LONCIN YF300 User manual

1
Foreword
The types of motorcycles increased day by day due to new structures
and new technologies are adopted. For users and maintainers knowing
well about the maintenance, adjustment and repair technologies of
LX178MN engine, we made this maintenance manual for more
convenience and better guidance for users and maintainers of Loncin.
All the data, diagrams, informations, performance targets are the latest
when the manual is printing. Loncin motor co. ltd. reserves the right of
revising the manual at any time without notification in advance. All
rights reserved by Loncin motor co. ltd. for any parts of this manual,
and no reprint is allowed before agreed by Loncin.

2
Directory
1 .Summary............................................................................................3
2 .Lubrication system..............................................................................7
3 .Checking and adjustment..................................................................10
4 .Fuel system.......................................................................................13
5 .Cooling system..................................................................................16
6 .Cylinder and air valves......................................................................18
7 .Cylinder body and piston...................................................................28
8 .Clutch component..............................................................................33
9 .Gearshift system................................................................................38
10 Magneto and electrical starting component.....................................40
11.Crankshaft and transmission system................................................44
12.Fault diagnosis..................................................................................50

3
1
Summary
Precaution in maintenance Standard torque
Main technological parameters for performance Periodic chart for maintenance
Precaution in maintenance
1. Spare parts, lubricant and other auxiliary material adopted should be agreed or
recommended by Loncin. In case selected material failed to meet demands of Loncin
specification and requirement, the motorcycle may damage.
2. Washer, seal parts and split pin need to be replaced when re-intallation after
disassembly is needed.
3. Bolts and nuts should be fastened by the sequence of diagonal cross, and reached
stipulated torque by turning 2～3 times.
4. Flammable cleaning fluid for parts’washing is not allowed. Spread lubricant on
movable surface of parts before installation.
5. Inspect and confirm correct assembly after installation, check by means of turning,
moving and operation.

4
Technological parameters for main performance
Items
Type
YF300
Type
LX178MN
Style
Single cylinder, 4 stokes, standing type engine,
water cooled, 4 air valves, double OHV
Main
parameters
for
performance
Max. power and its
rotation speed
(19.3±5%)kW/(8500±1.5%)rpm
Max. torque and its
rotation speed
（24.5±5%）N·m/（7000±1.5%）rpm
Min. fuel consumption
≤340 g/km·h
Min. steady rotation
speed of idling
（1500±150）rpm
Main
parameter
for structure
Cylinder bore
78mm
Piston stroke
61.2mm
Total displacement
292.4ml
Compression ratio
11.0：1
Air intake
OHV
Ignition
CDI
Lubrication
Pressure and splash
Cooling
Water
Transmission
device
Type of clutch
Manual operation clutch, wet and plates
Gearshift
International gearshift
Primary ratio
2.864
1st gear
3
2nd gear
2
3rd gear
1.5
4th gear
1.25
5th gear
1.05
6th gear
0.905
Starting
Foot and electrical
Carburetor
Vacuum and diaphragm MV34-5A
Ignition advance angle curve or
working-set point
1700±200r/min when 0˚ ± 1˚
5000± 200r/min when 25˚ ± 1˚
Spark plug
Resistive B8RC
Lockage angle for air intake
valve
Open
BTDC 0°（Open is 1）
Close
ABDC 40°（Close is 1）
Lockage angle for air exhaust
valve
Open
BBDC 37°（Open is 1）
Close
ATDC 2°（Close is 1）
Brand of lubricant
15W/40-SE
Capacity of lubricant (mL)
1500±100mL
Net weight of lubricant (㎏)
34±1kg

5
Data of standard torque
Ref.No.
Parts name
Specification
Torque N·m
1
Spark plug
M10
15～20
2
Bolt on cylinder head cover
M6
8～12
3
Bolt for bracket of camshaft
M6
10～15
4
Fastening bolt of cylinder
body
M6
10～15
5
Fastening bolt for cylinder
head
M10
40～50
（Pre-fastening）
50～60
（Final-fastening）
6
Locking bolt for timing
driven sprocket wheel
M6
10～15
7
Fastening bolt of tensioner
M6
10～15
8
Bolt for oil tube
M8
10～15
9
Fastening nut of primary
driving gear
M12
90～100
10
Fastening nut of clutch
M12
70～80
11
Locking nut of impeller
M6
10～15
12
Controller valve comp. of
oil
M12
10～15
13
Fastening bolt of guiding
plate of ratchet
M6
8～12
14
Fastening bolt of rotor of
magnetor
M12
100～120
15
Fastening bolt of gearshift
drum plate
M6
10～15
16
Bolt of check plate
M6
10～15
17
Positioning bolt of gearshift
arm
M10
25～30
18
Oil drainage plug
M12
32～40
19
Pin axis of chain adjustor
M8
25～30
Except the key torque data in table above, others follow the table below：
Ref.No.
Parts name and
specification
Torque N·m
1
5mm Bolt and nut
5～7
2
6mm Bolt and nut
10～15
3
8mm Bolt and nut
15～20
4
10mm Bolt and nut
25～35
5
12mm Bolt and nut
30～40
6
5mm Screw
3.5～5
7
6mm Screw
8～12

6
Periodic chart of Maintenance
Times
Items
Mileage chart km
500
2000
5000
10000
15000
Clutch-adjustment
√
√
√
√
√
Clutch friction
plate-checking
√
√
Spark plug-Cleaning and
clearance checking
√
√
√
√
√
Valve clearance-Checking
√
Air filter-cleaning
Each 1000km
Air filter-replacement
When damage
Carburetor-inspection,
adjustment
√
√
√
√
√
Spark plug cap-Cleaning
Each 4000km
Oil filter-Replacement
√
√
√
Oil-replacement
√
√
√
Sprocket wheel-checking
√
√
Coolant-replacement
Each 2 years
Heat radiator-checking
√
√
Fuel system-cleaning
√
√
√
√
√
Bolt, nut, washer-checking
√
√
√
Lubricant system-checking
√
√
√
√
√
Maintenance of motorcycle should be conducted according to chart above
Items in chart above should be done by Loncin service maintainer, in case of self-maintenance,
reference to chart above is also necessary.

7
2
Lubrication system
Notice of maintenance Replacement of lubricant filter
Troubleshooting Replacement of decompression valve
Lubrication system of engine Assembly and disassembly of oil
pump
Checking of lubricant …Inspection of oil pump
Replacement of lubricant Wash oil screen net
Notice of maintenance
This section introduce washing, inspection and replacement of lubrication system and its
parts. This work could be done without disassembly of engine, but oil drainage is needed
before that.
Troubleshooting
A. Fast oil consumption B. Dirt lubricant
1.Oil leakage of engine 1. Replace oil without following chart above
2.Abrasion of piston ring .. 2. Thread damage of oil filling port
3.Abrasion of guiding rod of air intake and exhaust valve
4.Abrasion or damage of oil drip pan
C. Abnormality of lubricant
1. Low level of oil
2. Blocked oil passage or filtering screen
3. Oil pump damage
Lubrication system of engine
Lubricant is important to performance and working
Life of engine, select according to stipulation,
Substituted by common oil, gear oil, and plant
Oil is not allowed.
This motorcycle use oil of 15W/40SE grade when
It left factory, in case other lubricant is needed
, its quality should reach grade of QE or SF,
Thickness should be selected according to

8
different region and temperature in right picture
Before oil replacement, drain off old oil in
Crankcase first, and then wash by washing kerosene.
Lubricant checking
In case engine just stopped running, waiting for minutes
is needed which makes oil reach the bottom of crankcase.
Lay engine vertically to ground and check through view
window 3,, and the level should be within upper and lower
scale line.
In case higher than upper line 1, drain out surplus oil
In case lower than low line 2, add more lubricant 1. Upper scale line
2. Lower scale line
3. Oil view window
Replacement of lubricant
Replace lubricant before it cooled down,
in this case, complete oil drainage in
crankcase could be ensured. Lay one oil plate
under engine, and screw off bolt A for releasing
oil. Check seal washer, and replace if damage is
found. Screw up bolt A and washer when old lubricant
completely released
Fastening torque：18N·m
Fill new oil and check its level.
Requirement for newly added oil:
Fill oil by 1.5L when new engine left factory;
Fill oil by 1.3L when oil need replacing and
without replace secondary oil filter.
Fill oil by 1.4L in case secondary oil filter
also need replacement.
Replacement of secondary oil filter
Remove the cap of secondary oil filter, and take
out the old filter. Replace by new oil filter and install
its cover.
Replacement of decompression valve
Remove right crankcase cover, and screw off
decompression valve A, and then install new
one and tightly screw up.
Torque for screwing up：15N·m

9
Disassembly of oil pump
Remove right crankcase cover first,
Remove screw A and oil pump B
Assembly of oil pump
Clean up metal and dirt on screen A
Spray lubricant on oil pump needs installation.
Confirm positioning pin B and seal ring C and
filtering screen already installed.
Finally fill oil and fasten the screw.
Disassembly of oil pump comp.
Remove washer C and elastic washer B,
and then remove axis of oil pump.
Screw off screw E of oil pump cover,
and remove cover A.
Remove rotors of inner and outer.
Inspection of oil pump
Open oil pump and then check pump body A,
outer rotor B, inner rotor C and cover D, change
each damaged part or complete oil pump in case
any damage is found.
Washing of oil screen
Remove right crankcase, and take out oil screen
and wash up. No gasoline washing is allowed.
Check damages, replace if damage is found.
Install oil screen back to crankcase and assemble
right crankcase.

10
3
Checking and adjustment
Notice in maintenance Spark plug
Technological requirement Valve clearance
Carburetor idling Timing ignition
Test for cylinder pressure
Notice in maintenance
This section introduce checking and adjustment of YF300 engine and its each
part, and also introduce technological requirement when it is in checking and
adjusting.
Technological requirement
1. Engine
Recommended spark plug B8RC
Clearance of spark plug 0.6～0.7
Clearance of valves Air intake valve：0.1～0.19
Air exhaust valve：0.15～0.24
Lead angle for ignition 1700±200r/min when 0˚ ± 1˚
5000± 200r/min when 25˚ ± 1˚
Rotation speed in idling 1500±150r/min
Pressure of cylinder ≥1200kPa
Spark plug
Remove spark plug by its sleeve, and visually
check damages on insulator of spark plug, and
also check ablation on electrode, and replace
is needed in case damage is found.
Check clearance between electrodes by feeler
gauge. Clearance between spark plug and electrode
should be within 0.6～0.7mm.
Carefully adjust clearance. And then erase carbon

11
buildup and dirt by steel wire or spark plug washer.
Screw up spark plug by hand first and then by sleeve
when it is assembling, and then screw up cap of spark
plug.
Valve clearance
Caution：Engine should be under cold condition
when valve clearance is in adjustment.
Remove cylinder head cover, view-hole cap
and its decorative cover A.
Correctly aline the timing mark.
Turn crankshaft anticlockwise, aline timing mark
(T shaped line) on rotor and groove on view-hole
cap through viewing by view-hole on left front
crankcase cover, and at this moment, the piston
is at upper stopping point of compression stroke.
Timing scale line “—”on camshaft should be parallel
with joint surface on cylinder head.(Note: Air intake cam
corresponds scale line of “IN”while air exhaust cam of
“EX”.
Checking of valve clearance
Insert feeler gauge between camshaft and tappet rod for checking valve
Clearance.
Clearance of air intake valve：0.1～0.19
Clearance of air exhaust valve：0.15～0.24
Adjustment is needed when clearance is incorrect.
Adjustment of valve clearance
Remove bracket of camshaft, and then camshaft A,
tappet rod B, and finally remove adjustment washer
C; Select a new adjustment washer according to
valve clearance.
When installing adjustment washer, the side with mark
face to tappet rod of valve; and then install tappet rod
and camshaft, ensure position of timing; Measure valve
clearance after adjusted; In case re-adjustment is needed,
repeat adjustment according to steps above until it is correct;

12
Install bracket of cam and cylinder head cover.
Idling adjustment of carburetor
Note：Check and adjust idling speed of
Carburetor after all other performance
of engine reached stipulation range.
Engine should be under hot condition when it
is in adjustment, and motorcycle should be
supported by main stand, and turn adjustment
screw on plug
Idling speed：1500±150r/min。
Adjustment screw of idling speed
Pressure test of cylinder
Start engine for pre-heating,
and then turn off engine and remove
spark plug, and install pressure tube
B on installation position of spark plug,
and then install pressure meter A on
pressure tube B, completely turn on
choke and throttle, and finally turn on
starting motor for 4～6 times.
Note: Check air leakage on each joint
of pressure meter. Repeatedly start
engine until rise of pressure meter
stopped. Maximum data usually reached
after 4～6 times starting.
Pressure of cylinder：≥1200kPa

13
4
Fuel system
Notice in maintenance Adjustment for height of float
Trouble shooting Installation of carburetor
Disassembly for carburetor Adjustment for idling speed
Disassembly for float, float needle and injection nozzle
Notice in maintenance
Summary
1. Be careful when gasoline is in using, keep good air ventilation in working place,
and also keep far distance to spark and fire.
2. Pay attention to position of “Ｏ”ring when disassembling parts of fuel system, and
replace by new “Ｏ”ring when re-assembly.
3. There is oil drainage screw at the bottom of float chamber, and this screw could be
Loosened and drain off gasoline in float chamber
Troubleshooting
A. Engine could be ignited but unable to start C. High concentration of mixing gas
1. No fuel in fuel tank .1. Too high the fuel level in caburetor
2. No fuel entered carburetor 2. Air nozzle of carburetor blocked
3. Too much fuel in cylinder 3. Float seized ot float needle failure
4. Air filter blocked 4. Dirty air cleaner
B. Low concentration of mixing gas D. Unstable idling, stalling speed and bad rotation of engine
1. Nozzle of carburetor blocked 1. Incorrect idling adjustment
2. Breathing hole on fuel tank cap blocked .2. High concentration of mixing gas
3. Fuel filter blocked …… 3. Low concentration of mixing gas
4. Bad fuel flow in fuel tube 4. Low compression in cylinder
5. Float needle failure .5. Air filter blocked
6. Low fuel level in carburetor 6. Expired fuel
……..7. Impurity in fuel

14
Disassembly of carburetor
Close down fuel switch, and remove connection
of fuel tube, and then remove covers both sides
Loosen fuel drainage screw, and
drain off fuel in carburetor.
Loosen screw connects clamp of air intake tube
and carburetor.
Disassembly of float, float needle and nozzle
Remove cap of float chamber and its connective
Screw.
And then draw out pin of float arm. Remove
float and its needle.
Check abrasion or damage on contact surface
of float needle.
Replace float needle in case it is necessary.
Remove main jet, foam tube, main nozzle
and idling jet.
Caution: Keep in mind installation position
of screw and its turning times, or trouble will
be met in re-assembly.
Wash surface of carburetor, its holes and passage
by cleaning fluid, and then clean up dirt in passage
by compressed air, and then install idling jet, foam
tube, main jet by sequence of disassembly.
Insert pin of float arm after float and its needle installed.

15
Adjust the height of float
Measure the height of float by height gauge
first
Height of float D：17±0.5mm
A：Surface of end of float chamber
B：Needle of float
C：Float
Note: No pushing to needle is allowed when
Measure the float height.
When height adjustment is needed, slowly
change the angle of float arm, until end of
float arm precisely touched needle of float,
and float height could be also adjusted on
height gauge.
Installation of carburetor
After carburetor installed, adjust the
free moving distance of throttle lever
by adjustment device on throttle cable.
Free moving distance of throttle lever:
2～3mm
Adjustment for idling speed
Start engine and raise
its temperature to working condition, and adjust
throttle screw for raising idling speed to 1500±150r/min.
Repeatedly operate throttle lever for checking steady
acceleration and deceleration of engine.
Adjustment screw of idling speed

16
5
Cooling system
Notice in maintenance Disassembly of cooling pump
Troubleshooting Assembly of cooling pump
Notice in maintenance
Assembly and maintenance of cooling pump could be done only after its cover removed
No damage on two joint surfaces of cover of cooling pump is allowed.
Trouble shooting
In case there is failure in water cooling system, the engine may be overheated or
undercooled which bad for its performance, in this case, periodic maintenance and
troubleshooting for cooling system is necessary.
Coolant should be chosen according to different regions and temperature. The ice point of
coolant should be lower than its local lowest temperature, running or hard water for
substitution is not allowed due to water has cooling function only without functions of
antiscale, antifust, and raising boiling point, in this case, engine usually uses running and
hard water easily lead to rustiness on water pump shaft, scaling and bad heat radiation of
water passage, and overheating of engine.
Check coolant in water tank when engine is cold, in case much reduction is found, it
indicates there is coolant leakage, and further inspection for outside or inside leakage is
needed. View the color of oil could know the inside leakage of water cooling engine, in case
coolant entered oil, the oil may look milky white, under this situation, disassembly of engine
and inspection on parts related to water passage is needed, such as cylinder head, cylinder
body, gasket of cylinder head, and right crankcase.
Check outside leakage through viewing joints to cooling pump cover, heat radiator, auxiliary
water tank, and water pipes.

17
Disassembly for cooling pump
Before disassembly of cooling pump, lay
a box under engine first, and then screw
off drainage bolt of engine and drain off
coolant in engine.
Remove fastening bolt on cover of water pump,
and then remove pump cover.
Remove impeller of cooling pump.
Check damage on impeller, abrasion and
stretching scratch on static water seal
ring and water rotating ring. In case damage
is found, replacement is needed.
Check damage on end surface
of cooling pump cover. In case damage
is found, replacement is needed.
Installation of cooling pump
Press and install static water seal ring
on right cover.
Press and install water rotating ring on
impeller of water pump, whose surface
matches static ring faces outwards.
Tightly lock impeller
of cooling pump.
。
Locking torque of nut：10N·m
Install cover
of cooling pump(Note: Fasten two bolts on
positioning pin for ensuring smooth and
parallel joint)
Static water seal
ring

18
6
Cylinder head and valves
Notice in maintenance Disassembly of cylinder head Inspection for valve seat
Troubleshooting Break down cylinder head Inspection for valves
Disassembly for cylinder head cover Inspect valve and its guide tube Repair valve seat
Remove bracket of cam Inspect cylinder head Assemble cylinder head
Remove camshaft Inspect valve springs Install cylinder head
Inspect camshaft Replace guiding tube of valves
Install camshaft
Notice in maintenance
Summary
Engine must be disassembled when camshaft, cylinder head, and valve tappet rod is in
maintenance, and spread lubricant on camshaft and tappet rod when assembly is needed
for basic lubrication.
Size and specification for each part
Items
Standard data（mm）
Limits（mm）
Camshaft
Height of air intake cam
36.20～36.30
36.10
Height of air exhaust cam
36.17～36.27
36.07
Diameter of camshaft
22.967～22.980
22.94
Diameter of hole of camshaft
bracket
23.000～23.021
23.08
Clearance between
camshaft and bracket
0.020～0.054
0.15
Valves
Width of line of air intake
valve
0.7
0.45
Width of line of air exhaust
valve
0.8
0.5
Diameter of rod of air intake
valve
4.475～4.49
4.460
Diameter of rod of air
exhaust valve
4.455～4.470
4.440
Pore size of guiding tube of
air intake valve
4.510～4.522
4.59
Pore size of guiding tube of
air exhaust valve
4.510～4.522
4.59
Clearance between air
intake valve and guide rod
0.02～0.047
0.07
Clearance between air
exhaust valve and guide rod
0.04～0.067
0.08
Plate diameter of air intake
valve
28.9～29.1
/
Plate of diameter of air
exhaust valve
24.9～25.1
/
Clearance of
valves
Air intake valve
0.10～0.19
/
Air exhaust valve
0.15～0.24
/
Valve springs
Height of inner spring under
free condition
36.2
34.5
Height of outer spring under
free condition
41.1
39.4
Length of chain（20 links）
127.0～127.4
138.9

19
Troubleshooting
Low air pressure in cylinder：Blue smoke
1. valves 1. Abrasion of valves
Incorrect adjustment of valve clearance 2. Damage or leakage of oil drip pan
Poor seal of valves 3. Leakage of cylinder head gasket
Wrong timing of gas distribution 4. Wide clearance between piston rings
Crack of valve spring
2. Cylinder head Noisy
Poor connection between cylinder head and spark plug 1.Incorrect valve adjustment
Damage of leakage on cylinder head gasket . 2.Valve seized up or spring crack
Crack or sand hole on cylinder head 3. Camshaft worn out
3. Cylinder body, piston 4. Long timing chain
Wide clearance between piston rings or crack 5. Wrong timing of gas distribution
Pistion with crack or damage 6. Abrasion or damage on tensioner of timing chain
Big cylinder bore or with sand hole 7. Abrasion of timing sprocket wheel

20
Disassembly for cylinder head cover
Remove fastening bolt A on cylinder
head cover.
Remove cylinder head cover B.
Remove cam bracket
Remove cylinder head cover
Remove bolt connects bracket
Remove cam bracket
Removal of camshaft
Remove cylinder head cover
Remove tensioner comp. on cylinder
head and bolt on cylinder body
Remove bolt connects bracket
Remove cam bracket
Remove chain
Remove camshaft
Note：No timing chain drop into
crankcase is allowed.