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The gudgeon pin is typically a forged short hollow rod made of a steel alloy of high strength and hardness that may be physically separated from both the connecting rod and piston or crosshead. [1] The design of the gudgeon pin, especially in the case of small, high-revving automotive engines is challenging.
A hemispherical head ("hemi-head") gives an efficient combustion chamber with minimal heat loss to the head, and allows for two large valves.However, a hemi-head usually allows no more than two valves per cylinder due to the difficulty in arranging the valve gear for four valves at diverging angles, and these large valves are necessarily heavier than those in a multi-valve engine of similar ...
Pages in category "Piston engine combustion chambers" ... Hemispherical combustion chamber; Heron cylinder head
A cylinder head of a four valve Nissan VQ engine engine. A multi-valve or multivalve engine is one where each cylinder has more than two valves (an intake, and an exhaust).A multi-valve engine has better breathing, and with more smaller valves (having less mass in motion) may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.
This creates what is known as a low hemispherical shaped chamber. In this way, the "Hemi" moniker was used for the same kind of marketing cachet as Chrysler's 1950s-1970s Hemi V8 engines . The Hemi-6 valves are angled apart (splayed) 18 degrees (included angle) along the crankshaft axis, and the intake valves are as large as 1.96 in (50 mm).
The head is machined flat, with recesses only for inlet and exhaust valves, spark plugs, injectors and so on. The combustion chamber itself is contained within a dished depression in the top of the piston. The Heron head is suitable for petrol and diesel engines, for ohv and ohc valve-gear, and for small and large engine displacement capacities.
In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often coolant passages , Valvetrain components, and fuel injectors .
Revisions to the engine for 1986 included roller lifters with a slightly smaller camshaft (.435"/.438" lift and 194°/210° duration at .050"), new heads with smaller, swirl-port intake runners, floating piston pins, and larger piston dishes for lower compression (8.0:1 v. 8.4:1). These changes increased torque to 250 lb⋅ft (340 N⋅m) but ...