Issues from the rebuild process:
* Worn or damaged piston rings: This is a very common culprit. If the rings weren't properly seated, were damaged during installation, or were of inferior quality, they won't effectively seal the combustion chamber, leading to oil burning.
* Improperly honed cylinders: If the cylinders weren't honed to the correct specifications, the piston rings won't create a proper seal. This can lead to excessive oil consumption.
* Damaged or incorrect piston ring gaps: Incorrect ring gaps can prevent proper sealing and lead to oil burning. The gaps must be within manufacturer specifications.
* Valve stem seals: These seals prevent oil from leaking past the valve stems into the combustion chamber. If they are worn, cracked, or incorrectly installed, oil will burn.
* Improperly installed or damaged valve guides: Worn or damaged valve guides can contribute to excessive valve stem seal wear and oil burning.
* Cylinder head gasket failure: A blown head gasket can allow coolant or oil to leak into the combustion chamber, leading to oil burning.
* Incorrect valve clearances: Incorrect valve clearances can lead to excessive wear on valve components and potentially oil burning.
Issues that developed after the rebuild:
* Excessive engine wear: Even after a rebuild, if the engine is subjected to harsh conditions (over-revving, prolonged high-speed driving, lack of proper oil changes) it can wear down again, leading to oil consumption.
* Poor quality oil: Using low-quality oil can lead to faster wear and increased oil consumption.
* Broken or worn PCV valve: The positive crankcase ventilation (PCV) valve is crucial for managing crankcase pressure. A malfunctioning PCV valve can cause excessive oil to be drawn into the intake manifold and burned.
* Oil filter issues: A clogged oil filter can increase oil pressure and push oil past seals.
* Leakage from the oil pan gasket or other seals: While not strictly burning oil, this can lead to a noticeable decrease in oil level, which may be mistaken for oil burning.
Diagnosing the problem:
To pinpoint the cause, a thorough inspection is needed. This may involve:
* Compression test: Checks the condition of the piston rings and cylinders.
* Leak-down test: Helps identify problems with valves, piston rings, and cylinder head gasket.
* Visual inspection: A mechanic can visually inspect the engine for obvious leaks or damage.
* Oil analysis: An oil analysis can reveal the presence of fuel, coolant, or excessive wear metals in the oil, providing clues about the source of the problem.
It's crucial to take the vehicle back to the mechanic who performed the rebuild. They should be able to diagnose and repair the issue under warranty if it's related to their work. If not, an experienced engine mechanic will be needed to diagnose and repair the problem.
