DEFENDING champion Wong Chi-sum will be bidding for his fourth successive Sun Hung Kai China Coast Marathon title when the race is staged tomorrow. More than 400 runners are taking part in the event, which begins at 6 am and takes in a hilly course near High Island Reservoir in the Sai Kung Country Park. Wong, of Road Runners Athletic Club, clocked two hours 48 minutes 50 seconds last year, which is regarded as a respectable time on such a demanding course. The record for the present course, which was adopted in 1987 due to traffic problems in the area, is held by Kevin Ball with an impressive 2:38:44. Tomorrow's race has attracted nearly 50 runners from Japan.