Thanks for the responses. I kept firing it last night while it was screeching and then took it apart. I think I found out what I did wrong. when I installed the 70D sorbo I simply glued it to the pad on the cylinder head. This knocked the AOE well out. The teeth on the piston were worn quiet badly. I think the noise was coming from the gears sliding past the teeth.
The washer in the spring was from the spring guide that came loose. It was a guide off ebay, just a cheap one. I guess the end cap wasn't thread locked on. I just stuck the original one back in it.
The anti reverse latch has two arms on it, it's weird. It'll only go on one way and if it were on wrong it wouldn't shoot all together.
Here's what I've done this morning;
- Took the original rubber off the cylinder head and attached the sorbo back on.
- followed a different guide for AOE
- reshimmed it
- bought a new piston ( and piston head as I couldn't get the other one off)
- greased everything
It seems to be firing fine again. One of the screws that clamp the GB together was stripped at the head so I'm going to get another screw from work before proper testing it out.
To me it looks like all this started from being lazy with the sorbo and not checking the spring guide. Live and learn I guess!