blamester &
Russ Roth are on the right track.
In my experience with Ultegra 6503 triple Octalink cranks, the One-Key Release makes removal with an 8mm Allen wrench easy.
It is with reinstallation where the one key release can make you think that the splines are fully lined up when they are not. So
csibi_david - I believe with your 5500 crank the first thing you should do is to back off the 8mm Allen bolt and examine the spines on the back of the crankarms and also the BB axle splines for gouging. Hopefully they are not damaged.
For proper reassembly I have found that an 8mm Allen
socket mounted on a
sliding T-bar offers the necessary tactile feedback to apply even, 2-sided pressure to the bolt as it is snugged down. A short Allen wrench does not. I apply grease to the threads in the hollow axle in order for the One Key bolt to turn smoothly. Grease on the splines I believe is optional. As you start the threading the first turn or two with the T-bar onto the spline, you can wiggle the crankarm slightly forward and back to gauge if the splines are mating or “riding high”. If it is the latter, it will clunk down then you will feel that the splines are now squarely mating up on a sort of 8 point taper. Your T-bar with 8mm Allen socket can now be used to safely advance the crankarm with even pressure until it bottoms out. If you do it this way you will
feel the greased threads and
know that you have done it correctly, no torque wrench required.
The opposite crankarm installation is identical. You can visually tell if you are one spline off in which case
Bill Kapaun is correct and that would be an obvious macro mismatch of 45 degrees from horizontal (drive side to non-drive side).
If you do the technique I outlined above where you wiggle the crankarm side to side when you first start to attach the 8mm One-Key release bolt, it will drop onto the splines correctly and you can pretty much see from the get go that any wonky-ness (if there was any to begin with) has now been dealt with and the arms are completely tight on their splines and in line with each other.
I hope this helps.