Yamato 302 User manual

302
YAMATO MOTOR CO. LTD.
Ota • Japan
November 2012
M O D E L
M A N A L

YAMATO E ROPE
www.YamatoRacing.co.uk

I N D E X
FORWARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
I GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
II OPERATION OFMOTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1. Precautions prior to starting motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. How to start motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. If hull fails to plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Things to observe and adjust during operation. . . . . . . . . . . . . . . . . . . . . . 4
5. How to stop motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Care of motor after use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Submerged motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
III DISASSEMBLY, INSPECTION AND REASSEMBLY . . . . . . . . . . . . . . . . . . . 7
1. Power Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
A. Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
B. Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
C. Reassembly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2. Magneto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
A. Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
B. Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
C. Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3. Carburettor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
A. Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B. Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
C. Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4. Gearcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
A. Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
B. Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
C. Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
IV TRO BLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
V CROSS SECTION OFMOTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
VI PERFORMANCE C RVE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
VII SPECIFICATION FORMODEL 302 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

FO RWARD
The Yamato model 302 is a 396cc / 24. 2 cubic inch stock racing engine. Like it's
predecessors - the models 80, 102 and 202 - this motor was developed specifically
for use in the multi-billion Yen parimutuel boat racing industry in Japan. These
motors are required to run heats, day after day with perfect reliability at racing
speeds. Therefore, like engines in commercial aircraft, they have been “over-
designed” in relation to the job they perform.
Essentially, this 33 h.p. engine is a strong twin which has been detuned by use of a
low compression head, mild-port timing and one small carburettor. When putting out
33 h.p. at 6,600 rpm the 302 is just Ioafing. No wonder the Yamato has become the
biggest and most popular class in UIM and APBA racing. Compared with other stock
powerheads which vibrate, crack and fail at racing speed these engines are made
virtually "Bullet Proof". Ask any racer that owns a model 80, 102 or 202. You too will
be convinced that the model 302 is the best buy today on the motorboat racing
scene.
– 1 –

I. GENERAL
From the manufacturer of Yamato Motors, we sincerely thank you for selecting the
Yamato model 302 racing outboard motor. To operate this outboard motor safely and
efficiently, please read this instruction manual carefully. It will help you get a good
understanding of the precautions in operation and how to service and maintain it for
maximum performance, reliability and extended life.
As in most form of racing, there is risk which may bodily injury. The Yamato Motor
Co. suggest that extreme caution be taken whenever you operate this motor and
cannot be responsible or liable for any mishaps that may occur while operating this
motor.
– 2 –

II OPERATION OF MOTOR
II - 1 Precaution Prior to Starting Motor
A. Check thumb screw handles to be sure it is tight.
B. Check for oiI in gearcase.
C. Check condition of high tension wires and spark plugs. Ensure it is firmly tightened.
D. Check fuel in tank to be sure sufficient quantity remains for the anticipated run.
E. Check for proper engine height and angle.
F. Check steering system for proper installation and tightness.
G. Check throttle system for tightness. Be sure it is free from binding and free to
return to closed position.
H. When the motor is coId, it is suggested that the motor be warmed up prior to
launching. For safety sake, we suggest that the propeller be removed.
Caution: Remove spark plug wires whenever propeller is removed or installed.
II - 2 How to Start Motor
A. Set fuel cock in vertical position, air vent (located on fuel cap) opened, main needle
opened 1-1/2 turn, and spark plug wire attached to the appropriate plug.
B. Check float pin. Approximately 8mm (5/16") should be protruding above carburettor
float cover.
C. Set timing handle about midway of travel.
D. Pull choke lever (for cold motor only). See figure1.
E. On pre-heated motors, do not use choke. Instead, open throttle approximately 1/8
to 1/4. However for cold motor DO NOT OPEN THROTTLE.
F. Wrap starter rope 1-1/2 to 2 turns on starter pulley.
G. Pull starter rope vigorously, repeat if necessary.
H. As soon as motor starts, push choke in. See figure 2.
I. If motor starts but stops immediately, it may or may not be necessary to reset
choke.
J. Repeat step G and H.
. After motor starts, shift timing handle all the way to the right (exhaust side).
L. Increase motor RPM.
– 3 –

M. For safety reasons, we suggest that the air idling screw be set all the way in and the
throttle stop backed-off completely so that the motor will not continue to run if the driv-
er is thrown out of the boat.
Figure 1 Figure 2
II - 3 If Hull Fails to Plane
A. Stop motor after 30 seconds.
B. Check transom height and angle.
C. Check for foreign object around propeller and lower unit.
D. Check for damaged around / or wrong propeller.
E. Check motor. If motor lacks power, see trouble-shooting chart.
II - 4 Things to Observe and Adjust During Operation
A. Be sure timing lever (Magneto #1) is in full advanced position.
B. Open throttle for maximum power.
C. Adjust high speed main needle (Carb #16) for for maximum power.
D. Check water outlet. Be sure it is not steaming.
E. Check RPM (if tachometer is fitted). Do not exceed 8,000 rpm.
F. Listen for any unusual noise.
II - 5 How to Stop Motor
A. Release throttle lever.
B. If kill-switch is installed, use it to stop motor.
C. Alternate method of stopping motor is to shift timing lever toward the left (intake side).
– 4 –

II - 6 Care of Motor After se
A. Wipe spilled gasoline with clean rag.
B. Wipe water, around powerhead.
C. If motor has been used in salt water, flush motor internally as well as externally with
fresh water. CAUTION: Do not tip motor upside down. Water can enter the exhaust
port and can cause serious damage.
D. CAUTION: When laying motor on its side, be sure the exhaust side faces down.
II - 7 Submerged Motor
A. If motor, is submerged in water for any reason, take the following action immediately:
1. Remove propeller.
2. Remove spark plug and cylinder head (remove cylinder head only when sub-
merged at high speed). Cylinder head gasket is often bIown due to hydraulic ham-
mer. The gasket acts as a fuse which minimises further internal damage.
3. Turn motor by hand. If complete revolution is possible without any bind, complete
the following:
a. If motor has been submerged in salt water, flush motor with fresh water through
carburettor while turning motor slowly. CIean exterior parts with fresh water.
b. Remove starter pulley and coil plate assembly (see par III-2). Flush with clean
fresh water. Clean and dry all electrical parts. Reinstall starter pulley only.
c. Drain fuel tank, fuel line and carburettor.
d. Set motor with cylinder head facing down.
e. Crank motor several times.
f. Turn motor so that exhaust-side is facing down.
g. Repeat step e.
h. Repeat step d.
i. Crank motor. Repeat step dthru huntiI all water is expelled.
j. Flush with fresh mixture of petrol and oil.
k. Repeat step dthru h until most of the petrol and oil mixture is expelled. Wipe
all petrol and oil that may have spilled on motor.
I. Reassemble magneto assembly.
– 5 –

– 6 –
m. Attach high tension wires to spark plug. GROUND spark plug.
n. Pull starter pulley and check spark plug. Both plugs must be firing.
o. Reassemble (except propeller), refuel and run motor, for 30 seconds at intermediate
speed.
p. Replace propeller. CA TION : Remove spark plug wire when installing or removing
propeller.
q. Install on hull and run at least ten minutes at half throttle.
4. If motor binds when turned by hand, internal damage such as bent connecting rod, bent
crankshaft, crankcase and/or fracture in cylinder may have occurred. Remove as much
water as possible by following step 3-a thru 3-i. Wash and coat internal and external
parts with oil. Complete disassembly is recommended.

– 7 –
III DISASSEMBLY, INSPECTION AND REASSEMBLY
III - 1 POWER NIT
A. Disassembly
1. Remove magneto assembly (see magneto section).
2. It is not necessary to remove fuel tank. However, for the beginner, it will be easier
to work without it.
3. Remove carburettor.
4. Remove intake manifold assembly.
5. Remove reed valve assembly, exhaust flange, cylinder head.
6. Remove power unit by removing six 8 mm nuts using 12 mm box wrench or socket.
7. Separate power unit from lower unit.
8. Remove six 10 mm nuts using 14 mm box wrench to remove cylinder block.
CAUTION: Do not pry with screwdriver or other sharp tool.
9. Remove piston pin clips.
10. Remove piston pin.
11. Remove piston.
12. Remove three 6mm bolts holding lower bearing case assembly (P-18). It is not
necessary to remove tail flange assembly except when replacing oil seal.
13. Remove flywheel and key.
14. Remove four 6 mm bolts holding upper bearing case assembly (P-7).
15. Split crankcase by removing 8 nuts and 2 socket head bolts using 12 mm socket.
16. Split crankcase assembly by tapping with soft hammer. CAUTION: Do not pry with
screwdriver or other sharp tool.
17. Remove crankshaft.
18. Inspect lower bearing assembly without removing from crankshaft. If bearing is
defective, use special tool, Puller-bearing case lower, part # 102-809-0080.
CAUTION: Remove clip (P-24) prior to removing lower bearing assembly.
19. Remove clip (P-17) which holds split sleeve, centre bearing (P-15). CAUTION:
Slight discolouration of center bearing is not detrimental to the life of this bearing.
20. Clean all parts in solvent. Scrape-off carbon and gasket residue.

– 8 –
B. Inspection
1. Slight scratches on cylinder wall is permissible. Hone if necessary.
2. Replace piston rings if gap exceeds 0.812 mm (0. 032").
3. To check crankshaft, remove all bearings. Place "V" blocks on surface plate.
Support crankshaft ends on "V" blocks. Check by placing dial indicator on center
bearing surface while turning crankshaft. Maximum crankshaft deflection permissi-
ble 0.03 mm (0.0012").
4. Check upper and lower bearing for pits, excessive end play and wear.
5. Maximum bore wear 66.08 mm (2.602").
6. Minimum piston diameter 65.92 mm (2.595") measured at piston skirt, thrust side,
14 mm (9/16") above bottom.
C. Reassemble in reverse order with the following precautions.
1. Lubricate all bearings.
2. When placing crankshaft in crankcase, be sure knock pin (P-64) fits into split
sleeve of center bearing (P-15). Center bearing clip faces up. See figure 5.
3. After placing crankshaft in crankcase, install two 6 mm bolts on upper bearing
case assembly and one 6mm bolt on lower bearing case assembly on to
crankcase. See figure 3 and 4.
4. Use gasket sealer to seal crankcase mating surfaces.
5. Install two remaining bolts to top and one to lower bearing case. Torque all 6 mm
bolts 5.9 ~ 8.8 Nm (60 ~ 90 kg cm / 4.4 ~ 6.5 ft lbs).
6. Install remaining 8mm nuts and two bolts on to crankcase.Torque all 8 mm bolts
and nuts 20 ~ 24 Nm (200 ~ 250 kg cm / 14 ~ 18 ft lbs). See figure 6.
7. Install piston. Piston has an arrow stamped on head. This arrow must be pointed
up. Centre piston pin. Install piston clips.

8. Install piston rings. The side that faces cylinder head is marked with a “T”.
9. Be sure that cylinder block and crankcase is flush at bottom. Torque cylinder to
crankcase nut 30 ~ 34 Nm (300 ~ 350 kg cm / 22 ~ 25 ft lbs). See figures 7
and 8.
– 9 –
Figure 3 Figure 4
Figure 5 Figure 6

10. Be certain that exhaust pipe is flush with lower unit. See figure 9.
11. Torque cylinder head 20 ~ 24 Nm (200 ~ 250 kg cm / 14 ~ 18 ft lbs). See figure
10 for proper sequence. CAUTION: It is of utmost importance that all bolts and
nuts be torqued as specified. Over-tightening can cause distortion with notice-
able loss of power.
– 10 –
Figure 7 Figure 8
Figure 9 Figure 10

– 11 –
POWER NITGRO P

POWER NITGRO P
– 12 –

III-2 MAGNETO
A. Disassembly
1. Remove starter pulley bolt (P-67) and washer (P-82).
2. Remove starter pulley (P-28).
3. Remove key (P-98).
4. Remove four clamp plate nuts (M-42) washers (M-20) and clamp plates (M-41).
5. Remove coil plate assembly (M-1). Tap with soft hammer to lift up.
See figure 11.
6. Remove flywheel nut (M-46). Use special tool 102-809-0100. Clamp flywheel.
See figure 12.
7. Remove flywheel (M-44) using special tool 102-809-0200. See figure 13.
8. Clean all parts in solvent. Wipe dry or blow with air.
Figure 11 Figure 12
Figure 13
– 13 –

B. Reassemble in reverse order with following precaution.
1. Lubricate inside of coil plate assembly with grease.
2. Insure that flywheel key is seated properly.
3. Use clamp flywheel - special tool 102-809-0100 - when tightening flywheel. Tighten
54 ~ 63 Nm (550 ~ 650 g cm / 40 ~ 47 ft lbs).
4. Clamp plate (M-41) has one side protruding. This side faces up.
5. When setting ignition timing, spark advance lever can be adjusted by moving bolt
(P-72). Use dial indicator thru spark plug hole. Rotate pulley to mark (red line) on coil
plate assembly. Spark plug of #1 cylinder should spark when inscribed mark on
pulley on coil plate assembly. See figure 14.
C. Specification
1. Ignition timing when using dial indicator in spark plug hole 0.200 ~ 0. 250
(5 ~ 6.6 mm).
2. Spark distance:
min 0.24 (6 mm) / 500 rpm
min 0.40 (10 mm) / 3000 rpm
3. Fly wheel nut torque : 54 ~ 63 Nm (550 ~ 650 g cm / 40 ~ 47 ft lbs)
4. Pulley bolt torque : 20 ~ 24 Nm (200 ~ 250 g cm / 14 ~ 18 ft lbs)
III-3 CARB RETTOR
A. Disassembly
1. Remove 2 Phillip screws (C-45) from float cover.
2. Remove nut (C-9).
3. Remove banjo (C-8).
4. Float assembly can be removed from top. CAUTION: Do not bend needle.
– 14 –
Figure 14

– 15 –
MAGNETO GRO P

– 16 –
CARB RETTOR GRO P

– 17 –
5. Remove spring plate (C-17).
6. Loosen holder (C-12).
7. Remove main needle (C-16) assembly.
8. Remove plugs (C-36, 28) and pilot screw (C-38).
9. Remove jet (C-27, 30, 31).
10. Clean body and all parts in clean solvent.
11. If extremely corroded or dirty, soaking in commercial carburettor cleaner is recom-
mended.
B. Inspection
1. Inspect float needle for straightness.
2. lnspect float needle contact.
3. Inspect all passage ways and jets for obstructions.
C. Reassemble in Reverse Order
CAUTION:
1. Check throttle butterfly for smooth movement and proper return.
2. Set float level to 29 mm. Measure from tip of float pin to top of float. See figure 15.
Figure 15
3. Do not misplace main air jet, (C-30) and slow air jet (C-31). Main air jet has an I.D. of
1.5 mm (0.059”). Slow air jet (C-31) has an I.D. of 0.9 mm (0.036”) and is located
behind above jet.
4. Adjust link bar (P-87) only at closed throttle. Be sure throttle butterfly closes fully and
smoothly.
5. Turn pilot screw clockwise to its full and reverse 11/4turn for standard.