel-A2/set-screws-and-rods-A2/DIN-916-A2-cup-point/DIN-916-A2-M3/DIN-916-A2-SOCKET-SET-SCREWS-CUP-POINT-M3x4-Box-500-pcs.html

KCookie
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Joined: Thu Feb 12, 2015 9:40 am
Location: Pom living in Australia

by KCookie

New Part ordered from Germany now just got to wait, luckily I have a spare bike, albeit a little heavy. Lol. !!!

trimenc
Posts: 94
Joined: Mon Aug 01, 2016 2:39 am
Location: North Carolina

by trimenc

Mine definitely did not come with that on my instruction booklet. I am going to email THM and see if they will send them to me.

User Name
Posts: 603
Joined: Tue Jun 07, 2005 3:32 pm

by User Name

Possibly useless anecdote: :D

The bottom bracket shell on one of my frames is a smidge over 1mm wider than usual, and my left 7800 crank would never stay tight on it, even though there was only ~1mm less axle to grip onto. I used to check it every 10 to 20km, but it kept coming loose. I eventually used mild Loctite, which did the trick.

TheKaiser
Posts: 511
Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

User Name wrote:The bottom bracket shell on one of my frames is a smidge over 1mm wider than usual, and my left 7800 crank would never stay tight on it, even though there was only ~1mm less axle to grip onto. I used to check it every 10 to 20km, but it kept coming loose. I eventually used mild Loctite, which did the trick.


When you say "it kept coming loose", did you find that the pinch bolts on the crank arm were loosening, or were those bolts still torqued to spec, but the crank was just slowly working itself outward on the crank arm?

User Name
Posts: 603
Joined: Tue Jun 07, 2005 3:32 pm

by User Name

^ Hmm, it was 4 or 5 years ago, so I'm struggling to remember the exact details, to be honest. However, both occurred (it was off the axle a bit and the bolts were a little loose), yet I can't be totally sure now which came first.

I'm in the habit of doing up the bolts pretty tight.
The first time it happened it had come off the axle about 1.5mm, and the bolts were noticeably loose. I thought I'd wrecked the crank. After that I was onto it, so I checked very frequently. After I saw it about 0.5mm off, I'd obviously do it up again. After a few rides I gave up and put the Loctite on it.

Denavelo
Posts: 382
Joined: Wed Apr 08, 2009 8:01 pm

by Denavelo

I had the same issue with my THM Clavicula. It's all in the preload bolt and applying Loctite to the bolt. You tighten and back off when the crank rotation is smooth and not tight. The key is the loctite on the preload bolt...

I never had a crank arm fall off, but I would get sloppy front shifting and in some cases I couldn't shift into the big ring. This alarmed me and then I noticed the arms were loose. Loctite solved everything! The preload bolt is tiny and has a lot of responsibility..
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kode54
Posts: 1213
Joined: Tue May 23, 2006 9:39 pm

by kode54

i've never had any issues with the THM M3...and i have them on all bikes. i followed the instructions as RyanH described. no issues in several years. the new set screws for the SE must be new. i do have a few variations on the adjusting cap....some with holes and most without.
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trimenc
Posts: 94
Joined: Mon Aug 01, 2016 2:39 am
Location: North Carolina

by trimenc

I contacted THM and they are sending me the new preload bolt, no questions asked! Great customer service. :)

qorwlch
Posts: 18
Joined: Sun Oct 20, 2013 3:03 pm

by qorwlch

used canyon ultimate cf slx

clavicura se crank set

loose crank bolt ;(
:x

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