Nederlandse versie

This guide covers the bevel-drive Ducati 350 single, mainly the ‘wide case’ models of 1968–1974: 350 Mark 3, 350 Mark 3D / Desmo and 350 Scrambler. The older ‘narrow case’ 350 Sebring (1965–1968) has the same basis, but a weaker bottom end, shorter con-rod and different settings.

The text is our own summary of public sources (encyclopaedia, specification sites, owners’ forums). No original factory documentation has been copied. Where sources contradict each other this is noted; always check critical values in the factory manual or the Ducati OHC workshop manual before you start work.

Identify your engine

• Wide case: the rear part of the engine, where the frame mounts, is about 7–8 cm wider than the front. Five gears, larger sump capacity, 135 mm con-rod.
• Narrow case: narrow crankcase over its whole length, 125 mm con-rod, usually four or five gears depending on year.
• Desmo: the valve cover is larger and the camshaft operates the valves with separate opening and closing rockers. Otherwise desmo and non-desmo engines are the same.

Safety: work on a cold engine, put the bike firmly on a stand, and disconnect the battery when working on the electrics. Use new gaskets and lock tabs when reassembling.

Technical data

All 350s share a bore × stroke of 76 × 75 mm (340 cc); the differences are in compression, camshaft, carburettor and valve gear.

Differences between sources come from year, market (USA/Europe) and measuring method. If in doubt use the type plate and engine number to identify your model.

Engine layout

The heart of this Ducati is the bevel shaft: a vertical shaft with a pair of bevel gears at each end. So there is no chain or belt to stretch, but setting up the gears (shims) is precision work.

Read the drawing from bottom to top: each step turns the motion through a right angle or converts it. The engine is vertically split, with the cylinder inclined 10° forward, and acts as a stressed part of the frame.

Important when dismantling: note the thickness of the shims at both bevel gear pairs. Wrong shims give a whining or fast-wearing drive. The camshaft bearing caps must be fitted when measuring valve clearance; without the caps the shaft is not in its working position.

Periodic maintenance

Change the oil about every 2000 km and clean the oil strainer at the same time; these engines have no paper oil filter.

Oil: the factory specified SAE 40 or 20W-40 multigrade. The workshop manual gives about 2.1 litres; owners find that 1.8–2.0 litres is often enough. Always fill to the dipstick, not by the litre. After the first start some oil stays in the head, so check again afterwards.

Oil change, step by step

1. Warm up the engine, stand the bike upright and have a drain pan of at least 3 litres ready.
2. Undo the drain plug under the crankcase and let it drain completely.
3. Remove the strainer (gauze filter), rinse it in petrol or degreaser and blow it dry.
4. Check the oil and strainer for metal particles; bronze points to bearings or bevel gears.
5. Refit strainer and plug with a new gasket or copper washer; do not overtighten, the crankcase is aluminium.
6. Fill with oil to the top mark on the dipstick, let the engine run briefly and check again.

The intervals in the table are a practical guideline for a classic that covers few miles; follow your own manual if it says otherwise.

Adjusting valve clearance

Measure the valve clearance with the engine cold and the piston at top dead centre (TDC) on the compression stroke; then both valves are closed.

Sources give different values per year and camshaft. If in doubt, rather a little too much clearance than too little: too tight burns a valve.

The cam pushes the opening rocker up, which pushes the valve open (clearance A). On the Desmo the fork of the closing rocker pulls the valve shut again by its collar (clearance B). A non-desmo has only clearance A; there a hairpin spring closes the valve.

Method

1. Remove the tank, spark plug and valve covers; leave the camshaft bearing caps in place.
2. Turn the engine with a spanner on the crankshaft nut in the direction of rotation to TDC compression (both valves closed, piston at the top).
3. Measure A with a flat feeler gauge between rocker and valve cap. The blade should slide with slight resistance.
4. Desmo: measure B between the closing rocker and the closing collar. Turn the engine over a few times and check B at several points on the closing cam.
5. Too much or too little clearance? Replace the cap (opening) or the closing collar / half collets (closing) with one of the correct thickness. On models with adjusting screws, adjust with the screw and then lock it with the lock nut.
6. Turn the engine over two revolutions and measure everything again before refitting the covers.

Tip: you can pull the rocker spindles out with a suitable stud or old spoke screwed into the spindle; then the cap and rocker come free.

Ignition and timing

Set the wide case 350 to 33–36° before TDC at full advance; statically that comes to about 5–8° before TDC. Some manuals give 36–38° fully advanced.

The engine has no timing marks, so you need a degree disc on the crankshaft and a fixed pointer. You find TDC most accurately with a piston stop in the plug hole.

Adjusting the contact points

1. Remove the right-hand ignition cover.
2. Turn the engine until the points are fully open on the flat top of the cam.
3. Set the points gap to 0.3–0.4 mm and tighten the plate.
4. Check the condenser and the points: burnt or pitted = replace.

Setting static timing

1. Fit the degree disc and set it exactly to 0° at TDC compression.
2. Connect a test lamp or ohmmeter across the points (ignition on with a lamp).
3. Turn the engine back to well before the desired point and then slowly forward.
4. The points must open (lamp goes on or off) at 5–8° before TDC. Adjust the points plate until that is right.
5. Push the advance weights fully open by hand and check that the points now open at around 33–36° before TDC. If that does not come out, the springs or weights of the advance unit are worn.

Plug: choose a medium-cold plug; the NGK B7HS is widely used in these singles. A light brown insulator means a good setting, black is too rich or too cold, white is too lean or too hot.

Electronic ignition (on some later models): there is no points gap, only the position of the pick-up plate. Then follow the marks on rotor and stator from the manual.

Dell'Orto carburettor

The 350 has a 29 mm Dell'Orto: first the round SSI 29 D, from 1969 usually the square-slide VHB 29. Always tune in this order: idle, part throttle (needle), full throttle (main jet).

Note: the VHB values come from the 450 with the same VHB 29 AD; a 350 often runs a smaller main jet. Start with the value in your own carburettor and adjust by the plug colour.

Adjusting idle

1. Warm the engine up thoroughly (at least 10 minutes).
2. Turn the mixture screw lightly closed and then 1.5 turns open as a starting point.
3. Set the idle with the slide stop screw to about 1100–1200 rpm.
4. Turn the mixture screw in or out a quarter turn at a time until the speed is highest and smoothest.
5. Then set the idle back to the desired value with the stop screw.
6. Leave 1–2 mm of free play in the throttle cable, also with the bars on full lock left and right.

Recognising faults

• Popping on a closed throttle, runs better with choke: idle too lean or air leak at the rubber inlet stub.
• Surging at constant speed: raising the needle one notch (clip lower) makes it richer.
• Black plug, smell of petrol: too rich; start with the float height and the needle jet, which wears oval.
• A cracked inlet rubber is a known cause of uneven running; replace it if in doubt.

Clutch, drive and brakes

The crankshaft drives a wet multi-plate clutch via gears; the power then goes via the five-speed box and a chain to the rear wheel.

Clutch

• Adjust the clutch cable to 2–3 mm free play at the lever.
• If the clutch slips at full throttle, check the cable first, then the springs and the thickness of the friction plates.
• Use engine oil without friction modifiers; they make wet clutches slip.
• When dismantling: note the order of friction and steel plates and replace warped steel plates.

Chain and sprockets

1. Put the bike on the centre stand, gearbox in neutral.
2. Measure the slack halfway along the lower run: about 20–25 mm up and down.
3. Loosen the rear spindle and adjust both sides equally with the adjusters; check the wheel alignment.
4. Tighten the spindle and check the rear brake again, because the brake anchor plate can turn with it.
5. Replace the chain and both sprockets together when the teeth are hooked.

Brakes

• Drum brakes (180 mm front, 160 mm rear): adjust the cable or rod so the brake bites in the first quarter of its travel. On the twin-leading-shoe front drum both cams must engage at the same time; set that with the link rod.
• Disc brake (280 mm, later Desmos): replace the brake fluid every two years and check the pads for at least 2 mm of lining.
• Clean brake drums without compressed air; old brake dust may contain asbestos. Use a face mask and a damp cloth.

Electrical system and fault finding

The original installation is 6 volt: a dynamo of c. 30 W, a voltage regulator, battery, coil and contact points. Many faults come from poor earth connections and a flat battery, not from faulty parts.

Basic checks

• Battery voltage at rest: a full 6 V battery measures just over 6.3 V; below 6 V charge it first.
• Charging voltage at c. 3000 rpm: higher than the resting voltage, but not above about 7.5 V.
• Earth: sand the contact points of earth leads on frame and engine to bare metal.
• Testing the spark: lay the plug on the head, kick it over and look for a bright blue spark.

Many owners convert the system to 12 V or fit electronic ignition. That cures most starting problems, but keep the original parts if you want to keep the bike original.

Torque settings

Ducati gave almost no torque settings for these singles; even the cylinder head bolts appear in the factory documentation as “tight”. The values below are general guidelines for steel bolts in aluminium, not from Ducati documentation.

Tighten the cylinder head nuts crosswise in two or three stages and check them again after the first warm ride (engine cold).

Sources

Consulted on 17 October 2026; all text in this guide is our own work.

• Wikipedia: Ducati 350 Mark 3
• Wikipedia: Ducati 350 Scrambler
• Wikipedia: Ducati singles
• Motorcyclespecs: Ducati 350 Mark 3D 1971–72
• Motorcyclespecs: Ducati 350 Mark 3 1968
• Ultimatespecs: Ducati 350 Mark 3 (1972)
• RT Ducati: technical data 450 (valve clearance, points, carburettor)
• Ducati Meccanica: setting desmo valve clearance
• Vintage Veloce: setting the ignition on a Ducati single
• Motoscrubs: ignition timing 250/350/450
• Motoscrubs: valve clearance from the factory booklet
• Motoscrubs: oil quantity workshop manual
• Motoscrubs: carburettor setting VHB 29
• Motoscrubs: technical documentation Ducati singles
• Bevel Heaven: oil for Ducati singles