RE: .60 P-36 Black Horse
sounds like a cool plane,
THe 615's can be made to work OK the locking problem is usually the screw on the shaft where the cylinder actuator rod attaches, If it loosens up the gear will not lock down. My current set had that problem. the screw there had worked out 1/8" so when down it didn't pull over center. check for that, and #2 the set screws are a bugger. I tightened mine as much as possible and used loctite. that minimizes the issues with them.