Baseball cards and clothespins are CLASSIC , but when I was inspired to make my son's bmx roar like a real 110cc dirtbike, I couldn't pass it up! He had been wanting to get a dirtbike for quite a while, but not quite ready to take on the responsibility that comes with such great power. (We were listening, Uncle Ben!)
So I thought I would try one of these to quench his thirst for 2-stroke madness just a little longer....
This is designed to fit a 20” BMX bike wheel, but could easily fit a mountain bike, or be scaled down for a smaller bike. I think 1” pipe would work well on a 16” bike wheel.
Step 1: Materials
I'm sure everyone knows about PVC, but in case you're wondering, ABS is the black tubing usually near the PVC in the plumbing aisle. Mostly used for draining and other low-pressure stuff. Each type uses their own special glue, so that may be a deciding factor. I chose PVC this time, 1) because I already had the glue, and 2) I had made one of these once before in ABS, and wanted to see the differences to be sure it was the same either way.
I had most of the hardware in my garage, as well as the primer and scrap steel. The rest I purchased, and spent less than $20 total. The paint and decals alone were $10, so all the fittings and pipe were relatively cheap.
Start by digging around the garage/basement/lab and see how much of this you already have laying around, then make a run to your local hardware store:
• 1 ½” pipe, about 12” long. My hardware store sold it in 24” segments.
• 1 ½” wye, be sure each of the three ends are all the same size!
• 1 ½” 90* elbow.
• 1 ½” 45* street elbow. This means one end is male, the other female. I don’t know why.
• 1 ½” X 1” bushing. It doesn’t matter if the hole is threaded or not, but the outside needs to be a slip fit like the rest of the fittings. Try to get one that has solid walls.
• A piece of scrap steel, about ½” to ¾” wide, and about 10” long, sturdy but bendable in a vise.
• A piece of sturdy plastic. My favorite is five-gallon buckets or lids. Today I have a laundry soap lid.
• A lag-threaded eye-bolt, 1” long.
• A pipe strap. Rubber coated is best. The hole on the end needs to be a close match to the eye-bolt.
• A small screw and nut to fit both the eye-bolt and the pipe strap. I used ¼ - 20 with a nylok nut.
• 4 small pan head sheet metal screws, size 8 or 10 are good.
• A washer to fit one of the sheet metal screws, about ½” to ¾” wide OD.
• Primer to match your pipe material (PVC or ABS?)
• Glue to match your pipe material. They do make a general purpose glue that is made to bond ABS and PVC together, but not always available. This can be handy if you can’t find all the fittings in one type.
• Chrome spray-paint.
• Decals of choice.
Step 2: Tools
• A rasp file
• A clean wire brush
• Hand clamp
• Tape measure
• Drill, with a few bits: a little smaller than sheet metal screw, a little larger than the same screw, and whatever size your rear axle bolt is. Mine was 13/64”.
• Razor knife
• Pen or marker
After you’ve knocked the bumps down, use the sandpaper to smooth it out. The cleaner you make it now, the nicer the paint will look.
Step 4: Trim the Wye
If you were holding it like a letter Y, cut the base off right where it gets narrow.
You will be fitting this end into the 90 fitting, so the outside will need to be reduced a little more. Start by going all the way around with a rasp file, trying to keep it fairly flat. The tendency is to taper it down, but then it won’t fit very far into the 90.
After it has come down in size a little, start trying the fit on the 90. You will feel and see the parts that are sticking, and can go back at it with the file. Once it fits at least halfway in, start sanding it to smooth it out.
After the flare is trimmed, it should fit all the way up to the angle on the WYE.
Also cut the bushing in half. This should fit all the way in without being cut, but it is really hard to get it in, and PVC tends to push out while the glue cures. You want about ½” left below the hex part, enough to still get plenty of glue, but the hex should now touch the flare on the 90 elbow when it is inserted.
Step 6: Try It on for Size.
Now we need to size it to the bike. The flare on the lower end of the wye will be in line with the axle bolt, though at an angle. By this I mean it will be pointing at the axle bolt while the pipe is floating above the rear forks. Try to center the pipe over the rear forks, but keep it from getting too close to the tire.
Other things to check are where the brakes are, any trim pieces, reflectors on the forks? I put mine almost up to the brake pads, and made sure the pads don’t bump the pipe when the brakes are applied, but you decide what will work.
While holding it in the approximate spot it will be mounted, measure how long you want the top tail pipe to be. Mark the pipe with whatever measurements you chose.
I don’t recommend letting the pipes extend past the tire, simply because the kids will back into things too easily.
Step 7: Cut the Beveled Ends
Remember to make your mark the longest part of the pipe! It’s pretty easy to get started upside down, and have the angle start at the mark and get longer…
If you don’t have a miter saw, just clamp it down to your bench, and cut it to whatever angle looks good for the end of a tailpipe!
The nifty part is that you just cut both ends at the same time! After fitting the top piece into the assembly, set the angled end flush to the workbench. Now place the rest of the pipe next to the assembly, angled end down and flush to the bench. By lining it up just right, and eyeballing the lower fitting, you can see where you should cut next. Cut about ½” above the end of the fitting.
Step 8: Mr. Yuck Says...
Wear gloves! This glue is nasty stuff.
Ventilate! This glue is nasty stuff.
Don’t lick your fingers! This glue….
Start with the primer, and follow the directions on the can, it’s pretty straight forward.
Right after applying the primer, start gluing.
Be sure to hold the pieces tight for 30 seconds or more, the glue tends to spring back, making fittings spread apart in a few minutes.
Also, press it tightly down on its side, on a flat surface, to align everything between adding each piece.
When you get to the two straight pipes, look to see that the angled ends are parallel, and use a straight edge to make the angles line up nicely. A 2x4 made a handy straight edge to press against until the glue had started to set.
Step 10: Bend the Bracket.
Take the steel bar, and curl one end to fit the outside of a fitting flare. You can use the piece you cut off of the wye for a template.
I used a vise, and several different objects to help get the curve right. What works best is to start about 3” from the end, make a slight bend, slip it out about ¼”, and make another slight bend, and continue this until it makes almost a half circle.
You want it to cover the flare that will be in line with the axel bolt, along the side closest to the tire, starting at the top, or about 1 o’clock, and ending at about 6 o’clock. I ended up curving it too far, so I trimmed ¾” off the end of the curve with the hacksaw.
After getting a curve that will hug the muffler pretty close, mark the steel at about the 5 o’clock position. This is just because whenever I tried to bend it at the 6 o’clock spot, it would always add a little more, making it off by a little bit. About 6:34...
If you are using a vise, take a hammer to the 90* bend to flatten it out a little better.
Drill the 3 holes slightly larger than your sheet metal screws, and file/sand any burrs off.
If the glue has dried, hold the piece onto the muffler, and mark through the holes onto the flare, where the screws should go into the PVC. Drill these holes slightly smaller than your sheet metal screws.
While you have this same bit in the drill, make one more hole in the bushing end of the muffler. Holding the assembly vertical, with the tailpipes down and the bushing hole facing you, mark the bushing at the 3 o’clock spot. Drill here with the smaller-than-screw bit.
Step 12: Make It SHINY!!
I draped my workspace in plastic, but only because it was too windy outside to paint in the driveway.
Step 13: Cut the Flapper.
Use a razor knife if you can be sure you'll have a sturdy place to cut. Strong scissors work well for this, too.
If the paint is still drying, you’ll have to just wait. This would be a good time to look up your local Home Owner’s Association by-laws, as well as any local noise ordinances…
Step 14: Put the Screws to It.
Remove the rear axle nut. Holding the muffler in position, mark where the hole should go for the axle bolt. Drill this with a bit just slightly larger than the axle.
If your bracket arm is a bit long, trim it down to about 1” below the hole.
Step 15: Mount the Flapper.
Cut the plastic on this line.
Cut a second piece to lay on top of the first piece, only covering from the back (outside) end to the inside edge of the bushing, making the plastic 2 layers thick over the bushing hole only, single layered from the pipe to the spokes.
Drill a hole through both layers with the larger-than-screw sized drill bit, right where the hole is on the front of the bushing.
Using the last sheet metal screw and a washer, mount the plastic to the bushing, and put a few drops of superglue between the layers to keep them from spinning separate from each other.
Step 16: Mount the Muffler.
Mark the flare of the bushing end wherever seems best, and drill with a drill-bit slightly smaller than the lag threads on your eye-bolt. Screw the eye-bolt into the hole.
Place the pipe strap on the fork, line the eye-bolt up, and fasten with the screw and nut.
Make sure the nut is tight! I used a nylon locking nut, but if you don't have one, give the screw a little bite on the threads with a pair of pliers. This will give the nut some grip.
Step 17: Trim the Flapper to Size.
Turn it into the spokes, and make a mark about ¼” past the spoke. Trim here with the scissors. Sand any sharp edges and corners down, so the plastic doesn't scratch any stray ankles...
Turn the plastic out of the spokes (upwards on mine), and trim the plastic so it is just out of reach from the spokes. Now you can turn it on and off!
Now that they won’t get damaged, you can add any decals to your liking.
If you haven’t already, straighten the tire out, and tighten the axle bolt down. My bracket was so narrow, I added a washer to grip the bracket better.
Step 18: The Moment of Truth...
Let the neighbors know what you’ve been up to, where you are, and how far away you are, all at the same time!
This was my first Instructable, so thanks for your patience with my fumblings. Any suggestions are heartily welcomed!
I've tried to add a video, cannot get it to embed. I'll try again when I learn how...