Dropped valve??
Check to see if the underside of the rocker was catching the retainer or spring edge. I have see this on many rockers even T&D. Standard 340 stamped rockers are clearanced . If you compare them to 318's you will see the difference. We just saw this happen to a set of Indy heads with T&D. When ckecked at HTA's shop while they were building our engine 8 yrs ago No. 1 cyl. was good . But when we took it apart the rest were all over the place. My son had to make a fixture and clearance them when refreshing the engine. The rockers were hitting the springs. We were lucky, The keepers were no good but being 10's they didn't let go. The push rods were also gulled due to not having a ball end. Some things are always overlooked
Check to see if the underside of the rocker was catching the retainer or spring edge. I have see this on many rockers even T&D. Standard 340 stamped rockers are clearanced . If you compare them to 318's you will see the difference. We just saw this happen to a set of Indy heads with T&D. When ckecked at HTA's shop while they were building our engine 8 yrs ago No. 1 cyl. was good . But when we took it apart the rest were all over the place. My son had to make a fixture and clearance them when refreshing the engine. The rockers were hitting the springs. We were lucky, The keepers were no good but being 10's they didn't let go. The push rods were also gulled due to not having a ball end. Some things are always overlooked