Engine Upgrade Set

This part set represents my first attempts at using 3D printing for my model building hobby. After going through my sprue box for a model, I realized I had great upgrades for engines, but no engines to use them for...so I made one.
This also may be of use to scratch builders. More will be coming soon!
Also, this a major work in progress for me, so any comments or thoughts would be greatly appreciated!
I've printed this on various things ranging from a Makerbot thing-o-matic to a Markforged Mark 2