Here is a motor with a v8 configuration. It is two halves mounted ninety degrees from each other with the same crank shaft, connectors and pistons as the four cylinder just more of them. It is worth noting that they can be alternatively mounted flat or opposing piston configuration. I opted for the muscle of the V8!
I have added the crank shaft parts layout and the source file as separate files so if any parts brake, you don't have to print the whole thing again!
UPDATE: I have uploaded the fixed STL files, no more errors from Skeinforge! Thank you all for your valuable input as I am still learning too.
I have added a larger piston file but it requires good printer settings.
Use the file marked v8 layout fixed and V8 body #2 at the bottom of the file list for plate printing. One of the piston blocks wasn't on the build surface so now it is fixxed! Thanks to Thingiverse user JohnA for pointing that out!!
A little tricky to get together and a couple of approaches work so its up to you but here is how I did it. Look at the picture for some reference, the crank shaft is symmetrical and the same one as my 4 cylinder motor and the pistons have room on each mounting rod for two.
The pistons mount to the connectors with 3mm filament.
It helps to put the crank shaft together without the ends that it pivots on first, don't forget to put the pistons on as you go.
Then I put the piston and crank assembly in the cylinders then glued the blocks together. I used Krazy glue but what ever works for you, acetone, hot glue, etc. The cylinder blocks mount on each others end but note their is a rounded corner, I did this for a nice feel in your hand when holding the motor.
Finally I put in the two small rods that the whole thing rotates on and the crank handle.