9. (a) How long should the burning be done?
(b) How often is carbon burning recommended for a gas engine?
(c) If there are any carbon particles or sand left in the cylinder after burning is done how are they removed?
10. Describe how the carbon is removed from a four-cylinder engine, paying particular attention to details such as lighting, which part of the head the torch is played on first, what does the burning and where the carbon goes.
LECTURE NUMBER SEVENTEEN
Subject—Preheating Agencies
1. (a) What is meant by preheating as applied to the oxy-acetylene welding industry?
(b) What are several fuels which can be used very successfully for preheating?
2. Name the three principal reasons why parts to be welded are generally preheated.
3. (a) Why is charcoal considered the best preheating agent for general welding?
(b) Why should it not be used to any great extent in closed rooms during the winter months?