Workshop guide · Moto Guzzi · horizontal singles

Workshop guide Moto Guzzi horizontal singles

Maintenance of the horizontal overhead-valve singles from Mandello del Lario: Falcone, Nuovo Falcone, Astore and Airone.

Nederlandse versie

Introduction

This guide covers Moto Guzzi’s horizontal overhead-valve singles from Mandello del Lario, the classic Guzzi concept before the V-twin arrived. The 500 cc line runs from the Normale (1921) to the Nuovo Falcone (1976); the 250 cc line is the Airone.

Models in brief

Airone 250 (1939–1957): the little brother with 70 × 64 mm. From 1948 aluminium head and cylinder, from 1949 in Turismo and Sport versions. The best-selling Italian middleweight of its time.
GTV and GTW 500 (after the war): predecessors of the Falcone; the GTV carried on until 1953 as the Astore.
Falcone 500 (1950–1967): sports model with 88 × 82 mm. From 1953 as Sport (23 hp) and Turismo (the successor to the Astore, with its camshaft, valves and carburettor).
Nuovo Falcone 500 (1969–1976): thoroughly redesigned, first for army and police (Militare), later also as Civile and Sahara.

How to recognise it: all models have an almost horizontal cylinder pointing forward and a big flywheel on the left. On the old Falcone and Airone that flywheel turns in plain view (the "bacon slicer"); on the Nuovo Falcone it is largely covered. The old Falcone has a dry sump with oil tank and magneto ignition; the Nuovo Falcone has a wet sump, 12 volts and battery ignition.

The text is our own summary of public sources; the workshop manual for your own model remains the authority.

Safety: keep hands, clothing and tools away from the open flywheel when the engine is running.

Technical data

All 500s have 88 × 82 mm (499 cc) with low compression and low revs; the Airone has 70 × 64 mm (247 cc).

Model	Years	Bore × stroke	Compression	Carburettor	Power	Ignition	Lubrication
Airone Turismo	1939–1957	70 × 64 mm	6:1	Dell'Orto SBF 22 mm	c. 9.5–12 hp	magneto	—
Airone Sport	1949–1957	70 × 64 mm	7:1	Dell'Orto SS 25 mm	c. 13.5 hp	magneto	—
Falcone Sport	1950–1967	88 × 82 mm	6,5:1	Dell'Orto SS 29 A	23 hp at 4500 rpm	Marelli magneto	dry sump, c. 3 l
Falcone Turismo (ex Astore)	1953–1963	88 × 82 mm	lower	Dell'Orto MD 27 F	c. 19 hp	Marelli magneto	dry sump
Nuovo Falcone	1969–1976	88 × 82 mm	6.85:1 (Militare 7:1)	Dell'Orto VHB 29 A	26 hp DIN at 4800 rpm	12 V battery and coil	wet sump

Other features

All models: four gears, chain to the rear wheel, drum brakes.
Falcone: frame of tubes and pressed steel, rear suspension with springs in a box under the engine and friction dampers; top speed c. 135 km/h.
Nuovo Falcone: tubular frame with two shock absorbers, aluminium cylinder with cast-iron liner, final chain on the left, electric start via a Dynastart on some models. Ready-to-ride weight c. 214 kg.
From November 1952 the Falcone got a Marelli magneto with automatic advance; before that the advance was operated with a lever on the handlebar.

Engine layout

The horizontal cylinder points forward and sits low in the frame; this gives good cooling airflow and a low centre of gravity. The big external flywheel is the trademark.

drive of the horizontal Guzzi single · schematic

The valves are operated via a camshaft low in the crankcase, pushrods and rockers. On the early Airone the hairpin springs are still exposed; later models have enclosed springs.

Differences old and new

Item	Falcone (1950–1967)	Nuovo Falcone (1969–1976)
Lubrication	dry sump with oil tank	wet sump
Ignition	Marelli magneto	12 V battery and coil
Flywheel	open, visible	largely covered
Final chain	right	left
Frame	tubes and pressed steel	tubular frame
Rear suspension	springs under the engine, friction dampers	two shock absorbers

Periodic maintenance

Check the valve clearance every 3000 km; that is the most important recurring job on these engines.

Job	Interval (guideline)	Notes
Oil level	before every ride	Falcone: in the oil tank; Nuovo Falcone: in the crankcase
Change oil, clean strainer	every 2000–3000 km or yearly	drain warm
Valve clearance	every 3000 km	engine cold
Ignition (points or magneto)	every 3000 km	points gap, then timing
Plug	every 3000 km	judge the colour
Carburettor and air filter	every 3000 km	especially in dust
Adjust clutch and brakes	every 1000 km	see clutch section
Lubricate and adjust chain	every 500 km	c. 20–25 mm slack
Grease on pivot points	every 3000 km	swingarm, friction dampers, cables

Oil: the old Falcone has a dry sump with about 3 litres in the oil tank. The Nuovo Falcone has a wet sump; top up to the mark on the dipstick. For these low-revving engines a simple SAE 40 or 20W-50 engine oil without friction modifiers is usually used.

Changing the oil (Falcone with dry sump)

Warm up the engine.
Drain the oil tank and the oil left in the crankcase.
Clean the strainer in the oil tank and check the oil lines for cracks.
Fill the tank, start the engine and check that the oil returns to the tank (look at the filler cap).
Check the level again after a short ride.

Adjusting valve clearance

With a cold engine set the inlet to 0.10 mm and the exhaust to 0.20 mm; these are the factory values for the Nuovo Falcone and the values Italian sources also give for the older Falcone.

Valve	Clearance (cold)	Note
Inlet	0.10 mm
Exhaust	0.20 mm	some owners use 0.15 mm
Valve timing check	0.5 mm	only temporarily, to check the camshaft position

For the Airone sources give no single value; use the workshop manual or start with the same values and listen to the engine.

Method

Let the engine cool completely and remove the spark plug.
Turn the flywheel by hand in the direction of rotation until the inlet valve has opened and closed again: the piston is now coming up to TDC on the compression stroke.
Set the piston exactly at TDC. Both pushrods should now turn with your fingers.
Measure with a feeler gauge between rocker and valve stem.
Loosen the lock nut, adjust with the slotted adjusting screw and hold it while you tighten the lock nut. A socket with a welded-on handle helps here.
Measure again after tightening and turn the flywheel over two revolutions for a final check.

Too little clearance is more dangerous than too much: a valve that does not close burns, especially the exhaust. Some ticking is normal on a Guzzi single.

Ignition

The Nuovo Falcone sparks statically at 10° before TDC and fully advanced at 44°, with a points gap of 0.42–0.48 mm. The older models have a Marelli magneto.

Model	System	Values
Airone	magneto	per workshop manual
Falcone up to late 1952	Marelli magneto, advance with a lever on the handlebar	set the lever to retard for starting
Falcone from late 1952	Marelli MCR 4-E with automatic advance	per workshop manual
Nuovo Falcone	12 V battery, coil, contact points	points gap 0.42–0.48 mm; 10° static, 44° fully advanced

Setting the timing (Nuovo Falcone)

Put the piston at TDC compression; a degree disc on the flywheel makes the job much more accurate.
Set the points gap to 0.42–0.48 mm with the points fully open.
Connect a test lamp across the points and turn the flywheel back to well before the firing point.
Turn slowly forward; the points should open at 10° before TDC. Rotate the points plate until that is right.
Check with a strobe that the advance comes to around 44° at higher revs.

Magneto (Falcone and Airone): a weak spark is usually caused by burnt points, a bad condenser or a weakened magneto. Rewinding and remagnetising a magneto is specialist work. With manual advance always use the retarded position for starting: with a big flywheel and a 500 cc piston a kickback on the kick-starter hurts.

Dell'Orto carburettor

Each model has its own Dell'Orto; the Falcone Sport uses the SS 29 A racing carburettor with separate float chamber, the Nuovo Falcone the square VHB 29 A.

Model	Carburettor
Airone Turismo	Dell'Orto SBF 22 mm
Airone Sport	Dell'Orto SS 25 mm
Falcone Sport	Dell'Orto SS 29 A
Falcone Turismo	Dell'Orto MD 27 F
Nuovo Falcone	Dell'Orto VHB 29 A

Separate float chamber (SS type): the float chamber must be at the right height and level relative to the jet. If it hangs too high, the engine runs rich and leaks; too low gives a lean mixture. Check the mounting after every dismantling.

Adjusting idle

Warm up the engine; this big single takes a while to do so.
Turn the air screw lightly closed and then 1.5 turns open as a starting point.
Set the idle with the stop screw so low that the engine keeps running steadily and evenly; these engines can idle very slowly.
Turn the air screw a quarter turn at a time until the engine runs smoothest and then reset the idle.
Leave 1–2 mm of free play in the throttle cable.

Starting: the low compression and heavy flywheel make starting easy. Nuovo Falcone owners often bump-start it in second gear, because first is very short.

Clutch, gearbox, brakes and fault finding

On the Nuovo Falcone set the clutch lever to about 4 mm free play and both brakes to 20–25 mm of free travel before the lining touches the drum.

Clutch: wet multi-plate clutch. On the old Falcone the clutch mechanism is partly outside the crankcase; keep the pivots lubricated.
Gearbox: four gears. The Falcone gearbox comes from the Dondolino racer; changes are calm with a clear click.
Chain: 20–25 mm slack. On the old Falcone it runs on the right, on the Nuovo Falcone on the left.
Brakes: drums front and rear. Adjust with the nuts at lever and pedal; clean drums without compressed air.
Rear suspension old Falcone: adjust the friction dampers with the star knob; the springs are in a box under the engine.

Complaint	Possible cause	Check
Will not start, no spark	points, condenser, magneto or battery	spark test, points gap
Kickback on the kick-starter	ignition too advanced	manual advance to retard, static timing
Blue smoke	worn piston rings or valve guides, dry sump overfilled	compression test, oil level
Oil from the breather (Falcone)	scavenge pump or too much oil in the tank	is the oil returning to the tank?
Ticking from the head	valve clearance too large	measure valve clearance
Engine runs hot, loses power	valve clearance too small, mixture too lean	valves, plug colour
Runs rich, petrol leaks (SS carburettor)	float chamber too high or needle leaking	float chamber height, float needle
Battery not charging (Nuovo Falcone)	dynamo or regulator	charging voltage c. 14 V at raised revs

Torque settings

Few factory values are publicly available for these engines. The values below are general guidelines for steel bolts in aluminium, not from Guzzi documentation.

Bolt / nut	Guideline
M6 (covers)	7–9 Nm
M8 (general)	16–20 Nm
Cylinder head	crosswise in stages, per workshop manual
Flywheel nut	very tight and locked, per workshop manual
Spark plug (14 mm)	20–25 Nm

The flywheel nut deserves extra attention: a loose flywheel on these engines damages the crankshaft and is dangerous.

Sources

Consulted on 18 October 2026; all text in this guide is our own work.

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Workshop guide Moto Guzzi horizontal single (Falcone, Airone)