What is the difference between OHV, OHC, SOHC and DOHC engines?
OHV stands for overhead valve. That is the valves are located on top of the combustion chamber. These are normally operated by a cam shaft working off the engine. There are variations. On early engines the inlet could be atmospheric, opening with the vacuum created by the piston movement. Early engines placed valves to the side and under the combustion area and worked directly off the cam which was geared off the crankshaft, as it was the simplest solution. The downside was that it produced a strange combustion chamber shape, making it inefficient.
OHV engines were originally operated by a low cam shaft linked to push rods and rockers to transfer the movement to the tip of the valves.
OHC are OHV engines where the cam shaft has been transferred to the top of the engine, reducing the number of linkages.
SOHC is the above where there is a single cam operating the inlet and exhaust valves and DOHC is where there are two cams, one operating the inlet and the other the exhaust cams. So an OHC engine can be either single or double cammed.
The PDF you will download contain:
- OHV or Pushrod engine
- OHC or SOHC engine
- DOHC or Twin-Cam engine
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