CVH Engine : Seen in the Sierra and Sierra Sapphire in 1.6 (late-1991 onwards) and 1.8 (1987 onwards) capacities.
First introduced in the UK in the early Eighties, the CVH first found a home in the front-wheel-drive Fords : it was a mainstay of the Escort range, appearing in 1.3, 1.4 and 1.6L capacities. The Fiesta utilised it too, in 1.3 and 1.6L form initially, but then 1.4 and 1.6L.
Technical Overview :
The CVH engine is of the overhead camshaft design, utilising a cast aluminium-alloy cylinder head on an iron cylinder block with a pressed steel sump pan. The name CVH comes from the design of its combustion chamber: Compound Valve, Hemispherical chamber.
The crankshaft is supported in five main bearings and directly drives the oil pump which is mounted on the front of the engine. The camshaft is driven by a toothed rubber belt that Ford specify should be changed every 36,000 miles. Tappets are hydraulic throughout.
Early in the 1992 model year, with the final facelift to the entire range, Ford introduced 1600 CVH models fitted with Central Point Fuel Injection (CFi) and a catalytic convertor. At the same time the 1800 engine was revised slightly and fitted with a moderately different CFi system.
1800 carburettor'd engines have the distributor mounted on the front of the timing cover, and driven directly from the camshaft sprocket. Models fitted with the later CFi engines have no distributor as the EEC-IV engine management system drives an EDIS unit and a single coilpack, mounted low down on the inlet side of the engine.
Unlike the front-wheel-drive CVH's, there is little available in the way of tuning components for the rear-wheel-drive applications fitted to the Sierra. Although the 1.8 CVH is reputed to be based on the american tall-block 1900 CVH engine (and does get used as the basis for some 1900cc front-wheel-drive conversions) virtually nothing is available "off-the-shelf" to increase power output.
1800 CVH engine with carburettor:
1600 CVH engine with CFi (note the lack of a distributor on the front of the engine!):
What goes wrong? :
Headgaskets and cylinder head problems can be commonplace - especially if allowed to overheat seriously.
Timing belts break if not replaced or contaminated with oil. Serious engine damage can result from camshaft drive belt breakage in use - this is more likely to apply to all CVH engines, not just those of higher capacities (as in the Pinto's case) due to the finer tolerances in manufacture and the engine's more compact design.
Neglecting oil changes causes problems - the CVH shares the Pinto's appetite for fresh oil and neglecting the service interval can cause oil to sludge up and block oilways. The oil pump can fail, starving the top end too. Hydraulic tappets will get noisy as a result of either excessively dirty oil or low pressure.
Valve stem oil seals are notorious - this does not appear to be confined to particularly high-mileage units either, and several Ford magazines have often observed in the past that the ideal interval for a CVH top-end overhaul is around 80,000 miles. However valve stem oil seals can come adrift at any mileage leading to clouds of blue smoke on first startup or on overrun.
Fuel pump operating rods wear. CFi engines have an in-tank electric pump which addresses this problem but on older carburettor engines the fuel pump is driven from an eccentric on the camshaft via a short rod - over time the rod wears shorter leading to decreased travel on the mechanical fuel pump, causing fuel starvation at higher engine speeds.