Norwegian Heavy Diesel Engine Shows Gradual Hot Cylinder Contribution Loss Despite Acceptable Cold Injector and Compression Checks as Exhaust-Valve Rotator Operation Is Investigated

The Cylinder Became Weak Only After Extended Load

A heavy diesel engine operating in Norway showed acceptable cold compression and injector test results.

During prolonged high-load operation, however, one cylinder gradually contributed less and combustion quality deteriorated.

Because the weakness developed with heat rather than appearing immediately, technicians investigated the exhaust-valve mechanism, including the valve rotator where the engine design used one.

Valve Rotators Help Change Contact Position

Some heavy-duty engines use valve rotators to encourage gradual rotation of the valve during operation.

This can help distribute:

• heat;
• deposits;
• seat contact;
• and local wear

around the valve head and seat circumference.

The functional idea is:

Valve cycles → Rotator produces incremental rotation → Contact area changes over time → Heat and deposits are distributed

If the mechanism stops rotating as designed, one area can remain repeatedly exposed to the same thermal and contact condition.

Cold Checks Can Miss a Heat-Dependent Sealing Problem

At cold temperature, valve and seat geometry may still provide adequate sealing for a basic compression test.

After sustained heavy load:

• valve temperature rises;
• exhaust heat increases;
• local deposits can affect contact;
• and thermal expansion changes the sealing condition.

A localized seat problem may therefore become more evident hot than cold.

The Investigation Included Rotator Function and Valve Condition

Technicians reviewed:

• valve-rotator operation;
• valve-stem condition;
• spring and retainer assembly;
• rocker/bridge geometry where applicable;
• seat contact pattern;
• hot cylinder contribution;
• and exhaust-valve sealing.

The rotator was not assumed to be defective merely because the cylinder weakened.

It was evaluated as part of a temperature-dependent valve-sealing system.

Why Injector Results Were Important but Not Final

Acceptable injector performance helped move the investigation away from fuel delivery.

However, an injector test cannot confirm:

• exhaust-valve sealing;
• valve rotation;
• seat temperature distribution;
• or cylinder breathing under hot load.

The engine can receive the correct fuel quantity while losing effective cylinder pressure through a valve that seals poorly when hot.

Norwegian Heavy-Load Operation Provided the Trigger

The fault became most visible after sustained loaded operation, where exhaust-valve thermal stress was higher than during a short cold workshop test.

The regional application therefore entered directly into the technical scenario through long-duration operating temperature.

Technical Lesson

This case demonstrates that contact distribution over time can matter in diesel valve durability and sealing.

Where an engine uses exhaust-valve rotators, technicians diagnosing a hot-only cylinder contribution problem should consider whether the valve is rotating and seating as the design intends.

Cold injector and compression checks alone may not reproduce the operating state in which the fault develops.

FAQ

Can a valve-rotator problem contribute to hot cylinder weakness?

On engines using valve rotators, abnormal rotation can contribute to uneven valve-seat thermal and deposit conditions.

Why can cold compression still look acceptable?

Some valve-sealing problems become more pronounced only after components reach sustained operating temperature.