V-twin air engine (modular)

I had a couple of people asking me to make a v8 out of my earlier designs but i wanted to make a dual valve head anyway, so i made a new design.

This engine can be run as a single or a v configuration. All parts can be tacked to make an inline 1-many or a vtwin, v4, v6, v8, v10 and then you'll propably have to much crankshaft flex :P
I've made the v-twin version, it runs really nice and is a lot more efficient then my earlier designs. Who's going to be the first to make a v8? :)

Parts..
Plastic...
m3x35 bolt for the cylinders
m3x20 bolts vor the crankcases
m2x10 bolts for the tumplers and pistons
2mm rod for the crank and cam follower
1mm rod vor the valves and pushrods.
m3-someting for the crank
6x15x5 mm (inner/outer/thickness) ball bearings for the crank.(2 per v-twin) (https://www.ebay.nl/itm/10pcs-696ZZ-6x15x5mm-Ball-Bearings-Double-Shielded-Miniature-Ball-Bearing/142842244270)
2x5x2 mm bearings for the conrods and cam follower. (4 per cylinder) (https://www.ebay.n