The tension between them grew in season 4 as Piney didn't agree with the club's plans to run drugs for a cartel, which along with him knowing too much about Clay, JT, and what happened to the latter led to Clay killing him at his cabin and framing the Lobos Sonora cartel.

Why did Clay kill John?

In "Brick" it is revealed that Clay had murdered J.T. and was sleeping with his wife. ... She says that Clay tried to kill J.T. by sending him into a Mayan ambush, then had forced Lowell Harland Sr. to sabotage J.T.'s bike and killed him to conceal the crime.

Does Clay get caught for killing Piney?

A police officer and two civilians were killed during the assault. Meineke dropped his cell phone at the scene, and his last calls had been from the Teller-Morrow Automotive Repair shop. When the ATF found the phone, they arrested Clay and raided the clubhouse. Clay was later released because no evidence was found.