L10, M11, And N14 Engine Overspeed. Junio, 1994

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e Service Bulletin

L10, M11, and N14 Engine Overspeed

1208Subject

BulletinNo.3666107

1

Date:

June, 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

. Fuel pump tampering (PT pumps ol)ly)

Diagnosing Engine OverspeedFailures:

Common signs of angina overspeed are as follows:

. Bent or broken push tubes

. Worn valva collets

. Cam gear walk-off

. Stuck fuel pump governor plunger (PT pumpsonly) ,. .

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.

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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

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L10, M11, and N14 Englne OverspeedPage 2

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Overspeed Symptoms - Base Engine ComponentsThis section outlines the base angina component symptoms that indicate angina overspeed.

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Pistons

Examine the tops ot the pistons tor marks left by valva-to-piston contact.

NOTE:On N14anginas, the exhaustvalvestypicallycontactthe pistons beforethe intakevalvas.On L10/M11anginas,the intakevalvestypicallycontactthe pistens first.

Cylinder Head

Checktorwornor brokenvalvacollets.Worncolletswillappear sunken intothe springretainers.

NOTE: L10, M11, and N14 anginas tend te exhibit more wearon intake valva collets than exhaust valva collets tromoverspeed.

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Check tordislocated or missingvalvacollets.Single beadcollets can dislodge as a result otexcessive wear causadbyoverspeed.

Check colletstor excessivewearor deformationot thecollet bead(s).

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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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L10, M11, and N14 Englne OverspeedPage 4

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Vibration Damper and Flywheel

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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L10,M11,and N14Englne OverspeedPage 5

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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L10, M11,and N14Englne OverspeedPage 6

CELECTTMInjector (Top-Stop Injectors Only)

Check for a broken injector bottom-stop.

NOTE:Ifa bottom-stopfailureiscausad byoverspeed,other

componentdamage resultingfromoverspeedwillbe evident.

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. ' ""

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Documents

L10, M11, And N14 Engine Overspeed. Junio, 1994