This 136-piece set in the series involves a jungle theme. With Gears! Gears! Gears! Movin' Monkeys you can either build the scene shown here or invent your own mechanical-jungle configuration.
The monkeys hang from various appendages to assorted parts of your contraption. I wouldn't necessarily have put gears and monkeys together, but I have to admit the gears and cranks DO look even more fun with tropic foliage and primates all around them.
Here's a product page for Gears! Gears! Gears! Movin' Monkeys from Learning Resources.