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Your Camshaft worn out? » Read more about common malfunctions • Repair • Replacement manual
Reliable valve control with the camshaft
As an essential component of every piston engine the camshaft is responsible for valve control. The camshaft is a very precisely built, single piece component and usually lasts a long time. Faulty maintenance or excessive strain can cause untimely wear. Its replacement is a moderately difficult repair.
Location and function of the camshaft
In average overhead camshaft engines, the camshaft is positioned in the cylinder head above the combustion chamber. A different construction places the camshaft next to the crankshaft. In these cases, valve control is actuated by pushrods and tappets. Every cylinder bank in an engine is equipped with these components. The camshaft is supported by bronze bearing cups on both sides and in its centre. On one side, either a belt disc or a cam chain sprocket is flanged to it. They synchronise camshaft and crankshaft. The camshaft is equipped with oval tappets (cams or valve lifters). The elongated part of each of them protrudes from the camshaft under a different angle. They open the valves by pressing on them. The valves return to their original position by small valve springs. The camshaft is set in rotation by the timing belt or chain. At every rotation cycle it opens the intake valve and subsequently the outlet valve. The rotation ratio between camshaft and crankshaft is 1:2. This ensures that both valves are closed during the power stroke.
A camshaft can fail due to two causes:
- wear of the tappets
- fracture of the shaft.
A camshaft is a single-part die-cast component and post-processed on precision devices. Possibilities for its repair are severely limited. Theoretically, in case of tappet wear, the original shape of the tappet can be restored by welding and turning. Practically, this is almost never done. In case of shaft fracture, replacement is the only option. Tappet wear is unavoidable after a certain mileage. Even when driving in a careful manner and observing all maintenance intervals, a camshaft hardly ever lasts beyond 250.000 km. Deficient maintenance and engine treatment can severely shorten its life span. The main cause of tappet wear is inadequate lubrication. There are four grounds for this:
- driving with an insufficient amount of oil
- driving with inferior oil
- accelerating too fast with cold engine
- oil is too runny due to an overheated engine.
A camshaft is constructed by casting, turning, annealing and tempering. Underneath the tempered surface, the material is very soft. When the tempered layer of the camshaft wears off, the progress of wear is accelerated.
Camshaft repair requires the following steps:
- removing the valve cover
- unscrewing the bearings
- removing the timing belt or chain
- removing the camshaft disc (connection with the belt or chain)
- removing the camshaft holders
- removing the camshaft
- replacing the bearing cups
- replacing the gaskets
- assembling everything.
This all sounds very easy, although it requires a certain amount of experience and special tools. It is very important that all bolts around the camshaft are removed simultaneously. Removing one bolt after the other creates a tension which can cause fracture of the camshaft. Usually, the bolts fixing the camshaft holders are expansion bolts. They have to be disposed off and replaced by new ones.
Useful additional repairs
Camshaft replacement goes hand in hand with plenty of disassembly, providing an excellent occasion for performing additional maintenance repairs. This saves you a lot of work that needs to be done sooner or later anyway. Useful additional repairs on occasion of camshaft repair are:
- replacement of timing belt or chain including tensioner
- replacement of water pump
- oil & filter change
Purchasing a camshaft
A camshaft is a precision component. Its price strongly depends on manufacturer and the car model. An average price indication for a decent camshaft from a branded manufacturer, e.g. FEBI BILSTEIN, starts at 100 EUR (± £90). Depending on type, a new camshaft can cost up to 500 EUR (±£ 450). Choosing a branded component is very important in case of the camshaft; otherwise you run the risk of incurring severe engine damage. Many manufacturers offer camshafts including a complete repair set. This includes several additional components – e.g. hydraulic tappets, which should be replaced along with the camshaft.