Loose crank arms
I seem to need to retighten the bolt holding my crank arms in place every four or five rides. The cranks begin to wobble. Is there anything I can do to prevent it from loosening so quickly?
Are you torqueing the cranks tight enough? They should be torqued to about 30-35 foot pounds.
I have experienced this same problem with my Ultegra cranks when they were brand new. I had to tighten them up several times in the first few months, but now they stay tight. Do not ride with them loose as the spline bottom bracket can easily damage the crank arm if the crank is allowed to wobble a lot.
Richards’ Bicycle Repair Manual recommends checking the tightness of new cranks every 25 miles (40km) for the first 200 miles (320km) of use.