piston failure analysis en finale - efco... emak s.p.a. member of the yama group † 42011 bagnolo...

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Emak S.p.A. Member of the Yama Group • 42011 Bagnolo in Piano (RE) Italy • Tel. +39 0522 956611 • Fax +39 0522 951555 • service@emak.it • www.emakgroup.it

Piston failure analysis

1. Bad fuel-oil ratio (a)

Deep scores on the piston. Damaged piston caused by lack of lubrication

2. Incorrect oil (b, m)

Excessive carbon deposit can build up and seize the piston. The rings stick because of oil carbon, allowing gases to pass the piston and cause exhaust side seizures. The carbon deposit damages the surfaces, reducing lubrication

4. Lean carburettor adjustment (c, h)

It causes insuffi cient lubrication normally associated with overheating. Damage caused by lean carburettor adjustment

3. Overspeeding (g, h, l)

Oil fi lm break down. Damage caused by lean carburetion, ignition coil problem (broken speed limiter), air leaks and/or dirty fuel fi lter

The piston skirt material is worn off and the diamond marks disappear. Damage caused by worn air fi lter

6. Worn, damaged or missing air fi lter (d)

The piston top shows evident impact signs and the skirt shows deep scores, caused by damaged or missing air fi lter

5. Overheating (e)

Overheating expands the piston skirt on the exhaust side. Damage caused by overheating

7. Pre-ignition, detonation (f, h, i)

Damage caused by explosion: old fuel, low octane level, excessive alcohol level, excessive compression value

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11

01

65

0

Diamond marks are easily noticeable. These are important to use as reference for further description

Piston failure check lista. Bad fuel-oil ratio: insuffi cient quantity of oil (1)

b. Incorrect oil: bad oil or oil for outboard, diesel, 4-stroke engines; does not lubricate enough the engine (2)

c. Lean carburettor adjustment: incorrect air/fuel ratio (4)

d. Worn, damaged or missing air fi lter: dust particles and water go through the engine causing faster wear or components failure (6)

e. Overheating: obstructed cylinder fi ns, blocked air cooling fl ow (5)

f. Pre-ignition, detonation: fuel with low octane level or old fuel, wrong sparkplug thermal grade, defected ignition system and carbon deposit (7)

g. Air leaks: from engine, crankshaft seals, crankcase gasket, impulse tube, leaning fuel mixture and make the engine work over speeding, as a wrong carburettor adjustment does (3)

h. Oxygenated fuels or with alcohol/ethanol content: clean fuels are formulated with higher levels of oxygen, which can increase combustion chamber temperatures and pressure, the consequences are similar to a unit which has very lean setting (3, 4, 7)

i. Old fuel or fuel with low octane level: it does not burn properly creating an excessive pressure on internal components (7)

l. Dirty fuel fi lter: it stops the fuel going inside carburettor and the engine works using too much air. Carburettor inspection and cleaning is suggested (3)

m. Carbon deposit: excessive carbon deposits can build up and seize the piston. The rings can stick because of oil carbon allowing gases to pass the piston and cause exhaust side seizures (2)

Carbon deposit (m)

Obstructed cylinder fi ns (e)

Air leaks in engine, crankshaft seals, crankcase gasket (g)

Error in mixing ratio, fuel with low octane level, high level of alcohol (a, b, h, i)

Dirty fuel fi lter (l)

Damaged impulse tube (g) Wrong carburettor adjustment (c)

Worn, damaged or missing air

fi lter (d)

Dirty particles in the internal carburettor mesh fi lter or between main passages (l)

Sparkplug thermal grade too hot (f)

Air leaks in inlet boots or manifold, fuel line intake gasket,

fuel system (g)

Intake side Exhaust side

New piston profi le

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