Make sure the spindle and mating surface of the crank arm are perfectly clean and greased. Then use a torque wrench at around 20 lbs-ft. The less torque you use the better as every time you take it off and put it on, it stretches the soft aluminum of the crank arm, which makes the crank arm fit closer and closer to the BB, changing the chainline, among other ills.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1