8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994 http://slidepdf.com/reader/full/l10-m11-and-n14-engine-overspeed-junio-1994 1/6 ~ --" ~ v e Service Bulletin L10, M11,and N14 Engine Overspeed 1208 Subject BulletinNo. 3666107 1 Date: June, 1994 The purpose ofthis bulletinis to iIIustratethe causes and effectsofangina overspeed and to assist indiag- nosing overspeed relatad angina failures. Definition of Engine Overspeed Engine overspeed is defined as the speed in revolu- tionsparminute(rpm)that exceeds the maximumgov- erned speed plus governordroop. At a sufficiently high degree of overspeed, damage to angina components will occur. Base angina compo- . nent ranuras associated withoverspeed generally re- sult from valve-to-pistoncontact or a no-followcondi- tion in the valva and injection train. Fuel system component failures associated with overspeed gener- ally result from excessive pump speed (PT fuel pumps only) and no-follow in the injection train. ~ Valve-to-pistoncontact occurs when a piston is at (or . near) top dead cantar (TDC).At high degrees of overspeed, the intakeand exhaust valves do not clase completely.This conditionis commonlyreferred to as "valve floating".Valvafloatingresultsinanginadam- age when a piston strikes an open valva. Valve-to- piston contact results inbent or brokenvalves,piston damage, cylinderhead damage, and the possibilityof extensiva progressive damage to the other cylinders, cylinderheads, and the turbocharger. No-followis induced by rapid changas in valva and injectiontrainacceleration, resultingin impact loading between the components in the train. Impactloading can bendorbreakpushtubes, damage injectors,crack cam followerpins,cause surface distress on camshaft robes, and cause excessive valve colletwear. ExcessivePTfuelpump speed causes damage tothe internalpump components. The most common dam- age to the pump is a stuck governorplunger and bro- kan drive tangs. Extreme wear and heat generated fromprolongadexposure tooverspeed conditionscan cause a worngovernortorque spring, a broken pump shaft,andworngears. Causes of Engine Ove~speed Possible causes for angina overspeed are as follows: . Improper gear shift . Excessive vehicle speed down hills in the wrong gear . Excessive amounts of combustible vapors in the intake system . Fuel pump tampering (PT pumps ol)ly) Diagnosing Engine Overspeed Failures: Commonsigns ofangina overspeed are as follows: . Bent or broken push tubes . Worn valva collets . Cam gear walk-off . Stuck fuel pump governor plunger (PT pumps only) ,. . When diagnosing a possible overspeed failure, always check for these common signs in additiori to other component ranuras. If a component shows damage as described in the sections on Overspeed Symptóms, but the angina does not sho\y any of the common signs ofoverspeed, then overspeed is not the probable cause of the component failure. Situations of extreme angina overspeed will result in excessive angina vibration. Exposure to excessive vi- bration for prolongad periods of time will cause the damper and/or flywheel capscrews to loosen. This fail- ure moda occurs at very high angina rpm. If a loose flywheel or damper is causad by overspeed, one or more of the common signs of overspeed will algo be evident. ~ f Cu-mmins Engine Company, Inc., Columbus,-Indiana 47202-3005 C ummi ns E ng in e C ompa ny Ud., D av en try, N orth an ts , E ng la nd NN11 5NU Registered Office: 46-50 Coombe Road. New Malden. SlJrreyKT3 4QL Registered No. 573951 England .ti Copyri\Jht @ 1994 i!' Cummms Engine Company. Inc. ;¡ Al! rights reserved Paga 1 of 6
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8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994
The purpose of this bulletinis to iIIustratethe causesand effects of angina overspeed and to assist in diag-nosing overspeed relatad angina failures.
Definition of Engine Overspeed
Engine overspeed is defined as the speed in revolu-tionspar minute(rpm)that exceedsthe maximumgov-erned speed plus governor droop.
At a sufficiently high degree of overspeed, damage toangina components will occur. Base angina compo-
. nent ranuras associated with overspeed generally re-
sult from valve-to-pistoncontact or a no-followcondi-tion in the valva and injection train. Fuel systemcomponent failures associated with overspeed gener-ally result from excessive pump speed (PT fuel pumpsonly) and no-follow in the injection train.
~ Valve-to-pistoncontact occurs when a piston is at (or. near) top dead cantar (TDC). At high degrees of overspeed, the intakeand exhaust valves do not clasecompletely.This conditionis commonlyreferred to as"valve floating".Valvafloatingresultsin anginadam-age when a piston strikes an open valva. Valve-to-piston contact results in bent or broken valves, pistondamage, cylinderhead damage, and the possibilityof extensiva progressive damage to the other cylinders,cylinder heads, and the turbocharger.
No-followis induced by rapid changas in valva andinjectiontrainacceleration, resultingin impact loadingbetween the components in the train. Impact loadingcan bend or break push tubes, damage injectors,crack cam followerpins, cause surface distress on camshaftrobes, and cause excessive valve collet wear.
Excessive PT fuel pump speed causes damage to theinternal pump components. The most common dam-age to the pump is a stuck governor plunger and bro-kan drive tangs. Extreme wear and heat generatedfromprolongadexposure to overspeed conditions can
cause a worn governor torque spring, a broken pumpshaft, and worngears.
Causes of Engine Ove~speedPossible causes for angina overspeed are as follows:
. Improper gear shift
. Excessive vehicle speed down hills in the wronggear
. Excessive amounts of combustible vapors in theintake system
When diagnosing a possible overspeed failure, always
check for these common signs in additiori to othercomponent ranuras. If a component shows damage asdescribed in the sections on Overspeed Symptóms,
but the angina does not sho\y any of the common signsof overspeed, then overspeed is not the probable causeof the component failure.
Situations of extreme angina overspeed will result inexcessive angina vibration. Exposure to excessive vi-bration for prolongad periods of time will cause thedamper and/or flywheel capscrews to loosen. This fail-ure moda occurs at very high angina rpm. If a loose
flywheel or damper is causad by overspeed, one ormore of the common signs of overspeed will algo beevident.
~f
Cu-mmins Engine Company, Inc., Columbus,-Indiana 47202-3005Cummins Engine Company Ud., Daventry, Northants, England NN11 5NURegistered Office: 46-50 Coombe Road. New Malden. SlJrrey KT3 4QLRegistered No. 573951 England .ti
Copyri\Jht @ 1994 i!'Cummms Engine Company. Inc. ;¡Al! rights reserved
Paga 1 of 6
8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994
It the angina experiences a bent or broken valva, check all the pistons tor signs ot valve-to-pistoncontactoCheck all the valva collets tor excessive wear.
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Check the bent or broken valva tor signs that a colletdislodged as a result ot overspeed.
Todetermine ita colletdislodged,examinethevalve stemarea below the collet groove tor wear. It one collet dis-lodges, the spring retainerwillunevenlyload the remain-
ing collet, causing it to wear a mark on the valva stembelow the collet groove.
~;heCk Ior radial cracks on t he undersides 01 Ihe valva
spring retainers. Cracked spring retainers result trom ex-cessive stresses induced by impact loading.
Push Tubes
Check tor bent or broken push tubes or rods.
NOTE:Pushtubes or rodscan break butremaininposition.Close tolerances betweenthe blockand head can hold abroken push tuba in place. Be sure to check all the pushtubes.
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L10,M11,and N14 Engine OverspeedPage 3
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8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994
Check for a 100gBdamper or flywheel. Excessive vibrationcausad by overspeed can loosen flywheel and dampercapscrews, resulting in fretting of the mounting surfaces,cracked capscrew horas, or broken capscrews.
NOTE: This failure occurs only in the most extreme andprolongad overspeed situations. If causad by overspeedother signs of overspeed damage will be evident.
Camshaft
Check the location of the gear relativa to the cam. Helicalcamshaft gears will tend to "walk" out on the cam nasa
as a result ot axial torees induced by the gears during
overspeed.Check tor signs ot excessive heat build-up at the tront camsupport and rear cam bushing.
Check for signs ot rallar skidding and damage on theinjector and valva lobes causad by excessive stress on
the cam.
NOTE: Lobe damage and rallar skidding failures by them-selvas are not likely to haya resultad from overspeed. Checkfor other signs of overspeed in addition to these symptoms.
Cam Followers
Check tor bent, cracked, or broken follower pins causadby valve-to-piston contact or no-tollow impact loadingCheck tor damaged rollers.
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8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994
Overspeed Symptoms - Fuel System Componentshis section outlines the fuel system component symptoms that indicate angina overspeed.
CELECTTMElectronic Control Module
Check for Fault Coda 234. CELECT'"anginas will lag
Fault Coda 234 when engiQespeed exceeds 2730 rpm.
FAUL T CODE
234
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PT Fuel Pump
The most common overspeed damage to the fuel pumps a stuck governor plunger and broken drive tangs.
Check for signs of a stuck governor plunger, worn gov-ernor torque spring, broken pump shaft, and worn gears.Excessive wear and internal heat results from extended
exposure to overspeed conditions.
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PT Injector
Check for injector plunger crimp failures.
NOTE: Plunger crimp failuras result from extended expo-sure to overspeed and overload conditions.
f a plunger crimp failure is causad by overspeed, othersigns of angina overspeed damage will be evident.
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8/20/2019 L10, M11, And N14 Engine Overspeed. Junio, 1994
Cummins Policy Regarding Overspeed Related Engine Failures.
Since overspeed failures are causad by exceeding an engine's intended operating speed, overspeed relataddamage is considerad to be the result of angina abuse. "
Cummlns Is not responslble for fallure or damage resultlng from what Cummlns determinaste be abuse orneglect, Includlngbut not limitadto angina overspeed. ' ""