Introduction: Toilet Paper Engine

Simple, easy to make, and fun, this model engine is made from cheap easy-to-find materials. It runs on compressed air supplied by your lungs as you blow the piston down and then suck it back up! It demonstrates principles of motion and engine operation, and allows students to learn the main parts of any engine: Crankcase, Crankshaft, Connecting Rod, Piston, Cylinder, and Flywheels.

I can't take credit for "inventing" this cool project but I've adapted this to make it a lot easier to build, and it can be done very quickly. This is an activity I do with my 7th and 8th grade students in a Small Engines Repair class, but it could be used for many other activities like drafting, measuring, studying the laws of motion, or even a history project, as it closely remembers an old hit and miss engine. 

Content Learning Objective:

By building a Toilet Paper Engine, students will understand the basic principles of operation in an Internal Combustion Engine.

Language Learning Objective:

By building a Toilet Paper Engine, students will identify engine parts using their correct names; i.e.- a ping pong ball is not a ping pong ball, it is a Piston.

Please find included below an Instructions Booklet .pdf, a Template .pdf, and a Measurements Worksheet .pdf. Also included is a Google Sketchup model of the completed engine

Other Resources:

I have had a few people ask about other resources relating to engines that could be used when teaching, so here are a few! Excellent website that shows cutaway animations of just about every type of engine you could imagine! Wikipedia's take- a couple of great animations, TONS of information, and lots of other links to more websites. A couple of animations of different motorcycle engines- neat because you can hide different parts of the engine while the animation is running.

Step 1: Gather Materials and Tools

Lets start by getting everything we need together.

Tools Needed:

Hot Glue Gun
Wire Cutters
Drill or Drill press and Drill bit


Approx. 2 sq feet of cardboard  
Toilet paper roll or paper towel roll cut in half
8" of wire (a wire hanger would be perfect)
Piece of wood dowel ( just over 4" long and about 3/8" dia)
Ping Pong Ball
2 used or worthless cd's
Duct tape (you never know, right?)
Glue sticks for the hot glue gun
Small piece of sandpaper or file

Additional items that come in handy (especially if building with large groups):

Trace-able templates for the cardboard parts made in step 2. 
Several crankshaft bending templates
Instructions book
Pre-cut and drilled dowels for the connecting rods.

COST:  I estimate each engine has roughly $1.00 worth of materials.  The only things I had to buy was the Ping Pong ball (40 cents), the dowel ($1.00 was enough to make at least 6), and the wire (large role cost me $4.00).  I had sandpaper, tape, hot glue sticks, and everything else laying around.

Step 2: Cut Out "Crankcase" Parts

Plug your hot glue gun in, your going to need it in a minute!

Cut out the 4 main parts:  Base, Spacer Plate, Cylinder Support, and Crank Support.  Use the measurements found Picture 1 below.  Also refer to Picture 4 to see what they look like before they are folded. These pieces are all cut out of the same thickness corrugated cardboard.  You may want to label them, as the Cylinder Support and Crank Support are close in size and can be mistaken for the wrong part.

     *TIP- If doing this activity with a large group, make sure everyone writes their names on every single piece!  Things tend to get set down and then forgotten or picked up on accident by someone else.

Glue the main parts together:  Mark on the Base the mounting location (measurements shown in Picture 2) for the Cylinder support and Crank Support.  Mark on the Cylinder Support and Crank support the bend lines as seen in the last picture (measurements again found in Picture 2).  Score the lines and fold the parts.  Glue them to the base as shown in Picture 2.  Insert the spacer plate.  It is important to get it far enough down that the connecting rod doesn't hit it, but far enough up that it strengthens the supports.

     *TIP- If doing this activity with a large group, making templates of these four parts first can speed up the process, but its good practice with the ruler if you don't!

Attach the "bearings":  Cut out two squares of cardboard.  Size doesn't really matter on these but they should be at least 1" square.  Glue them to the outsides of the Crank Support as shown in Picture 3.  They should be as close to centered as possible and the same distance from the top- later we use these to line up the holes for the crankshaft.

Step 3: Build and Assemble Engine Internals

Now for the bits that move!

Connecting rod:  Cut the dowel so it is 4.25  inches long.  Drill a hole near one end that is slightly larger than the diameter of your wire.

Crankshaft:  Make a pattern on a piece of paper using the measurements shown in Picture 2.  Starting from one side and working towards the other, make the first two bends.  BEFORE you make the third bend, slide the connecting rod on as shown in Picture 1 and Picture 6!  The bends need to be as sharp and as square as possible otherwise the connecting rod can slip over to the side and seize the engine.  Finish making the bends and trim the wire down if needed.

*TIP-  For the engine to work well, the crankshaft should be as perfect as possible.  Spend time making sure the bends are all square and that the two ends of the crank line up when you are finished.

Piston:  Once the rod is on the crank, glue the Piston (ping pong ball) to the end of the rod as shown in Picture 1.  Get it as centered as possible on the rod, but it doesn't have to be perfect.

Flywheels:  Cut out 4 more squares of cardboard, roughly 1"x1".  Glue one square over the hole of a CD on each side as shown in Picture 3.

Step 4: Put It All Together!

Lets get it all in one piece.

Using your ruler, mark an X on the crank bearings as shown in Picture 1.  Poke a hole all the way through the Bearing and Crank Support, then repeat on the other side.  CAUTION-  Don't poke your fingers...  Insert the crankshaft as shown.

Cylinder:  set the Toilet Paper roll on top of the Cylinder support but DO NOT GLUE IT YET!  Spin the Crankshaft over a few times and make sure the Connecting Rod DOES NOT contact the Cylinder at the top or bottom.  If it does, slide the cylinder away from the Crankshaft until there is no contact and glue it down.  PLEASE NOTE that there should be some room between the piston and the cylinder- you do NOT need a perfect seal.  You want as tight a seal as you can get but still have the ping pong ball slide with zero friction.

*TIP- At this point, I like to demonstrate to my students the purpose of the Flywheels.  Try spinning the engine and see how many revolutions it will make before stopping.  Install the Flywheels, and try again.  Big difference!  Newton really knew his stuff!

Flywheels:  Mark as closely as possible the center of the cd's on the cardboard that was glued to them.  Punch holes in them with the crankshaft or an extra piece of wire.  CAUTION-  Don't poke your fingers...  Using the sandpaper, rough up the ends of the crankshaft to help the glue stick.  Install the Flywheels on the Crankshaft as shown in Picture 3, keeping them as far away from the bearings as possible but with at least 1/4" between the end of the Crank and the Flywheel for glue, and glue them on.

*TIP- I have found that putting glue on the end of the Crankshaft and then sliding the Flywheel on helps tremendously to hold them still.  You will need to glue both the outside and inside, as this is a weak point on the engine- the Flywheels tend to break free of the crankshaft.  Epoxy would probably work better here than hot glue, but if you are thorough, it will be fine.

Ready to try it out?

Step 5: Testing, Troubleshooting, and Running the Engine

Fire it up!

The engine should spin freely.  If it feels stiff or catches in spots, identify the location and see what you can do to fix it.  For common issues, see the troubleshooting list below.

Set the engine with the Piston near the front of the engine, away from the Crankshaft.  It CAN NOT be all the way to the front, it needs to be just off of Top Dead Center.  Put the Cylinder to your mouth and blow!  It takes some practice to get the timing down, because when the Piston gets to the bottom (far end) of the cylinder, you have to suck it back up and then start over.   See how fast you can make it spin, and see how slow you can make it spin. 

TROUBLESHOOTING: There are some common problems to watch out for.  See the last 3 pictures below for more info.

1.  Connecting rod hits the cylinder and stops the engine- Either move the cylinder away from the crankshaft of cut notches in the cylinder to prevent the rod from hitting.
2.  Rod falls off the side of the crankshaft- make tighter bends on the crankshaft or drill a smaller hole in the connecting rod.  Also make sure that the crankshaft is straight and installed as level as possible in the crank supports.
3.  Flywheels not attached-  hot glue is not the best for this application, and the flywheels can come loose.  Make sure to sand the crankshaft where it gets glued and spread the hot glue up the crankshaft a ways in front of and behind the flywheel.  Take care to keep it off the bearings though!
4. Engine hard to spin-  Check the ping pong ball in the cylinder- some toilet paper rolls can be too tight.  The easiest way to fix this is by getting a different roll, but you can also slit the roll lengthwise, spread it out a little, and then cover it with Duct Tape (told ya it would come in handy!).  Also check that the glue holding the flywheels on is not rubbing on the crank bearings and that the connecting rod isn't binding up.
5.  Engine spins freely but no matter how hard you blow the piston doesn't move fast or at all-  the toilet paper roll can be to big.  The easiest way to fix this is by getting a different roll, but you can also slit the roll lengthwise, overlap the edgest a little, and then cover it with Duct Tape (again, told ya it would come in handy!).

So there you go.  I've been toying with a few ideas on valves to make it a "blow" only- more steam locomotive engine style.  There are lots of different possibilities for this depending on your age group, supplies you have at hand, and the amount of time you spend on it.  Good luck, and have fun!

Hope you enjoyed my first ever instructable! Please let me know if you have any questions or suggestions.

Step 6: Variations

"Ride on toy dude" asked about the possibility of making multi-cyclindered engines, so I tried it out.  Here is an opposed "boxer" style engine you might find on a BMW motorcycle, or similar to a Volkswagen or Subaru motor but this one is only a two cylinder.  I built it with the same patterns, just flipped them around and extended the spacer plate and base.  The crankshaft is pretty straight forward- you could use the original crankshaft and just put two connecting rods on it but I chose to make it a "boxer", with both pistons going out at the same time.  I had to off-set the cylinders a little to account for the double connecting rods and the fact that they aren't centered on the crank, but other than that it was pretty straight forward.  Check out the pics, vid to come soon!

Step 7: Variations 2

Knocked out a new version today- The V4!  It would be very easy to add a few cylinders to this and make it a V6 or V8 as well.  I will eventually get around to posting more details but for now here's the quick version...

I took 2 cylinders and glued them together and repeated the process for the other side.  Built a base to help strengthen each bank and give me something flat to glue to.  That was the easy part.

The hard part was coming up with the cylinder supports that would keep the cylinder banks the right distance apart from each other and at the right angle.  I came up with a simple reversible plate that is glued to the side of one bank and then hooks underneath the other bank.  The plate is identical for the front and rear, just one is flipped over.  Took some measuring, but was quite simple with a ruler and a Combination Square to mark the 45 degree angles.

Next step was to figure out the crankshaft.  The first attempt looked good, but didn't work to well.  I attempted to make it like the crank on the Boxer engine, but it put the connecting rods and pistons out of line with the cylinders- it was just too fat. So I remade it and had two connecting rods share one crank journal, and that gave me a lot of flexibility in lining them up with the cylinders.

Assembly was a bit tricky- had to stick one end of the crank in, figure out which two pistons went in the first bank (took me about 3 tries to finally get it right), then put the other two pistons in the other bank of cylinders, and wiggle the crank through the other side.  Then it was a simple matter of lining the sides up and gluing them, then gluing it to the base.

I only wanted one flywheel like you would find on an automotive style engine, but I was worried that this larger engine would need more weight to power it through so I glued two CD's together and stuck them on the crank.  As you can see I balanced it with a quarter- You wouldnt need to do that if you bent the crank with journals at 180 degrees, instead of at 90 degrees like I did on this one.

There you go!

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