Basic Specifications

Models

5101 / UJ - Atomic Four 

5111 / UJS - Atomic Four Stevedore (Atomic Four configured for direct drive - power limited to 18 hp with intake manifold restriction)

5102 / UJR - Atomic Four with Paragon reduction gearbox mounted on transmission

5112 / UJSR - Atomic Four Stevedore (Atomic Four configured for direct drivet - power limited to 18 hp with intake manifold restriction) with Paragon reduction gearbox mounted on transmission

5103 / UJVD - Atomic Four with Walter V drive gearbox mounted on transmission

5113 / UJSVD - Atomic Four Stevedore (Atomic Four configured for direct drive - power limited to 18 hp with intake manifold restriction) with Walter V drive gearbox mounted on transmission

Type

Vertical, in line, 4 cycle, L (flat) head

Serial Number Locations

Pre 1969: stamped on right, forward side of block above starter motor

Post 1968: stamped on block above flywheel housing, and on an id tag glued to top of manifold

Post 1977: stamped on block above flywheel housing, on an id tag glued to top of manifold, and on an id tag glued to front of the flywheel housing cover

Universal Foundry ("UF") Casting Part Numbers

block: UJ-1 (595369)
head: UJ-2
pan: UJ-4
marine gear housing: UJ-5 (121571)
camshaft: UJ-8
connecting rod: UJ-10
main bearing cap, front: UJ-15
main bearing cap, rear: UJ-16
oil pump cover: UJ-17
camshaft timing gear: UJ-27
auxiliary drive pulley (early pulleys made for engines with generators had thinner sheave sides: than later pulleys intended for use with alternators): UJ-79
rear thrust bearing outer plate: UJ-90
idler gear: UJ-96
V-drive manifold end cap: UJ-410

flywheel housing, old style:
flywheel housing, new style:
flywheel cover - pre 1978):
manifold:
head to manifold coolant tube - pre 1969:
thermostat housing:
block plate - pre 1969:
valve cover - pre 1969:
rear thrust bearing inner plate:
flywheel:
crankshaft:
crankshaft timing gear:
crankshaft drive gear:
oil pump gear:
auxiliary drive housing:

Dimensions

Cylinders

4

Nominal bore

65 mm / 2.562 in

Nominal stroke

79 mm / 3.125 in

Nominal engine displacement (swept volume)

1056 cc (1 litre) / 64.44 cu in

Nominal stroke / bore ratio

1.22 (under square)

Nominal compression ratio

6.3:1

Nominal peak (maximum) piston speed

1825.8 ft / min

Nominal piston to head clearance

? in

Nominal piston to crank clearance

? in

Nominal rod ratio

1.917

Piston pin offset

0.00"

Nominal deck height

8.993 in

Nominal connecting rod length

6.0 in

Nominal crank throw

1.565 in

Nominal piston deck clearance

0 in

Nominal piston compression height

1.428 in

Weight

UJ (direct drive): 310 lb
UJR (reduction drive): 330 lb
UJVD (V drive): 335 lb

Nominal peak (maximum) power output

Standard Atomic Four: 30 hp @ 3,500 rpm
Atomic Four Stevedore with intake restrictor: 18 hp @ 2,500 rpm

Nominal peak (maximum) Brake Mean Effective Pressure (BMP)

103 psi

Nominal rated torque at peak (maximum) rpm

Standard Atomic Four: 45 lb ft @ 3,500 rpm
Atomic Four Stevedore with intake restrictor: 37 lb ft @ 2,500 rpm

Nominal peak (maximum) rated torque

Standard Atomic Four: 45 lb ft @ 3,500 rpm (maximum rpm)
Atomic Four Stevedore with intake restrictor: 39.5 lb ft @ 2,125 rpm (85% of maximum rpm)

Nominal torque rise

Standard Atomic Four: 0%
Atomic Four Stevedore with intake restrictor: 7%

Nominal peak (maximum) specific output
(power/piston crown area)

Standard Atomic Four: 1.46 hp / sq in
Atomic Four Stevedore with intake restrictor:  .877 hp / sq in

Nominal weight / power ratio (direct drive model)

Standard Atomic Four: 10.33 lb / hp
Atomic Four Stevedore with intake restrictor:  17.22 lb / hp

Nominal weight / displacement ratio (direct drive models)

4.81 lb / cu in

Nominal peak (maximum) power / displacement ratio

Standard Atomic Four: .47 hp / cu in
Atomic Four Stevedore with intake restrictor: .28 hp / cu in

Torque / RPM / Power
(standard Atomic Four)

Torque / RPM / Power
(Atomic Four Stevedore with intake restrictor)

Components

Cylinder block

Cast en-block with marine chrome nickel iron alloy crankcase & full length water jackets

Cylinder head

Marine chrome nickel iron alloy detachable head

Crankshaft

2 main bearing, high carbon steel, fully counterweighted, statically and dynamically balanced, uses insert (Vandervell shell type) bearings

Connecting Rods

Drop forged, high carbon steel, floating piston pin, insert bearings, new style rods with thicker I beam section: weight = 480 g / 17 oz

Pistons

Cast aluminum, flat-top, 3 ring - 2 compression rings and 1 oil control ring, full floating piston pin retained by steel circlips, 0 pin offset, expansion slot on non-thrust skirt

Oil pan

Marine chrome nickel iron alloy, one piece, partially baffled marine type, integral engine mounts

Manifold

Marine chrome nickel iron alloy water jacketed exhaust and intake manifold in one casting. Separate exhaust flange tapped 1 1/4 in NPT bolts to manifold with two 3/8" NC cap screws or studs at exhaust opening at rear of manifold. V drive models use same manifold with cap over rear opening and front opening machined for exhaust flange so that engine can be mounted facing backwards, as required for use of V drive.

Exhaust pipe attachment

1 1/4 in NPT female pipe thread in removeable flat flange held on by 2  3/8" NC studs or cap screws

Lubrication

Full pressure to mains, connecting rod big ends, idler gear stud, camshaft bearings, transmission sun & planet gear assembly
Marine type fine brass mesh oil pump pickup screen surrounding pickup to retain oil in rough seas and prevent oil pump ingesting air, exterior oil pressure adjustment

Water jacket cover

Removeable mild steel block water jacket plate (stainless steel plates available from after-market suppliers but not recommended, they encourage galvanic corrosion of the block instead of the cover plate... for the same reason do not use stainless steel nuts and bolts)

Cooling system

Constant flow, double-acting thermostat, rubber impellor water pump (later models)

Thermostat upper plate height

Original OEM Holley 3 spring: closed (cold) 8.3 mm / .325 in / open (hot) 15.9 mm / .625 in
Replacement OEM Westerbeke single spring: closed (cold) 5.1 mm / .2 in / open (hot) 20.3 mm / .8 in

Thermostat housing bypass boss depth

10.2 mm / .4 in

Mechanical fuel pump pushrod size

39.37 mm / 1.550 in long x 9.53 mm / .375 in diameter

Marine gear (transmission)

Paragon OXKB: combined engine / marine gear lubrication system with marine gear running in engine oil, sun and planet gear type, forward uses multiple plate clutch pack with over-centre pressure and lock, reverse uses clutch band on sun gear housing, the carrier gear assembly is pressure lubricated via a port on the crankshaft rear main bearing, the rear thrust bearing at the drive flange is splash lubricated via a bearing shield which meters the oil to and from the bearing / rear seal.

direct drive output flange: 3.5" overall diameter, 3 hole X 3/8" NF, 1.375" radius holes @ 120°, 1.875 diameter X .125" protruding centring rign 

Reduction Gear (optional)

Single step, internal helical and pinion type, Paragon #RO-20, 2.04:1 ratio standard, 3.01:1 ratio optional

reduction gear output flange: 4" overall diameter, 4 hole X 3/8" NF, 1.625" radius holes @ 90°, 2" diameter X .125" recessed centring ring

V drive (optional)

Single step, internal gear type, Walter Machine #RV-10T, 24° V angle, 1.00:1 ratio standard... 1.29:1 / 1.67:1 / 2.0:1 ratios optional

V drive output flange: 2.875" overall diameter, 3 hole X 5/16" NC, 1.125" radius holes @ 120°, 1.25" diameter X .125" protruding centring ring

Carburetor

Updraft Zenith marine non-drip type carburetor, upturned air horn with flame arrester screen:
1949 - 1968: Zenith type 61, cast-iron (adjustable main jet)
1969 - 1984: Zenith Bendix type 68-7 - 13355, aluminum (fixed main jet)

Starting System

1948: - 1967: Prestolite starter, 12 volt DC Prestolite solenoid
1967 - 1984: Delco Remy 1107679 starter, 12 volt DC Delco solenoid

Charging System

1948: - 1967 - dual foot saddle mount 6 (later 12) volt Prestolite marine generator, mechanical generato-mounted voltage regulator
1967 - 1984: single 2" foot mount 12 volt DC 35 amp Motorola (optional 50 amp Leece-Neville or Motorola) marine alternator, transistorized alternator-mounted voltage regulator

Ignition System

1948 - 1967: Prestolite 1Gw60032E1X distributor, Prestolite coil
1967 - 1984: Delco Remy #1112446 - 2G11/6C16/3HI8 distributor, Delco Remy 070FLX 12 volt coil

Propeller rotation

Right hand (clockwise facing the rear of the propeller) (all models)

Propeller shaft / coupling inner diameter

Direct Drive: ¾ in, 7/8 in, 1 in
Reduction Drive: 1 in, 1 1/8 in
V Drive: 7/8 in, 1 in

Propeller Size
Note: propeller fitted to direct drive and V drive-1:1 ratio models must allow the engine to reach at least 1,800 rpm during hull speed / full throttle testing. Propellers fitted to reduction drive and V drive-reduction ratio models must allow the engine to reach 3,300 rpm during hull speed/full throttle testing

2 blade (cruising / racing standard)
Direct drive: 11" x 7", 12" x 6", 13" x 5"
2:1 reduction or V drive: 15" x 8", 16" x 7", 17" x 6"

3 blade (cruising standard & recommended for use on sailboats in areas with severe currents, winds, tides)
Direct drive: 10" x 6", 11" x 5"
2:1 ratio reduction or V drive: 13" x 8", 13 1/2" x 7 1/2", 14" x 7", 15" x 6"

Note: + / - 1 inch change in pitch or diameter changes maximum rpm by approximately - / + 100 - 200 rpm
Note: to roughly size a 2 blade prop add 2" to the diameter of a 3 blade & keep the same pitch... and vice-versa

Crankshaft rotation

Counter-clockwise viewed from flywheel end
Clockwise viewed from rear of engine/reduction box/V drive output shaft (ie all models use a right hand prop)

Fuel

Original specification was "standard 92 - 94 octane gasoline", later revised to "regular 90 - 94 octane" (when the specifications were written all gasoline contained lead, which was used to raise the octane rating and extend valve seat life). Modern "Regular" 87 or 89 octane non-leaded gasoline is OK as long as the compression is below 120 psi and the ignition timing is set by adjusting distributor at full cruise speed to give maximum tachometer rpm. Octane booster & lead additive is not recommended or necessary.

Dimensions

Maximum operating angle

15°

Maximum rotation angle

25°

Length overall

UJ: 26 ¾ in, UJR: 31 15/16 in, UJVD: 35 13/16 in

Height above crankshaft centreline

13.125 in

Maximum width

18.250 in

Offset – crankshaft to propeller shaft

UJ: 0 in
UJR: 1.042 in
UJVD: na

Base depth below centreline

6 in

Firing order (#1 cylinder: flywheel end)

1 2 4 3

Valve timing

Inlet valve opens: 5  BTDC
Inlet valve closes: 50  ABDC
Exhaust valve opens: 45  BBDC
Exhaust valve closes: 10  ATDC

Valve guide dimensions

1.5 in long x .502 in outer diameter x .315 in inner diameter

Valve guide bore in block

.500 in inner diameter

Valve length

3.685 in

Intake valve head diameter

1.500 in

Exhaust valve head diameter

1.030 in

Valve spring outer diameter

1949 – 1967: .785 in
1966 – 1967: .800 in
1968 – 1984: .810 in
1995 - present: .800 in

Valve spring inner diameter

1949 – present: .62 in

Valve spring free length

1949 – 1967: 1.825 in (coil bound at .76 in)
1966 – 1967: 1.925 in (coil bound at .80 in)
1968 – 1984: 2.075 in (coil bound at .81 in)
1995 - present: 2.2 in (coil bound at .80 in)

Valve spring pressure

compressed to 1 in: 50 - 60 psi

Valve spring coil direction

left hand

Valve tappets

Diameter
all years: .810"

Length
19? – 19?: 1.725 in overall / 1.575 in bucket
19? – 19?: 1.975 in overall / 1.595 in bucket
19? – 19?: 1.910 in overall / 1.725 in bucket
19? – 19?: 1.975 in overall / 1.790 in bucket

Note: When installing replacement new or used tappets check to make sure tappet is long enough to allow clearance to grip flat section with a open-end wrench so the valve clearance adjustment can be accomplished.

Compression

90 psi – 125 psi, optimum 104 psi

Alternator drive ratio (through PTO gear & V belt pulley)

1.75:1 (1 turn of engine crankshaft = 1 ¾ turn alternator)

Flywheel ring gear & housing dimensions

1949 – 1967 (Prestolite starter): ring gear OD / flywheel housing ID 11 in

1968 – 1984 (Delco starter): ring gear OD / flywheel housing ID 11.5 in

Fuel consumption

Approximately 4 litres/hour (1 US gal/hour) @ 2,000 rpm under load depending on boat size & winds/currents

Primary fuel filter/water separator recommendation

Filter mesh size & type rating: 10 micron with water separator section & metal bowl (ie Racor 320R-RAC-02) [Note: do not use 2 micron filter elements in primary water separator filters... they are too fine and can cause fuel pump failure]

Minimum Flow Rating: 15 litre / hour

Mechanical fuel pump

AC Delco mechanical rubber diaphragm type, maximum pressure 3.0 psi
Auxiliary sediment bowl with internal mesh filter

Electric fuel pump

Facet 574A, 12 volts, maximum pressure 4.0 psi
Internal mesh filter accessible by removing cam lock bottom cap
In-line fuse/breaker 10 amp
Should be fitted with oil pressure safety switch (Hobbs 76576 - 10 n.o.) to stop pump if engine stalls or ignition switch left in "on" position

Pipe / Hose Sizes

Exhaust flange: 1 1/4 in NPT - 1 1/2 in or 1 /5/8 in hose
Water pump inlet: 3/8 in NPT - 1/2 in or 5/8 in rigid (wire reinforced) hose
Water pump outlet: 3/8 in NPT - 1/2 in hose
Fuel pump connection: 1/8 in NPT - 5/16 in OD copper pipe, double flared or 1/4 in ID hose (alcohol compatible)

Oil dipstick Sizes

Direct drive (DD): full mark - 6 3/8 in, low mark - 6 3/4 in
(direct drive old style dipstick top notch = new style dipstick full mark)

V drive (VD): full mark - 6 3/4 in, low mark - 7 1/4 in

Design Changes

Engine Specification Updates

circa 1949: > Serial #70000 (estimated)
Zenith series 61-M2AE7 cast iron carburetor with adjustable main jet
single metal head gasket
Dole thermostat
Auto-lite ignition
Fairbanks Morse magneto (optional)
Auto-lite 6 volt starter
Auto-lite 6 volt generator
Prestolite distributor (1Gw60032E1X)
bronze gear water pump
old style heat exchanger kit (optional)
5 unit control panel with mechanical tachometer, mechanical oil pressure gauge, mechanical water temperature gauge

circa 1962: Serial #?
Jabsco rubber impellor water pump (available as a replacement)
Prestolite 12 volt starter
Leece Neville 12 volt alternator (optional)

circa 1963: Serial #?
Prestolite 12 volt generator
Auto-lite 15 amp 12 volt generator (optional)
Delco Remy 24 amp 12 volt generator (optional)
Prestolite 35 amp 12 volt alternator (optional)
Prestolite 40 amp 12 volt alternator (optional)

circa 1964: Serial #?
Ongaro - Teleflex electric control panel with electric tachometer (optional), electric oil pressure gauge, electric water temperature gauge

circa 1964: Serial #?
single metal head gasket replaced with 2 composition gaskets

circa 1965: Serial #?
"old" Sherwood (7 end cover screws) rubber impellor water pump

circa 1967: Serial #79476
new style cylinder head with integral thermostat housing
Holley thermostat
new style Sendure heat exchanger kit (optional)
Medallion 6 unit control panel with electric tachometer (optional), electric oil pressure gauge, electric water temperature gauge

circa 1967: Serial #170509
Zenith series 68-7 13355 alumininum alloy carburetor with fixed main jet
Delco Remy distributor (#1112446 - 2G11/6C16/3HI8)
Delco Remy 070FLX 12 volt coil
Delco Remy 1107679 starter and new ring gear to fit
larger flywheel housing to fit new ring gear
Motorola 35 amp 12 volt alternator (Motorola 51 amp 12 volt alternator optional)
Oberdorfer model 202M3 rubber impellor water pump (fitted to most engines)

circa 1967: Serial #171514
external valve chamber oil line no longer fitted

circa 1968: Serial #174340
Oberdorfer model 202M3 water pump standard

circa 1969: Serial #174802
new style valves (often stamped "Eaton" or "Etn", but new OEM valves now come without markings)

circa 1969: Serial #175503
new transmission housing, oil fill moved to front

circa 1970: Serial #176500
valve guide inner diameter revised to .3145 - .3150 in (new valve guide/valve stem clearance specification of .003 - .004 in to prevent valves sticking in guides)

circa 1972: Serial #178801
Paragon marine gear updated with new outer plate combined with pressure plate, and new wider metric gear carrier ball bearing

circa 1975: Serial #192787
new style deep flywheel housing and flat sheet metal cover

circa 197?: Serial #?
new style electric instrument panel (electric tachometer optional)

circa 1979: Serial #202987
mechanical fuel pump replaced with Facet electric fuel pump and low oil pressure shut-off switch

circa 1980: Serial #20?
production stopped (sales continued to 1984)

Wear Limits / Machining Specs

Bore

to fit OEM Universal/Westerbeke "Mahle" pistons
Std size: 2.5625 in (+ - .0005 in)
.010 in oversize: 2.5725 in (+ - .0005 in)
.020 in oversize: 2.5825 in (+ - .0005 in)

to fit EGGE Pistons
same as OEM pistons above... EGGE pistons are designed to fit standard bore sizes

Maximum cylinder bore ovality

maximum .002 in

Maximum cylinder bore taper

.008 in

Piston skirt clearance

OEM Universal/Westerbeke "Mahle" pistons - all bore sizes
.0015 in  (+ - .0005) [feeler blade to 5 lb pull]

"EGGE" pistons - all bore sizes
.003 in (+ - .0005)

Piston ring gap

.007 in - .015 in (check near bottom of bore in area of minimum wear/minimum bore diameter... use a piston to push ring down into position for gap measurement)

Piston ring installation

OEM Westerbeke - Standard Bore Size (OEM #287761 - STD)
1. No longer uses an inner expander ring with the oil ring
2. Top 2 rings are the same... both install with the inner bevel up

OEM Westerbeke - Oversize Bore Sizes (OEM #287873 - .010 in, #287874 - .020 in, #287875 - .030 in)
1. Uses an inner expander ring with the oil ring
2. Top ring installs with the inner bevel up
3. Second ring installs with the outer lip down

Hastings or Ertel rings - Standard Bore Size (6520 - STD):
1. Uses an inner expander ring with the oil ring... ensure it is fitted beneath the oil ring with the spring end gaps over the oil drain slot in the bottom of the piston oil ring land (located over the vertical expansion slot in the piston skirt)
2. Top ring installs with the inner bevel up
3. Second ring installs with the outer lip down

Hastings or Ertel rings - Oversize Bore Sizes (6520 - .010 in, 6520 - .020 in):
1. Uses an inner expander ring with the oil ring... ensure it is fitted beneath the oil ring with the spring end gaps over the oil drain slot in the bottom of the piston oil ring land (located over the vertical expansion slot in the piston skirt)
2. Top 2 rings both install with the inner bevel up

Note: Install both types of rings with gaps staggered about 120 degrees around piston. Do not locate any gaps in the middle of the thrust side (the thrust side of the piston has no vertical expansion slot in the piston skirt)

Piston ring side clearance

Top (compression): .0015 in - .003 in
Middle: .001 in - .0025 in
Bottom (oil): .001 in - .0025 in

Connecting rod small end ID (no bushing)

.750 in

Piston pin diameter

.6880 in

Piston pin rod bushing ID (installed & honed)

.6885 in - .6890 in

Piston pin clearance in rod bushing

.0005 in - .001 in

Piston pin clearance in piston (light push fit)

.0001 in - .0002 in

Cylinder head, manifold, block head deck, & block manifold deck surface roughness specification

rotary broach: #125 RA (this is the OEM surface roughness specification) / #139 RMS 
surface grinder: #95 RA / #105 RMS
belt sander: #110 RA / #122 RMS

(Note: most automotive machine shops grind Atomic Four heads, manifolds, blocks too smooth... tell them you want a finish which feels slightly rough to the finger-nail if they don't understand what #125 RA means)

Cylinder bore honing finish

OEM & Hastings rings - 45 degree crosshatch with #20 RA / #25 RMS to  #24 RA / 30 RMS finish (220 grit stones)

Oil pump drive end play

.001 in - .003 in

Oil pump gear backlash

.003 in - .005 in

Camshaft gear backlash

.002 in - .004 in

Idler gear backlash

.002 in - .004 in

Accessory gear backlash

.002 in - .004 in

Connecting rod big end side play on crankshaft journal

.004 in - .008 in

Crankshaft end play (at front main bearing)

.002 in - .003 in

Valve face angle

45°

Valve seat angle

45°

Valve seat width

1/32 in

Valve stem diameter

.3115 in - .312 in

Valve stem / guide clearance

cast iron guides: .003 in - .004 in (OEM guides are cast iron)
bronze guides in fresh water cooled engines with 180 thermostat: .0035 - .0045 in

Valve guide internal diameter

.3145 in - .3160 in to give correct clearance (see valve stem/guide clearance above)

Valve spring installed length - no cam lobe lift (intake & exhaust)

1.19 in

Valve spring length - cam lobe full lift (intake & exhaust)

.94 in

Maximum cam lobe lift

.239 in

Front main bearing width:

1.620 in

Crankshaft main bearing journal

Std: 1.9880 in, +.0005 in / -.0000 in
.010 in undersize: 1.9780, + .0005 in / - .0000 in
.020 in undersize: 1.9680, + .0005 in / - .0000 in
.030 in undersize: 1.9580, + .0005 in / - .0000 in

journal fillet radius: 1/16"

Crankshaft rod bearing journal

Std: 1.5625 in, +.0000 in / .-.0005 in
.010 in undersize: 1.5525 in, + .0000 in / - .0005 in
.020 in undersize: 1.5425 in, + .0000 in / - .0005 in
.030 in undersize: 1.5325 in, + .0000 in / - .0005 in

journal fillet radius: 1/16"

Marine gear forward clutch plates

Pre serial #178801 (Dec. 15, 1972) with old-style thinner inner ball bearing Universal #285945-A (NTN SC0820)
3 fibre plates (#285992)
3 steel plates (#285993)
+ outer finger plate #285994 (Paragon OXK-11A)

After serial #178800 (Dec. 15, 1972) with new style thicker inner ball bearing Universal #285945-B (SKF 61908)
3 fibre plates
2 steel plates
+ outer finger plate #285994 (Paragon OXK-11A)

Clutch plate thickness:
fibre: .100",  +/- .002
steel: .070",  +/- .002

Crankshaft marine gear sun & planet carrier bearing journal

1.869 in, +.0005 in / .-.0000 in

Main bearing clearance

.001 in - .0025 in

Rod bearing clearance

.001 in - .0025 in

Rod big end diameter (no bearing shell)

1.6685 in (maximum ovality .0003")

Rod side play on crankshaft journal

.004 in - .008 in

Rod installation

Cylinder no stamped on rod big end towards camshaft, #1 rod at front (flywheel end) on #1 piston, #2 rod second from front on #2 piston, etc

Camshaft bearing journal

1.3745 in, +.0005 in / -.0000 in

Camshaft bearing clearance

.0015 in - .0025 in (line ream after installation)

Camshaft bushing inner diameter

1.376 in – 1.377 in

Valve tappet OD

Valve tappet bore ID

Valve tappet clearance

.8125 in

.813 in

.0005 in

Piston installation

Arrow on crown pointing to rear (towards marine gear... yes - even though the piston is marked "Front"), vertical expansion slot on skirt facing away from camshaft, #1 piston at front (flywheel end), #2 piston second from front, etc

Piston skirt diameter (bottom of skirt near expansion slot at right angles to pin)

Note: pistons are not round when at room temperature because they are cam ground oval so they expand to round when at engine running temperature

Std: 2.560 in
.010 in oversize: 2.570 in
.020 in oversize: 2.580 in
.030 in oversize: 2.590 in

Idler gear

idler gear bushing bore ID: .988 in

Idler gear shaft
Note: the idler gear shaft is held in the bore in block with 2 allen set screws, one on top of the other. Remove the screws and then use a special puller to withdraw the shaft

idler shaft bore in block ID: .623 in
idler shaft section pressed in block OD: .625 in
idler shaft / section in block interference fit: -.002 in

idler gear shaft OD: .875 in

Idler gear bushing

bushing length: 1.0 in (grind flush with gear after installation)
bushing OD before installation in gear: 1.002 in (bushing interference press fit -.004 in)

installed bushing honed ID: .876 in
bushing to shaft clearance: .001 in
Note: to restore worn shaft grind undersize and hone new installed bushing to .001 in clearance

Oil pump drive end play

.001 in - .003 in

Distance from top of cylinder head spark plug thread to cylinder block deck

.980 in - 1.175 in

Distance from bottom of spark plug thread to cylinder head surface

.480 in - .625 in, average approximately .525 in

Cylinder head combustion chamber volume with piston at TDC (including spark plug hole)

40 cc - 51 cc, average approximately 50 cc

Cylinder swept volume + combustion chamber volume with piston at BDC (including spark plug hole)

313.5 cc, average approximately 314 cc

Maximum cylinder head warp

.006 in

Valve spring compressed length (full lift of camshaft lobe)

?? in

Valve spring installed height (with valve clearance)

?? in

Valve spring pressure at full lift

60 psi

Coil primary resistance

Internal ballast type: 3 - 4 ohm (standard 12 volt OEM Delco coil)
(Note: External ballast type (.5 - 1 ohm) is not necessary or recommended. If fitted an external ballast resistor (2 - 3 ohm) must also be installed in series.)

Starter solenoid current draw

Starter winding current draw

approximately 20 amps

approximately 150 amps

Starter Battery Specification

12 volt, minimum 90 - 125 ampere hours

Intake manifold vacuum

Idle: 16 in Hg
2,000 rpm under load: 14 in Hg

Exhaust system back pressure (measured at water injection point before water lock muffler)

<= 1.5 psi / 2 in Hg / 27 in H2O at rated rpm, top speed /  full load / wide-open throttle

Crankcase sump flow / pressure (indicating piston ring and valve guide combustion blow-by)

New engine: approximately .25 cfm / +0.5 in H2O / .036 in Hg / 0.018 psi at full speed / load
Worn engine: approximately .50 cfm / +1.0 in H2O / .072 in Hg / 0.036 psi at full speed / load

(Test pressure at valve cover breather tube with oil fill tube breather cap removed and oil fill tube blocked)

Cylinder leak-down test (indicating piston ring/cylinder and valve/valve seat leakage)

New/rebuilt engine: 15% - 25%
New/rebuilt engine after break-in: 10% - 20%
Used engine in good condition: 25% - 50%
Worn engine: 50% - 100%

(Test leakdown with engine hot and each cylinder at TDC)

Distributor rotor position @ TDC#1 (compression stroke)

#1 terminal at 09:00 viewed from front of engine (pointing to extrusion on distributor plate which fits into slot in cap and is also at 09:00)

Adjustments

Nominal Ignition timing

Stock Delco distributor:
Static: No advance = 0° BTDC / Full advance = 12° BTDC*
Dynamic: < 1,000 rpm = 2° BTDC / 2,000 rpm = 6° BTDC / 3,000 rpm = 12° BTDC*
*Note: factory specifications state full advance is 17°, but testing has shown the late model Delco distributor only advances 12° with standard weights. That is a another good reason to set the timing by slowly turning the distributor at full throttle while tied to the dock or at top boat speed to get maximum engine rpm, rather than assuming setting the timing to 0° BTDC with engine off will be accurate at full cruise speed. (The other reason to set the timing at full speed is because optimum timing varies with elevation, fuel octane rating, compression ratio, and carburetor jet spec.)

Atomic Four Engine Service "Hi-Torque" distributor (for direct drive engines only):
Dynamic: 1,000 rpm =  3° BTDC / 2,000 rpm = 6° BTDC - maximum advance

Valve tappet clearance

Stock camshaft:
Intake: .008 in hot, .010 in cold
Exhaust: .010 in hot, .012 in cold

Atomic Four Engine Service/Colt Cams "Hi-Torque" camshaft (for direct drive engines only):
Intake: .013 in hot, .015 in cold
Exhaust: .013 in hot, .015 in cold

Distributor dwell

Prestolite: 38°
Delco: 31°  - 34° 

Distributor points gap

Prestolite: .018 in - .020 in
Delco: .025 in
magneto: .014 in - .018 in

Spark plug gap

.035 in

Alternator belt tension (50 / 60 / 70 / 90 amp alternator with 3/8" wide belt)

new belt tension: 90 lb  (3/8 in depression between centres, pressing firmly with one finger until  the belt can just be turned sideways))

old belt tension: 70 lb

Oil pressure relief valve

35 psi at 2,000 rpm (or top cruising speed) hot

Paragon marine gear forward clutch pack

approximately 30 - 50 ft lb torque on shift shaft to force 3 pressure plate arms over bulge in throw-out bearing

Paragon marine gear reverse band

with gear lever in neutral tighten reverse band adjusting nut (holes in flats so a nail or pick can be used as an adjusting tool) until output shaft turns stiffly, then back off 1 - 2 rotations until shaft turns freely

Walter V drive tapered roller bearing clearance

input & output shafts tapered roller bearing clearance (cold): No preload ->.005" endplay on both shafts.

Note: adjust clearance at bearing flange caps:  Use extra bearing flange cap gaskets to increase clearance & round metal shims under bearing flange caps pressing on outer bearing race to reduce clearance.

Lubricants

Lubricating oil

Quantity:
Depending on installation angle of engine: 4 litres – 6 litres to full mark on dip stick (different dip sticks for direct drive/reduction drive (UJ / UJRD) and V drive (UJVD).

Type:
non-synthetic

API rating:
SG or SG equivalent

Viscosity:
Average temperature under 10°C / 50°F: SAE 10-40
Average temperature over 10°C / 50°F: SAE 20-50

Atomic Four Engine Service recommends only the motorcycle oils listed below in order to prevent forward clutch slip while providing maximum engine protection and optimum piston ring break-in. All the oils listed are available in both 10-40 and 20-50 viscosities.
Castrol Grand Prix 4 Stroke Motorcycle Oil
Shell Advance SX4 Motorcycle Oil
Valvoline 4-Stroke Motorcycle Oil
Belray EXL Motorcycle Motor Oil
Pennzoil Motorcycle Motor Oil
Quaker State 4-Cycle Motorcycle Engine Oil

Notes: Never use ANY oil additives. Do not switch brands.

V Drive Oil

.5 litre of SAE 80W90 hypoid oil (SAE 30 motor oil is also acceptable)

Water pump grease

Waterproof grease (white lithium, boat trailer wheel bearing grease, Lubriplate #115, or any good quality water resistant grease)
Note: waterpump gease does not stop the pump from leaking, it lubricates the bearing and seal. If the pump leaks it needs to be rebuilt.

Fastener Torque

Note: Lubricate threads and base of bolt head / nut with oil

Cylinder head stud nuts

35 ft lb, 3 stages: 10 lb ft / 25 lb ft / 35 lb ft (apply engine oil to threads and bottom of nuts), use shop manual torquing diagram or torque from centre of head out to ends. Retorque to 35 lb ft after 1 hour of running & cool-down.

Note: install cylinder and manifold studs into block with gasket cement or Loctite "red", and coat sides of studs with Never-Seize to prevent studs from seizing to head or manifold

Connecting rod bolt nuts

25 lb ft 

Flywheel stud nuts

35 lb ft 

Main bearing stud nuts

60 lb ft 

Manifold stud nuts

30 lb ft 

Spark plugs

30 lb ft (apply Never-Seize to threads)

Valve cover cap screws

20 lb in (with cork gasket)

Flywheel cover cap screws

85 lb in

Idler Gear stud nut

40 lb ft  (use purple Loctite)

Oil pump cover screw

7 lb ft (use blue Loctite & new "high-collar" lock washers))

Oil pan & block 5/16" cap screws

14 lb ft 

Transmission output shaft flange nut

60 lb ft (use blue Loctite & tab lock washer)

Crankshaft channeled gear retaining bolt

30 lb ft (use blue Loctite)

Service Parts

Spark plugs

Specified plug:
Champion #871 (old number RJ8C)

Recommended plug (slightly hotter, helps stop plug sooting):
Champion #592 (old number RJ12C)

Other plugs used (nominal Champion RJ8C equivalents):
NGK BR6S [not recommended - too cold]
Bosch W7EC, W7E, W9EC
AC R43, R44, R45
Autolite 304
Motocraft A3C, A3CU, A3X, A5X, A5CU
Denso W20S, W20SR-U, W20S-U

Contact Breaker (points)

Prestolite Distributor:
Echlin CS-709
Neihoff AL-533

Delco Distributor:
Delco D108P
Echlin CS788P
Niehoff DR6-HV

Capacitor (Condenser)

Prestolite Distributor:
Echlin AL38
Neihoff AL-38

Delco Distributor:
Delco D203
Echlin RR-176
Niehoff DR-22
Borg Warner G126

Rotor

Prestolite Distributor:
Echlin AL58
Neihoff AL-54

Delco Distributor:
Delco 423R
Echlin RR-182R
Niehoff DR-53A
Borg Warner G152

Cap

Prestolite Distributor:
Echlin AL91
Neihoff AL-79A

Delco Distributor:
Delco D322R
Echlin RR-181
Niehoff DR-74

Coil

for both Prestolite or Delco 12 volt Distributor:
Prestolite ?
Delco 070FLX
Echlin IC64
Niehoff DR-180 (standard)
Niehoff UN171 (epoxy heavy duty)
Standard UC15
Borg Warner E40BAP
UAP Napa IC64SB (this is probably a US part number... Canadian UAP Napa part numbers are often different

Specifications:
Primary Winding: 12 volt, internal resistor: 3 - 4 ohms

Distributor

Prestolite distributor:
IGW4116C / 60032E1X

Delco distributor:
1112446 - 2G11/6C16/3HI8

HT Leads (spark plug wires)

Atomic Four Engine Service A4HTset

Specifications:
Wire type: 7 mm high tension wire, carbon core resistor type
Wire terminals & lengths (add 1 in to length when cutting cable for custom wires to allow for stripping insulation for terminal installation):
Coil/distributor lead: straight terminals, 9 in
#1 plug lead: straight distributor terminal/90 degree plug terminal, 16.5 in
#2 plug lead: straight distributor terminal/90 degree plug terminal, 13.5 in
#3 plug lead: straight distributor terminal/90 degree plug terminal 10 in
#4 plug lead: straight distributor terminal/90 degree plug terminal 8 in

Generator/Alternator

Prestolite 6 or 12 volt generator:
obsolete - substitute Delco alternator below:

Motorola alternator:
Motorola MR12N4510 - type B (Voltage Regulator 8RG 2010A), 35 amps, negative ground, internal voltage regulator, 3/8" pulley with a diameter of 2 1/2"

Alternator upgrade:
Note: Maximum size which can be used with the existing alternator drive pulley on the auxiliary drive is 90 amps. Some 90 amp alternators charge so aggressively when the batteries are low that they can cause the belt to slip and subsequently burn... 70 amps is a safer size maximum for the stock 3/8" pulley. The existing auxiliary drive pulley can be machined wider to fit a 1/2" belt, but there isn't room to fit a double pulley on the alternator and still clear the distributor, and because the auxiliary drive alternator pulley is integral with the auxiliary drive flange it is difficult to fit a different pulley on the auxiliary drive anyway. Theoretically the alternator output should not be larger than the maximum + reading of the ammeter, so the ammeter will not be damaged when the alternator is generating maximum amperage. If the alternator output exceeds the ammeter maximum do not replace it with a larger ammeter, replace it with a voltmeter, which is the preferred choice for modern engines and automobiles... and is much simpler to install.

Specification: Specify a 12 volt marine rated alternator (enclosed, sealed brushes) with negative ground, integral solid state adjustable voltage regulator, a clockwise (RH) fan, a single 2" foot mounting configuration, and a 3/8" pulley (or 1/2" if the auxiliary drive pulley has been machined to 1/2" - see above) with a diameter of 2 1/2" or 3", rated at 35, 55, 70, or 90 amps.

Starter

OEM Prestolite:
MBG4129 (solenoid Wilson 60-01-6029)

OEM Delco:
Delco 1107679
Wilson 91-01-3736 (starter drive Wilson 61-01-3455, solenoid Wilson 60-01-3541)
Aqua Power 2826

Specifications:
12 volt (early models were 6 volt), negative ground, marine type

Note: Prestolite and Delco starters use different flywheel ring gears

Alternator belt (automotive type belts are used to fit the automotive pulleys on alternators)

Dayco: 11A0635 (10A0635 also used)
Gates: 11A0635 (10A0635 also used)

Engine coolant hoses

1/2" id automotive heater hose & stainless steel gear clamps

water pump outlet to block water plate "T": 10.5 in
block water plate "T" to thermostat housing inlet 90° fitting: 6.5 in
thermostat housing outlet to manifold inlet: 4.5 in

Temperature Sensor (electric)

SW 280ED-F
General Marine GEN26630
Aqua Power AP1943
Faria FAR90405

Specification:
1/2" NPT, 12 volt to match control panel temperature gauge(s)

Oil Pressure Sensor
(electric)

SW 279A
General Marine GEN24880
Faria FAR90512

Specification:
1/8" NPT, 12 volt to match control panel oil pressure gauge(s)

Seawater pump belt (pump over starter)

Dayco: 11A770
Gates: 11A770

OEM flange mounted water pump - gear driven off PTO unit
(Used as sea water pump when engine is raw water cooled with no heat exchanger. When heat exchanger is fitted used as engine coolant pump, except when electric pump is fitted, when it is used as sea water pump and electric pump is used as an engine coolant pump.)

After 1969 OEM pump was Oberdorfer 202M3 (2 US gal / minute, 15 psi max @ 1,000 rpm)
Cam thickness .105 in (half cam)

Note: 202M3 is usually upgraded to Oberdorfer 202M7 when rebuilt or replaced by installing M7 cam. M7 was used on older diesels
Oberdorfer 202M7 (3 US gal / minute, 20 psi max @ 1,000 rpm)
Cam thickness: .150 in (full cam)

Impellor:
Oberdorfer B6593
West Marine 241044
Globe 815
Barco 815
Sherwood 295628

Sea water pump used with heat exchanger
(Belt driven off pulley on end of crankshaft at flywheel, driven directly off end of crankshaft, belt driven using alternator drive belt, or electric motor pump)

Sherwood R30G / Jabsco 2620-1001 / Oberdorfer 201M (or any pump with a continuous capacity of 20 litres /  minute @ 1,800 rpm and a rpm rating of at least 3,000 rpm)

belt type & size: FHP (fractional horsepower) type 4L (1/2") belt (not automotive type used on alternator) is used so as to match same type FHP pulleys used on water pump & crankshaft

water pump / crankshaft pulley ratio: 1:1

Carburetor Jets

1948 – 1968 Zenith 61-M2AE7:
main jet #24, Zenith C52-6-24 & adjustable main jet needle assembly
idle jet #10, Zenith C55-6-10 (.019 in drill size)
well vent jet #22, Zenith C77-18-22 (.043 in drill size)
main discharge nozzle #50, Zenith C66-26-1-50

1969 – 1984 Zenith Bendix 68-7 13355:
venturi #16
float needle & seat #25
main jet #21, Zenith C52-7-21 (.041 in drill size)
idle jet #12, Zenith C55-22-12 (.023 in drill size)
well vent jet #21, Zenith C77-18-21 (.041 in drill size)
main discharge nozzle #55, Zenith C66-114-4-55 (3 x .039 in drill size)
idle bleed hole, fixed plug (.039 in drill size)

Trouble-Shooting

No-Start

1. bad coil - replace
2. bad points - gap/replace (grease distributor cam with tiny amount of high melting point grease)
3. defective/corroded coil primary wire or ignition switch
4. blown head gasket - replace
5. water/dirt in fuel: carb/pump/tank - fuel tank condensation, leaking tank filler cap (no "O" ring)
6. dead battery - accessories left on with engine off
7 dead battery - defective alternator
8. vapour lock in fuel line - relocate electric pump to below carb, cool electric pump and fuel line
9. fouled plugs (especially NGK B6) - replace with Champion 592

Low power

1. running on 3 cylinders - repair
2. fuel starvation - repair
3. tight prop shaft packing gland - repair
4. blocked exhaust - repair
5. incorrect ignition timing - adjust

Low speed miss

1. incorrect carb adjustment - repair
2. water in fuel - repair
3. carb or manifold air leak - repair
4. bad condenser - replace
5. dirty/plugged flame arrester
6. flooding carb - check fuel pump pressure

High speed miss

1. fouled spark plugs (especially NGK B6) - replace
2. defective coil - replace
3. defective high tension leads/distributor cap/condenser - replace
4. water in fuel passed through to carb & blocked main jet - clean carb & fuel tank & filters
5. plugged fuel filter - replace
6. plugged fuel tank vent - repair
7. running on 3 cylinders - repair engine