Question 1

What part is the Neiman fixed to on the DERBI SENDA BAJA 125 SM motorcycle?

Accepted Answer

On the DERBI SENDA BAJA 125 SM motorcycle, the Neiman is fixed by a part called Neiman support or switch support. This part is generally attached to the upper fork yoke of the motorcycle.

Here’s how the Neiman is held:

The Neiman support is securely screwed onto the fork yoke.
The Neiman fits into this support, which holds it in place and ensures its proper positioning.

To remove or replace the Neiman, you need to unscrew the screws that fix the Neiman support to the fork yoke, then extract the Neiman from the support.

This fixing ensures the stability of the Neiman and its proper functioning for starting and the safety of the motorcycle.

Question 2

Why does my DERBI SENDA BAJA 125 SM motorcycle start and then stall immediately?

Accepted Answer

If your DERBI SENDA BAJA 125 SM motorcycle starts but stalls immediately, several causes may be behind this problem. Here are the main points to check:

1. Fuel Check

Make sure the tank is sufficiently filled with good quality fuel.
Old or contaminated fuel can prevent the engine from functioning properly.

2. Air Filter Check

A dirty air filter limits airflow and disrupts the air/fuel mixture.
Clean or replace the filter if necessary.

3. Spark Plug Condition

A worn or dirty spark plug can cause poor ignition.
Check its cleanliness and gap, then replace it if needed.

4. Fuel Supply System

Check that fuel is flowing correctly to the engine.
Inspect the hoses, fuel tap, and carburetor for any leaks or blockages.

5. Idle Speed Adjustment

An idle speed that is too low can cause the engine to stall.
Adjust the idle screw to achieve a stable speed.

6. Electrical Issues

A problem with the ignition, battery, or electrical connections can cause stalling.
Check the cables, connections, and the condition of the battery.

By checking these elements, you can often identify and resolve the cause of starting followed by stalling on your DERBI SENDA BAJA 125 SM.

Question 3

What is the valve clearance for the DERBI SENDA BAJA 125 SM motorcycle?

Accepted Answer

For the DERBI SENDA BAJA 125 SM motorcycle equipped with a single-cylinder 4-stroke engine, the valve clearance is a fundamental parameter to check regularly to ensure the proper functioning of the engine and its longevity.

Prescribed adjustment values:

Intake clearance: 0.10 mm
Exhaust clearance: 0.15 mm

These measurements correspond to the space between the rocker arm and the valve when the engine is completely cold. This clearance should be measured before any engine start to obtain precise and reliable values.

Verification procedure: Use appropriate thickness gauges (feeler gauges) to check the exact clearance between the rocker arm and the valve. If the clearance is not compliant, loosen the adjustment screw and adjust until the prescribed value is obtained, then tighten securely.

A clearance that is too small leads to overheating of the valves and a risk of annealing the valve seat, while excessive clearance causes rattling noise and accelerated wear of the rockers and valves. Adhering to these values ensures optimal combustion and maintains the mechanical reliability of your engine.

The manufacturer DERBI recommends checking the valve clearance every 6,000 km or according to your vehicle's maintenance schedule.

Question 4

How to adjust the valve clearance on a DERBI SENDA BAJA 125 SM motorcycle?

Accepted Answer

Adjusting the valve clearance is an important operation to ensure the proper functioning and longevity of your DERBI SENDA BAJA 125 SM engine. Here are the general steps to perform this adjustment:

Steps to adjust the valve clearance

Preparation: Place the motorcycle on a stable stand and ensure that the engine is cold for accurate measurements.
Accessing the valves: Remove the necessary covers or protections to access the rockers and the valve adjustment screws.
Engine positioning: Manually turn the engine (using a wrench on the crankshaft) until the piston is at the top dead center (TDC) of the relevant cylinder. This allows for the correct clearance to be measured.
Measuring the clearance: Use a feeler gauge to measure the space between the valve stem and the rocker. Compare this value to the manufacturer's specifications, usually indicated in millimeters.
Adjustment: If the measured clearance is out of tolerance, loosen the locking nut of the adjustment screw, then adjust the screw until the recommended clearance is achieved. Then tighten the locking nut without altering the setting.
Final check: Re-measure to confirm that the clearance is correct after tightening.
Reassembly: Replace the removed covers and protections, and ensure everything is securely fastened.

Important tips

Perform this adjustment regularly according to the intervals recommended by the manufacturer to avoid premature engine wear.
Always use appropriate tools to avoid damaging components.
If you are not comfortable with this operation, it is advisable to seek professional help.

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