Franklin 6A4-150-B3 User manual

SERVICE MANUAL
FRANKLIN AIRCRAFT
ENGINE
M ODELS 6A4-150-85, 851, & 6A4-165-B5
4IRCOOLID MOTOIS, II~.
SYRACUSB. HEW YORI: V.I. A.
C A.La ADDRES. AIRCOOLED

FRANKLIN AIRCRAFT ENGINES
Model 6A4 - 150-B5,· B51, & 6A4-165 - B5
"NOT LIABLE FOR ACCURACY
AND EFFECTIVENESS OF
ORIGINAL TEXT."
Air Service Caravan Co., Inc.
INSPECTION, MAINTENANCE
AND
OVERHAUL INSTRUC T IONS
C LLEGt FI '0 J ST. I L TECH OLOG
AIRCOO LE D MOTOR S, I NC.
SYRACUSE 8, NEW YO RK

TA BL E OF CONTENTS
Se cti on
Page
S ection
P age
In tro d uction ______ ___ _____ _ _____ _ ___ ____ ____ _ _____ __ 5
XVII Valves and Va lve Sprin gs ....... ___ ..... _____ 25
Valves __ ..._ ....... __. .... _...... _______ ._._ ..._.. 25
II Wa rran ty ____ ______ __ ____ _____ __. ________ ____ ._____ __ 5
Valve Sprin g s_ ...._. ____ ._. __ .._ ___ ... _____ ..._ 25
XVIII Valve Actuati ng M ec hanism. ____ . __ ..__ __ 26
III Omit 7
Hydraulic Li ft er s ____ . __ .. __ ....._..__.....____ 26
Hydraulic Li ft er (Servicin g) ........... _ 27
IV Repl ace me nt Parts and Shipping
Lifter Rods and T ube s_...... _. __ __ .. _______ 28
In stru c tion s ____ _ __ _______ __ ___ _ __ ____ ____ _ __ __ _ 8
Rocker Pins a nd Rockers ______ ..._... _. __ . 28
V Eng i
ne Spe c ifications __ __ ____ __ __ __ ____ ___ _____ 9
XIX Lubricating System _ __ .._... __ ._ ...._.._.._. ..... 29
Lubricating Syste m- I nspection
and Se rvicing ._ . ___ . ___ ...... _._ .._.. ___ . __ 29
VI Table of Limits and Tolerances _ __ _ ____ __ 10
Oil Pan _._.. ___ ____ .. ___ . ______ ... _. __ ._ ...... ____ . 30
Oil Pump __ _._ __ ... __ .. ___ ....._ _______ _ _____ .. _. __ 30
VII Re comme nded T ightening Torque
Oil
Inlet Flo at (Floto) _.. ___ ._. __ . __ ._ . ___ 30
Valu es __ __ _ ____ ____ ___________ __ ____ __ ___ _________ 12
Oil By - Pass Plate ____ __ ____ _ ___ __. ______ .. _. ___ 3 1
VIII ~Overhaul Perio ds and
XX Inlet Manifold __ ____ ...__.__ __ .. __ ___ ___ .._.... ___ 32
I Perio dic Ins pec tions Check List ____ __ 12 - 13
XXI Accessory Gear Train ___ __ . __________ ._. ____ .._ 33
IX En gin e L ubricat i on-GeneraL __________ __ 14
Magneto Drive Geor an d Hub._. _____ ._ 33
Magneto Driven Gear ___ . __ .. _._ ..._... ____ 33
Generator Driven Ge ar ___ .__. __ .._.. _. ____ 33
X Crankc a se ______ _ _____ ___ ._ ____ _ __ __ _____ ____ ______ _ 14
Tachometer Drive.__.. __ ... __ . ___ .. ___ _ ._. ___ 33
Starter Gear Assemb ly..._ .. . ____ .. ___ .. ___ . 34
X I Cr a nk sh aft _ ____ ______ ____ _ _______________ _ _____ _ __ 15
C ran ks haft B ear ings_ __ __ ______ ____ _ ____ ____ 16
XXII Ignition __ ___ ___ __ . __ _______ ..._____.__ ___ ... _._ .. __ ._ 35
Cr a nks ha ft Oil Seal. - __ ___ ___ __ __ __ ________ 16
Magnetos-Pri nci ples of Op eration 35
1m ulse Star t er on th e LA-6 and
XII Ca msha ft ___ ____ __ ________ _ ___ _ ._._ .____ _ _____ _ ______ 17
S6RN-21 Ma gneto s _ _______ _ ._. _._. ____ 36
Magneto Install at i on .__ ._ .. ___ __ ._________ 39
Eisemann Magne t os -M inor
X I
II Timi ng Gear Ca se_ _______ .. ____ _ ___ _ ______ _______ 17
Inspection . __ .... __ ._ .. _. ___ __ . ________ ... _. 37
Magn eto T i ming C heck __ __ . ___ .._. .. __.. ___ 38
XIV Con ne ct ing Ro ds _________________ __ ____ _.. ______ __ 18
Bend ix-Scint i110 M ag neto __ _____ .._ ___ ._. 38
Spa rk Plugs __ .. __ _ ___ . ____ ._ .._... __ .___ ._. ______ 38
XV Pi st on , Pis ton Pi ns a nd R ings ___ ___ _. _____ _ 19
Pis ton _ ____ __ .____ __ ______ ___ ____ _ ___ _________ ___ ___ 19
XXIII Carbureti on ..__ __ _.. _______ __ ____ ._ ____ .__ ___ __ ____ 40
Pis ton Pin _ __ ______________________ ____ __ _________ 19
Pist on Ri ngs __ __ __ ___ . __ ______ __. _____ ___ _____ __ 20
XXIV Generator and Volta ge Regulato r ._ .. ____ 42
Gen era t or .... __ ___ ._ .__ _____ . ___ ... _____ ._ ___ _ __ _ 42
Volt
age Reg ula tor __ ___ .. _. __ _ _______________ . 42
XVI Cy linder Assemb ly _ __ ______ _____ _ ___ ..__ __ ___ _ __ 2 1
Cylin d ers __. __ . ______ _ ___ _ ___ __ ._. __ _. __ ... __ .... 21
XX V Startin g Mo tor _._ .._.. _. ___ _ ._. _ ______ ... ____ ..... 43
Va lve Guides ________ __. ______ __ . __ ..... _ __ ._ ___ . 21
Valve Seat In ser ts _ ___ ____ _____ _ __ _ _______ .. _. 22
Studs and Fast en in gs ..__ __ __.___ ____ .. _. __ 22
XXVI Engine A ss em bly. ____ . __ _. __ _ __ . ___ . ____ ...... __ 44
Fins __ ...._.. ___ _.___ __ ..._ ._ ... __ _ __ _..._ ._. _ __ ..._ 23
He licoi Is ._ ..__ ._ .... __ ...._ __ _._......_. ___ __ _.. __ 23
XXVII Engine R un -In S che du le and Test i ng __ 48

T
-I TRODUCTION 7 0
Years of Franklin engineering experience plus the highest quality in materials and wo rkm ans hip, t o-
gether with the most modern manufacturing methods are back of eve ry Fr an klin engine shipped from
our factory.
It is the purpose of this manual to furnish ready reference and practical in formation on the operation,
inspection, preventive
maintenance and complete overhaul of the model 6 A4 -1 50 -83 and 831 and
6A4-165-B3 Franklin engines and their accessories. The name and data plate, which is located either
on the starter Bendix housing or on the lower right hand side of the c rankca se just ab ove the oil pan,
indicates the engine model.
An
eff o rt has been mode to arrange the material in the manual so that the description, function, in-
spection and repair of the component parts of the engine and its accessories are com pl etely covered
in their individual sections.
In referring to locations on
the engine, it is assumed that the observer's position is at the ac cessory
end of the engine, facing forward in line with the crankshaft. Hence, t he p ro peller end will be r eferred
to as the front of the engine irrespective of the p03ition the engine occu pi es in th e air craft. Cylinders
number 1, 3, and 5 are on the left side of the engine and cyl inders numb er 2, 4, and 6 are on the right
with numbers 1 and 2 at the rear.
It
is recommended in the interest of safety, operating economy and max i mum service life of the engine
that the operating limits, inspections, tolerances, maintenance and overhaul instruct ions and methods
be strictly
adhered to. It is also recommended that existing instructions of the various air craft, pro-
peller
and accessory manufacturers regarding the servicing of their products be rigidly followed.
Additional or revised information will be issued as it becomes available. Pl e as e keep us adv is ed of
your current mailing address to insure prompt receipt of this mat erial.
To insure
that your best interests be served and satisfaction be gu ara n teed, we re com mend th at
replacements be made with genuine Franklin parts only. A list of authorized Franklin d istribut ors,
together with shipping instructions, appears on page 7.
Please
address all technical service inquiries or comments to Service Division, Aircooled Moto rs , Inc.,
Syracuse
8, New York. They wi II receive prompt and courteous atten tion.
11- WARRANTY
Aircooled Motors, Inc., warrants each new Franklin engine or new part manuf ac tured by it again st
defects in material or workmanship under normal use, but its obligation under this warra nt y is spe ci f i-
cally Iimited to replacing or repairing at its factory any such engine or pa rt wh ich shall, within 90
days after delivery ther e of to the original purchaser and prior to 50 hours of operati on, be returned
to Aircooled Motors, Inc., with its permission, transportation charges prepaid, and wh ich upon exami-
nation by Aircooled Motors, Inc., is determined by Aircooled Motors, Inc. to be defective.
This
warranty shall not apply to any such engine or parts which have bee n repaired or alt ered outside
Aircooled Motors, Inc. factory in any way so as to affect, in i ts judgment , its op er ation, or which h ave
been subjected to misuse, neglect, improper maintenance or accident, or which sha ll ha ve b ee n oper-
ated at a speed exceeding the factory rated speed.
Aircooled Motors, Inc. makes no warranty with respect to ignition apparat us, ca rb uretor s, in st rument s,
tr
ade accessories, or other equipment which it does not itself build or m anuf a ct ure in as mu ch as such
eq
uipment is usually guaranteed by the respective manu fa cturers thereo f.
The foregOing is the exclusive warranty made by Aircooled Motors, Inco Th er e are no other w arranties
expressed or implied, in fact or in law, made by Aircooled Motors, Inc.
AIRCOO
LED MOTORS, INC.
Syracuse 8, New York
5

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en
Ai

II - PARTS A D SERVIC E
IMPOR T A~T
Save time and shipping expen se by ordering all parts from the
Distributor in your territory. Send your order directly to him. Be sure
to specify model and serial number of engine for which parts are ordered.
AUTHORIZE D FRANK LIN DISTRIBUTORS
ALABAMA
Southern Airways
527 Come r Bldg., Birmingham 3, Ala.
ALASKA
Pacific Airmotive Corp o ration
Sherrill Field, Anchorage, Ala s ka
ARKANSAS
Arkansas Aviation Service
Grider Field, Pine Bluff, Arkans as
Central Flyi ng Service
Municipal Airp ort, Little Rock, Ark.
CALIFORNIA
Faulkner Aviation Industries
Long Beach Municipal Airport
L ong Beach 8, Californ ia
Hagel in Aircraft Motors Co.
933 Airway, Glend a le, California
Rankin Aviation In dustries
Tulare , Califo rnia
CANADA
Le avens Bros. Air Services, Ltd .
Barker Airport , To ront o, Canada
Macleod Airc raft Limited
55
15 Cypr ess St., Vancouver, B. C.
Northwest Industri es, Ltd.
Mup i cipa l Airport,
P. O. Box 517 , Edmon to n, Alb erta
COLORADO
Moun tain States Aviation , Inc.
38 00 Dah lia Street, Denver 16, Colo.
CONNECTICU T
Simsbury Flying Service, Inc.
Simsbury Airport, Si msbury, Conn.
DELAWARE
Aircrafters. Inc.
Airport , Rehobo th Beach, Delaware
FLORIDA
Wall ac e Ai r craft Company
Sarasota, Florida
Palm Bea ch Aero Corp.
L
antana, Fl orida
GEO RG IA
Aviation Supply Corporation
Atlanta Municipal Airport
Atla nta , Georgio
IL L INO IS
Sny de r Ai rcraft Cor porat ion
53 15 We
st 63rd St ., Ch icago 38, II I.
INDIA A
Air Sales & Se rvice, Inc.
Wier Cook MuniCipal Airport
In dianapo lis, In diana
Munci e A viati on Corporation
MUncie Airport , Munc ie, Indiana
Roscoe Turn er Aero. Corporation
Muni ci pal Airp ort, India napolis, Ind.
Sky
Service Corp orati on
Mun icip al Airport, Evansville, Ind.
IOWA
Hunter Flying Service
P. O. Box 183, Ce
da r R apids. Iowa
KANSAS
Harte Flying Service
Munic i pal Airp o rt , Wichi ta, K ansas
KENTUCK Y
Kentu cky Air Transpor t, Inc.
Bo
wman Field, Louisville 5, Kentucky
Louis vi ll e Fl ying Se rv ice
Bowman Field, Louisville 5,
Kentucky
MAINE
Airways, I nc .
Munici pa l Airp ort, W aterville, Moine
Sky Harbor Flying Service
A
ubu rn-Lewist on Airp o rt
Auburn, Ma ine
MARYLAND
Capitol Airc raft Sa les
Hy
de Field, Clinton, Mar yland
MASSACHUSETTS
Eastern Aviat i on , Inc.
Wenham, Massachusetts
JenninQs Bro . Air S ervice
Gra ft on Airport, North Graft on, Mass.
7
MICHIG AN
Aircraft Sales Corporation
1040 Buhl Bldg., Detroit 26, Mich.
Baker-Eberle Aviation Corp.
Detroit City Airport, Detroit 5, Mich.
Barr Aviation Corp .
Detroit City Airport, Detroit, Mich.
Michiqan Central Airlines, Inc.
Bishop Flying Service Division
Flint,
Michigan
Northern Air Service
Grand Rapids Airport
Grand Rapids 8, Michigan
MIN NESO TA
American Aviation Corporation
Flying Cloud Field, Hopkins, Minn.
Hinck Flying Service, Inc.
Metropolitan Airport
Minneapolis, Minnesota
Van Dusen Aircraft Supplies
200 4 Lyndale Avenue, South
Minneapolis 5, Minnesota
MI SSO URI
Brayton Flying Service, Inc.
Lambert-St. Louis Airport
St. Louis 21, Missouri
Hampton Aircraft, Inc.
5852 Hampton Avenue
St. Louis 9, Missouri
Ong Aircraft Corporation
P. O. Box 214, Kansas City, Mo.
Springfield Flying Service, Inc.
Municipal Airport, Springfield, Mo.
Supply Division, Inc.
Lambert Airport, Robertson, Mo.
N EBRA SKA
Omaha Aircraft Company
Municipal Airport, Omaha, Neb.
N EW HAMPSHIRE
Wm. E. Martin Flying Service
P. O. Box
276/ Concord, N. H.
NEW JER SEY
Safair Flyi~g School
Bendix
Airport, Teterboro, N. J.

NEW Y ORK
Buffalo A eronautical Corp.
Hangar One, Buffa lo Airport
Buffalo, New York
Haven Flying Service
Sche
nectady County Airpo rt
Schenectady , New York
Ithaca Fl ying Service, Inc.
Mun icipal Air port, Ithaca, N. Y.
Leech Aircr aft, Inc.
42 0 Lexington A venue
Ne w York 1 7, Ne w York
O'Conn
or Air cra ft C om p any
Albany Air port, Albany, Ne w Y ork
NORT H CAROL I NA
Piedm ont Aviati on , Inc.
Sm
ith -Reynolds Air port
W inston-Sale m I, Nor th Ca rolina
OHIO
Harrington Air Serv ic e, Inc.
M up ici pa l Airport, Mansfield, Ohio
M
etc alf Fl yi ng Se rv ice, Inc.
Toledo Municipal Airport, Toledo, O.
Northw
ay Flying Service
Norton F ie ld, Columbus, Ohio
Tri-St
at e Avi atio n C or p.
Cincin
nati Airport, Sharonville, O.
Tuscarawas Co
unty Aviat io n, Inc.
Mu nicipal Airport
New Phila
delph ia, Ohio
OKLAHOMA
Fr ank Clarks
12 25 North Robinson
Oklahoma
Cit y 3, Oklaho ma
OR EGON
Westem Sk yways Service
18 04 N. E. Union Av en ue
Portl and 12, Oregon
A.
W. Wh it ak er
5001 - 50 15 N. E. Uni on A venue
Port land, Oreg on
PENNSYLVANIA
Boulevard Airp ort , Inc.
G etty sburg, P ennsy lvania
G. D. Kelsey
Philadelph ia Mun i ci p al Air port
Philadelphia 42, Pennsylvania
Krantz
Aeronau tical C orp .
Part Erie Airport, Erie, P enn .
Philadelp
hia Aviation Corp.
1607 Fin an ce Building
Philadelph ia 2, Penn sylvania
Scholter Aviation Compa ny
Pitt sburgh - But le r Airport, Butler, Po.
SOUTH CAROLINA
Carolina Aviat ion, Inc.
Municipal
Airport , Gre en ville, S. C.
Dixie Aviation Co mp any
Municipa l Airport, Col umbia, S. C.
Hawth orne Aero Supply
Hawthorne Field, Orange burg, S. C.
SOUTH DAKOTA
Dakota Aviation Co.
W . W . Howes Municip
al Airp ort
Huron, South Dako ta
TENNESSEE
Capitol Airways, Inc.
Howse Field, Nashville,
Te nnessee
Southern Air Services
Municipal Airport, Memphis, Tenn.
TEXAS
A ircraft Sales Company
Meacham Field, Fort Worth, Texas
Ca nyon Aviation Service
Canyon, Texas
Southwest Aircra ft , Inc.
Mea
cham Field, Fo rt Wo rt h, Te xas
Wea th erly-Campbell Aircraft
Highland Park Airport, Dallas, Te x.
VIR GI NIA
Coastalair Corporation
Virginia Beach Airport
Virginia Beach, Virginia
Virginia Airmotive
Woodr um Field, Roanoke, Va.
Virginia Cub Distributors
Shadwell, Virginia
WA SH IN GT ON
Northwest Aircraft Distributing Co.
Box
649, Vancouver, Washington
Northwest Air Service, Inc.
Boeing Field,
Seattle 8, W ash.
WEST VIRGI N IA
Glenn T. Clark
Clark Field, Winfield, West Virginia
WIS CON S IN
Fliteways, Inc.
P.
O. Box 1808, M il W aukee 1, Wis.
Racine Flying Se"rvice
Horlick Racine Airport, Racine, W
is.
IV - EPLACEMENT PARTS AND SHIPPING INSTRUCTIONS
When con tactin g your au thorized Franklin distributo r or the fa cto ry concerning par ts or service,
ple
ase give bot h the engine model and the engine serial numb e rs as st amped on the data plate on the
engine. This infor mation will insure prompt, accurate service and pre vent undue delay. Due to periodic
c
hange s in engin es, the engine number is most important.
Wh en returning par ts to your Franklin distributor or the factory, at t ach a tag to each part with yo ur
n
ame, ad dr ess and the model and serial number of the en gi ne from wh ic h the part was removed,
togeth er with the da te of your original letter of refer ence to th e p art in que stion. This will assure the
prom pt handling of your service requests. When shipping parts to the factory, be sure they are shipped
pre
pa id and that they are carefully packed to prevent damage.
Inform at ion regarding p ar ts avail able in oversizes or undersizes may be found in the Parts Book on
the 6A 4- 1S0-B3 and 831 and 6A4-165-B3 engines.
Shou
ld any problem arise which presents the need for spe ci a l handling, or which requi re s special
inform
atio n, we suggest that you contact the neatest Fra nk lin Authorized Distributor or th e factor y
and every
eff ort will be made to assist you.
SPECIFY MODEL AND
SERIAL NUM BE R O F ENG I N E
8

fiG. 2. Three Quarter Right Rear View
v-ENGINE SPECIFICATIONS
Model
Number of Cylinders
Bore
Stroke
Piston Displacement
Compression Ratio
Rated Speed in RPM
Rated
Brake Horsepower
Idle Speed in RPM
Crankshaft Rotation
Propeller
Shaft Rotation
Propeller to Crankshaft Ratio
Maximum Cylinder Temperature
Maximum Oil Temperature
Oil Pressure
Oil Pressure
at Idle
Oil
Capacity
Oil Specifications
Heavy Duty
Heavy Duty
Maximum Operating Time between
Oil
Changes
Valve Clearance with lifters Bled
Down
and Engine Cold
Firing
Order
Spark Timing
Spark Plugs
Spark Plug Gap
Fuel Minimum Octane
Fuel Pump Pressure (Bellanca Only)
Starter
Generator
Magneto Breaker Point Gap
Maximum Drop Single Magneto
6A4-150-B3 6- B3 1
6
4.5"
3.5"
335 cu . in.
7:1
2600
150 HP at 2600 RPM
500 to 600
Clockwise
Clockwise
1:1
520°F Max i mum Spark Plug
230°F "
30 to 50 PSI Maximum
10 to 20 PSI Minimum
8 Quarts
Free Air
Temperature
Viscosity
Above
40°F
SAE 40
Below 40°F
SAE 20
25 Hours. More often if condi-
tions warrant.
.040"
Cylinders 1 -4-5-2-3 -6
28 Degrees BTC
Champion J- 10
.014" to .018"
80 Nonleaded Aviat io n
7 1 12 PSI Maximum
12 Volt
15 Amp. to 25 Amp.
.
019" to .021"
200 RPM
9
6A4-165-B3
6
4.5"
3.5"
335 cu. in.
7:1
2800
165 HP at 28 00 RPM
500 to 6
00
Clockwise
Clockwise
1:1
52 0°F Maximum Spark Plug
2
30
0
30 to 50 PSI Maxi" mum
10 to 20 PSI Minimum
8.8 Qua rts
Fr
ee Air
Tempe ra ture Viscosity
Above
40°F
SAE 40
Below 40 °F
SAE 20
25 Hours. More often if condi-
tions warrant.
.04 0"
Cy li n der s 1 -4 -5- 2- 3 -6
32 D egre es BTC
Cha mpion J- l 0
.0
14" to .018 "
80
Non l ea de d Av iation
7 1 12 P SI Maximum
12 V olt
25 Amp.
ot Specified
2
00 RPM

VI -TABLE OF LIMITS AND TOLERANCES
Descripti on of Limits
Cra
nkc ase & T hr ust Wash er Dowel
Thrust Was her & Cr ank case Dowel
Crankcase Half & Dowel
Cra nk sh a ft Bu s hing & Crankshaft
Cranksh af t En d Clearan ce
Co nnecting Rod Bushing & Crankshaft
Connecting Rod & Bol t (Diam.)
Co
nnecting Rod Side Clea ran ce
Crank cas e & Mounting Bra ket Dowel
Mounting Bracket & Cr ankcase Dowel
Camshaf t Bushing & Camshaft
Camshaf t En d Cl eara nce
Crankshaft Gear & Crankshaft
Cam sha ft Gear & Ca msha ft
Cr ankshaft & Camshaft Gea rs (Backlash)
Cr ank s haft & Magneto Drive Gear Hub
Cra nk sh aft R un Out
Ma in & Crank Journ al Fillet Radii
Cr a nksh aft & Dowel (Flange)
P is ton & Piston Pin (Hand Push Fit with Piston
at Ro om Temperature )
C
onn e cting Rod & Piston Pin
Piston Pin &
Plug
C ylinder Li ner Exte nsion Below Cylinder Flange
Cylinder Barrel & Piston Pin (End Clear .)
Cylinder Barrel & Pi
ston (Skirt)
Cylinde r Barrel & Piston ( Top land & lands
between grooves)
Piston Ring
Gap (All Rings)
Piston & ,Top Piston Ring (Side
Clearance)
Piston & 2nd Piston Ring (Side Clearance)
Pi sto n & 3rd Piston Ring (Side Clearance)
Bushing & Valve R ock er Pin
Mfg.
Min.
. 0008T
.00lT
. OOOST
.002l
. 008
.001Sl
.000Sl
.008
,OOOST
.OOOST
.001Sl
.006
.00lT
.OOOST
.004
.002T
.125
.0015T
.0000
.0007L
.000Sl
. 500
.015
.002l
.028L
.013
.00SSl
.0035l
,002l
.002l
10
Mfg .
Max.
.0017T
.OOST
.001l
. 004l
. 020
.0034l
. 002l
.014
.001l
. 00ll
.002Sl
.010
.002T
.002T
.012
.0038T
.002
.140
.003T
.
0012 l
.002Sl
.51S
.033
.0035l
. 030l
.023
.007L
.005l
. 003Sl
.0035L
Max.
After We a r
.004l
.010l
.001l
.0 06l
.026
.00 55L
.002l
.018l
.002l
.002l
.004l
.014l
.00lT
.OOO ST
.016
.002T
.004
.00lT
.OO OSl
.0 02l
.004l
.O SO
.007L
.036l
.040
.009l
. 00 7l
,005Sl
.007L

Va lve Rock er Suppor t (Stamped) & Val ve Ro cke r Pin
Valve Rocker Support (AI. Bl oc k) & Valve Rocker Pin
Valve R ocker E nd Clearance
V alve Guide & Cylinder Head (Early Engin es)
V alve Guide & Cylind er Head (la te Engines)
Valve Guide & Intake Valve
V alve Guide & Exh au st V alv e
C
ylinder Head & In take Valve Seat In sert
Cyl inder Head & Ex haust Valve Seat Inse rt
Val ve Lifter & C ran kcase
Oi I Pum p Gea r & Sha ft
Oi I Pump Drive Sh aft & Pump Body
Oil
Pump Dr iv e Gears & Shaft
Oil P ump St a t ionary Sha ft & P ump B ody
Oil Pu mp Driv en Gea r & Shaft
Oil Pu mp Gea rs & Pu mp Bo dy
Oil Pu
mp G ears ( Backlas h)
Oil
Pump Drive & Driven ( Back lash)
Mag. Drive G ear Hu b & Gea r
M
ag . D ri ve G ea r H ub & Tach. Dri ve Ge ar
M ag. Dr iv e & Driv en Ge ars (Backlash)
M ag . & Mag. Adapt er
Mag. Driven Gear & Mag net o, Driven Gear Hub
S tarte r Gear Hub & Crankshaft
Tach. Drive & Driven Gear s (Backl ash)
Ta ch. Drive Co nn ector & Ta ch. Driven Gear
Tach. Connector Sleeve & Tach . Drive Conn ec tor
Tac h. Conn ector Sleeve & Ta ch. Drive H ousing
Gen erat or G ear & Hu b
G
enerat or Drive & Driven Ge ars (Backlash )
C
ra nk case & Dowel (Timing Case)
Timing Gear Case & Crankcase Dowel
T
iming Gea r Ca se & Mag. A dapt er
Tim ing G ea r Case & Sta rt er
Timing Gear C ase & Ge nerator
.001T
.001T
.003
.003T
.002T
.0
02Sl
.00 2Sl
.004T
.
00 41T
.001 l
.
OOOST
.00l l
.
0000
.OOO ST
.
000Sl
.002 l
.
004
. 00 4
.002T
.OOOST
.006
.000Sl
.00 0Sl
.004T
.001
.001 2T
.
OOO ST
.001Sl
.000 6l
.006
.0
00l T
.000lT
.00 0Sl
.00 0Sl
.0 00Sl
.00lS l
.
000Sl
.008
.004T
.003T
.
004 3L
. 00 43l
.00 6T
.0061T
.00
2l
. 00 2T
.
00 2Sl
.0 0l ST
.001ST
.00 2l
.007l
.008
.008
.003ST
.
002 T
.010
.0045L
.
00 25l
.0052T
.003
.00 2T
.0
0l3T
. 00 3Sl
.00 26l
. 010
.0013T
.0013T
.
004 Sl
.00 4Sl
. 00 4SL
.0
02 SL
.001Sl
.00 8l
.0 02T
. 002 T
.
006 l
.
006l
.0 03T
.003T
.004l
.
OOO ST
.004L
.
000
. 000
.0 04l
.010 l
.01 5
.01 2
.0
02
. 00 05T
.016
.0
04l
.003T
.
01 0l
.001T
.O OO ST
.008l
.0 04l
. 016
.001 l
.001 L
.008l
.008l
.0 08 l
11

VII- RECOMMENDED TIGHTENING TORQUE VALUES
NAME
Stud
Stud
Stud
Stud
Screw
Screw
Screw
Nut
Nut
Nut
Standard
SIZE OF
THREADS
Studs, Screws
6'
1/4-20
5/ 16-18
3/8-16
7/16-14
1/4 - 20
5/16-18
3/8-16
1/4-28
5/16-24
3/8 - 24
Nuts
TORQUE VALUE FOR
TIGHTENING <INCH-LIS.)
MINIMUM-MAXIMUM
25 - 60
50 - 90
75-110
95-195
60-75
105- 120
120-145
60 - 75
1 10-130
300 - 360
Special Applications
Oil Pump Attaching Screw
1/4-20
55-60
Crankcase Cover Screw
5/16-18
Oil Pan Holding Sc rew
5/16-18
60-75
Cylinder Hold-Down
Nut
3/8-24
240 - 300
Cylinder Hold-Down Nut
7/ 16-20
300-330
Crankcase Tie Bold Nut
5/ 16-24
Camshaft Bearing Stud Nut
5/16-24
145 - 180
Mounting Bracket Stud Nut
5/16-24
Distributing Zone to Manifold Bolt
5/16-24
Starter Mounting Nut
3/ 8-24
145 - 180
Spark Plugs
14MM
180-240
Magneto Nut
7/16-20
240-300
VIII-OVERHAUL PERIODS AND PERIODIC INSPE TIONS
TOP OVERHAUL MAJOR OVERHAUL
The time at which a top overhaul will be neces- No
definite period is set for a major overhaul.
sary
will vary considerably with the type of opera-
Most engines will require an overhaul after 600 to
tion
and the care taken of the engine generally.
700 hours of operation. The periodic inspections
Proper i'1spections performed
at the specified
and general operating characteristics will indica te
periods (See inspection check list)
will reveal the
the necessity of a major overhaul if one is needed
necessity
of a top overhaul. If a top overhaul is not
sooner.
required
at 300 hours, the rubber magneto and
generator drive shock absorber cushions should be
inspected
at this time. Any worn cushions should
be replaced.
12

---- ------ ----------- ---- ------ ----- -- --- -- - ------ ---- ---- ---
---- ---- --- - ---- ------ -- ---- -------------------- --- ----
-- ---- -- --- -------------------------------- --
PERIOD C NSPECTIONS CHECK LIST
COVERING MODEL 6A4-150-B31, 6A4-150-13 and 6A4-165-83 ENGINES
Propeller Blades (Visual) x
Ignition Wires & Terminals (Visual)
x
AccessibJe Nuts , Cop Screws & Fasteners fV;suaJ) x
Fuel and Oil Level x x x x
-------------- - -- - ---- -- -
Engine Controls (Free Movement & Full Range) x x x x
--~------------------- ------------------------ --
Oil Leaks
x x x x
Fuel
Leaks
x x x x
Propeller Bolts (Check for Tightness & Safetying) x x x
I~nition Wires & Terminals (Check for Tightne ~- C~h a f in g & S ~~ ~ e re d ss , ~ ~~~- ~~ o ~-- ~---- ------------ ----- -- ~
Connections-Clean)
x x x
Accessible Nuts, Cap Screws & Fasteners (Check for Tightness & Safetying)
x x x
Engine Controls (Check Free MovemEmt, Full Range & Linkage System,
Lubricate) x x x
Oil Change (More Often if Operating Conditions Warrant) x x x
------ --~------------ ---- - ------------------ ~-- ---
Propeller Track
x x
Exhaust System (Check for Leaks & Tightness)
x x x
Ora in Plugs & Fi Ifer Cops (--=C:-=-h - ck fo n --- -- i - & sk --- ------------- ---------- - e ----, ~ - r---=T:-=ig=-:-h-t - es s , ---;:;S~a-;;-fe t y -,- n g ------;;; - --=G~a ----, ;-- e t
Condition)
x x x
Cooling Air Baffles (Check for Obstructions & Leaks)
x x x
Filters, Strainers & Sumps (Inspect & Clean)
x x x
Compression Check (Check all cylinders by pulling through Propeller) x x x
--~ ~~ - ~7- -- _7~--~~~ -- -------------- -- -- -- --
Manifold Equalizer Pipe Hose Connection (Check condition of Hose
and Tightness of Clamps)
x x x
Magneto Breaker P~o-in t s ----: & ::-:- - -- ib u t - r -----;- (-=C :-;:- - ck co- nd---;-:-it --=- ion of rotor & -~ :;;--;:: D i st r -----::- -- o - he- =------- -
Distributor & Point Condition & Gap)
x
x
Magneto Timing & Synchroniza _t_io_n _________ ~~~~ __ ~~~~ __ ~~ __ _________ ________ _
Spark Plugs (Clean & Regap)
x
~ -------- -~ ------~ ---- --------~----~~ --
Cylinder Fins (Check for Breaks--Clean)
x
-- - --- ,
Carburetor (Clean & Drain)
x
Fuel Lines (Check for Chafing-Blow Out ) x
------ --~ -------- ---~------ -
Engine Mounts (Chec for Tightness & Wear)
x
Generator (Check Connections, Charging Rate)
x
~--- ~ ~~ -- ----- ---~---- ~ --
Sta r ter (Check Connections & Operation of Bendix Drive) x
Valve Clearance (Check & Adjust) Every 200 Hours Minimum
Magneto & Generator Shock Absorber Drives (Replace worn absorbers)
Every 300 Hours Minimum
------ - - ------ -----~~-- --- ---- ~--
13
x

IX - ENG INE LUBRICA ION
T he pr imary purpose of engine lu br ica tion is to
prevent m et a l- to - me ta l contact be tween moving
par ts. T he friction acc o mpany ing such me ta l-t :>-
metal c on t act w ould result in a loss of power, ra pi d
wear, a nd a
temp era t ure rise th at mi ght cause pa rt s
to fa il. Th e a ction of th e oi l is to co at each m et a l
surface wi th a f il m. Between t he two fi lms, other
l
ayers of the oil sli de a long ov er each oth er , t hus
rep lacing th e high frict ion of metal-to-m eta l c on-
tact by the low inter na l fricti on of the oil.
In th e process of cir cu latin g th rough the e ng ine,
oil absorbs heat from
the va rious part s. Mo st of
this he at is dissipated when the oil flows through
the oi I coole r.
It is ver y im port ant that an o il of the proper vis-
cosity be used, si nce using too heavy an oil will
impair ci rculati on and insu fficient lubrication w ill
result.
Operating condition s will c on trol th e pe ri od be-
tween oil c ha ng es; however, t he m axim um time
s hould not ex ce ed 25 hou rs.
Th e S.A .E. lette rs on a n oil co ntai ne r do no t
det erm ine th e q ua li ty of th e lub ri c ant. The refiner's
rep utatio n is y our best guide to th e qua lity of the
product.
Pr
op er l ub ri cat i on of y our engine sh ould be given
your mo st ca reful a ttention si nce i mproper lubrica-
t io n is evid ence d only a ft er t he da m age to the
engine has occ ur red and is of ten ve ry cost ly . Using
the
proper grad e of a good lu brican t is c heaper than
repair bi ll s. We str ong ly recommend that our
s pe cifi cation and se rvice instruct io ns be st rictly
followed.
ENGINE
OI L SPECIFICA TIONS FOR MODEL
6
A4 - 150 -B3 AND 831 AN D 6A4-165-B3
ENG IN ES
S AE 40 w hen free air temper at ure is 4 0° F or
above.
SAE 20 when free a ir tem
perature is below 4 0° F.
x -CRANKCASE
The cr a nkcas e is built in two h alv es of high-
s trength a luminum alloy. (See Fig. 3. ) E ac h crank-
ca se half c on t ains three cylinder mounting p ads
and two e ngin e mo un t br ack et pads. The le ft c ase
half also includes pa ds for the o il pump a nd oil
b
y-pass pl at e. The cran kca se when assembl ed
as a unit has a top machined face to take a
cov
er and a bottom ma chined fac e on which the
o il pan is mounted . On the mo del 6A 4- 150-B3
a nd B31 eng ines, an oil se al is o bt ain ed bet w een th e
halves at the nose section by two .1 35 "-.14 5" di-
ameter synthetic rubber pa cking str ips. Th es e p ack -
ing
strips fit into grooves mac hin ed in to the ma ting
face of the right crankcase half . The se strips are
longer than the grooves so that th ey mu st be
t rimmed to length afte r the crank case is ass em bled
with the cra nksh aft a nd c am s ha ft. Ex trem e care
should be taken to trim t he en ds of t he p ack i ng
strips absolutely flush w ith the f ac e of the crank -
ca se. This is par t ic ula rly impo rt ant in t he nose oil
seal recess, as
an oil leak wil l oc cur if t he packing
protrudes a t th is loc ation . The m od el 6A 4- 165-83
en gi ne does not ha ve the r ub b er pa c ki ng strips be-
tw ee n the c ase ha lves, and the p ac king strip grooves
are omi t
te d. An oi l sea l is ob t ained on th is model
by
si lk th re ad s plac ed on the rig ht cra n kca se half
in
the sa me positi on as t he grooves w er e loca te d
in t
he ot he r mo de ls. Fig. 46 shows t he lo c ati on of
t he se gr ooves. Th e t hr eads a re also tr immed fl ush
wi th th e cra nkc as e fa ces oft er assembl y. It is im-
portant
that the small rub be r pocking rin gs at th e
through
st uds be in place b efore the case is r e-
asse mb l ed . On the mod el 6A4 -165- B3 engin e, it is
ne cessa ry to put a sm a ll fi ber w as her under t he o il
cro ss-ov er pa ssage se a l ring to pre vent it from fail-
ing in
to the p assa ge. It is advisable to hold the oil
sea l p ock ing s tr ips an d rings in p lace with a lig ht
coot of cup grease during assembly.
7
6
3
FIG. 3.
I.
Main Bearin g J ournal
2.
Propeller Shaft Bearing
Journal
3.
Nose Se al Adapting
Recess
4.
Engine Mounting
Bracket
5.
Cylinder Hold-Down
Stud
6.
Top Crankcase Cover
Mount i ng Pad
10
Crankcase
7.
Rear Through Tie Stud
8.
Crankcase Assembly
Stud
9.
Top Front Through Tie
Stud
10. Front Through Tie Stud
11. Thrust Washer Mount-
ing Pad
12.
Camshaft Through Tie
Stud
14
4

FIG. 4. Crankshaft and Main B arings 10
The crankcase on the model 6A4-165-B3 engine
has drilled oil passages and a mount pad to take a
propeller control valve'. This
pad is on the left front
of the crankcase just above the engine mount
bracket.
The two halves are joined internally bya series
of six special heat-treated 3/ 8" studs located at
the main bearing journals and four heat-treated
5/ 16" studs located at the camshaft be aring jour-
nals.
Castle nuts safetied with cotter pins and flat
washers are used on all internal studs . Two 3/ 8"
studs at the front bearing journal and t wo 3/ 8"
studs at the rear bearing journal, as we ll as one
5/
16" stud at the front top protrude through the
right
crankcase half. These five studs are secured
externally using
flat washers and elastic stop nuts.
Three 5/ 16"-24x7-3 / 16" hex head bolts are in-
stalled along the
top of the case, as well as three
5/ 16"-24 x 1-3/ 8" hex head bolts installed at the
front end of the engine straight through both
crankcase halves. Plain 5/ 16" washers are used
under bolt
heads and under the specified elastic
stop nuts.
When assembling the crankcase halves, observe
that the aligning dowels fit in their respective holes
and draw up the crankcase assembly nuts evenly.
XI-CRA
1
5
Wh en assembled with mating halves, the crank -
sh
aft m ain be aring hole is bored to 2,4 06 " to
2.407" and the camsha ft bearing hole is bored to
1. 12 45" to 1 .1250 ".
Each
of the six cy li nder pods are s tudded at th e
proper locations
as follows: Four studs, 7/ 16- 14 NC
stud end, 7/ 16 -2 0-NF- 3 nut end , dr iven to a h eight
above pad of 1 -1 / 8". Four studs 3/ 8-1 6 NC stud
end, 3/ 8-24 -NF-3 n ut end, driven to a height
above
pad of 1- 1/ 16".
One
pad is lo c ated at each of the four lo w er out-
side corne rs of the cra nk c ase to acc omm odate the
engine mounting brackets. Four d ow els are located
in the case to align the brackets, one do wel for ea ch
bra cket. On the early en gines, the brackets are
secured to
the ca se by mea ns of t wo studs.
5/
16-18 x 7/ 8" hex hea d cap screws ar e used on
the later engine . So me engi ne models u se flat
washers
and drilled he ad hex cap scre ws safet ie d
with lacing wire. On some engines
the l ow er righ t-
hand bra c ket is of special desi gn wi th a p ad for
fuel
pump a tt a chm ent.
When the cran kc ase is disassembled a t engi ne
overhaul, it is important that all plugs be removed
and the oil galleries and o il pass ages be th oroughly
flushed
out before reinstalling the pl ugs.
KSHAFT
1. Cr anks h af t Gear
2. Cente r Main Journal
3. Connec ti ng Rod Jo urnal
4. Front Main and Pro-
peller
Shaft Jo urna ls
5.
Re ar Ma in Journa l
6.
Re ar Ma in Bearing
7. Cente r M ain B ear i ng
8. F ro nt Ma in Bearing
9. Pr opeller Shaft Bearing
10.
Pr opeller Bolt Flan ge
Bushing
15

The crankshaft is a one piece, six throw, alloy
steel forging,
heat treated and designed to with-
stand high stress. It is drilled f or li ghtness and to
supply lubrication to all the bearin gs . (See Fig. 4. )
The fillets ground on the crankshaft have a .125"
to .140" radius on the main bearing journals and
connecting rod bearing journals. These fillets reduce
the tendency toward localization of stress and for
this reason it
is important that f il let specifica-
tions be observed
if the crankshaft is reground.
Also,
after regrinding the journals, th e fillets should
be
shot peened according to Aircooled Motors speci-
fication # 11981 .
CRANKSHAFT BEARINGS
The crankshaft is supported in the crankcase by
five
split steel-backed, main bearings of .0770" to
.0775" wall thickness after plating . (See Figure 4.)
The bearing shells have 0 crush fit to secure them
in the crankcase bore and insure rigid support for
the crankshaft. The five bearings are referred to by
number with the # 1 bearing at the rear of the
engine. It is essential that the bear ing shell halves
containing the oil holes be assembled so that they
motch the oil passages in the left crankcase half.
Figure
No.4 shows the #4 main bearing with a
single oil groove. This
bearing on the model
6A4-165-B3 engine has an additional oil transfer
groove to provide a passage for propeller control
oil. This bearing having
the oil transfer groove will
.be supplied for service replacement for the #4 and
#5 bearings on all model engines referred to in this
manual.
The crankshaft end-play, when the crankshaft
is fitted in the crankcase, is .008" to .020" and is
controlled by two split bronze thrust washers lo-
cated and doweled to the front and rear sides of the
crankcase web of the front center main bearing
support in both crankcase halves. The end play
should be
checked with both crankcase halves sepa-
rately as well as after assembly to make sure that
the .008" minimum clearance is obtainable. Thrust
washers must be replaced in pairs as slight varia-
tions in thickness exist between
different pairs.
The crankshaft main bearing journal diameter is
ground to 2.249" to 2.250" and the connecting rod
bearing journal
is ground to 1.9365" to 1.9375".
When assembled in the crankcase, the clearance
between the crankshaft journa ls and main bearings
is .002" to .004".
Eight bushings with inside diameter threaded
3/8" -24 NF-3 are pressed into the flange at the
front of the cra n kshaf t for attaching the propeller.
The .6265" to .627 0" major outside diameter of the
bushing is a . 0015" to .003" press fit in the .624"
to .625" reamed holes in the c rankshaft flange. The
model 6A4-150-B31 has a 5" diameter bolt circle
flange.
The model 6A4-150 - B3 and 6A4-165-B3
engines hqve a standard SAE-3 5.25" bolt circle
flange. Two
Woodruff key seats 3/ 16 by 1-1/ 8"
are cut in the rear main bearing journal extension
for
att aching the crankshaft gear, s tarter gear and
accessory drive gear.
The crankshaft runout, token with the shaft sup-
ported on its main
bearing journals, should not
exceed .002" total indicator reading.
The crankshaft of the 6A4-165-B3 engine is
drilled at the front main journal to provide a pas-
sage for propeller actuating oil from the crankcase
to the hollow propeller shaft. The aluminum plug
closing
the end of the propeller shaft should not be
removed
except possibly at a major overhaul when
it is desired to thoroughly clean the shaft. This plug
is assembled with a press fit in the shaft and is
safetied with a set screw. If the plug is ever re-
moved, it should be replaced by a new
part, as the
old one is usually damaged by removal. The 1/8"
pipe plug, which is installed in the center of the
aluminum plug, should also never be removed ex-
cept when a hydraulically actuated propeller is
installed
on the engine. The hollow propeller shaft
carries engine oil which will escape if either plug is
not in place during engine operation.
The crankshaft flange has the following mark-
ings on the rim of its outside diameter: "No. 1
U.D.C.,
24 and 28 degrees." The No. 1 U.D.C.
mark, when in line with the center line of the crank-
case at the top of the engine, refers to top dead
center of No. 1 cylinder. The 28 degree mark is
used for ignition timing on the model 6A4-1 50-B3
and B31 engines and, when 01 igned with the crank-
case center line, refresents 28 degrees before top
dead center on No. cyl inder when on the compres-
sion stroke.
The 32 degree mark is used for igni-
tion timing
the 6A4-165-B3 and, when aligned
with
the crankcase center line, represents 32 de-
grees before
top dead center on No.1 cylinder when
on
the compression stroke.
Before installation
at the factory, every crank-
shaft is 100 % magnetically inspected and tested
for dynamic and static balance.
CRANKSHAFT OIL
SEAL
!
4
FIG. 5. Crankshaft Oil Seal
1.
Crankshaft Oil Seal 3.
Oil Seal RetainerWasher
Spring
4. Retainer Washer
2. Crankshaft Oil Seal
Attachment Screw
Packing
A spring loaded all seal is installed in the 3.248"
to 3.250" recess in the front end of the crankcase,
formed by the assembly of the two crankcase
halves. (See Fig. 5. ) The free length of the spring
itself
in the open position should measure 7 -1 / 8" to
7-1/ 4". Be sure to specify the correct part number
when ordering the seal. (See Fig. 5-1.) The spring
side of
the seal is towards the rear of the engine
and a light coating of sealing compound is applied
to
the outside surface of the seal before pressing
the seal into place. The split in the seal should be
located
approximately 45 degrees from the crank-
case parting line to insure that no oil seepage will
occur where the seal ends come together. The seal
should be
topped into position evenly to prevent
distortion and insure proper seating in the crank-
case bore. A split retainer plate is used to hold the
seal in position. This plate is attached to the
front end of the crankcase by means of two
1/
4" -20 x 1/ 2" hex head cap screws and two 1/ 4"
shakeproof washers.
16

X II - CAMSHAFT
FIG. 6. Camshaft a nd Bearings
1. Ca mshaft Ge ar
2. Fuel Pump Cam
3. Valve A
ctuating Cam
The c amshaft in c orporate s six intake and six
exhaust lobes and has four bearing journals. (See
Fig.
6.) The bearing journals are ground .9985"
to .
999 ", and the journal clearance with the bear-
ing is .0015" to .0025". The permissible camsh aft
end ploy when assembled in
the crankcase is .006"
to . 010". The end ploy should be checked with each
cran kcase half separately, as well QS after assem-
bly, to mak e sure that the .006" minimum clear-
ance
is o btainab le. The permissible camshaft
runout is .00 2" total indicator reading. This read-
ing
is taken at the cent er of the shaft, while being
supp orted on the bearing journals.
The total thickness of the split camshaft bear-
ing shells is .0620" to .06225" when new. Care
should be taken when reassembling the bearings
in the crankcase. It is essential that the bearing
half co ntaining the oil hole be assembled in the
4. Camsha ft Bearing
Journal
5. Camsh aft Be a ring
6. Oil Pump Drive Gear
l eft half of th e cra nkcase so tha t thes e oil ho le s
wi
ll mate with th e oi l passages in the case.
A ca
mshaft from the 6A4-150 - B3 model should
never be interc
hange d with the camshaft from the
6A4-165-B3 model. The cam lobe dimens io ns are
diffe
rent on the two models. Interch ang ing cam-
shafts would c ause improper function of th e valves
and
damage to the valve operating parts .
Both
cast iron and forged steel cam s hafts have
been used on t he model 6A4-150-B3 eng in e. The
timing gear is located by a shoulder on the steel
shaft. There is no locating shoulder on the c ast
iron camshaft, however, and th e gear is pressed on
to a distance of 1.034" to 1. 036" from the fl an ge
face. As
the I.D. of the two timing g ears is differ-
ent, it is necess ary to consult the Par ts Book to
determine the prop er ge ar to o rd er for eit her sh aft.
XIII - TIMING G AR C ASES
The c as e en cl osing the accessory ge ar train con-
si st s of two a luminum-a llo y castings, the front
ti
mi ng or front acc essory ca se and the rear
accesso ry or re ar ti mi ng gea r ca se. (See Fig. 7.)
The front case which houses the cra nkshaft
and cams haft ge ars is at tached to th e re ar c rank -
case surface by eight
5/ 1 6"- 18 x 7/ 8" and two
5/1 6
"-18 x 2 -1/4" hex hea d ca p scre ws . The eight
sho
rt scre ws use plain 5/16" fl at w as hers and ar e
secured by lacing wire. The two long screws use
sha keproof wa she rs . The al ignment of this front
housing with the crankcase is
maintained by two
1/4" x 3/ 4" dowels em bedded in the r ear crank-
case ma ting surf ac e.
The rear
case which houses t he accessory gear
train is fa stened to th e front case by ten 1/ 4"-
20 x 5/ 8" and two 3/8 "- 16 xl" hex head ca p
17
screws. Shakep ro of washers are used thr ougho ut on
these screws. La ter model 6AL-150 - B3 and a ll
model 6A4-1 65-B3 engines incorp or a te two 1/ 4"
do wel bolts in pl ace of th e two l ar ge cap screws.
On
th e older st yle re ar timing g ear case, a te n-
non
th at m at ches a pi lot di am eter in the front
tim ing ge ar ca se is used to ma in tain alignment
in stead of the dowel b ol ts used on th e l at er engines.
Th
er efore, the o ld and new type timing ge ar cases
ar e not interc ha ngeable. It is important to cons ul t
the Parts Book
to d et erm ine the proper mat ing
timing gear
case when ordering repla ceme nt parts.
The
cra nkcase on all models will take either the
old or the new type timing gear cases.
Composition
gaskets are used between th e
c
rankcase and the front timing case, as we ll as
bet we en the two timing gear cases.

\ 5
REAR TIM ING GEAR HOUSING
FRONT TIMING GEAR HOUSING
FIG. ,. Timing Gear Housings
1.
Starter Mounting Pod
4. Rear Housing to Front
2. Magneto Mounting Pod Housing
Cop Screws
3. Generator Mounting
5. Oil Pon Support Studs
Pod
XIV - CONNECTING RODS
The connecting rods are an alloy steal forging,
magnetically inspected before being assembled on
the cranksh aft. (See Fig. 8,) They are a matched
we ight assembly and are stamped on the bolt
bosses
in relation to their cylinder position on the
crankshaft .
When reassembling the rods on the crankshaft,
it is important that they be returned to their orig-
inal position.
The rods are located in numerical
order with # 1 rod on
the crank throw which is
ne arest the gear end of the crankshaft and #6
rod is on the throw which is nearest the flange end
of the shaft.
The lo we r bushing is of the steel- backed split
type and
the halves are interchangeable. When
assembling the lower cap to the rod, cylinder posi-
tion numbers on
the bosses should be on the same
side of the rod. The # 2, #4 and #6 rods have the
finished r el i ef surfac e on the top cap towards the
f ro nt of the en gine while the reliefs on # 1, #3
FIG. 8. Connecting Rod Assembly
an d #5 ro ds face the rear of the engine. It is im-
p
ortant at assembly to see that the tongue on the
1.
Connecting Rod ond
4. Lower Cop Co
nnecting
bac k of the bushing fits the slot provided in the
Upper Cop
Rod B ea ri ng
conn ecting rod to prevent binding or movement of
2.
Connecting Rod Bolt
5.
Co nn ecting Ro d Lower
the bushing halves when installed. The wall thick-
Cop
3.
Upper Cop Connecting
ness of the bushing is .06105" to ,06150". The
Rod Bearing 6.
Nut-C onn ecting Rod
bushings ar e a crush fit when assembled in the
Bo lt
18

connecting rods. When assembled to the crank-
shaft, they have a cleardnce of .0015" to .0034"
on the crankshaft throws.
The connecting rod cap is assembled to the rod
by two alloy
steel, 3/ 8" - 24 NF rolled thread, upset
head bolts. The bolts are installed with the head
end toward the piston pin bushing. The two 3/ 8" - 24
slotted nuts must be drawn up evenly and safetied
by two 3/ 32" x 3/ 4" cotter pins. The side clear-
ance between the connecting rods and the crank-
shaft cheeks is .00 8" to .014".
Two holes are drilled in the connecting rod at on
angle of 36° to the vertical center-line. These holes
index with two holes in
the bearing bushing. The
xv-P STON, PISTON
The permanent mould cost aluminum alloy
pistons
are of a special design, which controls ex-
pansion to a high degree, permitting a close fit
between piston and cylinder wall. (See Fig. 9-1. )
This feature provides for long cyl inder, piston and
ring life and eliminates piston slap.
The clearance between the piston and cylinder
wall,
taken at the bottom of the piston skirt, is
.002" to .0035" and token at the top of the skirt,
just below the slot, is .003" to .0045". (See Fig.
10.) This clearance can best be taken by using a
long
feeler gauge, which will reach the length of
the cylinder liner. The piston should be installed,
without the rings, in its normal running position
within
the cylinder and the clearance taken at the
top and bottom of the cylinder bore A .002" feeler
gouge should indicate no drag when checking
piston clearance.
FIG. 10. Checking Pinon Cleoronce
19
holes permit oil to spray upwa rd a gain st the cyl-
inder walls
and pi st ons. To lubr ic ate the pi ston
pins and piston pin bushings , thr ee holes are dri ll ed
in
the upper end of the co nne cting rod an d pi st on
pin bushing.
The piston pin bushing is a press f it in th e
1. 0375" to 1. 0385" hole of the con nect ing rod.
After installation, it is bored to .9 84 7" to .9849".
The bushing must be insta ll ed with th e th ree
drilled holes indexing with
the thr ee holes in t he
connecting rod upper boss. Clearance betwe en th e
piston pin
and bushing is .0007" to .0012". T he
two bores of the conne cting rod mu st be pa rallel.
PINS AND RINGS
- - I
2 -·· ---- - ~~~~
Piaton ond Piston Pin
1. Piston
3 . Pi s ton Pin Plug
2.. Piston Pin
If at any time the piston with rings in st alled
should be inserted by hand in the cyl inder bor e,
do
not push the piston into the top of the cylinder
as the top groove piston ring will expand above
the upper rim of the cylinder li ner and lo ck th e
piston
in the combustion chamber .
The ring groove widths are as follows: T op
groove -,099" to ,100", middle groove -.097" to
.098", bottom groove -,1885" to .1895",
The diameter of the piston pin holes in th e
piston is .98415" to .9840". Pi s tons are pl at ed all
over with the exception of the pi s ton pin holes.
The pistons are stomped for lo ca tion on the
bottom of the piston pin boss. Th e number corr e-
sponds to the cylinder location on t he engine in
which
they are installed.
PISTON
PI N
The hollow piston pins are of a ll oy s te e l, heat-
treated and magnetic ally inspec te d. (See Fig. 9-2 .)
They are of the full f loating type an d a re a pa lm
push fit in the piston at room tempe ratu re (70°F).
They are finished inside to a diame ter of .619" to
.620" and ground outside to a di amet er of .9 838"
3

to .9840". The piston pin ends must De square with
their axis within .001" total indicator reading to
insure proper
bearing surface for the end plugs
and assembly end clearance. Two aluminum plugs
are installed in tne ends of the piston pin. The out-
side diameter of the plugs, where they fi t inside
the pin, is .6175/' to .61 85" .
The piston pins, when installed, give the piston
pin with
buttons assembled an end cl e arance in
the cylinder bore of .015" to .033". This clearance
is best checked by using a feeler gauge. Install a
piston pin
in the piston and insert the piston in the
cylinder bore far enough to permit checking the
piston pi n end clearance with a piston pin button
against one side of the cyl inder bore.
PISTON RINGS: (FIG. 12)
FIG. 12. Pist~n and Rings
1.
Top Compression Ring
3. Oil Control Ring
2. Middle or Scraper
4. Piston
Compression Ring
The piston is provided with three ring grooves
to accommodate three Perfect Circle piston rings.
The lower groove has holes drilled through the
piston wall to the inside of the piston for oil return.
The top ring is a compression ring with a width
of .0930" to .0935". It has an undercut on the
inside diameter of one face, around the circum-
ference of the ring. The ring must be installed
with its
undercut facing the top of the piston. See
Fig. 11 for
the diagram showing the proper ring
positions.
1--~
2--~
3 :LJ
FIG. 11. Piston Ring Installation
1. Top Compression Ring
2. Middle Compression-
Scraper Ring
3. Oil Control Ring
The middle ring is a compression scraper ring
with a width
of .093 0" to .093 5" . 1ts undercut is
on one edge of the outer circumference. This ring
must be installed with the undercu t faci ng the
bottom of the pi st on. This is important as reversing
the ring ot installation will caus e it to s crap e the
oil toward the combustion ch am be -r, resulting in
high oil
consumption and fouled spark plugs.
The lower groove ring is an oil control ring of
the slotted type, with a width of . 1860" to . 186 5".
It
may be installed in any position in th e low er
groove.
The piston ring gap for all three rings, when
measured in the cylinder, should be . 013" to .02 3".
(See Fig.
13 for method of measurement. ) The
top ring has a side clearance when installed in
piston groove
of . 0055" to .007". The center ring
has a side clearance of .0035" to .005", and the
bottom ring, .002" to .0035". When the pistons
are installed on the engine, the ring gaps are stag-
gered in relation to each other, before installing
the cylinders.
FIG. 13. Ring Gop Clearance
20

XVI-CY INDER ASSEMBLY
Franklin cyli nde rs are one-piece aluminum alloy
s
and castings, incorporating deep, closely spaced
fins to insure ample cooling under the various op-
erating conditions of the engine. (See Figs. 14
thru 17.) The piston bore of the cylinder is fitted
with a nickel-iron liner which extends the full
length of
the cyl inder barrel section and projects
.500 to .51 5 be . low the cylinder flange of the
cylinder casting. The liner is positionea by a lock
pin which
is held solidly in place by two lock screws.
(S ee Fig. 14 -3, 4.) To prevent oil leaks, the lock
pin
and lo ck screws are coated with a liquid joint-
ing compound
at assembly. The lock pin or lock
screws should never
be removed; replacement is
necessary only when installing a new Iiner. On
initial assembly,
the lock pin is installed before
the final grinding and honing of the cylinder barrel
operation,
and is, therefore, finished to size on
the inside of the cylinder bore when the bore
dia
meter is ground to size.
The
later model 6A4 - 150-83 engines have two
lock pins positioned
90 degrees apart to hold the
cylinder liner in position. The model 6A4-165-B3
engine has a step machined in the crankcase at
the cylinder mount bore. This step acts as a stop
for the cylinder liner and only one liner lock pin
is used in the cylinder.
The cylinder bore
is finish-honed to a diameter
of 4.500" to 4.501". The final finish is a fairly
coarse honing operation
to insure satisfactory seat-
ing of the piston rings contacting the liner surface.
Tests have proven that with the use of good lubri-
cants, changed regularly, the liners will show little
wear over a tong period of operation.
Cylinders for
the model 6A4-150-83 and the
6A4- 1 65-B3 are mode from the same costing.
Cylinders for
the 165 hp model have different
valve guides from the 1 SO hp model and an addi-
tional shot pee ni ng operation has been performed
on
th e cylinder base to provide added st rength.
It is, therefore, mo
st i mportant that a cylinder
originally
mahufactured for the 1 SO hp engine
MUST NOT be token from stock and assembled
on a 165 hp engine.
All cylinders for the model
6A4
-1 65-B3 engine have shot peened bases.
During initial assembly,
the aluminum cylinder
ca sting is heated and held for two hours at a tem-
pe rature between 62 50 and 650°F to anneal the
ca st ing and prepare it for installation of the liner,
valve se
at inserts and valve guides, all of which
are installed while the casting is in the heated
condition.
VALVE GUIDES
The intake and exhaust valve guides are a high-
quality
cast iron and are installed as previously
explained, when
the cylinder casting is heated.
(See Fig. 15-1, 2.) T he outside diameter of the
valve guides is .5640" to .5645" and the inside
diame te r of the reamed holes into which they are
pressed is . 5605" to .5610", giving a shrink fit of
.0 03" to .004". On later engines, the reamed hole
is .5615"
to .562" giving a shrink fit of . 002"
to .003". When installed, the distance down
from
the mac hined top surface of the cylinder to
the top of th e guide is .318" to . 354". The inside
diameter of both guides is . 375" to .376" on the
FIG. 14. Cylinder Liner Lock Pin and Set Screws
1. Cylinder liner
3. liner Lock Pin
2. Cylinder Hold-Down 4. Lock Pin Screws
Fl
ange
FIG. 1S. Valve Guides
and Top Face of Cylinder
1. Intake Valve Guide 5.
Topped Holes for Valve
Cover Screws
2. Exhaust Valve Guide 6.
Tapped Holes for Rocker
3. Intake lifter Tube Hole
Support Screws
4. Exhaust lifter Tube
Hole
early model 6A4-150-B3 and 831 engines. On the
loter model 6A4-150 - B3 engines, the diameter of
the exhaust valve stem was increased, which re-
quired
an increase in the insi de diameter of the
exhaust guide to .4375" to .4385". On the model
6A4-165 - 83 engine , the Inside diameter of both
5
21
2