Bosch 110 Armature Stroke Gauge Stand — Zero‑Offset Measurement For Solenoid Stroke Calibration

The Bosch 110 series injectors (CRIN 2/3 variants used in Daimler, Volvo, and MAN heavy‑duty engines) rely on a solenoid‑actuated armature that opens the control valve, releasing pressure from the nozzle control chamber to initiate injection. The armature stroke-the distance the solenoid plunger travels from its rest position to its fully seated position-directly determines the control valve opening time and, consequently, the injection timing and quantity. A stroke deviation of just 0.02 mm shifts the start of injection by 0.2° crank angle at rated speed, resulting in a measurable power loss and increased fuel consumption. Traditional measurement using a depth micrometer or a dial indicator on the injector body is prone to cosine error (misalignment with the armature axis) and zero‑shifting due to the spring‑loaded armature's tendency to settle at different positions. This Bosch 110 Armature Stroke Gauge Stand is a dedicated, reference‑plane‑defined measurement platform that ensures the dial indicator's probe is perfectly aligned with the armature axis, and applies a repeatable pre‑load to the armature, eliminating both zero‑shifting and cosine errors.

The gauge stand comprises a precision‑ground base plate (150×150 mm, grade 45 steel, 58 HRC) with a centring post (Ø 12.0 mm) that locates the injector body. A vertical column (Ø 20 mm, 300 mm height) carries a micrometer‑adjustable probe arm that positions the dial indicator (0‑10 mm, 0.001 mm resolution, included) over the armature's contact point. The probe arm incorporates a spring‑loaded plunger that applies a consistent pre‑load force (2.5 N ±0.2 N) to the armature, compressing the return spring to a defined position.

Parameter	Specification
Stroke range	0‑10.0 mm (0.001 mm resolution)
Pre‑load force	2.5 N ±0.2 N
Armature contact tip	Carbide, Ø 2.0 mm (flat or spherical, supplied)
Injector centring	Ø 12.0 mm post (interchangeable for 110 variants)
Base plate flatness	0.005 mm over 150 mm
Column perpendicularity	0.008 mm over 300 mm
Weight (complete)	3.8 kg

The stand includes a reference block (10.000 mm, ±0.001 mm) that allows zero‑setting of the dial indicator without the injector installed, ensuring a consistent reference plane across multiple measurements.

Injector Series	Armature Stroke (new)	Service Limit	Centring Post ID	Contact Tip Type	Torque (hold‑down)
CRIN 2 (early)	0.75–0.85 mm	0.70 mm	12.0 mm	Flat	3 N·m
CRIN 2.2 (Euro 4)	0.80–0.90 mm	0.75 mm	12.0 mm	Flat	3 N·m
CRIN 2.4 (Euro 5)	0.85–0.95 mm	0.80 mm	12.5 mm	Spherical	3.5 N·m
CRIN 3.0 (Euro 6)	0.90–1.00 mm	0.85 mm	12.5 mm	Spherical	4 N·m
CRIN 3.2 (marine)	0.95–1.05 mm	0.90 mm	13.0 mm	Spherical	4.5 N·m

The stand includes interchangeable centring posts (12.0 mm, 12.5 mm, 13.0 mm) and contact tips (flat and spherical) to cover the full 110 series range. The reference card (laminated) cross‑references the injector part number with the correct post and tip, eliminating guesswork.

Injector preparation - Remove the injector's solenoid cover and any electrical connectors. Ensure the armature is clean and free of debris.

Zero‑setting - Place the reference block on the base plate. Lower the dial indicator probe onto the block and zero the indicator (rotate bezel). Remove the block.

Injector mounting - Place the injector onto the centring post, aligning the armature axis with the post. Secure the injector using the hold‑down clamp (included) - tighten to the specified torque.

Probe positioning - Lower the probe arm until the contact tip touches the armature's top surface. The spring‑loaded plunger applies the pre‑load; the dial indicator will show a positive reading.

Measurement - Record the dial indicator reading. This is the armature stroke (the distance from the armature's rest position to the position under the pre‑load). For dynamic measurement (valve fully open), the injector may need to be energised-this stand is for static measurement only.

Comparison - Compare the measured stroke against the service limit. If the stroke is below the service limit, the armature or its spring is worn and must be replaced.

The stroke measurement, when combined with other tests, reveals specific failure modes:

Stroke reduction > 0.05 mm - Indicates armature wear or spring fatigue. The armature's working face (the surface that contacts the valve) may have worn, or the return spring has lost its pre‑load.

Inconsistent readings - If the reading varies by more than 0.01 mm between measurements, the armature may be sticking in its bore (due to varnish or wear) or the spring is binding.

Quick drop‑off - If the stroke measurement reduces rapidly over consecutive injections (simulated by repeating the test on a test bench), the spring is failing.

The stand's repeatability (variation < 0.005 mm across five measurements) ensures that these diagnostic insights are reliable, not artifacts of measurement error.

Q1: Can this stand measure the armature stroke with the injector fully assembled (i.e., with the solenoid coil installed)?
Yes-the stand is designed for fully assembled injectors. The probe accesses the armature through the solenoid's central bore (or through a dedicated access hole on some variants). Ensure the injector is clean and the armature is free to move. The stand's centring post aligns the injector so that the probe contacts the armature's centre.

Q2: What is the difference between static stroke and dynamic stroke, and which does this stand measure?
Static stroke is the armature travel measured under a constant pre‑load (no energising current). Dynamic stroke is the travel measured when the solenoid is energised (valve opening). This stand measures static stroke only. Dynamic stroke measurement requires the injector to be energised and is typically performed on a test bench. The static stroke measurement is used to determine if the armature and spring are worn before the injector is sent for dynamic testing.

Q3: Can this stand be used on Bosch 110 injectors from other manufacturers (e.g., Denso, Delphi)?
The stand's geometry (centring post, probe arm height) is calibrated for Bosch 110 series injectors. The centring post and contact tip dimensions for Bosch injectors are provided. For Denso, Delphi, or other manufacturers, we offer a separate set of conversion rings-please contact us with your injector details.

Q4: How often should the contact tip be replaced?
The carbide tip is rated for 5,000 measurements before significant wear occurs. Inspect the tip for wear (a flat spot) after every 500 measurements. If the tip shows wear, replace it-the spare tip is included.

Q5: Can I use the stand to measure armature stroke on an injector that is still installed on the engine?
No. The stand requires the injector to be removed and mounted on its base plate. This ensures the correct alignment and pre‑load. On‑vehicle measurements are not possible with this stand.

Q6: Is the stand compatible with digital indicators (e.g., Mitutoyo, Tesa) as well as dial indicators?
Yes. The probe arm accepts any indicator (dial or digital) with an Ø 8.0 mm shank. The standard version is supplied with a 0.001 mm dial indicator; if you have a digital indicator, you can use the stand without the supplied indicator. The stand's clamp ensures a secure fit for both types.

 

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