You would think but in the first post he said it was running fine just hard starting. Seems like most cases when button falls off then there is a no run problem. Wonder here the button / clip fell of when he removed the head. Since the button / plunger has some pressure on it from the tappet / cam could the button have stayed in place because the clip held it from going side to side. Just spit balling. We talked about it in a thread about the plunger sticking. If this happens and the gap between everything is there then the tappet and plunger come together with force could that knock off the clip and button. Then we have a no start problem. Good thing it is up and running with a new head and with new injectors it should be running tip top.
Nah James, you might be surprised to know I've had quite a few trucks where I've found the button and clip fallen off when I'm just doing hydraulic head o-rings on an otherwise good running truck. I'm inclined to think this is a compound issue of failed button retainers and tolerance stacking from worn components. I've also had a couple that started and ran fine, but lacked power. Pulled the heads to replace them, fiund the button off, reinstalled the button and put it back together and had good power.
I think the more years tick by, the more weird problems we are going to see with these pumps.
I guess my point is, he should hold onto the old head, it's probably still good.