Algodoo

Might wanna give the flywheel a nudge to get it going. S really kida acts like a brake come to think of it.

S acts as a brake because it is a friggin brake lel
use 2 keys, one to brake (which can be I) and one for the starter

For your second engine you should start from zero with this advice:

-Make it realistically sized: a 4 cylinder engine won't measure more than 0.75m * 0.5m. so if you're gonna make a 1 cylinder engine then make a 0.2m x 0.5m box and glue it to the background, and make your engine based on it

-Use 120 Hz: go to Settings (the gear) then Simulation tab, and put the silder in 120 Hz. Also use really high densities (100 - 300) as that makes collisions better

-Use a square as a piston, as it looks kinda better
also make the cylinder thin, it looks like crap

-Put the rod closer to the center of the flywheel. much closer, like at half of what it is on this engine

-Get rid of friction and restitution. friction obviously slows it down and restitution makes collisions worse

-Use a collision spawner, not lasers! You can copy one from me. Also you ONLY HAVE TO SPAWN ONE BALL, and this ball has to be spawned at the center of the cylinder and it HAS TO FIT PERFECTLY (not too big nor too little). you can change that at the radius part of the script

-Use a killer to delete the balls. much better at lower RPM

Also you should keep a good use of collision layers, they're really important in Algodoo!

Vaidas369 has a very good tutorial for spawn engines...