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Photo Report: Changing the head gasket on a Land Rover 2.5NA diesel engine

I first suspected I needed to change the head gasket when I removed the oil filler cap and there was excess pressure in the crankcase – when the engine was running, it was chuffing smoke like a train!

The second pointer to the head gasket failure was when I spilt some oil down the side of the head. It collected in the gap between the head and the block, and I noticed bubbles forming in the oil, which indicated that gases were escaping from the head gasket.

The third pointer was it was very slow to start in the mornings, and sometimes when hot too. This was pointing to a lack of compression.

I guess this was to be expected though, the Land Rover had only done 5000 miles in 17 years with its previous owner, and I had put 1000 miles on it in 2 weeks, so the old girl was asking for some attention!

Usually a head gasket replacement is something I dread doing on a modern car, but changing a head gasket on an old Land Rover is a lot simpler, and was something that I would enjoy doing. The ease of access on a Land Rover is great – just remove the bonnet and climb in the engine bay!

My 1961 Land Rover has been fitted with the later 2.5 naturally aspirated diesel engine out of an early 90/110 – also known as a 12J engine. These engines are bomb proof if looked after properly, and as such was the engine of choice for the military for many years.

Taking it apart

In about 1.5 hours the head was ready to come off, and I had only used a couple of sockets and a screwdriver – simples!

  • Unbolt the inlet manifold
  • Unbolt the exhaust manifold
  • Drain the water/remove heater pipes
  • Remove the fuel spill rail from the injectors
  • Unbolt the injectors
  • Unbolt the head oil feed from the rear of the head
  • Remove the rocker cover and unbolt the rocker gear
  • Remove the pushrods
  • Undo the head bolts

Note: When removing the head it is important to make a cardboard holder/template for the head bolts and push-rods as the bolts/push-rods need to go back in the same location as they were removed from.

Its all nuts and bolts mechanics, no sensors, no wiring, just basic engineering! As you will see from the photos below, the old head gasket just disintegrated when I removed it, so it was well past its sell buy date!

Clean up and inspection

After cleaning up the head and block and removing the old gasket, I inspected both for cracks and run a straight edge along the head/block – everything was ok! I inspected the pistons and inspected the bores – everything ok.

The “hot spots” or pre combustion chambers can be removed from the head and inspected. Sometimes these can crack, and replacements are easily available, but all of mine where ok.

With everything apart, I drained the oil, and fit a new oil filter – don’t forget to refill the engine with oil once everything is back in place! I was recommended to use a 15/40 mineral oil, as the engine is old technology. Modern oils can be too thin!

The new head gasket

I bought a head gasket kit, also known as a de-coke kit, which gives you everything you need for a complete head rebuild. The Land Rover 2.5NA diesel engine de-coke kit part number is STC1562 – cost is about £15

The head gasket can be put on upside down, (which blocks off some oil/waterways!) so double check you have the metal surface facing upwards, and all oil/water ways line up with the holes in the gasket.

Putting the head back on

Reassembly is the reverse of taking it all apart. The head bolts need to be tightened up in the correct sequence, starting in the centre of the head, and then working in a spiral out to the edges. The full sequence can be found in the Haynes manual. Make sure you use a good torque wrench and torque the head bolts up to 123Nm (91 lb ft)

When the head was back on, and the rocker gear secured in place, I took the chance to check and adjust the tappet clearances – some of them were a little off, so they needed adjustment. Tappet clearance should be 0.25mm

With that done, it was a case of replacing the rocker cover (with new gasket), bolting up the inlet and exhaust manifolds (with a new gasket in place) and putting the injectors back in place.

When refitting the injectors, use new copper washers and the smaller crinkle washers. Both of these washers come with the de-coke kit.

When everything is back together, remember to add water to the system and fill up with oil! The whole job takes about a day and is pretty straight forward if you work methodically.


Well the Land Rover started first time after about 5-10 seconds of cranking! Cold start has improved enormously, and it starts first time after about 10 seconds of glow plugs.

The crankcase is no longer chuffing out smoke from the oil filler, and crankcase pressure is vastly reduced. Performance has increased with a noticeable increase in torque. What used to be 3rd gear hills are now easily handled in 4th gear!

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