Bosch Spark Plugs Poster

Spark Plug

Spark plug design

• Alo ceramic insulator
• Nickel-plated spark plug shell
• Heat-shrinkage zone
• Conductive glass seal
• Captive Gasket
• compound center electrode (copper and nickel)
• Ground electrode

Spark-plug temperature response

Spark plug faces

• Spark plug with excessively high heat-range code number
• Spark plug with suitable heat-range code number
• Spark plug with excessively low heat-range code number

The working range temperature should be from 500 'C to 900 C for different engine performance ratings.

Spark plug concepts

Air gap design The ignition spark travels along direct path to the ground electrode and thus ignites the air-fuel mixture

Bosch

Surface gap design

The layout of the ground lectrodes such that only surface air gap sparks which are particularly long and powerful, can be formed.

Bosch

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Normal condition

No residues from lead fuel additives or engine-oil additives. No overheating

Insulator nose with color between whitish or yellowish-Brey and russet. Engine OK. Correct heat range mixture adjustment and timing OK; no ignition miss, cold-start enrichment functioning correctly. AE

Soot fouling

Insulator nose electrodes, and spark plug shell covered with felt-textured, matt-black coating of soot.

Cause: Incorrect A/F mixture adjustment. AlF mixture too rich; extremely dirty air automatic choke or manual choke actuated too vehicle only used for extremely short distances spark plug too cold, heat range too low. long

Effects: Ignition miss, poor cold starts

Oil fouling

Insulator nose, electrodes, and spark plug shell covered with shiny

Cause: Excessive oil in combustion chamber. Oil level too hich; severe wear of piston rings cylinder walls Too much oilin fuel mixture (two-stroke engines) .

Effects: Ignition loss, Starting difficulties

Remedy: Overheaul engine; use correct A/F mixture; replace spark

Severly eroded cente electrode

Cause Failure to observe spark plug replacement intervals. Effects: Ignition miss, especially during acceleration (ignition voltage not adequate for bridging wider electrode gap) . Starting difficulties

Remedy: New spark plugs

Severe lead deposits

Bosch

Thick, brownish-yellow glaze, thick in some places, possibly with greenish tint, has forme on the insulator nose

Cause Fue additives containing lead The glaze forms when the engine is operated at hich loads after extended part throttle operation,

Effects: At high loads the glaze becomes electrically conductive; leading to ignition miss

Remedy: New spark cleaning them pointless.

Ash formation

Thick ash coating from oil and fuel additives on insulator nose; in scavenging area