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MTD
Gas Walk-Behind Mower

Model # 12A-559K402 Official MTD lawn mower

Here are the diagrams and repair parts for Official MTD 12A-559K402 lawn mower, as well as links to manuals and error code tables, if available.

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  • In the search box below, enter all or part of the part number or the part’s name.

Not all parts are shown on the diagrams—those parts are labeled NI, for “not illustrated”.

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For DIY troubleshooting advice and repair guides, visit our repair help section.

Owner’s manual

Model diagram and schematic

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ALL PARTS
Showing 10 of 123 parts  |
Blade-21" Mu 742-0741
#41

Main frame diagram

Blade-21" mu

Part #742-0741

Replaced by #942-0741A

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Manufacturer substitution
This part replaces 742-0741. Substitute parts can look different from the original.
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Get free shipping with Automatic Reorder

$29.10
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17% OFF Phone Price : $35.10
In Stock
Lawn Tractor Screw (replaces 01000628, 01000865, 1186307, 1186308, 791-180288, 791-683298, 910-0599) 710-0599
#58

Main frame diagram

Lawn tractor screw (replaces 01000628, 01000865, 1186307, 1186308, 791-180288, 791-683298, 910-0599)

Part #710-0599

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This item is not returnable
$4.91
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17% OFF Phone Price : $5.91
In Stock
Cable Tie 726-0240
#19

Main frame diagram

Cable tie

Part #726-0240

Replaced by #726-0178

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Manufacturer substitution
This part replaces 726-0240. Substitute parts can look different from the original.
This item is not returnable
$2.16
In Stock
Yard Machines Lawn & Garden Equipment Cupped Washer 736-0270
#57

Main frame diagram

Yard machines lawn & garden equipment cupped washer

Part #736-0270

This item is not returnable
$5.10
| 
16% OFF Phone Price : $6.10
In Stock
Aircap Lawn & Garden Equipment Hex Screw 710-0896
#55

Main frame diagram

Aircap lawn & garden equipment hex screw

Part #710-0896

This item is not returnable
$5.22
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16% OFF Phone Price : $6.22
In Stock
Yard Machines Lawn Mower Throttle Control Housing 746-0883
#11

Main frame diagram

Yard machines lawn mower throttle control housing

Part #746-0883

This item is not returnable
$21.96
| 
21% OFF Phone Price : $27.96
In Stock
Yard Machines Lawn Tractor Screw 710-1007
#21

Main frame diagram

Yard machines lawn tractor screw

Part #710-1007

This item is not returnable
$9.03
In Stock
Lawn & Garden Equipment Screw 710-0606
#43

Main frame diagram

Lawn & garden equipment screw

Part #710-0606

This item is not returnable
$8.21
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11% OFF Phone Price : $9.21
In Stock
Lawn Tractor Hex Nut 712-0271
#74

Main frame diagram

Lawn tractor hex nut

Part #712-0271

This item is not returnable
$6.66
| 
13% OFF Phone Price : $7.66
In Stock
Oil Seal 721-0329
#19

Drive assembly diagram

Oil seal

Part #721-0329

Replaced by #921-0329

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Manufacturer substitution
This part replaces 721-0329. Substitute parts can look different from the original.
$17.66
In Stock

Symptoms for gas walk-behind mowers

Choose a symptom to see related walk-behind mower repairs.

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Why does my lawn mower vibrate a lot?

Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up...

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Why does my lawn mower cut unevenly?

Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade...

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Why does my lawn mower run rough?

Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key...

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Why won't my lawn mower move?

Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel...

Read more

Why won't my lawn mower start?

Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, ba...

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Why does my lawn mower stall?

Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent...

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Repair guides for gas walk-behind mowers

These step-by-step repair guides will help you safely fix what’s broken on your walk-behind lawn mower.

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How to rebuild a lawn mower carburetor

How to rebuild a lawn mower carburetor

The carburetor mixes air with fuel to drive the piston. Rebuild the carburetor if it's clogged or leaks....

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Repair difficulty
Time required
60 minutes or less
How to replace a lawn mower recoil starter on an OHV engine

How to replace a lawn mower recoil starter on an OHV engine

Replace the recoil starter if it doesn't move when you pull the starter rope....

Read more
Repair difficulty
Time required
15 minutes or less
How to replace a lawn mower wheel

How to replace a lawn mower wheel

Learn how replace a damaged wheel on a walk-behind lawn mower—it's a quick, easy fix....

Read more
Repair difficulty
Time required
15 minutes or less

Effective articles & videos to help repair your walk-behind mowers

Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.

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How to enjoy all the online benefits we offer on our Sears PartsDirect website

How to enjoy all the online benefits we offer on our Sears PartsDirect website

Learn about all the convenient features on our Sears PartsDirect website that make your parts purchases easier....

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Top questions about Sears and Sears PartsDirect

Get answers to frequently asked questions about Sears and Sears PartsDirect....

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Types of walk-behind mower blades video

Types of walk-behind mower blades video

Learn about the different kinds of mower blades and how to maintain them....

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