Class 2 (2nd Engineer) MEKM 📅 Apr 2024

Exam Question

With reference to timing chains:

(a) State the cause of chain elongation in service, using a sketch of a section of a camshaft roller chain to illustrate your answer. (4)

(b) State:

(i) The effects of increased chain length. (3)

(ii) The method of assessing percentage increase in length. (3)

(d) State why a limit is placed on percentage chain elongation and give typical example. (3)

Reference Answer

(a) Cause of chain elongation in service:
The primary cause of chain elongation is wear-down between the pins and bushes in the roller chain. Over time, this wear effectively increases the pitch of the chain (the distance between the centres of adjacent pins), causing the chain to elongate.
As the chain's pitch increases, it no longer matches the pitch of the sprocket teeth, leading to:
Excessive wear on the teeth of the sprockets.

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