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2.5 N/A head gasket replacement


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The following thread is replacement of a 'blown' head gasket on a 2.5 N/A Diesel, as fitted to early 90's and 110's prior to Land Rover bringing out the TD engine. This method is very similar to the same job on a series 2.25 D and the 2.5 TD engine.

The syptoms were excessive smoke, engine 'chugging', and general poor performance.

You will need a Head Set - sometimes also called a De-Coke Set, which is around £20, and the only special tools required are a torque wrench and a set of metric feeler guages. About 80 pictures in this thread, so at least you won't get bored :D

Drain the cooling system. I use the plug in the side of the block close to the starter motor (series vehicles may have a tap fitted). This ensure all of the water in the engine is removed.

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Disconnect the top breather pipe and remove filler cap.

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Also inlet manifold hose and air filter pipe.

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Disconnect both heater hoses - the pipes are copper, so be careful not to use excessive force as they could fracture.

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The heater hose has a clamp on the top of the rocker cover. Should be an 13mm acorn nut.

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Also disconnect the two pipes at the thermostat housing. The heater pipe assembly will then lift away.

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Remove the top radiator hose completely. The thin copper pipe you see in this picture is the temperature bulb for an electric fan. This is a non standard item.

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The link hose top jubilee clip has to be undone and then work a screwdriver around it as shown in this picture. The pipe has to seperate from the thermostat housing when the head is lifted off.

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Spill rail connections now. 13mm spanner to disconnect the return to the filter.

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The rail is a line of 4xbajo fittings and a pipe that connects to the injector pump. 11mm or 7/16" spanner to undo all 4. Leave the pipe connected to the injector pump and tie it out of the way. Put the banjo bolts back in the top of each injector.

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The injector pipes are in pairs - remove Nos 1&2 first, then it will be easier to remove 3&4. 5/8" or 17mm spanner.

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Disconnect the glow plug cable from No4 glow plug - 7 or 8mm spanner or socket.

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Oil supply to the rocker gear is supplied via an ecternal pipe at the rear of the cylinder head undo the banjo bolt with a 5/8" or 17mm spanner or socket. Carefully move the pipe away from the cylinder head to prevent it from being damaged during removal or replacement of the head.

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The injectors have to be removed in order to get at some of the head bolts/nuts. Undo the 13mm/ 1/2" nuts that retain them and then lever them up out of the head. Sometimes the stud comes undone instead, but it doesn't matter.

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All injectors are the same, so no need to keep them in order.

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Inlet manifold now - fixings are 13mm or 1/2". 4 along the top and 2 underneath.

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There should be now just three fixings holding the exhaust manifol on - one at either end and one underneath, centre.

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The exhaust manifold can stay attached to the downpipe - it'll move far enough away from the head.

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Disconnect thermostat as well, then remove the two remaining nuts that hold the rocker cover on and remove it.

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There are 5 x 1/2" or 13mm bolts through the rocker shaft pillars - remove them.

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And then the same amount of 19mm head bolts.

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Replace the rocker cover, replace the 3 nuts and then lift it back off again. The rocker assembly will come away with it.

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There should be valve caps on this engine - all 8 are missing, and there's now damage to the tops of the valves and the rocker pads.

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Undo the reamaining 11 head bolts and two nuts. The head is now ready to be lifted off.

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It's usual for the head to be stuck to the block. Using a large screwdriver or pry bar, break the seal.

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The head will come away from the block.

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The cylinder head is very heavy, so climb inside the engine bay or get someone to give you a hand. You can stand on the front axle and chassis rail. Place cloths or similar on the wing for the head.

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Postion yourself over the head, grasp it at the front and back, then lift it off the engine and place it on the wing.

Inspection of the gasket, block, and head face confirm there was compression loss between No's 2 and 3 cylinder.

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The gasket set comes with everything you need to completely dismantle the cylider head. so there will be some left over.

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The face of the block and cylinder head need to be carefully cleaned of oil, water, and bits of old gasket. A wire brush in an electric drill is suitable for doing this.

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Run one of the head bolts in each of the head bolt holes to remove any oil or water that may have got in them.

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The new gasket can be fitted incorrectly, and most, but not all holes will still line up. Make sure this corner is correct and the gasket will be on the right way.

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New gasket in place and ready for the head to be refitted.

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Clean the manifolds gasket face of the head.

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Also the gasket face - check also for cracking or loseness of the hotspots.

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Alloy connections tend to oxidise, so clean them up as well.

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Clean the head bolts with a wire brush and lightly oil them.

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Carefull lower the head back onto the block and hand tighten the head bolts. Place the inlet/exhaust manifold gasket on and attach the exhaust manifold by it's 3 fixings.

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replace the 8-pushrods, making sure they are correctly located in the cam followers.

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The new valve caps next. A small blob of grease on the top of each valve stem will keep them in place.

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Replace the rocker assembly - making sure that the ball of each roker arm is located in the top of the pushrod.

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The head bolts can now be tightened - the N/A and TD engines should be 91lbft (123nm). Tighten in stages from the centre of the head outwards in a diagonal pattern.

Check and adjust the tappets now - .25mm on this and the TD engine.

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Each injector should have two washers - one large copper one, and a smaller steel one. The old ones can be very fiddly to remove.

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New ones come in the gasket set.

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Fitted.

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New alloy washers for the spill rail banjo bolts - one either side of the bolt to effect a seal.

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Like this.

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Oil feed to head needs two new copper washers as well.

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Reconnect spill rail to filter pipe and glow plug wire.

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Clean the rocker cover and place a new gasket on it (I use the type that has a sticky face on one side)

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Three alloy washers for the retaining nuts.

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replace the nuts on just the front and rear at present - the centre nut also secures the heater hoses.

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The gasket face of the inlet manifold has to be cleaned of old gasket as well. I use a stanley blade and then a fine file to restore it.

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Replace the inlet manifold and secure it with the remaining 6- fixings. There's a new filler cap seal in the gasket set - lever the old one off and stretch the new one into place.

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Lightly oil the ribs of the new seal and put the cap back on the rocker cover along with the breather pipe.

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Both inlet and air filter pipes.

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Heater hoses back in position, and the engine is finally all back together.

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Refill the cooling system and watch for leaks.

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These engines are notoriously difficult to start after this kind of work. You can easily flatten the battery trying to get it running. I much prefer getting a tow start - a couple of hundred yards and the engine normally fires up. Once running - let the engine tickover for at least as long as it takes to get up to running temperature. Keep an eye open for leaks as the system pressurises, and watch the temperature guage. After a few days of steadydriving, check the head bolt again.

For the first hundred or so miles, be gentle with the engine - no high revs, especially out of gear, and check the water and oil levels each day.

Les.

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