2008 Mini Cooper S In-car Engine Rebuild
This vehicle arrived with complaints of very high oil consumption, a check/service engine light on, and poor running. When the spark plugs were replaced, the vehicle would run well. However, the car would quickly go back to running poorly. It was burning around a quart of oil in less than 1,000 miles. There were also many, many codes stored in the vehicle's computer associated with the check engine light.
The initial idea was that the intake valves had become carbon coated, or "gunked up" to the point that they had damaged the valve stem seals. This is a common issue for direct injection engines, and is explained in further detail here, and here. However, the oil consumption was so high that HPMotors believed there was probably an additional oil leak either in the turbo or bad oil control rings on the pistons. Investigation of the turbo, which is possible with the car mostly together, showed it to be in fair, serviceable condition. At this point, HPMotors theorized that the carbon fouling on the valve stems had become bad enough to damage the valve stem seals. This then led to too much oil entering into the combustion chambers, and then led to that level of oil overwhelming the oil control rings. Those rings are only designed to handle the film of oil on the sides of the cylinder bore, and small amounts of oil that enter the combustion chamber through other means.
There is no clear way to see the piston rings until the pistons are removed from the engine, which basically means disassembly of the entire engine to gain access. So, knowing that the car at least needed a head service, motor disassembly began.
***Note: This project will have more videos than pictures, as we did not have time to stop and take pictures during the various steps. Instead we simply shot quick videos after different procedures were completed.***
The initial idea was that the intake valves had become carbon coated, or "gunked up" to the point that they had damaged the valve stem seals. This is a common issue for direct injection engines, and is explained in further detail here, and here. However, the oil consumption was so high that HPMotors believed there was probably an additional oil leak either in the turbo or bad oil control rings on the pistons. Investigation of the turbo, which is possible with the car mostly together, showed it to be in fair, serviceable condition. At this point, HPMotors theorized that the carbon fouling on the valve stems had become bad enough to damage the valve stem seals. This then led to too much oil entering into the combustion chambers, and then led to that level of oil overwhelming the oil control rings. Those rings are only designed to handle the film of oil on the sides of the cylinder bore, and small amounts of oil that enter the combustion chamber through other means.
There is no clear way to see the piston rings until the pistons are removed from the engine, which basically means disassembly of the entire engine to gain access. So, knowing that the car at least needed a head service, motor disassembly began.
***Note: This project will have more videos than pictures, as we did not have time to stop and take pictures during the various steps. Instead we simply shot quick videos after different procedures were completed.***
Engine Disassembly
This process will start with removing the front body work and bumper/radiator support. From there the exhaust manifold, intake manifold, and head are removed.
This process will start with removing the front body work and bumper/radiator support. From there the exhaust manifold, intake manifold, and head are removed.
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Further Diagnosis and Analysis
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With the head off the vehicle we can now remove the oil pan, oil pump, and then finally the pistons with their connecting rods.
So, with the engine now completely apart we can finally do a complete investigation of what happened. As explained in the video on the right, it looks like we've found the smoking gun. After thinking about it more, HPMotors believes the original failure was most likely still the valve stem seals. Since the issue was left unrepaired for some time, the added oil in the combustion process led to the oil control rings eventually becoming stuck and failed. This is where it was confirmed that we would need to basically rebuild the engine in the car. With the head off and the oil pan/oil pump removed, both the top and bottom of the engine block are now exposed, making piston removal possible. Minis have weak timing chain chains and other components that are sensitive to heat. Running low on oil, or having low oil pressure, or contaminated oil allows them to get too hot. So a Mini that has seen low oil levels, and oil that is thick with combustion products would most likely benefit from having its timing chain components replaced. Minis use plastic components in their cooling system that like to fail as early as 60k miles. Since the vehicle had 78k miles on it, it was agreed to go ahead and replace the known weak points in the cooling system as well. The Parts List: Timing Chain Kit: Chain Tensioner Exhaust Cam Gear Crank Timing Gear 3 Tensioning Rails Crank Bolt 2 Cam Shaft Bolts and 3 Tensioner Bolts Cooling System: Water Pump Coolant Pipe Thermostat Housing Coolant Head Parts: Valve Stem Seals Cam Cover Gasket Head Gasket Various Sensor/Component O-rings and Gaskets Head Bolt Set Block Parts: Connecting Rod Bolt Set Connecting Rod Bearing Set Piston Ring Set Oil Pump & Pan: Oil Pump Sprocket Oil Pump Sprocket Bolt Oil Pan Gasket Miscellaneous: Exhaust Manifold Gasket Downpipe-to-Turbo Gasket Downpipe-to Midpipe Gasket Oil Filter Housing Gasket Set |
This is a VANOS solenoid that uses oil pressure to control valve timing on the cam shaft. The fine mesh filter you see filters the oil before it enters into the solenoid. It was covered in small pieces of metal from the broken piston rings, and is still covered in carbon and sludge. Lack of oil pressure to this component can cause running many types of running issues. This will be cleaned, and should remain serviceable. However, it's not uncommon for something like this to need replacement due to infrequent oil changes or other debris causing damage.
How the screen looks after some cleaning. After installation it was found to still be operational. Fortunately a new solenoid was not needed. However, it's important to keep in mind that parts like these can easily become damage from lack of proper maintenance or as a part of a bigger failure like this car experienced. In either scenario, it means incurring more unexpected repair costs.
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Assembly Time
With the pistons installed, the oil pump, with a new oil pump sprocket and bolt, is installed. This is followed by the oil pan with new gasket. Now we can install the head, and timing components.
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Video after head installation.
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Video after timing chain kit and turbo/manifold/oil filter housing installation.
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All Wrapped Up!
Normally we catch the initial cranking on video, but this time the battery was dead. So we put the rest of the front of the car together while the battery charged and took it on an extended test drive.
Normally we catch the initial cranking on video, but this time the battery was dead. So we put the rest of the front of the car together while the battery charged and took it on an extended test drive.
The car runs great, and did fine on the test drive home. The oil consumption issue has cleared up, while power and fuel economy are back to normal. Looks like it's time to hand it back to the customer!