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
Crank arm fell off. [thm clavicula]
Moderator: robbosmans
@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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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
Possibly useless anecdote: 
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.
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.
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?
^ 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.
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.
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..
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..
Rob English "Mudfoot" 29er | Focus Izalco Max | Firefly #194 Stainless XCR | Firefly #277 | Neilpryde Bura SL 11.9 | Crust Evasion Lite
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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- Factor LS Disc
- Specialized Aethos Disc
- Sturdy Ti Allroad Disc
- Guru Praemio R Disc
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Have had both Clavicula's, old and newer SE. Would be willing to bet it was an inproper install. Especially when the locking bolt was missing. When assembling they tell you to grease axle and bearing races, and be sure to remove all grease that is on axle after sliding it through bottom bracket. I always used alcohol on both axle and inside left crankarm. With torquing and locktight it won't slip. They also tell you to double check the torque after a couple rides.
