Recently, we discussed crankshafts, which are components that help transmit linear to rotary power in and engine. However, attached to the crankshaft is something called a camshaft, which is vital in helping to develop power in a machine.
Much like the crankshaft, proper maintenance of the camshaft has an important impact on your productivity.
This tip will discuss the camshaft, including detail on its function, location, components, design, maintenance, and more.
Simply put, a camshaft is a device which is designed to actuate the valves of a machine, most often an engine, in sequence. Like a crankshaft, it rotates and slides in order to turn rotational motion into linear motion.
This “in” and “out” motion by the camshaft lobe and is often called the throw.
While it may look like a crankshaft, a camshaft is different in form and function. It consists of a cylindrical rod which runs along the cylinder bank and contains protruding lobes which actuate the engines intake and exhaust valves. The camshaft also has support journals similar in design to the crankshaft, with the number depending on upon the length of the shaft.
Camshaft are made of many materials and are typically cast of iron or forged from steel. When made of steel, the camshaft is heat treated by gas nitriding, giving it a surface hardness near 60 HRC (Rockwell scale). The lobes of the camshaft are usually slightly tapered, helping to distribute wear on the parts.
The camshaft may operate from a number of different locations. Many have heard the term “overhead” cam. In this arrangement, the cam sits above the cylinder bank and actuates the rockers/valves directly.
Dual Overhead Cam Engine
In other designs, the cam is located below the cylinder and actuates the rockers and valves with the assistance of a pushrod. Both designs allow the cam to provide lift which results in a rise of a valve from its seat.
Most of today’s engines have one cam, but there are designs where multiple shafts are used, like in the image above. This is most often in “V” type engines, where one camshaft is needed per bank of cylinders. In other engines, the camshaft may be designated by valve type, intake and exhaust, which means an inline engine would have two cams, and a V-type four cams.
Cams, depending on location, may be driven by gears, chains or belts. These are routinely referred to as timing gears, chains or belts. Timing controls the sequence and duration that the valves in an engine are open and closed. The greater duration, the greater the horsepower developed.
Sliding friction is the primary cause of camshaft wear and may take place at the lobe or journal bearing shells. Proper surface hardness and the lubrication are needed to minimize these forces. Lubrication is provided to the camshaft at the bearing shell through pressurized oil holes, and must have the proper viscosity and additives (anti-wear) to minimize the impact of sliding friction.
I hope you enjoyed this week’s tip, and let me know if you have any questions!
¿la causa de avería en el árbol de levas es que el uso y los continuos giros del sistema acaben por provocar una holgura axial en el alojamiento,que significa esta situación?
what is causes for wear in camshaft and valves?
Jose - I have never come across "axial slack" in a camshaft. I'm not really sure what would cause it as axial movemt in a camshaft is limited by design. That said, the promary wear mode that I encountered during my career was flat cam lobes. This results in valves not opening as designed and causes a lack of power. Typical causes are bad metallurgy or excessive sliding friction wearing the cam lobe. Lack of lubrication may also play a role.
Younes - wear in a camshaft is most often a flat lobe casued by excessive sliding friction which may be the result of a soft cam (bad metallurgy) or lack of lubrication. As for valve failures, there are many causes to include: lack of lubbrication, over lubrication, over heating, improper seating, stem seal failure, wrong spring tension, etc.
Rick Russo,gracias por su comentarios y de sacarme de la duda que tenia sobre esta situación del árbol de levas,saludos.
Рик,вы описали классическую схему.Мне интересно,кто-нибудь пробовал использовать пневматический или электрический привод для открытия клапанов?Это было бы очень интересным решением.
According to my experience with Diesel heavy load trunk piston type engine,Lots of cam failures come with mineral multi-grade oil,even with the Multi-grade crank area sound level also very high. But with mineral Mono-grade oil failures very very low with same lubrication system.
Can you explain bit more about lubrication related to Cam with graphs & sketches ?
Dilupa: Lubrication of the Cam is fairly simple, an oil wedge is formed under the spinning cam preventing metal to metal contwct. The wear mode that predominates is from sliding friction. Most on-highway or off-highway diesel engines today call for a multi-weight 5W-40. I believe Detroit Diesel Series 60 engines may call for either a straight 30 or 40 wt depending on the climate. Oil analysis has shown that both multi-weight and straight weight oils provide sufficient cam and crank protection. Issues have occured in the past and have been attributed to poor metallurgy and/or a "lack" of lubrication.
As for graphs and sletches - try the internet and search for the information you deisre. Good luck.
SR. RUSSO, MUCHAS GRACIAS POR ESTE CONSEJO, YO APENAS TUVE UN PROBLEMA EN MI AUTOMOVIL CON EL ÁRBOL DE LEVAS Y EL CENSOR DEL ÁRBOL, Y AHORA CON ESTA INFORMACIÓN, ME RETROALIMENTA EN SU FUNCIÓN Y MANTENIMIENTO QUE SE DEBE DE TENER .. GRACIAS Y SALUDOS.