sestivers

I heard that this piece (#4 in the attachment), named "plate" by the Shimano technical documents, is supposed to keep the left crank arm pinch bolts from loosening. I don't see how it would accomplish this. Can anyone explain?

I removed mine because I thought it was making noise when I pedaled hard... it turns out that it wasn't the culprit. I don't feel like putting it back on, but should I?

Pete Hamer

That piece of plastic has a metal pin that fits in a hole on the axle. The left arm has to be all the way or mostly on for the pin to fit in the hole and the plastic piece to sit down flush with the arm. It is an indicator that the arm is installed far enough onto the axle. If the pinch bolts come loose it might help keep the left ccrank arm on.

sestivers

Good explanation, thanks.

Sheldon Brown

My guess is that the issue is the bolts loosening up and falling out while the crank, as a loose part, is in shipment.

You wouldn't want to tighten the bolts without a spindle, because it could overstress the arm by squinching it in too far. That little piece would permit the bolts to be at least lightly tightened withtout deforming the aluminum forging.

By removing it, you're probably saving the better part of a gram, so your bike should be MUCH faster!

Sheldon "Educated Guess" Brown

sestivers

Ha! You caught me. I actually did weigh it. My scale is accurate only to the nearest gram though, so it is somewhere between 0.5 and 1.5 g.

55-11

Sheldon, you dog... you feelin' better??? Well damn it, you better be!!! We NEED YOU!!!!