Four men pleaded guilty to a series of assaults in which a drug-injected boy was sexually molested. Henry Franklin Chapman, 53, his brother Delbert Edward Chapman, 56, James Andrew Rodriguez, 27, and Richard Dale Harrison, 46, entered the pleas before Riverside Superior Court Judge J. William Mortland. The assaults, which took place from 1981 to 1984, involved one of the men's sons, who is now 14. Deputy Dist. Atty. Paul Grech Jr. said that in each instance, one man restrained the boy while another assaulted him. Henry Chapman and Rodriguez already are serving 16-year state prison terms for sexually assaulting another boy, Grech said. In court, Henry Chapman and Rodriguez each pleaded guilty to two counts of child molesting. Chapman was sentenced to an additional 14 years. Rodriguez was sentenced to nine more years. Delbert Chapman and Richard Harrison both pleaded guilty to one count of child molestation. Mortland sentenced Chapman to five years and Harrison to three years.