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Diagnosis Exercise: Series Land Rover Lacking Power

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This month we are looking at a Series Land Rover fault diagnosis exercise. Symptoms of the actual problem will be described. You are encouraged to follow your own path to a diagnosis as to what may be causing the problem at the same time as following through the diagnosis strategy presented.

The vehicle is a Series 2A Land Rover with a standard 2286cc petrol engine. The engine was re-bored to +060thou about 3,000miles ago. Most recent engine issue was running for 20+ miles with 2litres of coolant missing. Otherwise no other recent problems.

lack of engine power on standing start and on hills
difficult to reach 40mph
clattery sound from top of engine

A clattery sound from the top of the engine suggests that the valve clearances may not all be correct. This would cause lack of engine power as some valves would not be opening and closing at exactly the correct time. So the first job is to remove the rocker cover and, using the rule of 9 check the valve clearances (valve 1 fully open check valve clearance on valve 8 etc). Result is that two valves have clearance of 0.012thou instead of 0.010thou. But this is not much error and only on two valves. An engine test confirms that the clattery sound has gone but the engine still lacks power on a road test.

Next thing is to look at the spark plugs as they can usually tell a story about what is happening inside the engine. The result is that three of the plugs have a light brown appearance (no problems there), but No.1 spark plug has wet black oil deposits on the electrode. So oil is getting into No1 cylinder somehow - this would be expected to cause a loss of power as too much combustible material is present in the cylinder at the point of ignition. Also, carbon deposits on the electrode can glow and be a cause of pre-igniton of the fuel/air mixture causing a knocking sound and possible damage to bearings and rings.

Plug OK

Oiled plug

So, to test if the problem is ongoing, a new spark plug is put into No1 cylinder and the Land Rover is road tested again. Result is a brief improvement in performance but then back to serious loss of power. On removing the new spark plug a drop of fresh oil is seen on the plug. At this point, shining a torchlight into No1 cylinder shows black oil deposits on the top of the cylinder head. So oil is entering No1 cylinder somehow.

A compression test is done on cylinders 1&2 and shows the pressures to be good and both equal. Well there are only two ways oil can get into No1 cylinder and they are: from the top via a damaged valve stem oil seal or from the bottom via a problem with the piston rings or worn cylinder bore (but only one cylinder is admitting oil, so general engine wear, in need of a re bore is not the cause).

So now time to remove the cylinder head and check the valve stem oil seals. Removing the cylinder head means disconnecting the exhaust and whilst doing this it is noticed that the rim of the exhaust down pipe has a black sooty deposit on it for about one third of its circumference (see photo). This suggests not only that the mixture being burnt was carbon rich (and oxygen starved), but also that exhaust gases were escaping through the poor seal between the down pipe and the manifold. A poor seal would cause lack of compression and hence lack of engine power.

On examining the valve stem oil seals they are found not to be damaged but may be slightly hardened. New seals are fitted.

So we may be looking at multiple causes for the power loss. We need to check the piston rings and bore. Although compression seems good, there may be a problem with the oil scraper ring, allowing oil to get past it and into the cylinder via the gaps in the compression rings.

None of the piston rings are broken, but it is noted that there are score marks on the cylinder wall in places that correspond to the location of piston ring gaps.

At the time of needing to post this online piston rings at +060thou are still being sourced, so this exercise will have to be updated later in the month. Watch this space.

New piston rings fitted and together with the new valve stem oil seals the problem seems to be solved. Suspect the seals where the main reason for the problem. Possibly running the cylinderhead hot due to lack of coolant had weakened them.

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