Build a SWB recumbent bike

How to Build a Recumbent Bike using
garage sale parts.
4/2014 - W. Beauchamp
These instructions describe how to build a dual 20" short wheelbase (SWB) recumbent bicycle using garage sale parts in 10 steps. If you have some scrounging and building ability, access to some tools, and some time, you will be able to build your own nice handling and comfortable recumbent bike. You will be able to find most of the items at garage sales or even put out on the curb as "junk" for for waste pick up.

Garage sale items
1) steel framed BMX bike, preferably with a front brake and at least a brake mount in the rear.
2) Steel framed road or mountain bike with decent aluminum cranks and gears
3) Long skate board. A longboard is best. You will use this for the seat back and idlers. Also good idlers can be made from inline skate wheels.
4) Golf clubs with steel shafts. You can also find these cheap at thrift stores. You will use these for seat stays.

Note: Find a BMX and a geared bike with the same number of spokes in the wheels.

Other stuff you will need:
1) Good rolling 20" tires.
2) 3 derailleur chains
3) Derailleur and brake cable housing
4) Tube for the handlebar riser

BMX bike
You will use the everything but the seat, tires, and wheel hubs. You can use the knobby BMX tires if you really want to, but you will be so much happier with some nicer tires. 2" wide 20" tires are best for the wide BMX rims.
Derailleur bike
Remove the seat, wheels, derailleurs, cranks, brakes. Heck, just take the whole thing apart.
Skate board or inline skates or both.
Remove the trucks and wheels.
Tools needed
Hack saw
Acetylene or MAPP torch set or MIG / TIG / Stick welder (or friend or friendly/bored muffler shop)
Files or grinder or both
Metric allen wrenches
Drill and bits
Various bike tools

1) Build wheels
Remove and save the spokes from the 20" wheels, or at least from the back wheel. It's nicer if both wheels have the quick release skewer hubs from the derailleur bike. You will need a spoke wrench. Remove the hubs from the derailleur bike wheels. If the hubs are close to the same diameter you will be able to use the same spokes. You will have to remove the gear cluster from the rear wheel to get to the spokes. There are special tools for that. True the wheels. How to build bicycle wheels
2) Build seat
Make the seat base from 1/2" or thicker plywood. It look something like this drawing.

Cut the BMX bike seat tube off flush with the top tube. Make a clamp to attach the seat base to the top tube. You can probably find a conduit clamp that will work. Use plywood for the seat back or cut off one end of the skateboard to use it as a seat back. Use a door hinge to attach the seat back to the seat base to allow the seat back angle to be adjustable.

Use foam to pad the seat. Two layers of different durometer foam are best. Find a thin sheet of hard foam and a thicker layer of softer foam. 2" - 3" overall thickness is plenty, what feels good will depend on your built-in butt padding. Stretch Lycra or other material over the seat foam and staple to the bottom of the seat. Pad the seat back too. You can use thin foam for that.

Cut the heads off of the golf clubs and peel the rubber off the handles. Drill holes in the end of the new seat stays. If you don't want to use golf clubs, you can find thick wall 1/2" steel or aluminum tubing at the hardware store that will work fine. I like using 1/4x20 nuts and cap-head bolts. They are readily available at hardware stores. You can use hardware store stock 1" angle aluminum for the brackets that attach the seat back to the rear fender screw holes by the rear dropouts. Drill holes in the bracket to attach it to the seat back, about halfway up.

Click on the image to see a bigger view.

3) Cut front boom from derailleur bike
Find your X-seam by measuring sitting against a wall with your legs outstretched and measuring the distance from the back of you butt to your heel. The back of your recumbent seat will be about where the old seat was on the BMX bike. Subtract the crank length from your x-seam (about 7 inches). This is the seat back to bottom bracket distance. It's best to use the seat tube as the new boom tube. The down tube will be your derailleur mount tube. Cut the derailleur bike frame tubes. Use a section of the top tube for a triangulation tube on the boom. One skinny tube is not enough to hold up to pedaling forces.
4) Attach the new boom
Remove the handlebars, front fork, headset and cups from the BMX bike so they are not damaged by the heat of welding or brazing. Mitre the boom tube so it fits onto the head tube. It's up to you to decide how high or low to make the bottom bracket, but make sure the cranks will have clearance to the front wheel. A bottom bracket that is a few inches above the seat base is best. Cut another tube from the bike to use for a triangulation brace. One skinny tube is not enough to hold up to pedaling forces. Be sure to spend lots of time making sure everything is square and straight before welding. Making a jig to hold everything straight is a good idea. Be sure to grind or file the paint away from the brazing / welding areas to enure a good joint and because the paint will make nasty smoke if it gets too hot.
4) Resize rear dropouts
Derailleur bike dropouts are 10mm wider than BMX bike droputs. You can widen the BMX bike dropouts a bit using the scissor jack from your car, or use a section of 3/8" threaded rod and some nuts and washers.

5) Mount tires
Use rim cloth tape instead of that rubber strip as high pressure tires will blow out if the rubber strip is used. Mount up your new tires!

7) Make an idler for the return chain
Use a bolt or threaded rod with washers and nuts to chuck up one of the skate wheels into a drill or drill press. Make a cutting tool to machine a slot into the rubber skate wheel about 1/2" wide and 1/2" deep. You will want to mount the return chain idler somewhere on the down tube just behind the head tube where it will make the return chain clear both the power side chain and the front fork. Either drill a hole through the frame tube or braze a nut to the frame to mount the idler. More details on making an idler

6) Check chain line
Re-assemble front fork, install seat, install wheels, install cranks. Use a straight edge to check your power side chainline. Will it rub anywhere? You should not need any power side idler. You may need to grind down the old BMX bottom bracket cup for clearance.

8) Make a rear derailleur hanger
Cut the rear derailleur hanger and surrounding dropout from the derailleur bike. The wheel on the BMX bike slides in from the rear. Bolt or braze the derailleur hanger to the BMX dropout. Also you may be able to find an old 10-speed bolt on derailleur. Install chain. Yes there is a special chain tool. In a pinch you can clamp the derailleur hanger to the outside out the BMX dropout with the hub's quick release skewer.
9) Make handlebars.
Basically you want to add a riser tube to put the handlebars somewhere where they will both clear your legs and be easy to reach when you are seated on the bike. You may be able to use the BMX handlebars or the derailleur bike handlebars. There are many methods to do this, depending on what kind of headset the BMX bike has.
Threaded: If it's a 1" OD threaded steerer tube you can press a 7/8" riser tube into it. Cut a slot in the steerer tube and then clamp the steerer tube onto the 7/8" tube with a seat clamp or similar item. If it's a 1-1/8" OD threaded steerer tube you can press a 1" riser tube into it. If you can't find an appropriate clamp, Mcmaster Carr has some aluminum ones.
Non-Threaded: These are typically 1-1/8" OD. A non-threaded steerer tube will need to have the riser tube clamped over the outside of the steerer tube, so you will need to find a riser tube that has a 1-1/8" ID. Be creative.
10) Add cables, brakes and derailleurs
If there are no mounting brackets for brakes, you can get braze-on brackets to attach disk brakes to the front fork or rear dropouts. You should be able to mount the old front derailleur to the new derailleur tube, and be able to adjust it to properly change your gears. Add the derailleur cable tubes and brake cables tubes. You can get these in bulk lengths from your LBS or online. Attach them with plastic zip ties, or electrical tape. If you want to get fancy you can use cable stop braze ons. You may need to use tandem length brake and rear derailleur cables. Adjust brakes and rear gears. Time for a test ride!

Now, take it all back apart and spay-paint it!

Examples of completed projects:

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