MTD P61 Series User manual

Professional Shop Manual
P61/P65/P70 Series Vertical Shaft Engines
Second edition
MTD Products Inc - Product Training and Education Department
FORM NUMBER - 769-03354A
08/2008
NOTE: These materials are for use by trained technicians who are experienced in the service and repair of outdoor power
equipment of the kind described in this publication, and are not intended for use by untrained or inexperienced individuals.
These materials are intended to provide supplemental information to assist the trained technician. Untrained or inexperi-
enced individuals should seek the assistance of an experienced and trained professional. Read, understand, and follow all
instructions and use common sense when working on power equipment. This includes the contents of the product’s Oper-
ators Manual, supplied with the equipment. No liability can be accepted for any inaccuracies or omission in this publication,
although care has been taken to make it as complete and accurate as possible at the time of publication. However, due to
the variety of outdoor power equipment and continuing product changes that occur over time, updates will be made to these
instructions from time to time. Therefore, it may be necessary to obtain the latest materials before servicing or repairing a
product. The company reserves the right to make changes at any time to this publication without prior notice and without
incurring an obligation to make such changes to previously published versions. Instructions, photographs and illustrations
used in this publication are for reference use only and may not depict actual model and component parts.
© Copyright 2008 MTD Products Inc. All Rights Reserved
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Chapter 1: Introduction ........................................................................................ 1
Professional Shop Manual intent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Spark plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Air filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Oil type and capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Changing the oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Fuel filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Valve lash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Exhaust system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Cleaning the engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
General torque specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Maintenance Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chapter 2: Basic Troubleshooting .................................................................... 11
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Steps to troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Define the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Identify factors that could cause the problem . . . . . . . . . . . . . . . . . . . . . .12
Repairing the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Prime test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Leak-down test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Compression test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
PCV testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Chapter 3: Air Intake and filter ............................................................................23
Air filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Paper air filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Foam air filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Carburetor Insulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Chapter 4: The Fuel System and Governor .......................................................29
Inspecting the fuel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Test fuel for alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Fuel tank vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
To test the cap vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
The fuel filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Inspect the fuel lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
The fuel tank. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Evaporative (EVAP) emissions system . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Charcoal canister fuel tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Roll over valve vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Table of Contents
I
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II
Charcoal canister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
EVAP fuel tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Manual Choke. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Autochoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
1P61/1P65 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
1P70 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Primer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Carburetors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Inspecting the carburetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Disassembly and rebuilding the carburetor . . . . . . . . . . . . . . . . . . . . . . . .42
Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Governor arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Governor shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Governor cup and the governor gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Chapter 5: Lubrication ........................................................................................ 51
Oil type and quantity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Oil dip stick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Dip stick tube removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Lubrication system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52
PCV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Chapter 6: Starters.............................................................................................. 57
Recoil Starter Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
Starter Cup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
Starter Rope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Starter pulley and recoil spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Electric starter relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Testing the starter relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Electric starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
Chapter 7: Ignition System ................................................................................67
Trouble shooting the ignition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
To test the stop switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
About the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Cleaning the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Inspection of the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Spark plug removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Ignition module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Module removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Installing the module and setting the air gap . . . . . . . . . . . . . . . . . . . . . . 73
Engine brake and stop switch (if equipped) . . . . . . . . . . . . . . . . . . . . . . . .74
Adjusting the brake assembly (if equipped) . . . . . . . . . . . . . . . . . . . . . . . 75
Flywheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Chapter 8: Exhaust ............................................................................................. 79
To remove/replace the conventional muffler. . . . . . . . . . . . . . . . . . . . . . . 79
Catalytic converter muffler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
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Chapter 9: Cylinder Head ...................................................................................83
Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Chapter 10: Crankshaft, piston and Connecting Rod ......................................87
Crank shaft inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Piston Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Connecting rod inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Cylinder inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Engine specifications chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Engine torque values chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Chapter 11: Failure Analysis ............................................................................101
Abrasive Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Insufficient lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Engine Overspeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Overheated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Mechanical Breakage/ Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Detonation/preignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
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Chapter 1: INTRODUCTION
1
Professional Shop Manual intent
This manual is intended to provide service dealers with
an introduction proven diagnostic and repair proce-
dures for the MTD vertical shaft engines.
Disclaimer: The information contained in this manual is
correct at the time of writing. Both the product and the
information about the product are subject to change
without notice.
About the text format:
NOTE: is used to point-out information that is
relevant to the procedure, but does not fit as a
step in the procedure.
CAUTION: is used to point-out potential danger
to the technician, operator, bystanders, or sur-
rounding property.
• Bullet points: indicate sub-steps or points.
Disclaimer: This manual is intended for use by trained,
professional technicians.
• Common sense in operation and safety is
assumed.
• In no event shall MTD or Cub Cadet be liable for
for poor text interpretation, or poor execution of
the procedures described in the text.
• If the person using this manual is uncomfortable
with any procedures they encounter, they should
seek the help of a qualified technician.
Fasteners
• Most of the fasteners used on the MTD engine
are metric. Some are fractional inches. For this
reason, wrench sizes are frequently identified in
the text, and measurements are given in U.S.
and metric scales.
• If a fastener has a locking feature that has worn,
replace the fastener or apply a small amount of
releasable thread locking compound such as
Loctite® 242 (blue).
• Some fasteners like cotter pins are single-use
items that are not to be reused. Other fasteners
such as lock washers, retaining rings, and inter-
nal cotter pins (hairpin clips) may be reused if
they do not show signs of wear or damage. This
manual leaves that decision to the judgement of
the technician.
Assembly
Torque specifications may be noted in the part of the
text that covers assembly. They may also be summa-
rized in tables along with special instructions regarding
locking or lubrication. Whichever method is more
appropriate will be used. In many cases, both will be
used so that the manual is handy as a quick-reference
guide as well as a step-by-step procedure guide that
does not require the user to hunt for information.
The level of assembly instructions provided will be
determined by the complexity of reassembly, and by
the potential for unsafe conditions to arise from mis-
takes made in assembly.
Some instructions may refer to other parts of the man-
ual for subsidiary procedures. This avoids repeating
the same procedure two or three times in the manual.
CHAPTER 1: INTRODUCTION
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Chapter 1: INTRODUCTION
2
MTD Vertical Engine Model Designators
Starter/Alternators
1=Recoil start
2=Electric start (12V)
3=E. start/alt.18W
4=E. start/alt.3A/5A
5= AutoChoke/ Recoil
6= AutoChoke/Electric Start
7= AutoChoke/Electric Start/
Alt
1 P 6 1 M U A
P= Vertical (1 cyl.)
Q= Vertical (2 cyl.)
Bore Dia. (mm)
End Product
B Mower (long shaft M0)
C Chipper/Shredder M Mower (long shaft/no shroud)
D Mower (long shaft M1) N Mower (short shaft M0)
E Mower (short shaft M1) P Mower (long shaft M0)
F Mower (short shaft/no shroud) Q Mower (short shaft M0)
R Mower (long shaft/no shroud) T Tiller
L Logsplitter W World Tiller
Compliance
U United States (50 State)
H Europe
C California
0 (Zero) 49 State
G U.S.(49) and Europe
W U.S.(50) and Europe
MajorRevision
Change
MTD Engine Serial Numbers
Model number
1P65FH/0510271A0023
MonthYear
Producing Line# and Shift#:
1A=Line 1, 1st Shift
1B=Line 1, 2nd Shift
2A=Line 2, 1st Shift
2B=Line 2, 2nd Shift
3A=Line 3, 1st Shift
3B=Line 3, 2nd Shift
4A=Line 4, 1st Shift
4B=Line 4, 2nd Shift
Date
Engine
number
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Chapter 1: INTRODUCTION
3
MAINTENANCE
The information in this manual applies to the MTD
engine. Some basic principles may apply to engines
produced by other manufacturers.
As the saying goes “an ounce of prevention is worth a
pound of cure”. The same can be said about preventive
maintenance on outdoor power equipment. By chang-
ing the spark plug, air filter, and oil at recommended
intervals many failurescan be avoided. Sometimes just
clearing off yard debris that has collected through use
can make the difference between a properly running
piece of equipment and the expensive inconvenience
of unplanned repairs..
Spark plugs
1. The spark plug used in the MTD engine is a
Torch model F6RTC gapped to .024”-.032” (.60-
.80 mm). See Figure 1.1.
NOTE: Champion RN14YC or NGK BPR4ES
are physically similar but do not match the
F6RTC in heat range. This difference in heat
ranges will effect performance and emissions. It
is recommended that only the torch F6RTC plug
be used in MTD engines.
Figure 1.1
2. Wear rate will vary somewhat with severity of
use. If the edges of the center electrode are
rounded-off, or any other apparent wear / dam-
age occurs, replace the spark plug before oper-
ating failure (no start) occurs.
3. Cleaning the spark plug:
NOTE: It is not recommended to clean spark
plugs. Use of a wire brush may leave metal
deposits on the insulator that causes the spark
plug to short out and fail to spark. Use of abra-
sive blast for cleaning may cause damage to
ceramic insulator or leave blast media in the
recesses of the spark plug. When the media
comes loose during engine operation, severe
and non-warrantable engine damage may result.
4. Inspection of the spark plug can provide indica-
tions of the operating condition of the engine.
• Light tan colored deposits on insulator and elec-
trodes is normal.
• Dry, black deposits on the insulator and elec-
trodes indicate an over-rich fuel / air mixture (too
much fuel or not enough air)
• Wet, black deposits on the insulator and elec-
trodes indicate the presence of oil in the com-
bustion chamber.
• Heat damaged (melted electrodes / cracked
insulator / metal transfer deposits) may indicate
detonation.
• A spark plug that is wet with fuel indicates that
fuel is present in the combustion chamber, but it
is not being ignited.
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Chapter 1: INTRODUCTION
4
Air filters
The main function of the air filter is to trap air borne
particles before they reach the carburetor that can
cause catastrophic internal engine damage.
MTD vertical shaft engines use two different air filters.
The first is a rectangular paper pleated filter with a
foam pre-filter. the second is an oval foam filter.
See Figure 1.2.
5. Air filters used on the MTD engine are designed
to prevent particles larger than 3-5 micron from
passing through into the engine.
6. The filter should be checked on a regular basis
possibly several times in a season.
See Figure 1.3.
7. Typically an air filter should be changed, or
cleaned if it is a foam one, before every season.
8. If a foam air filter or pre-cleaner is dirty and not
in to bad of condition it can be cleaned and
reused. The paper pleated filters can be shaken
or lightly tapped to free the debris from the filter.
NOTE: Never use compressed air on a paper air
filter. Compressed air will remove the tiny fibers
that are used to catch the dirt in the air. Without
these fibers the filter is useless.
9. Foam filters and pre-filters can be washer in
warm soapy water.
NOTE: When drying a foam filter either squeeze
it in side of a paper towel or let it air dry DO NOT
wring it because the filter will tear.
10. Before installing any foam filter, after it has been
washed, it needs to be free of moisture.
NOTE: Always check with factory specification
prior to servicing/replacing any engine compo-
nents.
Figure 1.2
Paper-Pleated
Element
Foam Pre-Filter
Foam filter
Figure 1.3
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Chapter 1: INTRODUCTION
5
Oil type and capacity
1. When checking the oil twist and remove the dip-
stick from the engine. Clean the oil off of the tip
of the dipstick. Re-insert the dipstick without
threading it in to get the oil level reading.
See Figure 1.4.
• SAE 10W-30 oil with a SF/CD API rating or bet-
ter is recommended for most operating condi-
tions up to 97o F (36oC).
• The oil capacity is 17.0- 20.3 fl.oz (0.5-0.6 liters).
2. The oil level is determined by the lowest point on
the dipstick that is completely covered with oil.
3. If the oil is noticeably thin, or smells of gasoline,
a carburetor repair may be needed before the
engine can be safely run.
• Check the oil level frequently and change the oil
more frequently in severe operating conditions
such as high ambient temperature, dusty condi-
tions, or high load use in exceptionally thick
grass.
• Synthetic oil is a suitable alternative, but it does
not extend service intervals.
NOTE: MTD recommends the use of petroleum
oil during the break in period to ensure the piston
rings correctly break in.
• Synthetic vs. Petroleum based oil: To simply look
at synthetic oil and to compare it with Petroleum
based oil there is very little difference. However,
when you look at the two through a microscope it
is easy to see the difference. Synthetic is made
up of smaller molecules. This allows the oil to
get into areas that petroleum based oil cannot.
Figure 1.4
• No oil additives or viscosity modifiers are recom-
mended. The performance of a good oil meeting
the API specifications will not be improved by oil
additives.
• Some oil additives may cause severe and non
warrantable engine damage, constituting a lubri-
cation failure. No oil additives or viscosity modifi-
ers are recommended. The performance of a
good oil meeting the SF/ CD specifications will
not be improved by the addition of any oil addi-
tives.
NOTE: Some oil additives may cause severe
and non warrantable engine damage, constitut-
ing a lubrication failure.
Changing the oil
NOTE: If the engine has been running, allow the
engine to cool before doing any maintenance
work.
NOTE: The oil should be changed after the first
5 hours of operation and every 25 hours there
after.
There are two methods of changing the oil. The appli-
cation the engine is mounted to will determine which
method to use:
1. The first method of draining the oil is by remov-
ing the drain plug located at the base of the filler
tube / dipstick tube, using a 10mm wrench.
See Figure 1.5.
NOTE: Replace the drain plug sealing washer
with a new one to ensure that it does not leak.
NOTE: Tighten the drain plug to a torque of 84
in. lbs. (10Nm) on installation.
Figure 1.5
Sealing Washer
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Chapter 1: INTRODUCTION
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2. The second method for draining the mower
engine oil is to tip the mower on its side, dipstick
tube down and dipstick removed, draining the oil
into a waste oil pan.
2a. Disconnect the spark plug lead and ground
it to the engine block.
2b. Lean the mower to the muffler side of the
engine. See Figure 1.6.
Fuel
Gasolines currently on the market are not pure gas.
Today’s fuels have alcohol and other additives in them
to reduce emissions. The fuel make up can vary sea-
sonally and geographically.
Fuel with alcohol added to it is sometimes referred to
as “oxygenated fuel”. The extra oxygen carried by the
ethanol increases the oxidation of the fuel. This speeds
up the process that causes the fuel to go bad.
Excessive alcohol in fuel creates a lot of problems for
gasoline engines. One of the biggest problems is that
alcohol attracts and holds water. This corrodes the
metal components of the fuel system, especially the
carburetor. Alcohol also does not produce as much
heat as gasoline when burnt. This results in less power
for the engine.
A 10% alcohol mix (E10) is acceptable for MTD
engines. Anything higher than that will result in perfor-
mance and starting issues.
NOTE: E85 and E20 fuels are not to be used in
any MTD engines.
• Use clean, fresh fuel with a pump octane rating
of 87 or greater.
• Stale or out-of-date fuel is the leading cause of
hard starting issues.
• Use of a high octane fuel may improve perfor-
mance in areas using high alcohol fuel blends.
Figure 1.6
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Chapter 1: INTRODUCTION
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Fuel filters
Dirty fuel can clog the carburetor and introduce abra-
sive materials into the engine. To help prevent that, the
MTD engine is equipped with a fuel filter.
1. Some of the early engines were equipped with a
fuel filter placed between the fuel tank and the
carburetor. See Figure 1.7.
2. Currently the engines are equipped with a fuel
filter installed in the fuel tank where the fuel line
connects. See Figure 1.8.
Figure 1.7
Fuel Filter
Figure 1.8
Valve lash
Valve lash is the clearance between the top of the
valve stem and the rocker arm. The valve lash should
be checked after the first 25 hours of use and every
100 hours after that. Valve lash can be checked and
adjusted using the following steps:
1. If the engine has been run, allow it to cool thor-
oughly. Position the mower for easy access to
the cylinder head.
2. Disconnect the high-tension lead from the spark
plug and ground it well away from the spark plug
hole.
3. Remove the spark plug using a 13/16” or 21mm
wrench. A flexible coupling or “wobbly” exten-
sion may help. See Figure 1.9.
4. Remove the four bolts that secure the valve
cover using a 10mm wrench, and remove the
valve cover from the engine.
NOTE: If care is used, not to damage the valve
cover gasket, it can be re-used.
5. Secure the safety bale with a spring clamp (if
installed on a mower), and slowly pull the starter
rope until air can be heard being expelled from
the spark plug hole.
Figure 1.9
Spark plug hole
High tension lead
Muffler
(plug removed)
Valve cover
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Chapter 1: INTRODUCTION
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6. Confirm that the piston is at Top-Dead-Center on
the compression stroke. See Figure 1.10.
• The compression stroke can be distinguished
from the overlap stroke by the presence of air
pressure at the spark plug hole and the fact that
neither of the valves should move significantly
on the compression stroke.
• There is an automatic compression release
mechanism that “bumps” the exhaust valve as
the piston rises on the compression stroke. At
TDC, the exhaust valve should be fully closed.
7. Check valve lash between each valve stem and
rocker arm using a feeler gauge.
8. Intake valve lash (top valve) should be .003”-
.005” (.10 + .02mm). See Figure 1.11.
9. Exhaust valve lash (bottom valve) should be
.005-.007” (.15 + .02mm). See Figure 1.12.
10. Use a 10mm wrench to loosen the jam nut, and
a 14mm wrench to adjust the rocker arm fulcrum
nut. See Figure 1.12.
• Tighten the rocker arm fulcrum nut to close-up
the clearance between the end of the valve stem
and the contact point on the rocker arm.
• Loosen the rocker arm fulcrum nut to open-up
the clearance between the end of the valve stem
and the contact point on the rocker arm.
11. Hold the fulcrum nut with a 14mm wrench,
tighten the jam nut to a torque of 88.5 in-lb.
(10Nm) using a 10mm wrench.
12. Double-check the clearance after tightening the
jam nut, to confirm that it did not shift. Re-adjust
if necessary.
13. Rotate the engine through several compression
cycles:
• Observe the movement of the valve gear.
• Return the piston to TDC compression stroke
and re-check the valve lash to confirm consistent
movement of the valve gear, including the slight
bump to the exhaust valve from the automatic
compression release.
14. Clean-up any oil around the valve cover open-
ing, clean the valve cover, replace the valve
cover gasket if necessary.
15. Install the valve cover, tightening the valve cover
screws to a torque of 71 in-lbs (8 Nm).
IMPORTANT: Over tightening the valve cover
will cause it to leak.
Figure 1.10
Valves closed
(push rods slack)
Probe to confirm piston
is at top of travel
Figure 1.11
Setting intake valve lash
.004” feeler
gauge
Figure 1.12
S
e
tti
ng ex
h
aus
t
va
l
ve
l
as
h
.006” feeler
gauge
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Chapter 1: INTRODUCTION
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16. Install the spark plug.
17. Release the spring clamp securing the
safety bail, start the engine and test run it
long enough to confirm correct operation.
Exhaust system
The exhaust system is a frequently overlooked
component of an engine. It is important to make
sure the muffler is in good condition and free of
blockage.
NOTE: A blocked muffler will result in poor
performance. If a muffler is completely
blocked the engine may not start.
Cleaning the engine
1. To maintain a proper operating temperature
and to keep the equipment looking good all
debris should be removed from the engine.
2. It is recommended to use compressed air to
blow all of the debris off of the engine.
NOTE: A pressure washer may be used to
clean outdoor power equipment but only
after the unit has been allowed to properly
cool.
NOTE: Debris can build up under the deck
and cause the engine to operate under an
unintended load.
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Chapter 1: INTRODUCTION
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General torque specifications
Maintenance Chart
size M4 M5 M6 M8 size M10 M12 M14
Grade 4.8 in-lbs 11 22 38 93 ft-lbs 16 27 43
Nm 1.2 2.5 4.3 10.5 Nm 21.7 36.6 58
5.8 in-lbs 15 28 50 120 ft-lbs 20 35 55
Nm 1.7 3.2 5.7 13.6 Nm 27.1 47.5 76
8.8 in-lbs 26 51 88 216 ft-lbs 35 61 97
Nm 2.9 5.8 9.9 24.4 Nm 47.5 82.7 132
10.9 in-lbs 36 72 124 300 ft-lbs 49 86 136
Nm 4.1 8.1 14 33.9 Nm 66.4 116.6 184
12.9 in-lbs 44 86 146 360 ft-lbs 60 103 162
Nm 5 9.7 16.5 40.7 Nm 81.4 139.7 220
in-lbs 18 35 60 150 ft-lbs 25 45 70
Nm 2 4 6.8 17 Nm 33.9 61 95
Noncritical
Fasteners in
Aluminum
Maintenance item Each use Each 25 hrs. use Each 50 hrs. use
Check oil *
Check air filter
(If applicable) *
Note on air filter
Note on pre-filter
Check & gap spark plug *
Check cooling fins
Check/clean spark
arrestor *
Change oil *
Note on oil:
Change air filter *
Note on air filter
Drain or preserve fuel
Fog or lube cylinder
Rotate engine to TDC
Before prolonged storage
Before prolonged storage
Before prolonged storage
Change oil after first 5 hrs. of use, and before
prolonged storage.
Dirt may be shaken or tapped out of the air filter, but
compressed air is not to be used for cleaning. Do not
wash or oil paper filter element.
Foam pre-filter may be washed in water and mild
detergent, and re-used. Do not oil.
Replace if worn.
Air filter and pre-filter life vary dramatically with
operating conditions.
After prolonged storage
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Chapter 2: Basic Troubleshooting
11
Definitions
Troubleshooting - The act gathering information by per-
forming tests and direct observations.
Diagnosis - A theory of what the problem is based on
the information gathered by troubleshooting.
Introduction
Diagnosing an engine is an art form that is built upon
several factors. First and most importantly is a good
understanding of how the engine works. The second is
skills that have been honed by experience. Finally the
use of visual observations and a structured, systematic
approach to troubleshooting a problem.
The first part of this chapter will outline the steps of
troubleshooting an engine so a technician can form a
proper diagnosis. The second half of this chapter will
describe specific procedures and tests to perform while
troubleshooting.
CAUTION: The first two rules in troubleshooting
is to cause no further harm to the engine and
prevent injuries. Always make sure to check the
oil for level and condition before starting an
engine. Also check attachments for damage and
make sure they are firmly mounted.
Steps of troubleshooting
NOTE: The steps and the order of the steps that
follow are a suggested approach to trouble-
shooting the MTD engine.
Define the problem
The first step in troubleshooting is to define the prob-
lem:
• Crankshaft will not turn.
a. Hard to pull rope, steady pressure
b. Rope jerks back
c. Rope will not pull at all
• Crankshaft turns, no start
• Starts, runs poorly
a. Starts, then dies
b. Runs with low power out put
c. Makes unusual smoke when running
I. Black smoke, usually heavy
II. White smoke, usually heavy
III. Blue smoke. usually light
d. Makes unusual sounds when running
I. Knock
II. Click
III. Chirp
IV. Unusual exhaust tone
There are tools that the technician can use in order to
define the problem, such as:
1. Interview the customer.
1a. Get a good description of their complaint.
1b. If it is an intermittent problem, verify what
conditions aggravates the problem as best
as possible.
1c. Get an accurate service history of the equip-
ment.
1d. Find out how the customer uses and stores
the equipment.
2. Direct observation:
2a. Do not take it that the customer is correct
with their description of the problem. Try to
duplicate the problem.
2b. Check the general condition of the equip-
ment (visually).
CHAPTER 2: BASIC TROUBLESHOOTING
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Chapter 2: Basic Troubleshooting
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I. Cleanliness of the equipment will indi-
cate the level of care the equipment
has received.
II. Make sure the engine and attach-
ments are securely fastened.
III. The tune-up factors.
NOTE: Most hard starting and poor running con-
ditions can be solved by performing a tune-up.
a. Check the condition and amount
of oil in the crankcase.
b. Check the level and condition of
the fuel.
c. Check the air filter and look for
signs of dirt ingestion.
d. Check the ignition and “read” the
spark plug.
e. Look for obvious signs of physical
damage, bent blade, exhaust sys-
tem blockage or cooling system
blockage.
3. Broken starter rope.
3a. Usually means the engine was hard to start.
3b. Makes it impossible to confirm any running
or hard starting symptoms by direct obser-
vation.
3c. Some inference can be made from checking
other factors of he general condition of the
equipment.
Identify factors that could cause the problem
This is the second step in the troubleshooting process.
1. Crankshaft will not turn.
a. Hard to pull rope, steady pressure. This
usually indicates a mechanical bind of
some sort. the likely suspects are:
I. A slightly bent crankshaft. in some
cases the drag may increase and
decrease as the crankshaft rotates.
This produces a pulsing feeling that is
different than a jerk back.
II. A parasitic load from a drive belt that is
not releasing or an implement that is
jammed.
III. An internal drag from a scored or
seized piston.
b. Rope jerks back. This usually indicates
that the piston is stopping before top dead
center on the compression stroke and is
being driven back down by compression or
combustion. The likely suspects are:
I. Compression that is unusually high.
a. valve lash.
b. a partial hydraulic lock.
II. Ignition timing is advanced.
a. Improper air gap.
b. Sheared or missing flywheel key.
c. The wrong flywheel or module is
installed on the engine.
III. Insufficient inertiato over-comenormal
compression.
a. Loose implement or blade.
b. A light flywheel used on a heavy
flywheel application.
c. Rope will not pull at all. This is usually
either a quick fix or a catastrophic failure.
The likely suspects are:
I. A broken starter recoil (easy fix).
II. Complete hydraulic lock (easy fix).
III. External binding/jammed implement
(easy fix).
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Chapter 2: Basic Troubleshooting
13
IV. Bent crankshaft (unrepairable)
V. Internal binding, crankshaft, connect-
ing rod or piston (unrepairable)
2. Crankshaft turns, no start.
2a. Most gasoline engine diagnosis involves iso-
lating problems in the four critical factors an
engine needs to run properly:
I. Ignition- sufficient spark to start com-
bustion in the cylinder, occurring at the
proper time.
II. Compression- enough pressure in the
cylinder to convert combustion into
kinetic motion. It also needs sufficient
sealing to generate the vacuum
needed to draw in and atomize the
next intake charge.
III. Fuel- correct type and grade of fresh
gasoline; in sufficient quantity, atom-
ized (tiny droplets) and in correct fuel/
air proportions.
IV. Flow- if all of the above conditions are
met, but the flow of air is constricted
on the inlet or exhaust side it will
cause the engine to run poorly or not
at all. This also includes ensuring the
valves are timed to open at the proper
time.
2b. Isolate the ignition system and compression
from the fuel system by performing a prime
test.
I. Burns prime and dies. This would indi-
cate a fuel system issue.
II. Does not burn prime. Not a fuel sys-
tem issue. Check for an ignition, com-
pression or flow problem.
2c. Compression or ignition problem
I. Check the engine stop and/or ignition
switch.
II. Test the ignition system using a proper
tester.
III. Replace the spark plug with a new one
or a known good one.
IV. Check compression or leak down.
V. Check valve lash.
VI. Check valve timing/actuation.
VII. Check exhaust.
3. Starts, runs poorly
3a. Starts, then dies
I. Run the engine with a spark tester in-
line between the spark plug wire and
the spark plug or use an oscilloscope
and see if the spark goes away at the
same time the engine dies.
II. Check choke operation.
a. Black smoke?
b. Wet plug?
III. Test for invisible damage to the air fil-
ter by starting the engine with the air
filter removed.
IV. Prime test immediately after engine
dies. If it restarts; this may indicate a
problem with fuel flow to the carbure-
tor. Check the gas cap, fuel line, fuel
filter, and the float in the carburetor.
3b. Runs with low power output.
I. Look for unusual exhaust color
(smoke).
II. Unusually hot muffler (may glow red).
a. Retarded ignition
b. Exhaust valve opening early (lash
too tight)
III. Mechanical bind
a. A slightly bent crankshaft. in some
cases the drag may increase and
decrease as the crankshaft
rotates. This produces a pulsing
feeling that is different than a jerk
back.
b. Parasitic external load. A bind in
the equipment the engine is pow-
ering.
c. Internal drag from a scored piston
or similar damage.
IV. Low governor setting or stuck gover-
nor.
a. Check RPMs using a tachometer.
b. RPMs should not droop under
moderate to heavy loads.
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Chapter 2: Basic Troubleshooting
14
V. Low compression
a. Check valve lash
b. Check compression
c. Check leak down to identify the
source of the compression loss.
VI. Flow blockage
A. Exhaust blockage, usually accompanied by
an unusual exhaust sound.
• Just as a throttle on the carburetor
controls the engine RPMs by limit-
ing the amount of air an engine
can breath in, an exhaust block-
age will limit engine performance
by constricting theother end ofthe
system.
• The muffler itself may be blocked.
• The exhaust valve may not be
opening fully, possibly because of
extremely loose valve lash set-
tings.
• The exhaust valve seat may have
come loose in the cylinder head.
This may cause a loss of compres-
sion, a flow blockage or it may ran-
domly alternate between the two.
NOTE: The cause of an exhaust valve coming
loose is usually over heating.
B. Intake blockage
• An intake blockage up-stream of
the carburetor will cause a rich
fuel/air mixture and constrict the
amount of air that the engine can
draw in, limiting performance.
NOTE: A blocked air filter is a common cause of
this.
• The intake valve not fully opening.
A possible cause of this is loose
valve lash.
C. Makes unusual smoke when running
a. Black smoke, usually heavy usu-
ally indicates a rich air fuel mixture
• Not enough air: air filter blockage
or a partially closed choke.
• Too much fuel: carburetor float or
float valve stuck or metering /
emulsion issues with the carbure-
tor.
b. White smoke, usually heavy
• Oil in muffler, usually the result of
improper tipping. the engine will
“fog” for a minute or so, then clear-
up on its own.
• Massive oil dilution with gasoline.
It may be caused by improper tip-
ping. It can also be caused by
leaky carburetor float valve, if
there is a down-hill path from the
carb. to the intake port. Check oil
for gasoline smell, repair carbure-
tor.
c. Blue smoke, usually light.
1 PCV system
• May be blocked or unplugged.
• May be over-come by massive
over-filling or oil dilution with gaso-
line.
• Will cause oil to exit the engine via
any low-resistance paths.
2Pistonrings
• Confirm with leak-down test.
• Smoke will be more pronounced
under load.
• Repair may not make economic
sense.
3 Valve guides (and intake valve
stem seal).
• Smoke will be more pronounced
on over-run.
A. Makes unusual noise when running
a. Knock
• Check for loose mounting of
engine or driven implement
• Rotate crankshaft back-and-forth
to check for loose connecting rod.
b. Click
• Clicks and pops on engine shut-
down: Compression release com-
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