Motor Vehicle Maintenance & Repair Asked by user15938 on January 5, 2021
I am trying to learn about engines, so my question is where do valves, camshaft etc go inside different engines? I see different engine have them in different places, base on if the engine is a inline, v-line or flat.
This will be for modern car engines. This does not necessarily include motorcycle, 2 stroke, or equipment (lawn mower), etc.. This is based on what I've seen so there may be other examples I am not aware of or have forgotten.
The cylinder head is installed on top of the block. There are a few common parts on all cylinder heads. Intake ports, Exhaust ports, combustion chambers, valves and valve springs. There are also passages for oil and coolant.
Valves will be in the cylinder head. They are held in place with the valve spring. You can see the valve stems and valve springs if you remove the valve cover.
Valves are opened by the camshaft and closed by the valve spring. The camshaft is typically in 1 of 3 locations.
In the block. In this case there is a lifter that rides on the cam shaft lobes, a push rod, and a rocker. The cam pushes the lifter, which pushes the push rod, this pushes up on one side of the rocker, which pushes down on the valve.
In the head, next to the valves. This setup has the cam, rocker, and at some point a lifter. The cam pushes the rocker, which opens the valve.
In the head, directly over the valves. In this configuration, there is a bucket over the valve and valve spring that cam touches directly.
Correct answer by rpmerf on January 5, 2021
Flat-head engines (older lawnmower engines, early car engines) have the valve ports actually in the block face opening upward (the head is an entirely passive piece with zero moving parts except for the coolant). The valve stems go downward into the block, and there are side compartments for access to the valve springs and lifter adjustments. The cam is below the lifters, so close to the crank that it's typically gear or chain drive.
Flat-head 'Vee" engines place the camshaft in the vee, directly above the crank.
Flat-head pancake engines (opposed cylinder) place the camshaft typically above the crank.
Not to be confused with opposed-piston engines, which have opposing crankshafts with pistons that mash together. They have no cam or valves; they have intake ports on one piston and exhaust ports on the other. Darlings of marine and early railroad, they're rarely seen elsewhere because the dual cranks and synchronization gear is heavy, and like any 2-cycle engine, it's VERY hard for them to pass Tier 3 emissions.
Overhead-valve engines have valves in the head opening downward. tend to place the cam in the same place as flathead engines. They use a long pushrod that push "up" and tip rocker arms which push the valves down. They're an obvious "mod" of the flathead design.
Overhead-cam engines have cams up in the head. They typically use a rubber toothed belt for drive, since it's quite a long distance from the crank (this gets outrageous on a "Vee" engine). The cam either acts directly on a lifter that cushions the valve stem, or via a "rocker arm" arrangement of some sort.
Dual-overhead-cam engines have two cams in the head, each handling half the valves.
Answered by Harper - Reinstate Monica on January 5, 2021
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