tgot 

All,

Last weekend while out on a tandem ride I stood up on a very modest incline, only to have my pedal drop completely, as the timing chain dropped off.

Looking at it, I was missing a chainring bolt (I hope that's the right term) and the chainring had buckled away from the cranks. This had allowed the timing chain to drop off. My presumption is that the lost bolt was first, and chainring buckled as the result.

My wife rode back and fetched the car, as there were more hills home than my 5-yo on the kidback was going to pedal us up!

Is this something that happens on tandems, that timing chain chainring bolts can loosen?

Is checking tightness on those a maintenance item?

This tandem doesn't get many hours, just when we go for family rides. After buying it used, and having the kidback put on my a tandem shop, I've basically just lubed the chain, and once replaced fron brakepads. But i don't check chainring bolts on my single bikes either.

My inclination is to treat it as a freak occurance, but I thought I'd ask here.

Eric

cale

It's a maintenance item but an easy one to overlook. Easiest way to member to tighten them is to add them to your crankset maintenance routine. Generally, that part of the crank is really maintenance free. Sorry about the ring and any damage to the crank.

zonatandem

In over 240,000 miles of riding 'in tandem' (since 1975) had this happen exactly once.

Chris_W

I've only ever had poor-quality aluminum chainring bolts work loose, never well-tightened steel bolts. Fortunately, I've found loose chainring bolts before they've fallen out completely. A good habit to get into before starting a ride is to lift just the front wheel up by a few inches and let it fall to the ground. If anything sounds loose then go hunting for it, but unfortunately chainring bolts are unlikely to make much noise.

merlinextraligh

Some locktite on the chainring bolts wouldn't be a terrible idea.

Paul J

Never lost a bolt but we actually had our chain ring bolts loosen-up on an out and back overnight ride this past spring. I didn't have a chain ring tool with me but was able to tighten the bolts with an allen wrench to get home. These were the bolts to the larger two rings. Yesterday as we will climbing a fairly long hill, over a mile, the drive train started making noise and the wife (Stoker) looked down and saw the granny ring was wobbling. We stopped and two of the bolts were loose but when I tried to tighten they just spun around and would not tighten. Not sure why that is happening? This is on a triple 9-speed Race Face crank. When I got home I tried again and they just spun loose and wouldn't engage.

jnbrown

It should be a maintenance item, but something I rarely check.
I also found that aluminum bolts are prone to cracking / breaking and steel ones rust, so I prefer stainless steel.
On the bolts that spin loose, you might need a spanner wrench to hold the mating half:

JanMM

No substitute for that tool for traditional style chainring fixing bolts.
Some cranks, such as the truvativ elita on two of my bikes, require two hex wrenches, one the next size larger than the other. Somewhat easier to use and no special tool required.

Paul J

Not to highjack this thread but on my small chain ring it threads into tapped holes on the crank arm.

JanMM

That would be the norm on triples, would it not?

Bezalel

IIRC those bolts are for doubles only so if you want them on your timing rings, you need to use spacers. And if you want to tighten them on the road, you need to make sure your hex tools aren't both on the same multi-tool.

JanMM

Yep. Right about that. And right that it would be hard to use more than one tool on a multi-tool at the same time.

Squeezebox

Or sparkly pink fingernail polish.

fxsvelo

Or just get the right length bolts. We acquired a tandem that used the wrong length bolts on the sync rings and the wrench wouldn't engage. I just ground off a mm or two. Just took a few minutes. Later realized I actually had a spare set of shorty bolts.

LastKraftWagen

OP, whether it's a normal maintenance item or not, it's something I doubt you will ever neglect to check again... Thanks for the reminder.

nfmisso

Hi Paul;

The crank maybe toast. To make sure; I would remove the crank from the bike, and take a close look at the threads in the holes to determine if it is salvageable. If you are lucky, it may just need longer bolts. If not, then you have to make some choices, all of which come at a price. I have enough parts laying around that I can just replace the crankset with another.

Most granny gear bolts are threaded into the crankset and not into seperate nuts.

Paul J

Nigel, took the crank off and yes as you thought the threads are toast. My lbs is going to see if he can save it with a helicoil. He has a small machine shop. We tried longer bolts. I've got an older 8 speed Shimano triple I'm going to put on in the mean time. I think I'll look around and see if I can find someone with a Race Face crank arm tucked away in a spare parts box.