No engines!
Yes! It's PISTON TIME!
You can use ONLY pistons to power your vehicle!
BUT...
That doesn't mean you can't use fuel!
Use it as a counterweight if you want.
Send entries as a successor or link them in the comments.
An upvote will be given to the following categories:
Most interesting
Most practical
Most fun
Most unusual
Most impractical
Silliest
Most unexpected
And...
Most expected(yes, most expected)
Rules
1.Entries must be submitted in at least 1 method
2.No submitting other people's work
3.Maximum 2 entries per person
4.No mods (excluding XML)
5.Have fun
6.Have a nice day

Deadline is July 20 plus or minus a few days since I'm going to Japan and jet lag.

Good Luck All