Proper use of a spring type torque wrench?

[Tom]

So I put the right crankarm back on this morning after carefully cleaning all the surfaces with rubbing alcohol. I find a sample chapter of the Barnett's Manual online (!) with recommended torque values... 285-350 it says.

So I whip out my trusty torque wrench and tighten it... to where the pointer goes to about 350 just before the bolt turns, and then it goes down to about 310 or so. Odd, but that's not inconsistent with how these often behave for me.

Anyway, after about fifty miles of course you get the quiet little something - not exactly a creak, but a something every time I hit the right side when I'm climbing.

I really don't think the crank is on as far toward the frame as before, but I don't want to crush the damn thing.

Did I not clean it well enough or did I not tighten it enough?

What's your guess?

I'm planning to check it again and see what gives.

[dave thompson]

.

[zank]

Did you grease the bolt threads, underneath the bolt head and both faces of the washer? It sounds like you had some stick-slip. Once you broke the bolt free, it moved with a lower torque. This is common when there is not enough (or any) lubricant. One thing that I will never forget from one of my engineering profs was that most (I say most because there is always an exception) torque values are based on a bolt being adequately lubricated with grease or anti-seize. You can lose up to 20% of the bolt pre-load if you torque it dry.

[Tom]

I check it now. I may have stopped too soon tightening it down. I don't want to round the thing out, but I don't want to split it either.

Normally I'm the jamoke that smashes stuff by going "Just another quarter turn" and I'm trying to break that habit.

[Brian Smith]

Once you pedal the bike hard enough, the crank squirms farther onto the spindle, and your bolt will "appear" more loose to your torque wrench eye.
It's like Zank says, lubrication on the fastener and washer mating surfaces, but I would add also lubrication on the threads (I like to grease the female side to prevent as much from flowiing out of the threads into the inside of the square.)
The torque value should be read while the wrench is still in motion, move in a controlled smooth manner with the qrench and your body in orientations that allow you to clearly read the wrench while doing this.

My experience is that often once a crank has been installed with a sub-optimal amount of torque and then ridden, that the crank will no longer remain as steadfast on the spindle even when later properly reinstalled.

Acetone will do an even better job cleaning oils off the spindle and crank mating surfaces, if that's what you want to do. I like Barnett's, and it's hard to go terribly wrong with their method, I've never split a crank with it.

[Tom]

Second ride, no noise at all. Beats the heck out of me. And I was chasing a couple of the locals up hills west of town that had me reasonably cross eyed by the top, so I was definitely putting some juice into it.

All I know is I'm going to get my rear kicked so bad over at Jiminy this weekend that I may give up cycling completely. It's going to be humiliating. The difference between riding around and going over hills by yourself and going over the same hills trying to hold onto people's wheels is ridiculous. These ex racer types are just plain annoying because they ought to get slow when they quit competing but of course they don't and they make it look so easy.