Is this normal wear on a crank?

Was doing some deep cleaning and noticed this. Is this normal wear?

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Yes. Normal. At least that’s what my Shimano cranks look like on both my road & mtb.


When you put them back together put a nice coating of grease on that spindle.

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Are you sure? What experiences have you had that led you to this conclusion? Per Shimano’s installation of this specific crankset, grease is only used on the axle of the spline.

Have been doing it forever…it keeps water and dirt from getting in…reduces friction, makes it come apart easier. There is really no reason it would hurt anything.


Right on, thanks for the insight. I see the logic in that.

Cool…im a big grease fan…thru axles, cassette bodies, inside headset cups were the bearings sit, and pedal threads. Can’t go wrong greasing those areas.


Definitely not normal, my Shimano cranks always had way less wear on it than that.


They have 11,000 miles on them. GRX crank.

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In looking at the photos again this morning on my desktop the area right next to the splines does look more chewed up than I remember seeing on either of my spindles. The shiny areas look about like mine but the area between the shiny area and splines doesn’t. That area is covered by the crank arm I believe since it is after the spindle exits the BB. Maybe dirt is getting in there and grinding away? I also grease up the spindle before assembly and have never had an issue doing so.

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Afaik that is where the bearings sit. Occasionally they might lock up a bit and rotate on the spindel instead of within themselves. Think it’s pretty normal.

I’m also a fan of greasing most things where metal meets metal.


Plus, the grease will likely help with water intrusion, something the bearings will appreciate, too.

Doesn’t really reduce friction, there should be no sliding between this and the inner race of the bottom bracket bearing, the bearing itself should be spinning.

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How’s it look once you clean the black gunk off?

I wouldn’t go heavy on the grease. The bearing has to do the work. If the inner ring doesn’t grip the spindle the bearing won’t turn.

Personally I only put a slither of grease on the splines.

It will be from worn bearings meaning the spindle spins against the bearing, instead of the bearing doing the rotating. grease the spindle lightly, make sure your BB is in good condition.

First, let me qualify myself as someone who sells lubricants for a living and has decades of experience in industrial service and repair and has spent many years in a machine shop. (71 year old)

The condition you are seeing is what would be referred to in industry as a “spun” bearing; a condition in which the race of the bearing is spinning on the journal of the shaft. I suspect that the shiny areas are caused by micron-sized wear metals that act as polishing compounds when mixed with the lubricant. Bike components are very light duty, slow moving applications that do not require close tolerance fits compared to industrial applications. If this were an industrial application, there would be a slight interference fit between the shaft and the bearing. Bikes don’t require that kind of precision.

It seems to me that the only kind of prevention that could be done is yearly or semi-yearly disassembly and cleaning. If you are able to maintain a grease film between the bearing race and the shaft then you are already in trouble because it should be a tight slip fit at the least. Greasing for assembly is okay, but don’t think it will do anything besides that. The bearings should be filled 2/3 full of grease upon installation and then should not require greasing after that. I ran a BB bearing through our precision lubrication tool and the regreasing interval does not even register. My advice would be to use the best (Enduro or Kogel) bearings you can buy and use a grease that uses a calcium sulfonate thickener with a base oil viscosity (ISO VG) of ~220. NLGI #1 or #2 doesn’t matter for this application. I would never use a lithium thickened grease because those greases have the poorest water washout ratings. I have tried to find out the specs on bike greases sold by various companies such as Park Tool and they don’t furnish that information.

I looked around on the internet to see if I could find a grease I would recommend and most commodity greases are pretty poor. I did find a Lubriplate grease that I would recommend here: LUBRIPLATE SYNXTREME FG-2, 14 oz. Cartridge, (1 CT/EA) You might think $30 per tube is high but you get what you pay for. This tube would last you a lifetime but it is good grease. Don’t worry that it says FG (Food Grade). Most high quality grease suppliers are going to food grade because so many industrial customers want it. The quality doesn’t suffer. Also, don’t worry about synthetic vs. mineral. The quality of oils is so high nowadays that it doesn’t matter for greases. Again, bikes are about as low-tech as you can get.

Finally, how would you repair such an issue? In an emergency, a machine shop will knurl, or lightly indent the shaft at the bearing journal to create slightly raised areas to functionally increase the diameter of the shaft. Then the bearing would be heated and slipped over this area. This would be a last resort and could never be used again. Backyard mechanics when faced with this type of issue will sometimes use a center punch to lightly punch the circumference to create raised areas. Again, this would be an emergency, low-tech option and not one I would recommend.

I apologize for the long-winded reply but I thought some might be interested. Thank you.



This was fantastic! I learned a lot about machining and bearing science. Thank you.

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Shimano does use those plastic cups on the inside of their BB. I recall installing a GRX crank and Shimano BB in my wife’s bike and thinking what a s***load of grease there was on one of the parts from the factory - forget which, pretty sure it was the BB. Even if Shimano pre-greases the splines, there was enough to grease the whole shaft.

If you’re using someone else’s BB, especially Enduro which makes a 24mm ID bearing, I’d use a lot of grease. Use water resistant grease in any case- that’s what it’s for.

Edit: heres a Shimano BB fresh out of the box pre-greased on the spindle side.

Thank you Paul. Amazing reply.