Can't get crank arms on after removal

[Tom3holer]

Hi,
The most curious thing happened as I was replacing my crank arms and gear for a larger size to help with ghost pedaling.
Both the gear and opposite arm came off very easily with the park tool.

When I went to replace the gear and associated arm neither would go on very far. I was afraid I was going to strip the hex bolt.
I then decided to replace them with the original set and had the same issue.
There is a couple of pictures. Thought I best stop and ask the experts.
The bike is a K6 Euybike but the fact that the original ones will not go on any further that the new ones is a puzzle.
My thought was to coat the spindle with Never-seize. I do have an impact wrench with the correct allen socket but from what I have read and videos it should not came to that.
Has anyone seen this before?

 

[stompandgo]

Those look like square taper cranks. Those have four flat sides. Is that what you have? If so, never lubricate square taper crank mating surfaces. Clean both the spindle ends and the insides of the cranks with a clean rag and isopropol alcohol. It's possible that your fit issue is due to the crank machining not being uniform on each side. The cranks may only fit on one way. Try the non-crank side first. Try each side until you get the fit you expect, then orient the crank side 180 degrees out from that. Tighten with a torque wrench. Do not use an impact wrench.

 

[Tom3holer]

Thank you very much for the information.
I will try what you suggested; yes it is 4 sided.
Why don't ever use lubricant?
I will try tomorrow, and I have several torque wrenches. What setting should I aim for?

 

[stompandgo]

Lubricating a taper shaft throws off the torque reading. The steel spindle will damage the aluminum crankarms if overtorqued.

The torque setting is very dependent on the bike itself. I don't know what your manufacturer recommends. Off the seat of my pants, I'd say between 30-40Nm should be close.

 

[indianajo]

I always put anti-sieze on my crank arms. Something about them NEVER coming off until I bought a fiddly excruciatingly correct Pedro crank removal tool. Worn out cranks with 15 deg play would not come off my previous bikes.
You can determine the crank has touched bottom by the rapid increase of the torque at a certain position of the wrench. That, and not the absolute value of torque, tells the experienced mechanic that the part is fully installed. Second the recommendation not to use an impact wrench. Use those on 35 ton semi-trailer brake drums, not bicycles.

 

[Base]

Square taperd bottombracket spindles came in 3 types of sizing. Most common is JIS. The crank bolt would go 38 to 42Nm based on the steel axle and alu crank. And indeed that is a bit of force.... Generally these are mounted with 40Nm, like the lockring of the centerlock rotors and the lockring on the casette.