Gas Engines on Bikes

Custom Recumbent Bike

Electric and Cargo Trikes

Power Fork I, the first powered-fork trial.
Power Fork II, a better design.
Power Fork III, the best design uses all belts.
Power Fork III all-belt drive detail.
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                      POWER FORK II
    This design uses very good Echo engines that wind out at 9,000 RPM.
The engine pulley is 1.5" and the driven pulley is 7".  That's a ratio of
4.66:1.  The cog has 14 teeth and the sprocket on the front wheel has
52T, so that's a ratio of 3.71:1.  The final ratio is 17:1.  The main
objective of this version was to keep the engine weight (6 lbs.) close to
the steering axis and put some mass behind the steering axis for balance.
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                          POWER FORK III
   This has the same Echo engine but has an all-belt drive.  Both small
pulleys are 2" and the big pulleys are 7.5" for a ratio of 14:1. Both
belts are 4L350 (35").  The belts can be tightened by hand easily.  And the
secondary pulley can be disengaged for zero drag while pedalling if out of
fuel or if the engine won't start.
  All bikes with the powered forks need to be pedalled up to about 10 to 14
MPH first and then the engine will pull the bike up to 35 MPH.
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                         MICRO UTILITY TRUCK
  The MUT has a sweet Robin EY08D 2 HP, 4-cycle engine weighing 19 lbs. It
always starts with one easy pull. The centrifugal clutch is a Comet 350 with
2.5" pulley, engaging at 1800 RPM. The big pulley shown is 5", so the belt
reduction is 2:1.
  The size 25 chain sprockets are 16T and 80T, so the chain reduction is 5:1.
Thus the overall reduction is 10:1. Since 1800 RPM is 30 RPS, the drive wheel
turns at 3 RPS when first engaged. The tire circumference is 2.75 ft., so the
lowest speed is 8.25 feet per sec., or 5.6 MPH.  This can be made higher or
lower by changing the pulley.
  The tires are 10" diameter pneumatics.  All wheels have ball bearings. The
front frame is a modified BMX bicycle. The brake pad acts on the clutch drum.
The chain is adjusted by sliding the jackshaft support arm on the fork.  The
belt is 1/2" x 47" (4L470).  Tension is adjusted by adjusting the bike stem.
The flatbed is 21" wide by 24" long.  A plastic storage box fits in the bed.
The Micro Utility Truck.
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                  ADD A POWER UNIT TO ANY BIKE FORK
   A strong steel fork, like those with straight legs made for 26" cruiser
bikes, can be used for a power fork frame.
The bike fork frame power unit.
The drive wheel, modified sprocket and brake disk.
  The 44T sprocket is bolted to the 20" front wheel hub where a brake disk
would go. The brake disk was used as a guide for drilling the holes in the
sprocket.  The brake disk could also be bolted to the hub as usual and then a
sprocket could be bolted, riveted or welded to the brake disk.  The sprocket
was hole-sawed to 1 & 3/8" to fit over the bearing flange.
The steel parts used.
  The cruiser fork and dropout ears to be welded to the legs.  The top has
been cut at an angle for the 1/4" caliper brake bolt hole, which needs to be
drilled last so that it mates properly with the bike's brake hole.
  The attachment base parts are: steel plate, square tube for bearing pipe
support (fishmouthed, but not yet cut to length), jackshaft bearing pipe (not
yet cut to length), pivot/guide ears and U-bolts.
  The engine support parts are: square tube, two sizes of angle iron and
engine plate cut out for the clutch, but not yet drilled for the engine bolts.
The completed parts.
  The attachment base is a 1/8" x 4" x 8" plate that will be U-bolted to the
cruiser fork legs and bolted at the brake hole.  The base pivots to adjust
the chain by the bolt.
  There are 1/8" pivot ears on the front of the base plate for the engine-
mount square tube.  A hardwood wedge between the square tube and the base
plate maintains belt tension. The engine mount can take different plates for
accommodating other engines.  This particular engine was what we had on hand.
The small pulley on the clutch hub.
  A diecast 2" pulley for 1/2" shaft bored to .600" is on the centrifugal
clutch bell.  A modified hairpin clip secures it to the string trimmer's drive
cable socket, which has been shortened and drilled.
The power fork seen from the right.
  Bicycle shift cable is used for throttle control.  The kill button is on
the engine plate.  The bike has a coaster brake.  The small sprocket is on a
freewheel so the bike can always be pedalled normally.  That's important!
  The spreader to adjust the chain is two 3/8" bolts joined in a coupler nut.
To adjust chain tension, remove the lower bolt, turn the spreader at least
half a turn and then reconnect the bolt.  (It is not a turnbuckle.)
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                 ENGINE MOUNTED INSIDE FORK LEGS
   This design was to put the weight more in line with the steering axis and
also to use belts only.
Modified Stihl FS 45 engine.
   The front of the housing has been cut off. The drive cable socket has been
cut off of the centrifugal clutch bell.  A 2 1/4" pulley will clamp onto the
3/4" part of the clutch bell.  The wires for the kill switch have been routed
away from the flywheel and out an existing oblong hole.  The 1/4"-20 tap will
be needed for enlarging a bolt hole for the recoil starter housing.
The drive wheel and pulley.
   The 7" pulley's hub was hole-sawed out and 5/16" holes have been drilled to
match the bolts holding the wheel halves together.  The bolts are 5/16" x 3"
long and the spacers are 2" long. A 1 1/4" wide anti-torque brace was welded
between two of the spacers.
The freewheel and jackshaft pulley.
   The freewheel for a trike axle was bored out 5/8" for the jackshaft and a
3/16" keyway was broached.  A steel belt pulley was welded to the freewheel.
Engine mounting bolts. 
   The 1/4"-20 bolt at the top and two muffler bolts at the bottom will
secure the engine to the pivot bar.  A 1/8" steel ear welded to the engine
plate will go to the 1/4" bolt for a third anchor point.  Some of the plastic
had to be cut away.
The frame, engine pivot and jackshaft hanger.
The complete power attachment. 
   This can be welded to the back of a kick scooter or to a bike's cut-off
fork.  The right side belt is 34".  Tension is adjusted by 5/16" bolts used as
spreaders.  The black cable is the throttle control.
From the left side. 
   The left belt is 29".  The two wires will go to the kill switch.
   Engage RPM is 2800 and maximum RPM is 9500. The total belt reduction is
about 12 to 1 with the 8" pulley and about 9 to 1 with the 6" pulley.
2800 RPM requires pedalling to 7 MPH to engage the clutch with the 8" pulley
and top speed will be 28 MPH.  With a 6" pulley, engagement would be at 9.5
MPH and top speed will be 32 MPH.
THE POWER FORK ON A 20" BIKE.
   The blue handle is the throttle.  The rear wheel has a coaster brake.
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OTHER BIKES:
Electric trike for a handicapped boy.
Custom recumbent.
From other side.
Campus cargo bike.
  The cargo frame attaches to the rear V-brake brake bosses, the caliper brake
hole and the rear axle. A removeable plastic storage box fits the cargo bed.