Hi, I've got a Toro irregation system and on 2 of the many 4" popups, the heads keep popping off. When the head comes off there is a thin metal post that must fit down inside the water tube and somehow hold the head on the body of the popup. The end of the metal post/rod is flattened so it looks like you stick it down in the hole and turn it to lock in into place....but the heads continue to pop-off. I can't find a diagram of the internals otherwise I could probably fix it. Before I go spend $20 on a new pop-up, does anyone know why this is happening and how to fix it?

Thanks!

Here is a link that might be useful: {{gwi:329927}}