PSA: Chainwheels are nasty
 

This is what happens when you get impatient removing a crankset.

https://cimg2.ibsrv.net/gimg/bikefor...0e8b490893.jpg

In the ER awaiting my 5 stitches. Hastily bandaged at home so as not to bleed all over my car. Also, don't go back and finish the job before the lidocaine wears off. When they tell you not to use the hand, don't use the hand. Now I have nice, new chainrings on a bike I can't ride.

have you tried the head in the vise trick?

Not since I retired. Saved a sh&%load of money on Advil.

Did you see bone? When I did it gave me a sick feeling. Mine came when tightening a Stronglight 99 crank with it's 16mm arm bolt. needless to say I think about that every time I touch a wrench to a crank arm retaining bolt. Andy

Sorry about the wound. I hope it heals rapidly and fully.

Wrap the chain around the (big) ring.

And put a rag over the chain. Chain will bloody knuckles every time.

I'm pretty sure it cut to the bone, but the wound was too bloody to see. I take blood thinners, which compounds the problem quite a bit. It was very painful after the anesthetic wore off, and I was worried that I had popped a stitch by continuing to work on the bike after I got back from the ER. I took the dressing off and the stitches were intact, but I'd aggravated the wound enough that it started bleeding like hell again. Plavix will do that. It looked a lot better when I changed the dressing this morning. I did a little light work on the bike today, but I didn't use my left hand for very much.

The chain was already off the bike. I was doing a complete drivetrain overhaul – repacked the wheel bearings, overhauled the rear derailleur, new cassette, chain, chainwheels. The fixing bolt on the crank arm was a little stubborn, and when I put a little more oomph into the wrench, it let go and my hand went into the chainring. That was incredibly stupid. I knew better than to loosen it the way I did, but I was getting impatient; wanted to finish the job so I could ride the bike.

I did almost the same thing about 2 weeks ago. I also had the chain off, switching out chain rings. When I did it, I lost my balance when the bolt let go, and my arm scraped along the big ring . I had a nasty scratch from the heel of my hand all the way up the inside of the forearm, and a couple of inches above the elbow. The wound was not dirty as the rings were brand new. It bled a fair amount and for the next few days people kept asking my how I got a such a long, jagged scratch on my arm. My answer was impatience and a moment of stupidity.

I feel your pain.
Okay, not really.
Almost did myself a bad too a couple weeks ago as I was working on my cranks.
I usually err on the side of haste gets you injured but I stared at that narrow wide bad boy for a second and decided that I'm too old for that *****. Wrapped the ring with a rag. Twice.
Still hurt when I broke the pedal and hit the ring but at least I didn't break skin.
Put on some Neosporin to help that boo boo along.

Good tips, but if I had been patient enough to wrap a rag around the chainwheel, I'd have been patient enough to get a different grip on the wrench. I've done this job dozens of times, too.

I've learned, the hard way, to either push with an open hand, or if you have the option, to pull up on a wrench.

But I still make mistakes, like crushing my finger in a fold-up bed. At least that was a hospital's fold-up bed, so the A&E ("accident and emergency"; or "emergency room" for North Americans) was right there. Pro-tip: if you tell the A&E receptionist you suffered your injury in the hospital, they don't even ask you about insurance details, and you get to skip the queue...

I did, but my ears got in the way. It made me forget about the pain in my hand though.

I hurt my hand every time I do this, which was as recently as yesterday. I never take the time to wrap a chain on the big ring and/or wear work-gloves.

But I should. I think you just convinced me.

I wear leather welder's gloves for jobs like that.

Whenever I'm working on the crankset, I angle the wrench so I can grab the crank arm and the wrench with both hands and squeeze. Always breaks easily and no chance of mangling anything.

My grip isn't that strong. If the crank bolt really doesn't want to break free, I take the bike off the stand and back on the floor and put my shoulder into it . Same for the pedals...

Sorry for your injury. Here's to healing quickly, and fully!

Been there. Done that, but not quite as severely. You did it big time. I think that the judges would give you a 7 of 10 style points, where 10 is the loss of a digit or limb. I hope you heal rapidly and completely.

Your sharing may help several people avoid this disaster, so thanks.

Practically, this points out that
1) Folks applying large forces in the vicinity of sharp bike objects should be aware of potential injuries like this and take steps to avoid, to wit:
2) One should have a safety chain to put around the chainring. Home mechanics if possible. Shops, for sure.
3) One should avoid applying a lot of torque to a crank when balancing the force with the pedal or crank ON THE SIDE OPPOSITE THE WRENCH. This means
a) If you can, get the wrench handle set up nearly parallel to the crank arm on the same side. This results in applying two forces in opposite directions. So tightening (or loosening) involves squeezing the arm and wrench rather than trying to apply 100 lbs or more of force to the wrench arm on one side of the crank, and balancing this with more than 100 lbs force using the crank arm on the side opposite the wrench. So that if something lets go you are applying a couple hundred pounds of force in the same direction.
b) I find squeezing the crank arm and wrench together is easy and best for me but I have large hands. If squeezing doesn't work for you then with the wrench and crank arm on the same side you can at least have one hand straight out bracing the crank arm, and the other straight out pulling(best) or pushing (ok). With both arms straight, the force is through your shoulders, and if something lets loose there's not a lot of travel that your arms traverse before the force is disippated.
4) Best to do work so that if something does let loose the hand that is freed and traveling at high velocity is not oriented to travel towards the chainwheel, or the floor, or your chin.

This also points out why you should use as short a socket as possible so that the force of the wrench is entirely tranlsated to bolt torque, and so that you don't have to use one hand to balance the socket end of the wrench. The Park Tool is nice because the socket is so shallow and very little axial moment is introduced. This also pointed out to me just how well-suited-to-purpose the old stamped steel wrenches were. Force was applied just about as close to the center plane of the bolt head as possible.

Don't ask me how I know this stuff or why I thought through it in such detail.

https://cimg7.ibsrv.net/gimg/bikefor...414978afbd.jpg
https://cimg2.ibsrv.net/gimg/bikefor...6a9baa6080.jpg

A follow up, post stitches, picture is warranted.

Addendum: the swelling in my thumb was down enough for me to ride the bike I was working on when this little tragedy happened. New rings, chain, and cassette – ah, the dead quiet and silky-smooth shifting of a new powertrain.

It should leave a pretty impressive scar. I already have quite a collection. It's why I never felt the need for a tattoo.

Soo ... which blood type makes the best chain lube?

O negative would be the universal donor chain lube - good for all chains...........

+1 for any version of peanut butter wrench... Deep socket bad.

I got my wrist/forearm scar trying to remove a freewheel incorrectly, while under the influence of cold medicine. Another form of impatience. A stupider form.
Heal well.