Lycoming YO-233-B2A User manual

© 2021 Avco Corporation. All Rights Reserved.
Engine Maintenance Manual
YO-233-B2A Engine
February 2021
Part No. MM-YO-233-B2A
(Supersedes Maintenance Manual LM-YO-233, dated June 2012)

YO-233-B2A Engine
Maintenance Manual
Lycoming Part Number: MM-YO-233-B2A
Contact Us:
Mailing Address:
Lycoming Engines
652 Oliver Street
Williamsport, PA 17701 USA
Phone:
Factory
U.S. and Canada Toll Free:
Direct:
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[phone]
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•[phone] (Toll Free)
•[phone]
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Lycoming’s regular business hours are Monday through Friday from 8:00AM through 5:00PM
Eastern Time (-5 GMT).
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NOTE:
Lycoming recommends that owners of this manual sign up for email notification on the Technical
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or revised service document.

TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved Record of Revisions
February 2021 Page i
YO-233-B2A Engine Maintenance Manual
RECORD OF REVISIONS
Revision
Revision
Date
Revised By
Revision Description
Original
Original Release of Maintenance Manual –MM-YO-233-B2A
(Supersedes Maintenance Manual LM-YO-233, dated June 2012).
MM-YO-233-B2A has been formatted and incorporates changes
included in recently released and FAA approved maintenance
manuals. This manual contains the same basic information as LM-
YO-233 with significant changes to several chapters including 05-
00, 05-30, 05-50, 12-10, 72-30, and 74-30. This manual also
includes a description and instruction for an approved alternate
ignition system.

TEO-540-A1A Engine Maintenance Manual
Record of Revisions © 2021 Avco Corporation. All Rights Reserved
Page ii February 2021
YO-233-B2A Engine Maintenance Manual
This page intentionally left blank.

TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved Service Document List
February 2021 Page iii
YO-233-B2A Engine Maintenance Manual
SERVICE DOCUMENT LIST
NOTICE: The following is a list of service documents referenced in or incorporated into the
information in this manual. Although the YO-233-B2A is not currently certified by the
FAA it is recommended that all inspections, procedures, and guidelines in the latest
revision of any service document (including any supplements) be followed to maintain
continued airworthiness.
Supplements to a service document contain information relevant to the service
document but not yet added to the service document.
The latest revision of all service documents in this list can be downloaded from our
website https://www.lycoming.com/contact/knowledge-base/publications.
To narrow the search parameters and limit the number of returns, enter only the
numerical portion of the service document number in the Search box on the website.
Number
Incorporation
Date
Subject
S.B. 369
02/21
Engine Inspection after Overspeed
S.B. 388
02/21
Procedure to Determine Exhaust Valve and Guide
Condition
S.B. 398
02/21
Recommended Corrective Action for Use of
Incorrect Fuel
S.B. 399
02/21
Action to Take If Loss of Oil Pressure
S.B. 401
02/21
Recommendations for Aircraft Struck by Lightning
S.B. 480
02/21
I. Oil Filter Change and Screen Cleaning
II. Oil Filter/Screen Content Inspection
S.B. 533
02/21
Recommendations Regarding Accidental Engine
Stoppage, Propeller/Rotor Strike or Loss of
Propeller/Rotor Blade Tip
S.I. 1014
02/21
Lubricating Oil Recommendations
S.I. 1042
02/21
Approved Spark Plugs
S.I. 1043
02/21
Spark Plug Heli-Coil Insert Replacement
S.I. 1080
02/21
Maintenance Items for Special Attention
S.I. 1191
02/21
Cylinder Compression
S.I. 1409
02/21
Lycoming Engines P/N LW-16702 Oil Additives
S.I. 1425
02/21
Suggested Maintenance Procedures to Reduce the
Possibility of Valve Sticking
S.I. 1462
02/21
Propeller Oil Control Leak Test Procedure
S.I. 1530
02/21
Engine Inspection in Particulate-Laden
Environments
S.I. 1566
02/21
Lycoming Engines Approves the Use of Safety
Cable

TEO-540-A1A Engine Maintenance Manual
Service Document List © 2021 Avco Corporation. All Rights Reserved
Page iv February 2021
YO-233-B2A Engine Maintenance Manual
SERVICE DOCUMENT LIST (CONT.)
Number
Incorporation
Date
Subject
S.L. L162
02/21
Heli-Coil®Service Repair Kit
S.L. L171
02/21
General Aspects of Spectrometric Oil Analysis
S.L. L192
02/21
Spark Plug Fouling
S.L. L197
02/21
Recommendations to Avoid Valve Sticking
S.L. L283
02/21
Alternate Ignition System

TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved Table of Contents
February 2021 Page v
YO-233-B2A Engine Maintenance Manual
TABLE OF CONTENTS
Subject Page
Title Page _______________________________________________________________________
Record of Revisions.............................................................................................................................. i
Service Document List.......................................................................................................................iii
Table of Contents................................................................................................................................ v
Abbreviations and Acronyms ...........................................................................................................xi
Introduction......................................................................................................................................xiii
Required Maintenance ................................................................................................. 05-00
—General..................................................................................................................................... 1
—Tools for Maintenance............................................................................................................. 1
—Engine Overhaul vs. Engine Rebuild....................................................................................... 2
—Time Between Overhaul (TBO)............................................................................................... 2
—Safety Precautions - Before Engine Maintenance.................................................................... 2
—Maintenance Practices.............................................................................................................. 2
—General Engine Inspection Criteria.......................................................................................... 4
—Requirements for Engine Maintenance.................................................................................... 4
—Approved Parts......................................................................................................................... 4
—Corrosion Prevention............................................................................................................... 5
—Painting the Engine and Engine Components.......................................................................... 5
—Limits and Clearances.............................................................................................................. 7
—Inspections ............................................................................................................................... 7
Time Limits / Inspections............................................................................................. 05-10
—General..................................................................................................................................... 9
—Engine Inspection Schedule for YO-233-B2A Engines .......................................................... 9
Time Limits / Maintenance Checks-Scheduled Maintenance Checks ..................... 05-20
—Visual Inspection..................................................................................................................... 11
—10-Hour Initial Engine Inspection for YO-233-B2A Engines................................................ 14
—25-Hour Engine Inspection for YO-233-B2A Engines........................................................... 15
—50-Hour Engine Inspection for YO-233-B2A Engines........................................................... 18
—100-Hour or Annual Engine Inspection for YO-233-B2A Engines ....................................... 24
—400-Hour Engine Inspection for YO-233-B2A Engines......................................................... 29
—500-Hour Engine Inspection for YO-233-B2A Engines......................................................... 31
—1000-Hour Engine Inspection for YO-233-B2A Engines....................................................... 32

TEO-540-A1A Engine Maintenance Manual
Table of Contents © 2021 Avco Corporation. All Rights Reserved
Page vi February 2021
YO-233-B2A Engine Maintenance Manual
Subject Page
Cleaning......................................................................................................................... 05-30
—Cleaning Guidelines................................................................................................................ 33
—Table 1 - Cleaning Guidelines for Engine Components .................................................... 34
—Grit-Blasting............................................................................................................................ 35
—Soft Carbon Removal.............................................................................................................. 36
—Hard Carbon Removal ............................................................................................................ 37
—Cylinder Cleaning................................................................................................................... 37
—Piston Cleaning....................................................................................................................... 38
—Steel, Aluminum, or Magnesium Parts Cleaning.................................................................... 39
—Spark Plug Cleaning................................................................................................................ 39
—Lead Deposit Removal............................................................................................................ 40
—Volcanic Ash Removal ........................................................................................................... 40
—Cleaning Guidelines for a Soaked Engine .............................................................................. 40
—Cleaning Methods for Non-Destructive Testing..................................................................... 41
Time Limits / Maintenance Checks –Unscheduled Maintenance............................ 05-50
—Lightning Strike - After a lightning strike .............................................................................. 43
—Engine Overspeed ................................................................................................................... 43
—Table 1 - Overspeed Values for YO-233-B2A Engines .................................................... 44
—Incorrect Fuel or Fuel Contamination..................................................................................... 45
—Soaked Engine......................................................................................................................... 46
—Engine on Fire or Near a Fire.................................................................................................. 47
—Hydraulic Lock ....................................................................................................................... 47
—Volcanic Ash/Particulate Contamination................................................................................ 47
—Table 2 - Action to Take in Volcanic Ash Conditions....................................................... 48
—Valve Sticking......................................................................................................................... 49
—Oil Starvation/Sudden Loss of Oil Pressure ........................................................................... 50
—Metal Contamination of the Lubrication System.................................................................... 51
—Propeller Strike, Sudden Engine Stoppage or Loss of a Propeller Blade TipCh_12_10........ 51
—Non-Destructive Testing
(Magnetic Particle Inspection and Fluorescent Penetrant Inspection.)................................... 58

TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved Table of Contents
February 2021 Page vii
YO-233-B2A Engine Maintenance Manual
Subject Page
Servicing - Replenishing............................................................................................... 12-10
—Refueling................................................................................................................................. 59
—Oil Level Check...................................................................................................................... 59
—Oil Consumption..................................................................................................................... 60
—Oil Type and Viscosity ........................................................................................................... 60
—Add Oil to the Engine ............................................................................................................. 61
—Oil Leak Check ....................................................................................................................... 61
—Oil Servicing Schedule............................................................................................................ 61
—Oil Change Procedure............................................................................................................. 62
—Oil Filter Replacement............................................................................................................ 64
—Oil Suction Screen Removal/Installation................................................................................ 65
—Oil Filter/Oil Suction Screen Inspection................................................................................. 65
—Identification of Metallic Solids After Oil Servicing.............................................................. 65
—Visual Inspection of the Oil Filter Element and Oil Suction Screen...................................... 66
—Table 3 - Guidelines for Identification of Metal Particulates
and Chips & Corrective Action.......................................................................... 67
—Table 4 - Guidelines for Particle Quantity and Size on Oil Filter or Oil Suction Screen.. 69
—Recommended Corrective Action Options............................................................................. 71
—Table 5 - Recommended Corrective Action Options......................................................... 71
Fault Isolation................................................................................................................ 12-30
—General.................................................................................................................................... 73
—Fault Isolation Guide............................................................................................................... 73
—Table 1 - Fault Isolation Guide.......................................................................................... 73
Reciprocating Engine –Removal/Operational Ground Check ................................ 72-00
—Engine Removal Prerequisites................................................................................................ 87
—Engine Removal Procedure..................................................................................................... 87
—Engine Installation Preparation Requirements........................................................................ 89
—Engine Installation.................................................................................................................. 90
—Operational Ground Check After Maintenance...................................................................... 90
—Idle Speed Mixture Adjustment.............................................................................................. 90
—Engine Mount Inspection........................................................................................................ 91
—Return to Service Procedure ................................................................................................... 91

TEO-540-A1A Engine Maintenance Manual
Table of Contents © 2021 Avco Corporation. All Rights Reserved
Page viii February 2021
YO-233-B2A Engine Maintenance Manual
Subject Page
Reciprocating Engine –Crankcase ............................................................................. 72-20
—Crankcase System Description................................................................................................ 93
—Crankcase Maintenance .......................................................................................................... 93
—Crankcase Inspection Procedure............................................................................................. 93
Reciprocating Engine –Cylinder Inspections............................................................ 72-30
—General.................................................................................................................................... 95
—Table 1 - Regularly Scheduled Cylinder Inspections......................................................... 95
—Visual Cylinder Inspection...................................................................................................... 95
—Cylinder Compression Check ................................................................................................. 96
—Table 2 - Summary of Cylinder Compression Check Results and Corrective Action..... 100
—Intercylinder Baffle Inspection ............................................................................................. 101
—Cylinder Borescope Inspection............................................................................................. 102
—Table 3 - Borescope Inspection Steps, Results, and Corrective Action........................... 103
—Exhaust Valve and Guide Inspection.................................................................................... 103
—Cylinder Removal................................................................................................................. 109
—Piston Removal..................................................................................................................... 112
—Connecting Rod Removal..................................................................................................... 113
—Cylinder Assembly Inspection.............................................................................................. 114
—Piston Inspection................................................................................................................... 119
—Connecting Rod Inspection................................................................................................... 123
—Connecting Rod Bushing Replacement ................................................................................ 126
—Connecting Rod Parallelism/Squareness Check ................................................................... 128
—Connecting Rod Installation.................................................................................................. 129
—Piston Ring Replacement...................................................................................................... 131
—Piston Installation.................................................................................................................. 132
—Intake Valve Replacement .................................................................................................... 133
—Exhaust Valve Replacement ................................................................................................. 133
—Cylinder Installation.............................................................................................................. 134
—Corrective Action for Valve Sticking ................................................................................... 142
—Intake and Exhaust Valve Guide Replacement..................................................................... 143
—Intake and Exhaust Valve Seat Replacement........................................................................ 143
—Barrel Glaze and Varnish Removal from Interior Cylinder Barrel....................................... 144
—Heli-Coil®Replacement........................................................................................................ 144