The Eagles have won just once at Selhurst Park in the league since the turn of the year and the City substitute ensured a pointless afternoon for Neil Warnock's men as he raced on to Jon Stead's pass and chipped the ball over the stranded Julian Speroni.
Neither side was able to fashion a proper opening in the early stages and Palace's Darren Ambrose had the first serious effort on 28 minutes, but his low shot squeezed through the legs of Keiren Westwood and beyond the goalkeeper's left-hand post.
A mistake by Nick Carle gave Coventry a chance to go in front in the 41st minute. The Australia international was stripped of possession in the box by Carl Baker but his shot was blocked by Clint Hill and Michael McIndoe could only prod the loose ball wide from close range.
As the game sparked into life, Ambrose had a shot cleared off the line by Richard Wood and the Sky Blues had the last notable effort of the opening period when Stead's fierce strike was beaten away by Julian Speroni.
Palace broke dangerously in the 55th minute as Ambrose lifted the ball out to Carle on the right flank. His cross was met by the head of Johannes Ertl, whose header was pushed behind by Westwood.
Aron Gunnarsson wastefully fired straight at Speroni in the 74th minute, after Clinton Morrison's back-heel had put him clean through on goal.
Carle was denied his first goal of the season as Westwood made a superb reaction stop from his fierce shot but, with time running out, it was left to Bell to score late in the day to send the Sky Blues home happy.