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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 07-08-07, 04:26 PM   #1
merlinextraligh
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Don't stick your hand through the Timing chain

Just a little lesson learned. Dropped the drive chain today. In putting it back on I reached through from the left side of the bike without even thinking about it. As the chain went on, and I pulled my hand back, my index finger got caught between the timing chain, and the spinnning chain ring, creating a nice little puncture wound where the tooth went into my finger.

In hindsight, it was obviously stupid to reach through from the left (or at least, not through the timing chain.)
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Old 07-08-07, 04:29 PM   #2
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Fixed gear bike drive trains and tandem timing chains: evil things....

Special attention to children around such things is always warranted and prudent.
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Old 07-08-07, 04:30 PM   #3
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Yup, chainrings have real metal teeth!
Put some peroxide on that wound . . .
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Old 07-08-07, 09:31 PM   #4
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Is that tandem that bit you up to date on it's shots?
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Old 07-09-07, 08:27 AM   #5
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Has anyone ever thought to put a tensioner on the timing chain? It seems like it would be more forgiving of those momentary lapses of judgement.
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Old 07-09-07, 11:46 AM   #6
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Hmmm. I'm new to this timing chain stuff. Do they tend to fly off often?

Andy
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Old 07-09-07, 12:27 PM   #7
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The timing chain didn't drop off - the drive chain did.
Apparently, tension devices (similar to what you would use for a singlespeed with vertical dropouts) have been used on timing chains. More common is an eccentric bottom bracket for the captain that can be adjusted for proper tension.
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Old 07-09-07, 01:48 PM   #8
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Ah, thanks for the clarification. Now I know why that eccentric gizmo is there.

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Old 07-09-07, 03:27 PM   #9
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If you dropped timing chain, your feet would suddenly spin and stoker would be doing all the work. That's why eccentrics/tensioners exist, to keep timing chain from falling off.
Worse is to break the timing chain . . .
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Old 07-13-07, 08:00 AM   #10
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My timing chain is on the right side, and has a tensioner (old cheap tandem). When I ride with my son as stoker, he tends to suddenly stop pedalling, or suddenly to pedal hard. This causes whip in the chain due to the flexibility afforded by the tensioner, the chain comes off, and gets stuck between it's rear chainring, and the drivechains rear chainring. It's my least favourite thing.
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Old 07-13-07, 12:43 PM   #11
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Pardon my mechanical ignorance but maybe you could fix that whip problem with the spring loaded section of a derailleur that takes up the slack when you shift gears. I've seen one picture of a home-made tandem that used two of the for taking up the tension on the timing chain. This might take up the whip as it can dynamically add or remove tension.
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Old 07-13-07, 01:53 PM   #12
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Well, at least you got to keep your finger. Unlike the guy whose photo an overzealous moderator has removed, not realizing it's from Sheldon Brown's website, and is definitely educative material.

Last edited by wroomwroomoops; 07-16-07 at 10:46 AM.
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Old 07-16-07, 03:59 AM   #13
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Or you could use the rather cool Sheldon Brown method and place a slightly larger chainring in between the timing chain to hold it tight. Some fiddling is required to get the right size, but once fitted the chainring just sits there and rotates. Very cool.
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Old 07-16-07, 07:57 AM   #14
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Quote:
Originally Posted by mrfish
Or you could use the rather cool Sheldon Brown method and place a slightly larger chainring in between the timing chain to hold it tight. Some fiddling is required to get the right size, but once fitted the chainring just sits there and rotates. Very cool.
I've seen that referred to as The Magic Chainring.
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Old 07-16-07, 10:48 AM   #15
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Originally Posted by mrfish
Or you could use the rather cool Sheldon Brown method and place a slightly larger chainring in between the timing chain to hold it tight. Some fiddling is required to get the right size, but once fitted the chainring just sits there and rotates. Very cool.

That's not really Sheldon Brown's own method, he didn't invent it. And it doesn't always work fine, regardless of your efforts: the ghost or floating ring can fly off at higher cadence, and then you're slightly screwed.
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Old 07-16-07, 07:00 PM   #16
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Quote:
Originally Posted by merlinextraligh
Just a little lesson learned. Dropped the drive chain today. In putting it back on I reached through from the left side of the bike without even thinking about it. As the chain went on, and I pulled my hand back, my index finger got caught between the timing chain, and the spinnning chain ring, creating a nice little puncture wound where the tooth went into my finger.

In hindsight, it was obviously stupid to reach through from the left (or at least, not through the timing chain.)
So I'm not the only one silly enough to do this! I did this to my middle finger many years ago when I was new to tandeming.
Still have the scar.

Cheers

Geoff
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Old 07-16-07, 07:58 PM   #17
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Have used the 'floating chainring' idea back in the mid-1970s on our Follis tandem.
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Old 07-17-07, 07:37 AM   #18
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I'm a member of the club, too! I was lubing the timing chain, spinning the cranks using my index finger on the crank spider. My finger slipped of the spider and into the chainring-chain junction. OUCH!! I've haven't tried that trick again!
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Old 07-17-07, 08:02 AM   #19
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While we're issuing warnings, let me offer mine. When the wheel sensor on your bike computer is not picking up the spinning spoke magnet, do not attempt to make the adjustment when you are cruising down the road. I learned that one the hard way. One of the spokes came around and took a nice flap of skin off of my thumb. Ouch. Bled for the remaining 28 miles of the ride and then some. Take it from me - stop the bike and fix the issue on the side of the road.

Here's another one that fortunately didn't happen to me. It happened to a participant on our club's annual multiday event. A guy on a single bike rode over some glass, so he thought he would use the palm of his glove to brush any imbedded glass off his tires to avoid flatting. When he reached for his back tire, his hand got caught between the tire and the brake calipers. Stopped the bike, causing him to crash, and tore off his thumb! Double ouch!! Fortunately they were able to stitch his thumb back on. Don't try this at home kids. Better to get a flat tire.
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Old 07-18-07, 02:19 AM   #20
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Stopped the bike, causing him to crash, and tore off his thumb! Double ouch!!
I'll say!!
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Old 07-18-07, 08:26 AM   #21
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We all do dumb things once. Problem is doing it twice. Good to hear warnings from others.

While riding along I saw a beer can on the road, and thought I'd try and ride over it to squash it. As you can imagine the can somehow wrapped itself round the tyre and got stuck between the fork and the tyre. Luckily it was a gradual deceleration so I didn't do a superman over the bars.

...some years later...

While riding into town I thought my front QR looked a bit loose and being clever thought I'd kick it while riding along to get it properly closed to avoid an accident (ha ha). I gave it one good kick and my foot bounced off and nothing happened. So I gave it another good kick. This time my shoe bounced sideways into the front wheel, stopping the bike dead. I faceplanted, blacked out for a few seconds and ripped my new down jacket. After the ambulance had checked me out, I made it back home with only facial grazes to show for my stupidity. Turned out the QR was practically rusted solid and could not be moved.
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Old 07-18-07, 11:09 AM   #22
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While riding into town I thought my front QR looked a bit loose and being clever thought I'd kick it while riding along to get it properly closed to avoid an accident (ha ha). I gave it one good kick and my foot bounced off and nothing happened. So I gave it another good kick. This time my shoe bounced sideways into the front wheel, stopping the bike dead. I faceplanted, blacked out for a few seconds and ripped my new down jacket. After the ambulance had checked me out, I made it back home with only facial grazes to show for my stupidity. Turned out the QR was practically rusted solid and could not be moved.
I know you didn't mean this in a humorous way. I laughed my balls off anyway.
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Old 07-18-07, 12:13 PM   #23
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Here's anothter one. You're riding your road tandem (or half bike) and you glance down and notice that one of the plugs that secure your handlebar tape is backing out. Your initial response may be to pop it back in using the palm of your hand to give it a sharp impulse. Don't do it!!! Your steering will likely go unstable and you will probably crash. If you can't push it in with light finger pressure, you're better off stopping or even losing the plug altogether. This hasn't happened to me - I was fortunate enough to learn this lesson the easy way. I watched someone else make the mistake.
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Old 07-23-07, 06:32 AM   #24
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wroomwroomoops, glad you liked the story. Enough time has passed that I can smile about it.
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