What is a motorcycle cam shaft?

What is a cam shaft and what does it do? A camshaft is a vital component of many motorcycle engines (basically, without the cam shaft the engine won’t run).

ZXR750 cam shafts
Kawasaki ZXR750 J inlet and exhaust cam shafts

Cam shafts are located in the top of the engine, above the cylinder head and are used to open and close the fuel/air mix inlet and exhaust valves to allow a motorbike engine to run (more info about how engines work can be found here).

Cam shaft lobes
Cam shaft lobes
Cam shaft lobes
Motorbike cam shaft lobes, used to open and close the valves. These cam shafts were taken from a 750cc bike with 30k miles and show some light signs of wear.

The cam shaft has egg shaped, metal lobes on it (see above pics) that open and close the inlet and exhaust valves. There is usually a spacer between the cam lobes and the valves (called a ‘shim’).
Shims are designed to wear and be replaced with thicker ones at certain service intervals. Using shims helps to reduce the wear on the valves and cam shafts (shims are alot cheaper to replace then valves and cam shafts).

Cam shaft sprocket
Cam shaft sprocket, mounted to 1 end or sometimes the middle of the cam shaft. The sprocket above is from a cam chain driven camshaft.

Cam shafts are connected to the engine by either a cam chain, belt or rotated by a gearing system (as used in the Honda VFR750) to enable them to open and close the valves at the correct time during the engine firing sequence.
As a general rule, gear driven cams are the most reliable but are alot more expensive to manufacturer then cam chain or belt driven systems.

VFR750 camshafts in the engine
Inlet and exhaust cams in the engine
Inlet and outlet camshafts of a Honda VFR750 (these are gear driven cams with a central gear sprocket).

The above pictures show the inlet and outlet camshafts in an engine. When the bike is running there are numerous metal parts (cam lobes, valves, shims etc) coming into contact with each other which is why the cam shafts need to be lubricated by the engine oil when the bike is running.

Cylinder head with the cams removed
A ZXR750 cylinder head with the cam shafts removed

The picture above shows a motorbike cylinder head with the cam shafts removed showing where the inlet and exhaust cams sit as well as the inlet and exhaust valves.

Obviously, the actual way cams operate, there design and shape etc is alot more complicated but hopefully this post has given a brief overview of what camshafts are and what they do (and why they should be lubricated with a GOOD QUALITY engine oil).

The information provided on this page is ‘to the best of our knowledge’ and should not be taken as 100% accurate!!

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