The Alfa Romeo engine we are going to disassemble belongs to the Twin Spark engine family. Twin Spark translates to “double spark”. These gasoline engines actually have two twin spark plugs for each cylinder. In general, Alfa Romeo engineers created a racing engine with two spark plugs per cylinder back in 1914.
They returned to a similar solution for motorsport engines in the 1960s, and in 1986 they introduced production engines with double the number of plugs. For the sake of fitting their engines into stricter environmental regulations. Purely technically, two spark plugs, providing two sequential or simultaneous sparks, allow a gasoline engine to run successfully on a fairly lean mixture. Also, two spark plugs increase the combustion rate of the fuel-air mixture, which means that it is possible to reduce the ignition advance angle, which gives some power gain.
All mass-produced Italian engines with Twin Spark technology were 4-cylinder engines with displacement from 1.4 to 2.0 liters. The first ones had a single camshaft and two valves per cylinder. The later ones were 16-valve. Among them were engines with cast-iron blocks and chain-driven timing.
We’ll take apart one of the latest versions of the Twin Spark engine, a 2-liter engine (AR32310) removed from a 2001 Alfa Romeo 156.
First generation Alfa Romeo Twin Spark engines
In 1986, the first engine from the new Twin Spark series debuted on the Alfa Romeo 75. This 2.0-liter motor was a real innovation for the time. The main feature was an ignition system with two spark plugs per cylinder, which significantly improved the completeness of combustion of the fuel-air mixture and allowed to operate in economical mode with a poor mixture. The engine had the following key technical features:
- Distributed fuel injection – the injection system was advanced for its time, improving power and economy.
- Aluminum cylinder block with wet liners – this reduced the weight of the engine and increased its durability.
- Chain-driven timing – which improved reliability and durability over belt drive.
- Aluminum dual camshaft (DOHC) head – even though the engine had only 8 valves, it performed well.
First generation Twin Spark engine lineup:
| Engine displacement | Engine code | Power | Torque | Vehicle Models |
|---|---|---|---|---|
| 1.7 liter | AR67105 | 115 hp | 146 Nm | Alfa Romeo 155 |
| 1.8 liter | AR67101 | 129 hp | 165 Nm | Alfa Romeo 155 |
| 2.0 liter (1962 cm³) | AR06420 / AR06224 | 148 hp | 186 Nm | Alfa Romeo 164, Alfa Romeo 75 |
| 2.0 liter (1995 cm³) | AR64103 / AR67201 | 143 hp | 187 Nm | Alfa Romeo 164, Alfa Romeo 155 |
First generation advantages:
- Combustion efficiency thanks to two spark plugs per cylinder.
- Economy – ability to operate with poor mixtures at reduced loads.
- Reliability due to chain-driven timing and robust construction.
Disadvantages:
- Labor-intensive maintenance: the twin plug system required more frequent replacement and calibration.
- 8-valve design limited potential at high rpm.
Second-generation Alfa Romeo Twin Spark engines
In 1996, with the introduction of the Alfa Romeo 155, the second-generation Twin Spark engines entered the market. These engines had a significantly revised design:
- Cast-iron cylinder block – provided greater strength and reliability compared to the aluminum block of the first generation.
- Belt-driven timing – which was easier to service, but required regular replacement.
- 16-valve block head – this improved the dynamic performance of the engine, especially at high rpm.
- Variable Variable Valve Timing (VVT) – on the intake, which improved engine performance at low and high rpm.
- Variable intake manifold geometry (VLIM) system – used on the 1.8 and 2.0 liter versions to improve engine dynamics at different rpm.
The second-generation Twin Spark engine lineup:
| Engine displacement | Engine code | Power | Torque | Vehicle Models |
|---|---|---|---|---|
| 1.4 liter | AR38501 | 103 hp | 124 Nm | Alfa Romeo 145, 146 |
| 1.6 liter | AR67601 / AR32104 / AR37203 | 105 – 120 hp | 140 – 146 Nm | Alfa Romeo 145, 146, 147, 156 |
| 1.8 liter | AR67106 / AR32201 / AR32205 | 140 – 144 hp | 163 – 169 Nm | Alfa Romeo 145, 146, 155, 156, GT II |
| 2.0 liter | AR67204 / AR32301 / AR32310 / AR34103 / AR36301 | 150 – 155 hp | 181 – 187 Nm | Alfa Romeo 145, 146, 156, GTV II, 166 |
Benefits of the second generation:
- More powerful 16-valve versions – increased engine performance, especially at high rpm.
- Fasoregulator and intake geometry modification system – provided better dynamics at all operating modes.
- Reliability: Despite belt drive, the engine remained one of the most reliable in its class.
Disadvantages:
- Frequent timing belt replacement: the belt drive required regular maintenance, which could be expensive.
- Complicated ignition system: the dual spark plug system (one large and one small) required replacement sets of plugs, which increased maintenance costs.
Alfa Romeo engine won’t start
The capricious Alfa Romeo engine can fail to start for a number of reasons: due to failure of the crankshaft position sensor, coolant temperature sensor or immobilizer antenna malfunction. The easiest way to diagnose the failure of the crankshaft sensor: Check Engine lights up and the engine does not start only when hot.
RPMs float when coasting in neutral gear
If the Twin Spark engine rpm starts to float when coasting in neutral, it is necessary to check the crankcase gas ventilation valve. It is located on the back side of the throttle plate. In the valve, the spring is weakened or clogged. Because of this, the regulation of crankcase gas discharge is disturbed. The valve can be bought and replaced in its entirety. But such a move as cleaning and unbending the spring will also work. True, such repairs will help for six months to a year, then the revs will start floating again for the same reason.
If the engine 2.0 Twin Spark holds elevated idle speeds, then the cause may be a malfunction of the sensor of mass fuel consumption (DMRV) or antifreeze temperature sensor. Also, if the flow meter is faulty, the engine may pull poorly when cold or make popping noises when the gas pedal is pressed hard.
Inlet manifold
The 1.8 and 2.0 liter Twin Spark engines use a variable length intake manifold. This applies to later versions of the motors, which are characterized by plastic valve covers.
Up to mid-range speeds (up to 2800 rpm), air flows through the short manifold channels. At mid-range speeds (2800 to 5200 rpm), air is routed through long ducts, which facilitates cylinder filling through resonance and flow acceleration. Above 5,200 rpm, air is switched back to the short channels to provide minimal flow resistance and reduce inlet rarefaction.
The intake manifold geometry flaps are controlled by a vacuum system via electronic commands. The system is generally reliable, but there are instances of rod jamming or vacuum leaks.
Spark plugs
Twin Spark 16-valve engines are equipped with 14mm and 10mm spark plugs. The 14mm plugs are centered in the center of the combustion chamber dome. The 10mm plugs are on the side of the combustion chamber. In the development of the “double spark” system the Italians were assisted by the Japanese from NGK company. Twin Spark system does not cause any special problems and malfunctions. Except that you have to buy twice as many plugs.
Ignition coils
Until 2000, four adjacent ignition coils were used on 16-valve Twin Spark engines. That is, one ignition coil provided “working” spark to one spark plug in one cylinder at the end of the compression stroke and “idle” spark to one spark plug in the other cylinder at the end of the exhaust stroke. Curiously, with this scheme the engine continued to run relatively well when one of the coils failed. However, this scheme increases the load on the coils: they must provide a spark every 360° of crankshaft revolution.
Since 2000, each cylinder received individual ignition coils. One coil gave spark to both plugs of one of the cylinders. In this mode of operation coils give spark every 720° of crankshaft revolution (remember that all 4 working cycles of the engine are made for 2 revolutions of the crankshaft) and it becomes possible to control the angle of advance.
The timing belt
The timing belt should be checked every 60,000 km and replaced at an interval of 115,000 km or once every 5 years. Specialists advise halving the timing belt replacement interval, as they consider it too delicate.
There are no marks anywhere in the timing mechanism on Twin Spark engines. Special shaft retainers must be used to align the shafts correctly.
Balancer shafts
Only the 2-liter versions of the Alfa Romeo Twin Spark engine use balancer shafts. They are driven by a separate toothed belt (60620443). The balancer belt must also be changed at intervals of 115,000 km. In fact, its breakage does not threaten the engine. A lot of 2-liter Twin Sparks are driven without a timing belt at all. However, if it breaks, it can get under the timing belt, and then the engine will get “major” damage.
Headershell
Twin Spark 16-valve engines have the same cylinder heads, but there are differences on camshafts – on the profile of cams. On the older 1.8 and 2.0 liter engines, the camshafts are the same. The valves are driven by hydrocompensators placed in tappet cups. This is a standard scheme for an engine designed for high revolutions, because there are no extra masses in the valve train – rockers.
However, where there are no rockers, there are no rollers. Therefore, the friction between the cams and cups is considerable. Hydrocompensators protrude high out of the wells, so they tend to jam due to lateral loads. A worn hydrocompensator produces a clear, rhythmic sound. It should be replaced immediately, because the corresponding camshaft cam starts to wear out and chip. In general, camshafts for Twin Spark engines are in steady demand.
Often Twin Spark engines are let down by the workmanship: the valve guides and the camshafts themselves are not very successful and durable.
Phase shifter
The phase shifter is fitted to the intake camshaft of all Twin Spark engines from 1998. The hydro-mechanical clutch is similar in design to the clutch on Volvo engines (which we have already covered). The intake camshaft pulley is displaced by a piston, which rotates the clutch housing on oblique splines.
The clutch of the timing mechanism is short-lived. It requires replacement at regular intervals of 100,000 – 150,000 km of mileage due to wear of shaft splines and gears. A junk clutch makes a rattling sound when the engine is running. But the worst thing is that through its oil seals the oil, which should go to the cylinder head, escapes.
As a result, camshaft cams wear out due to low oil pressure. A badly worn phase shifter with a weakened spring can cause the timing belt to jump.
The phase shifter solenoid valve is quite resilient, but often leaks oil from underneath.
Oil pump
The Twin Spark engine oil pump fails due to the slightest contamination. Reduced oil pressure affects the life of the camshafts and their crankshaft liners.
Pistons
The 2.0 Twin Spark engine under Euro 3 differs from the same engine under Euro 2 in its pistons. Of course, the later and more environmentally friendly version has lighter pistons and thinner piston rings. The height of such a piston is only 51.3 mm. For comparison, the Euro 2.0 Twin Spark has a piston height of 56.0 mm. But there are even more colorful values: the engine 1.8 Twin Spark under Euro-2 and Euro-3 respectively has piston heights of 60.15 and 50.45 mm respectively.
On the engine 2.0 Twin Spark you can put the old pistons on the condition of installation of the old-style cylinder-head gasket: its height (thickness) is 1.85 mm against 0.38 mm in the engine for Euro-3.
Unfortunate geometry of the piston group and crank of the 2.0 Twin Spark engine
The 2.0 Twin Spark engine is derived from the 1.8-liter engine by increasing the piston diameter by only 1 mm (from 82 to 83 mm) and significantly increasing the piston stroke from 82.7 to 91 mm. The connecting rods are the same length (145 mm). And it just so happens that in the end, the geometry of the 2.0 Twin Spark engine was very unsuitable for a gasoline motor. There is such an important parameter as RS – the ratio of connecting rod length to piston stroke (crank diameter). So, if in 1.8-liter engine this ratio is equal to the classic 1.75, then in 2-liter – 1.59. This is a characteristic of not even a passenger car, but a tractor diesel.
Hence, there are a lot of technical problems. Piston stroke was changed, connecting rods were left old – so the connecting rod more “rocking” “tablet” (i.e. with low height) pistons from side to side. And also at low RS parameter the piston experiences very sharp accelerations, which strongly loads the whole crank mechanism. At high rpm, such an engine experiences tremendous stresses from the sudden change of acceleration, which literally bangs and beats its crankshaft.
Probably, for the sake of mitigation of such side loads, Italian engineers were forced to use balancer shafts on the 2.0-liter Twin Spark. After all, the shafts can not only counteract the masses, but also have a decent inertia, softening the work of the engine at a sharp pressing and releasing of the gas pedal.
Oil burn
All 2-liter Twin Spark engines have a considerable oil appetite. According to the factory data, the permissible oil consumption is up to 1 liter per 1000 km. But this value only covers the peculiarities of this motor.
Oil consumption is provoked by the wear of cylinders and piston rings, clogging of oil rings. On Twin Spark motors, the oil rings are of the box type, with tiny holes for oil drainage. If they get clogged, the oil appetite becomes very large.
And on Twin Spark engines under Euro-3, the height of oil rings is reduced from 3 to 2 mm.
In a word, weekly checking of oil level on these engines is a must.
TOTAL
It is the engine Alfa Romeo 2.0 Twin Spark is the most short-lived – all because of the very unsuccessful geometry of the crank group, because of which it goes for overhaul barely reaching 250 000 km.