Mixing parts between used gearboxes

[Jackarutu]

Before I can begin this discussion I must first define the two half of the gearbox so my description is easier understood. When looking at the rear of the gearbox let’s call the left hand side the left side and the right hand side the right side. So okay with that definition in hand lets all agree when we assemble a gear box we start with the left half on the work bench and start assemble the internal parts into the left half and as we finish we then join and close the right half.

Now I don’t know about the rest of you but I have parts bins for each part.

When it comes to a part like a trigger for an M4/M16/AR15/M733 a trigger is a trigger to me. So if I dissemble a used gearbox that used trigger might end up in the bin with the new ones. But what harm can that cause? A trigger is a trigger yes? I mean for the most part what can go wrong with a trigger?

So yesterday I was whizzing along assembling a version 2 gearbox when it became apparent the two half’s of the gearbox didn’t want to set flat in the area around the trigger. So I take it apart, put it together, Take it apart, put it together. Hum . . .this is something different.

Long story short. The shaft that the trigger pivots on would not fit into the hole on the right gearbox half. It would start to engage but then the hole got too tight before the casting half would mate up. So I had to rim the hole slightly in order to get the gearbox to seal up correctly.

Is it all my bad living catching up with me or do any of you have these minor set-backs too?

[venture]

I have heard a lot of doom scenarios from mixing/matching parts, but personally I have not had too much trouble. Little things like you mentioned. I had to dremel an aftermarket pistolgrip for the motor to fit freely enough to be adjustable. Probably just a defective run in yet another Chinese factory.

Not that I have a great amount of experience. Perhaps some of the more experienced docs have some good horror stories.