O.S. engine MAX-21TM User Manual (English)

Questions and Answers:

P
pjonesAug 4, 2025
Why is my O.S. Engine not reaching expected peak r.p.m.?
- C
  Chelsea CrawfordAug 5, 2025
  If your O.S. Engine is not reaching the expected peak r.p.m., it might be due to insufficient warming up or running-in. Ensure you set the needle only after warming up the engine and complete the running-in process. Also, check if the silencer or manifold isn't securely connected or is disconnected. Replace the seal ring and secure the connections. A split or broken fuel tubing from the tank can also cause this issue, so replace the tubing.
J
johnwilliamsAug 9, 2025
What to do if O.S. engine fires intermittently but does not run?
- H
  heatheracostaAug 9, 2025
  If your O.S. engine fires intermittently but does not run, it could be due to insufficient fuel in the tank, so fill the tank with fuel. A deteriorated glowplug can also cause this, so replace the glowplug. Check for a clogged fuel filter or dirty air cleaner and silencer inside and clean or replace the fuel filter; replace the cleaner element and clean inside the silencer. If the engine overheated, wait until the engine is cool. Ensure the clutch release is correct by adjusting the tension of the clutch spring. Avoid disconnecting the starting battery too soon; wait until the r.p.m. becomes stable. Vibration causing air bubbles in fuel can also be a factor; install "O" rings to the tank screws to prevent bubbles.
I
iparkerAug 15, 2025
How to fix poor response on my O.S. Engine?
- H
  hmillerAug 15, 2025
  If your O.S. Engine has poor response, consider these potential causes. A deteriorated glowplug may be the culprit, so try replacing it. Incorrect carburetor settings can also lead to poor response; readjust the low r.p.m. range using the metering needle and mixture control valve. Additionally, check the transmitter setting for an incorrect Exponential function. Finally, ensure the throttle servo linkage does not bind and is connected correctly.
A
Amber ParrishAug 20, 2025
Why is the idle unstable on my O.S. engine?

O.S. engine MAX-21TM Specifications

General

Brand	O.S. engine
Model	MAX-21TM
Category	Engine
Language	English

Summary

SAFETY INSTRUCTIONS AND WARNINGS

WARNINGS

Events which might involve serious, even fatal, injury.

NOTES

Cover many other possibilities, less obvious dangers causing damage or injury.

ENGINE CONSTRUCTION

Piston and Cylinder Clearance

Piston fit in cold engine is tight; clearance achieved at operating temperature.

NOTES WHEN APPLYING AN ELECTRIC STARTER

Over-priming and Fuel Removal

Avoid over-priming to prevent hydraulic lock and engine damage.

BEFORE STARTING

Items Necessary for Starting

Lists tools, fuel, fuel pump, fuel line, and glowplug igniter required for operation.

Fuel Information

Details on fuel type, nitromethane content, and storage precautions.

BASIC ENGINE PARTS

Engine Component Identification

Labels for heatsink head, cylinder liner, crankshaft, and carburetor.

CARBURETOR CONTROLS

Four Adjustable Controls

Explains Needle-Valve, Mixture Control Valve, Metering Needle, and Throttle Stop Screw functions.

FACTS ABOUT GLOWPLUGS

Glowplug Role and Life

Explains glowplug function, ignition timing, and life extension tips.

When to Replace Glowplug

Symptoms indicating glowplug replacement is needed.

INSTALLATION

Engine Mounting and Flywheel/Clutch Setup

Steps for mounting engine, installing flywheel and clutch.

Model-Specific Installation Details

Installing starter, manifold, and connecting throttle linkage for T-Maxx/Revo.

STARTING THE ENGINE & RUNNING-IN

Preparation for Starting

Fill tank, check glowplug, install air cleaner and muffler system.

Initial Running-in Procedure

Running engine on the track with rich settings, using throttle control.

Stopping the Engine Safely

Procedures for safely stopping the engine and warnings about hot parts.

FINAL ADJUSTMENT

High-Speed Tuning with Needle Valve

Adjusting Needle-Valve for optimal speed on straight course.

Idle and Acceleration Tuning

Adjusting Metering Needle for smooth idle and acceleration.

Mixture Adjustment Warnings

Warnings against 'no-load' adjustments and benefits of slightly rich settings.

CARBURETOR CLEANLINESS

Realignment of Metering Needle and Mixture Control Valve

Procedure to reset Metering Needle and Mixture Control Valve to standard positions.

CARE AND MAINTENANCE

Fuel System Maintenance

Cleaning fuel filters and preventing foreign matter entry.

Post-Operation Engine Care

Draining fuel, running out residual fuel, and injecting after-run oil.

Exterior Cleaning and Bearing Caution

Using methanol for exterior cleaning and caution regarding rear crankshaft bearing heat.

CHECKING THE ENGINE

Symptoms of Worn Parts

Identifies signs of performance loss due to worn bearings, piston, or connecting rod.

TROUBLE SHOOTING

Engine Fails to Fire - Causes and Actions

Lists reasons engine won't start and corrective actions.

Engine Fires Intermittently - Causes and Actions

Lists reasons engine starts but stops and corrective actions.

Unstable Idle and Peak RPM Issues

Troubleshooting unstable idle and not reaching expected RPM.

Poor Response and RPM Drop

Troubleshooting poor throttle response and RPM drop.

21TM (T-Maxx) ENGINE PARTS LIST & EXPLODED VIEW

T-Maxx Engine Parts List

Comprehensive list of part numbers and descriptions for the T-Maxx engine.

T-Maxx Engine Exploded View

Diagram showing the assembly of the T-Maxx engine with numbered parts.

21TM (Revo) ENGINE PARTS LIST & EXPLODED VIEW

Revo Engine Parts List

Comprehensive list of part numbers and descriptions for the Revo engine.

Revo Engine Exploded View

Diagram showing the assembly of the Revo engine with numbered parts.

11K CARBURETOR PARTS & EXPLODED VIEW

11K Carburetor Exploded View

Diagram showing the assembly of the 11K carburetor with numbered parts.

11K Carburetor Parts List

Comprehensive list of part numbers and descriptions for the 11K carburetor.

11K-R CARBURETOR PARTS & EXPLODED VIEW

11K-R Carburetor Exploded View

Diagram showing the assembly of the 11K-R carburetor with numbered parts.

11K-R Carburetor Parts List

Comprehensive list of part numbers and descriptions for the 11K-R carburetor.

O.S. GENUINE PARTS & ACCESSORIES

Glow Plugs and Seal Rings

Lists available O.S. glow plugs and exhaust seal rings.

Dust Caps and Socket Wrench

Lists optional dust cap sets and long socket wrench with plug grip.

21TM (T-Maxx) THREE VIEW DRAWING

T-Maxx Specifications and Dimensions

Provides detailed specifications and dimensional drawings for the T-Maxx engine.

21TM (Revo) THREE VIEW DRAWING

Revo Specifications and Dimensions

Provides detailed specifications and dimensional drawings for the Revo engine.

Related product manuals

O.S. engine MAX-21XM

22 pages

O.S. engine max 21 RZ-M

9 pages

O.S. engine MAX-21RG Series

O.S. engine MAX-25AX & MAX-35AX