The Ford I4 DOHC engine is a straight-four automotive internal combustion engine with two overhead camshafts, produced by the Ford Motor Company. It was initially available in a 2.0-litre 8-valve version, and later in 2.0 and 2.3-litre 16-valve versions from 1989 until 2006. It powered various Ford models in both front wheel drive and rear wheel drive applications. The I4 DOHC was Ford's first in-house DOHC engine design to reach volume production.[1]
This engine is known by the somewhat anonymous designation of "I4 DOHC", with Ford's technical reference calling it the DOHC.[2] Some sources call it the Sierra engine, but only when used in that car, and in some enthusiast forums it is known informally as the "twincam", or the "twink". Its lack of recognition extends to the aftermarket, as few tuning shops offer options for the engine, and it does not appear in Ford's own list of four-cylinder racing engines.[3][4]
The engine was designed to replace the 2.0-litre OHC Pinto engine, which by the late 1980s was lagging behind the competition in terms of power output, efficiency and refinement. Apart from the inline configuration and approximate displacement, the I4 DOHC shares nothing with the Pinto engine, and is described as a "clean sheet" design.[5][6]
In late 1989, the I4 was launched in 8-valve form in the rear-wheel drive Ford Sierra, Sierra Sapphire, and Scorpio (in the United Kingdom and Ireland, the MkI Scorpio retained the previous model's name and was sold as the Ford Granada MkIII). In these cars it was mated to either the new all-synchromesh MT-75 5-speed manual transmission or the existing A4LD four-speed automatic. The engine received mixed reviews, being seen as an improvement over the Pinto, but not the leap forward expected.[1]
The MkV Escort had been launched in 1990 to disappointing reviews, and Ford were looking to boost the image of this critically important range. To that end they introduced two high-performance Escorts to compete in the hot hatch market, using the well known XR3i and RS2000 badges. The Zetec engine in development for the new Mondeo was a still a year away, so rather than wait for that engine to become available, Ford opted to mount the I4 DOHC transversely in a FWD application using a revised block with different mount locations. Engines in these cars also received a new multivalve cylinder head and tubular exhaust manifold. In the Escort RS2000 16V, the 2.0-litre I4 DOHC developed 150PS (110kW; 148bhp).[7]
The Sierra was discontinued in 1993 and the RS2000 in 1996, but the I4 DOHC continued in use in the Ford GalaxyMPV launched in 1995. By this time, a 2.3-litre 16-valve version of the engine was offered alongside the original 2.0-litre in both 8-valve and 16-valve versions. The 2.3-litre also appeared in the Ford Scorpio and the Ford Transit van. The I4 remained the main petrol engine for the original Galaxy until its 2006 redesign, after which production of the I4 ended.
Versions and features
All I4 DOHC engines have a cast iron block and an aluminium cylinder head.[8][6] The sump is also of cast aluminium with built-in webs and serves to stiffen the whole engine assembly. The block has five main bearings for the crankshaft.[2]
The two overhead camshafts are driven by a timing chain. Each camshaft has five bearings.[2] The camshafts operate the valves and dual valve springs through hydraulic tappets.
The oil pump is driven off the crankshaft by a single roller chain.[2]
8-valve, 2.0L engines
2.0L 8 valve in Ford Scorpio
The 8-valve, 2.0L I4 is a "square" engine, with bore and stroke measuring the same at 86mm (3.39in). There are two valves per cylinder. The compression ratio is 10.3:1 in early engines, and was reduced to 9.8:1 in some later applications. The intake camshaft profiles for carburettor and injection engines are different, while the exhaust camshafts are the same.
N8A/N8B
One 2-barrel Weber 2V TLD carburettor, no emission controls.[2]
Power: 107hp (80kW) at 5600rpm.
Torque: 180N⋅m (133lb⋅ft) at 3000rpm.
N8C/N8D
One 2-barrel Weber 2V TLD carburettor, unregulated catalytic converter
An enlarged, slightly undersquare version of the engine was developed with bore × stroke increased to 89.6mm ×91mm (3.53in ×3.58in), for a total displacement of 2.3L (2,295cc).
Another change for the 2.3-litre was the addition of two engine balance shafts located in a new taller sump. The shafts were driven from the oil pump drive chain, made longer for the purpose. The system was developed jointly by Ford of Europe, Cosworth Engineering, and FEV Motorentechnik[de].[9][10]
Tthe I4 DOHC is reported to exhibit certain weaknesses or be prone to particular types of failures, without clarifying whether they are the result of design flaws or poor maintenance.[11][5][8] These issues may include:
Timing chains that strech or break.
A blocked cooling system, potentially leading to overheating and a failed cylinder head gasket.
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