View Full Version : Sheared chainring bolts: Near disaster

CNY rider
04-10-2008, 05:50 PM
So there I was JRA......

I was out yesterday on my relatively new rando bike (ridden one month last fall, then in the basement until 2 weeks ago).

First ride of the spring, 2 weeks ago, chain slipped off the inner ring. I figured it was a slight misadjustment of the FD low limit screw from the bike sitting all winter. I tightened the screw, no problems on the next ride.

Yesterday, the chain fell off the little ring twice in the course of about an hour. A creak also started that sounded like it was from the bottom bracket. I was then heading up my final climb to home, went to shift to the little ring, and dropped the chain again. Luckily I clued in at that point that something wasn't kosher.

What I found was shocking. There was a bolt holding the little ring on that was protruding inward, with the head in the process of being sheared off. Unfortunately it also took a good paint gouge out of the BB lug. The other bolts were loose. Looking at them, it seems like they are not long enough to go all the way into the hole in the spider and get good purchase.

Has anyone seen anything like this with a TA Carmina spider and Zephyr rings? I didn't put it together myself and have no experience with non-Shimano cranksets. Should the chain ring bolts be longer? I've tried to show that they don't come into the spider very far. If these really are the right bolts then how do you tighten them down?

This has me pretty shook up. I think a few more pedal revolutions on that ring and there would have been a distinctly unhappy ending if you get my drift.
View of the missing bolt:


Note the short appearing bolts in the 74 bcd holes

The sheared bolt:

roman meal
04-10-2008, 06:05 PM
Are they the alloy ones?

CNY rider
04-10-2008, 06:19 PM
I think so, but how would I know for sure?

04-10-2008, 06:31 PM
Inner chainring bolts typically come in three lengths, 10, 12.5, and 16.5mm. It looks like your crankarms have some threads showing and could take a longer bolt than those which were provided. Check to see if the threads are intact and if they're still good buy a longer replacement set and torque them to spec. Avoid alloy models and stick to steel or titanium.

04-10-2008, 06:43 PM
I think so, but how would I know for sure?

i'm no dr, but...

04-10-2008, 07:46 PM
The guy who built up my mtb boldly declared that the bolts he used--though shorter than recomended--were "long enough." (Hey, a few turns on the threads are all you really need...)
That turned out a little less happily than your incident.

Too Tall
04-10-2008, 08:02 PM
Call me crazy....but. I took a look at the mfg.'s site and your bolts don't look long enough however that's prob. not the problem. It is pretty SOP to double check triple bolts after the first outing and I always use blue loctite. I think your's loosened and broke. They just screw into the crank arm.

04-10-2008, 08:12 PM
Alloy bolts are fine but must be used with care. heavy oil is a preferred lube for the threads because it will help prevent corrosion. Also, a fine film on the whole thing is good. Just keep it clean. Finally, lubing the threads makes it very easy to overtighten and break them. But alloy bolts are a cool psychological advantage. But be careful with them.

Peter P.
04-10-2008, 08:40 PM
If there's not enough thread engagement, get longer bolts as someone else suggested so well by listing the exact lengths available.

Apply Loctite 242 (Blue) to the threads.

Avoid alloy bolts. Get steel. Check them by using a magnet.

CNY rider
04-10-2008, 09:00 PM
Thanks to everyone who has chimed in.
The depth of knowledge here is awesome.

Blue Jays
04-10-2008, 09:39 PM
Had super-lightweight bolts one time in my years of riding. The constant creaking gently reminded me something bad could potentially happen. Returned to steel and never looked back.

04-10-2008, 10:30 PM
I recently purchased a 7410 DA crank / rings off eBay. The crankset came with black anodized chainring bolts. I checked the tightness on them before swapping them onto my TG in place of my Ultegra set. Everything seemed fine. After about a week of riding, I managed to drop the chain going to the inner ring 3 times,, just like you did. I, too, thot it was the low limit screw out of adjustment, since the spacing on the 7410 is a little different than the Ultegra. On a whim, I decided to check the tightness of the chainring bolts again. A couple seemed a little 'loose'. So I dutifully got out my chainring nut tool to hold the backside with and proceeded to torque them down. I wasn't putting too much 'on' the first one and the head sheared right off. I had some extras, so I got one and swapped it in. But I had to use the spare nut to go on the 'new' spare bolt. Seems there was a discrepancy in diameter. I then tried to tighten another of the black bolts and, again, the head sheared off. At this point, I took all the black ones out and replaced with the chromed steel. Turns out, the black ones were aluminum. I'll not use that type again. Skeery.

Mike in AR:beer: