The Ducati That Ron Built
THE DUCATI THAT RON BUILT
A 391-cc Dirt Special That Is Almost Too Pretty To Ride
WHEN RON WOOD, of Costa Mesa, Calif., decided to build a "play bike," he certainly wasn't "playing." Beginning with an old Ducati 250 engine he had around the house, and a Bultaco Metisse frame that was given to him, Ron started burning the midnight oil and came out with a truly beautiful and unusual creation.
The engine features a 350 Ducati crankshaft and connecting rod assembly which is capped with a piston made from a Forgedtrue blank, machined to give a compression ratio of 9:1. Early oiling problems were finally solved by using a Perfect Circle three-piece oil ring. An increased bore size of 81-mm necessitated making a new sleeve, giving the engine a new capacity of 391-cc or 24.2 cu. in.
Cylinder head work includes enlarging and reshaping the inlet port out to 1 3/16 in. A 1 3/16 in. Amal Monobloc carburetor is now used with a filtron air cleaner element. A larger inlet valve has been fitted and the original hairpin valve springs have been replaced with double coil springs which have titanium collars. A sports grind cam from a 450 Ducati has intake and exhaust lifts of 0.400 in. and 0.385 in. respectively. The exhaust port has also been enlarged and a 1 5/8 in. diameter header pipe 21 in. long fits into a short, shallow-taper megaphone, which helps maintain good low-end pulling power.
Aluminum bronze valve seats are used, an additional spark plug is mounted at an almost horizontal position just behind the cam drive tower, and two additional oil drains emerge from the valve pockets on the left-hand side of the head.
Thirty bhp at 8750 rpm were achieved at the rear wheel on C.R. Axtell's dynometer recently, with good power coming on from 6500 rpm. It's certainly no trials bike, but it compares very favorably with 360 two-stroke motocross machines.
Ignition is accomplished using 12-V electrics. Honda coils are fed by the original alternator which was rewound to get the necessary 12-V current. Ignition timing is now set at 39 degrees BTC with no automatic advance.
Below, all the gears and the clutch wheel were drilled for lightness. A more recent five-speed scrambles gearbox helps keep the revs up and the power coming.
But, however interesting the engine modifications may be, the frame claims just as much of the spotlight. Ron first sandblasted and thoroughly cleaned the frame, inspecting everywhere for cracks or broken welds. Then he set about the coup de grace: a rubber-mounted engine! Using Norton. Commando "Isolastic" suspension components, he cleverly grafted them into the Bultaco frame. By changing the thickness of the spacers, the engine can be more or less rigidly mounted to achieve the desired results. Some experimentation was necessary, but the machine is now quite free of vibration, which has always been a problem with mediumand largedisplacement, single-cylinder machines.
After the engine suspension components were installed, Ron filled all the welds with a plastic filler, ground them smooth and painted the frame with a special, high-gloss black paint. Front suspension is Ceriani. A 175 Ducati front hub is laced to a 21-in, alloy rim which sports a 275-21 Dunlop Trials Universal. The rear hub is laced to an 18-in, alloy rim, and a 4.60-18 Dunlop Sports knobby is fitted. The only other frame modification was the repositioning of the rear shock absorbers to clear the chain. Weight with a half-tank of fuel is 256 lb.
A homemade seat graces the topside and a coat of "Kawasaki racing green" (also called competition yellow) finishes one of the prettiest "play bikes" we have ever seen.
