Piaggio 350 Engine

Piaggio’s newest engine - the 350 is packed with a host of great features including:

·         4 valve head with roller cam followers.

·         Shim valve clearance adjustment.

·         Dry crankcase lubrication system with reed valve scavenge.

·         Coaxial coolant and oil pump drive.

·         Wet multi-plate centrifugal clutch.

The design of the 350 engine is all about performance and efficiency and provides equivalent output to the 400cc master engine with better fuel economy and lower emissions than the 300cc Quasar.

The 350 is only 60cc larger than the existing 300 but develops 50% more power!

Servicing:

Service intervals for the 350 are 10,000 km as per most of the Piaggio Vespa range however 15W – 50 engine oil is specified rather than the usual 5W – 40.

Full synthetic engine oil is specified as per usual. Oil volume for the 350 is 1500 ml.

80W – 90 gear oil to API GL4 is specified for the reduction gearbox (rear hub) which also lubricates the multi-plate clutch housed inside the newly designed rear hub.  Hub oil volume is 500 ml.

Valve clearance adjustment is via interchangeable shims which sit directly on top of the valve stems and are accessed by removing a snap-in control block which allows the rockers to be moved sideways for ease of access.

The 350 engine is currently available in the Beverley 350 & X10 350 models.  It's likely that this engine will eventually be used in other models such as the Yourban.  It's unlikely to be fitted to the Vespa frame however as the 350 is possibly too powerful for that frame and suspension format.

 Piaggio 350 Engine – Technical Specifications

Engine: Single-cylinder 4-stroke.

Engine capacity: 330 cm³.
Bore x Stroke: 78 mm x 69 mm.
Timing: 4-valve single overhead camshaft with roller rockers.
Cooling: Liquid.
Lubrication: Dry Crankcase.
Starter: Electric.
Gearbox: Speed CVT with torque server.
Clutch: Automatic centrifugal multi-disc oil bath.
Emissions: Euro 3.

Engine Knock - "Detonation Danger"

Detonation, also called knocking, pinging or pinking occurs in petrol engines when one or more pockets of the air-fuel mixture explodes (detonates) in an uncontrolled manner within the combustion chamber but outside the normal zone of combustion.  The normal combustion process should grow progressively from the point of ignition (the spark plug) and burn all the available fuel so that maximum power and efficiency is gained from the fuel-air charge and peak cylinder pressure is reached at the optimum part of the cycle, generally a few degrees after the piston has reached the top of the compression stroke.

Detonations create shock waves within the combustion chamber that are heard as the characteristic metallic "pinging" sound and cause the cylinder pressure to increase dramatically and at the wrong part of the cycle.  Allowed to continue, detonation or “engine knock” will cause serious long-term damage to the engine and even catastrophic failure.

The smaller more regular detonations can erode the surface of the piston and cylinder head, wearing away metal fragments which end up in the oil causing damage to other components.  The larger more violent ones can rupture the combustion chamber by breaking sections of the pistons away and punching holes right through pistons or the cylinder head itself.

The main causes of detonation are:

1.         Using fuel with too low an octane rating for the engine.  Octane is the index of a fuel’s resistance to detonation (see previous articles on fuel)

2.         Fuel-air mixture too lean causing higher combustion chamber temperature.

3.         Ignition timing overly advanced.

4.         Excessive engine load caused by incorrect gear selection or throttle opening too high for current engine speed.

Detonation can (and should) be avoided by:

1.         Using fuel with the correct or higher octane rating.

2.         Ensuring that fuel mixture is correct – i.e. correct carburettor or injection system settings.  (Richer air-fuel ratio will help limit detonation).

3.         Ensuring that ignition settings are correct.

4.         Correct gear selection allowing engine to operate in the optimum range and not be lugged under load in higher gears.

Engine design is also important in terms of the proclivity for detonation.  Factors such as compression ratio, the amount of turbulence generated in the combustion chamber during induction and compression, the shape of the combustion chamber and position of the spark plug are some of the factors which are considered.  These factors are generally outside the control of vehicle owners however and in most cases the problem can be avoided by considering points 1.& 4. In the above causes and strategies for avoidance.

The images below show some of the damage detonation can cause -