Weedeater Outboard Motors
4-CYCLE WEEDEATER OUTBOARD MOTOR
The weedeater power unit.
This is a Ryobi C430, a 30 cc, 4-cycle engine with overhead camshaft and oil
in the sump, not mixed into the gas. It has a centrifugal clutch.
The outboard mounted on a work stand.
Because of the way the Minn Kota MKP-2 prop is made, it pulls instead of
pushes when turning clockwise, so the boat's direction is to the right here.
The cone on the hub is a modified funnel for streamlining.
The outboard in reverse.
The motor must be held back when turned this way to back up. And the prop
can be swung out of the water while the (air-cooled) engine is running.
The outboard foot on the drive tube.
The foot drive is from another weedeater. It reduces RPM by 3/4. So since
the prop turns at 6,000 RPM out of the water, the engine is running at 8,000.
The expanded bottom part of the Ryobi drive tube was cut off. A 2 & 1/8"
length of 1" O.D. steel tube is clamped and riveted into the foot drive to
allow it to mate with the 1" O.D. drive tube. They will be aligned using the
1" I.D. part of the Ryobi drive tube that was cut off.
The flare part of the drive tube that was cut off is cut again 1 & 3/4" from
the bottom. Then the slot was cut all the way through to form a split sleeve
that will clamp the 1" O.D. tubes together. A 2 & 1/2" length of 3/16" square
lathe bit connects the drive cable socket to the foot cable socket.
The split sleeve is clamped by the original clamp used to join the power
unit to accessories, but the alignment boss must be drilled out first. After
the split sleeve is clamped to the 1" O.D. tubes, the clamp, the split sleeve
and inner 1" tubes are pop-riveted. A 1/4"-20 x 1/2" Allen head bolt replaces
the thumb bolt on the original clamp.
The transom clamp is the base from a workshop bench lamp with a 1/4" plate
to hold the drive shaft tube. The drive shaft tube is held in aluminum
saddles on the plate by U-bolts. The motor can be turned in a complete circle.
All nuts used are nylon-locking. The pivot bolt is 1/2".
The throttle is on the tiller.
The kill switch was snapped into an opening on one plastic guard. The total
weight of the outboard is 10 lbs.
Video of the outboard on a jon boat.
This is Mike Fogle, sheet metal wizard. The engine is laboring too hard
even with the small MKP-2 prop and so cannot reach its RPM power peak.
To achieve a better match between the Ryobi RPM/power curve and the prop,
various right-angle-drive reductions were checked. The prop needs to turn at
1750 RPM for the MKP-2 prop. So the ideal reduction for an 8,000 RPM gas
engine would be 4.5:1. A 30,000 RPM power tool motor gearbox with that
reduction would turn the power tool's output shaft at 6700 RPM.
Considereing only right-angle gearboxes, a Milwaukee 4 & 1/2" angle grinder
has a 3:1 reduction and reverses direction. A car polisher gearbox is 10:1
and also reverses direction.
This is a car polisher gearbox on the Ryobi.
Since the reduction is 10:1 reversed and the maximum RPM measured 1,000 at
the prop, we used an MKP-6 prop, not the MKP-2. The prop is on "backwards"
and so it pushes like a normal transom-mounted outboard.
Video of Ryobi engine, 10:1 gearbox and MKP-6 prop.
Young's Props has a great selection of small aluminum props for either
rotation. (youngprops.com) MKP props can be found at Wal-Mart.