Algodoo

This is better but it has several problems
1 the box the crank is hinged to collides with the piston easy fix
2 the spawned circles need to be bigger try.21 also move the killer down
3 select the whole thing and set restitution to 0 you dont want bouncy parts
4 the piston needs to be slightly longer than the bore for stability and the rod
should be longer and hinged to the center of the piston or close to the center
5 needs more flywheel weight
6 the spawn box needs positive stops so it cant fly out of position up or down
I tried to "fix" it but realy couldnt without a complete rebuild
keep working on it, I'll help

i couldnt speak good english but i write in german you can translate it whit google ...

die wand des zylinders muss aus einzellnen rechtecken bestehen. der kolben darf keine reibung haben. die kurbelwelle muss schmehrer sein, ebenso auch die pleuell stange und der kolben selbst. wenn du illst verbessere ich dier diesen motor und stelle ihn erneut rein?

I agree with pfeff all major or crittical parts should be boxes or circles
you can use polygons for decorative parts that dont collide with anything
I uploaded a response that works fairly well without realy changing the base design
exept for the piston but to make a nice engine you need to do another build from scratch