Why does this hollowtech crankset have play?

Question

Background

• Shimano deore crankset (not XT)
• The crankset has done about 10000km (6200miles).
• It is from a touring bike.
• Most of those 10000km was done with the bicycle loaded (bags on both front and back racks).

Problem

The crankset in the picture has play in the directions shown by the arrows.

However in this position (180deg opposite) the crankset does not have play.

I do not notice the play while riding. I notice the play when tugging at the cranks with both hands.

When I take off the crankset, clean everything, then grease and re-install the crankset, the play is gone but comes back after about 100km (62miles). The play does not seem to get worse.

On half of the inside of the crank (non chain wheel), there are teeth marks. The teeth marks are smooth as far as I can tell.

Here the marks.

Here on the other half no marks.

On the axle / spindle there are similar marks on the one side but not the other side.

Here with the marks. Again the teeth marks are smooth.

Here the half without the marks.

Questions

1. Is the play indeed due to a worn out crank? (I have not got the tool to remove the bottom bracket, so I cannot test to see if it is the BB)?
2. Are the markings, or rather this type of wear normal? The original crankset was a deore XT which never had play and did about 20000km (12400miles).
3. When buying a new crankset, should I buy the more expensive or the less expensive? I was told expensive means light materials but quicker wear of the chain wheel, and cheap means heavy materials (metal) but the chain wheel lasts longer?

Answer 1

The marks on the splines look about normal. It's hard to tell absolutely from the pics. You're looking for any sign of deformation or rounding, which occurs if the pinch bolts are loose while riding. Always make sure the pinch bolts are nice and tight, 14Nm or about as much as you would ever put through a long-handled 5mm L-wrench.

You need to be able to torque-check your BB cups to go further. If one is loose that can cause all the issues you're experiencing. Replacing the BB entirely at this mileage is within reason too, although if it still works and feels great then by all means keep with it. Note they can have issues with looseness that's not accompanied by poor bearing feel. For example, the black plastic "top hat" of an HT2 BB can get cracked or come apart and preload will be erratic like you're experiencing even if the bearing feel is good.

Answer 2

In Shimano cranks the plastic bolt is hand tightened prior to tightening the pinch bolts to 'preload' the bearings and take up play. When the plastic bolt is tightened the crank arms press on the inner bearing races only which is what takes up the play. If you remove the left crank arm and take away the preload you will feel a some play in the bearings.

I'd say try installing the left hand crank arm and adjusting the play take up properly with the plastic bolt. Also make sure you are doing the crank pinch bolts up to the correct torque so the crank arm is not working loose on the axle.

As usual Park Tool has a great video that shows how to do this.

Answer 3

Looks like it was ridden while the bolts were not tight enough. Possibly only hand tight. I've seen similar wear several times. Only takes a few miles of riding to incur the initial damage and then the left arm will not seat correctly again. Your bb is probably ok along with the crank spindle. I would look into replacing only the left side arm.

Mark

Answer 4

Check the bearings and make sure they haven't seized, resulting in the axel rotating inside seized bearings and wearing out, causing play. If this has happened you will need a new chainset, and bearings.