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Timing Chains



  chains do not stretch but they do get longer

Students sometimes have difficulty in visualising the effects of the elongation of a timing chain on the timing of the camshaft. This model may help in understanding what happens.

  the polygon effect causes vibration

When a chain is engaged around a sprocket wheel it does not form an arc of a circle, but instead forms part of a polygon, the length of each side corresponding to the pitch of the chain.

  chains are renewed every 15 years

The camshaft chains will have to be replaced when their elongation reaches 1% or after 15 years. The reason for placing a limit on itís elongation is that as the chain gets longer the pitch increases.

  chains must be correctly tensioned to prevent excessive wear

Medium speed four stroke engines and small two stroke engines use a simple method of checking and adjusting chain tension.

  how the camshaft is retimed

When the timing chain elongates, the timing of the camshaft is affected. The timing chain layout is such that the timing is retarded when the engine is running ahead.

  lanchester balancers prevent vibration

Second order moments can cause resonance with 4 and 5 node modes of hull vertical vibration. The resonance causes vibration of high amplitude which can damage components.

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