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Locating and Curing Detonation and Pre-Ignition Problems: Service Engineering Bulletin

When fuel ignites in an engine, it should burn in a controlled manner and not explode, as explosions can damage engine components. Detonation occurs when fuel ignites too early or is overcompressed, causing high combustion pressures. Detonation is heard as a metallic "pinking" and causes damage like burned or eroded piston crowns. Pre-ignition alone increases combustion temperatures and harms valves and spark plugs. To remedy issues, replace damaged parts and locate the underlying cause, such as using too low a fuel grade, improper ignition timing, air leaks, or overheating.

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19 views2 pages

Locating and Curing Detonation and Pre-Ignition Problems: Service Engineering Bulletin

When fuel ignites in an engine, it should burn in a controlled manner and not explode, as explosions can damage engine components. Detonation occurs when fuel ignites too early or is overcompressed, causing high combustion pressures. Detonation is heard as a metallic "pinking" and causes damage like burned or eroded piston crowns. Pre-ignition alone increases combustion temperatures and harms valves and spark plugs. To remedy issues, replace damaged parts and locate the underlying cause, such as using too low a fuel grade, improper ignition timing, air leaks, or overheating.

Uploaded by

dalla.s0975
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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SERVICE

ENGINEERING
BULLETIN

SB2103.1

Locating and Curing Detonation


and Pre-ignition Problems
When fuel ignites in an engine, it should burn
in a rapid but controlled manner: it should not
explode. The power from fuel exploding can
damage the valves, spark plugs, pistons and
bearings.

Most fuels detonate when sufficiently


compressed. Fuels with a higher grade or
octane rating have a greater resistance to
detonation.

Pre-ignition can cause detonation by igniting


the fuel too early in the engine cycle. This
causes very high combustion pressure when
the piston is at the top of its stroke; the high
pressure causes any unburnt fuel to
detonate. Detonation in an engine can often
be heard as a sharp metallic knock or
"pinking". Detonation damage to pistons is
easily recognisable from burning or severe
erosion to edges of the crown. Piston ring
lands may also fracture; the fracture starts at
the second land and may damage lower lands.
(Diagram 1) The piston crown may crack or
have a hole punched through. (Diagram 2)

Pre-ignition, even without fuel detonation,


causes higher than normal combustion
chamber temperatures. It damages valves
and spark plugs; may distort piston crowns
and can overheat piston rings, trapping them
in their grooves with consequential damage to
the rest of the engine. (Diagram 3)

Replace the damaged components if


detonation or pre-ignition occurs in an engine.
But of equal importance, locate and correct
the cause of the problem.

All trademarks shown are owned by Tenneco Inc. or one or more of its subsidiaries, in one or more countries
SERVICE
ENGINEERING
BULLETIN

SB2103.1

Locating and Curing Detonation


and Pre-ignition Problems
Some of the more common causes of detonation and pre-ignition are:

1.Using too low a fuel grade

2.Incorrect ignition timing

3.Malfunction of the ignition auto advance

4.Incorrect type or damaged spark plugs

5.Lean fuel mixture or poor mixing of fuel and air

6.Air leaks between carburettor and combustion space

7.Compression ratio too high

8.Localised overheating caused by engine cooling problems.

9.Hot glowing carbon on metal projections in the combustion space

10.Poor driving technique e.g. low engine speed with high load

11.High quantity of oil in the combustion chamber

12.Damaged or leaking valves, or insufficient valve clearance

All trademarks shown are owned by Tenneco Inc. or one or more of its subsidiaries, in one or more countries

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