OCR Text |
Show Knocks Indicate Trouble Somewhere in Engine Ability to tell one knock from another an-other forms an important part in the education of the motorist. They may be classified under the four genera! heads: Spark too far advanced, overheating, over-heating, carbon in cylinder head, and loose or worn parts. A spark knock occurs only when the engine is pulling against heavy load, as on a hill. If the knock disappears dis-appears when the spark is retarded and comes on again when the spark Is advanced, it Is evident that excess carbon is the trouble. A knock due to overheating will also be noticed on a hill, but it occurs on level roads. As It Is always accompanied accom-panied by steam from the radiator, It Is not difficult to identity. Carbon knocks may be mistaken for a knock due to overheating, as it Increases In loudness on a hill and has another symptom In common, thatj of causing the engine to run after the switch has teen opened. To make! sure of this trouble remove a spark plug or a valve cap and look into thej cylinder. If the parts are slightly discolored there Is nothing to fear, but if there is much carbon It will be obvious. ob-vious. Having eliminated all three above, there remains the possibility of piston slap or of some bearing working loose. Piston slap occurs mostly in old engines and cannot be removed without regrlndlng cylinders and fitting fit-ting new pistons and rings. This knock is not dangerous. But a part 1 coming loose may wreck the engine, j so do not experiment, but have an expert take up the search at this point |