Fix a warped Td5 exhaust manifold

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01 February 2018
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Td5_manifold : credit: © Dave Barker
Stop listening to your engine whistling and save cash by dealing with it quickly, as Dave Barker explains

Model: Td5 Discovery and Defender
Time: 3 hours
Difficulty: 3/5 stars
Tools needed: General workshop tools, including 6 mm, 8 mm, 13 mm, 14 mm sockets and spanners.
Cost: Replacement exhaust manifold for Td5 Defender (LKC102020), from £180 to £370. In this case an exchange second-hand skimmed manifold was used costing £75. New exhaust manifold gasket (LKC100470), around £7;  turbocharger oil feed, banjo to turbo washer (FF006350), around 40p. Note, prices do not include the labour cost of fitting the replacement manifold.
Contact: Maddison 4x4, Water House Farm, Station Road, Topcliffe near Thirsk, YO7 3SG. Tel: 01845 587407 maddison4x4.com

 

The problem with the exhaust manifold warping on the Land Rover Td5 engine is well known and affects both Td5 Defender and Discovery. One theory suggests the cause is the different rates of expansion between the Td5’s aluminium head and the cast iron exhaust manifold, compounded by high temperatures when the engine is being worked hard, especially on engines that have been tuned for performance.

The problem originally seemed worse on the later Td5 models, and it was thought that possibly early manifolds had different metallic properties to the later ones, perhaps made by different manufacturers. In most cases the first indication of the manifold starting to warp and bend away from the head is often a metallic sound as the vehicle accelerates, caused by the metal manifold gasket being vibrated by exhaust gasses passing through the gap, or more commonly a whistling noise coming from this area. In the worst cases (usually when the symptoms have been ignored for some time) the manifold can warp so badly that it snaps an exhaust stud or even pulls one out from the relatively soft aluminium head. If you start to hear a rattle or whistle, check for other signs of a warped manifold, such as a slight increase in fuel consumption or loss of power and exhaust soot building up on the exhaust manifold and cylinder head, especially at the front or back of the head. If the exhaust manifold studs are undamaged, then replacing the manifold is relatively a straight-forward job, maybe just a little awkward getting the manifold off. The owner of the Y-plate Td5 Defender shown here had heard the noise and acted quickly before further damage could happen. 

Since manifold warp has become so common, several options have been developed to cure the problem, including modified exhaust manifolds and special manifold stud kits which allow for expansion. In the case shown here, the manifold had warped only slightly, and no exhaust studs had snapped or pulled out of the head, meaning all that was needed was a refurbished manifold (or have the existing manifold refurbished) plus a new exhaust manifold gasket. In the case of this non-modified working Defender Td5, the owner opted to simply fit a replacement second-hand manifold on which the flange faces that mate to the head had been re-machined flat. This low cost option would be adequate for this standard-spec engine, considering the first manifold had lasted for 16 years and 125,000 miles. To date, the refurbished manifold has stayed in shape.

Extra work

Before removing the manifold, confirm that none of the studs have pulled out of the cylinder head or snapped. If so, a stud extractor will be needed to remove the broken studs, and the thread in the cylinder head will need repair where any studs have pulled out, so you might want to entrust this work to a garage. Also, if your Defender has air conditioning fitted, you will need to remove the auxiliary drive belt and then release the air con compressor and move it to one side to gain access to the manifold.

Removing the exhaust manifold

Disconnect the air flow meter’s multi-plug (left arrow) from the socket (right arrow), and release the air intake hose from the filter box

Slacken the hose clip at the turbocharger and release the air intake hose from the turbocharger, then move the intake hose clear of the engine.

The exhaust manifold heat shield, secured by three bolts, needs to be removed. One bolt is at the rear and more tricky to access – use a quality spanner.

Once undone, the exhaust manifold heat shield can be lifted clear, giving full access to inspect the exhaust manifold and reach its studs.

The exhaust manifold and turbo-charger are now fully accessible, though reaching the lower row of nuts securing the manifold will need some care.

To remove the manifold you first need to remove the turbocharger. Start by releasing the three nuts securing the turbo to the exhaust manifold.

After cleaning to prevent dirt ingress, undo the oil feed banjo bolt from the top of the turbocharger, then move the oil feed pipe clear of the turbo.

Once the oil feed pipe is removed from the turbocharger, replace the banjo bolt to prevent dirt getting in there and damaging the turbo.

Carefully undo the ten nuts from the exhaust studs that secure the exhaust manifold to the cylinder head, and collect the washers.

Undo the securing screws that hold the cooling fan’s plastic upper cowl in position, then remove the cowl from the engine bay.

Using an Allen socket and extension bar, unscrew the two bolts which secure the EGR pipe flange to the front end of the exhaust manifold.

Once the bolts have been removed you will have enough room to ease the EGR pipe forward away from the manifold, leaving it in situ.

The exhaust manifold is now free and you should be able to carefully ease the manifold off the exhaust studs and away from the head.

While easing the manifold away, gently move the turbocharger, which is still attached to the exhaust down pipe, away from the exhaust manifold.

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You will now have enough room to completely remove the exhaust manifold from the head. Also remove the exhaust manifold gasket.

Once the exhaust manifold has been removed, we can now clearly see the black stains of the blowing exhaust gas around the rear port.

With a straight edge held against the manifold, we can see the extent of the warp – enough to cause a whistling noise, and some power loss.

Because no studs are damaged, all that’s needed to fix this Defender is a replacement straight exhaust manifold and a new gasket.

 

Manifold refurbishment

Depending on the amount of warp, it may be possible to re-use the original exhaust manifold after having the flange faces re-machined to ensure they are all in line to present a smooth flat face when refitted to the cylinder head. It’s worth getting a price from a machine shop before buying a new manifold, or taking the risk of fitting a cheaper secondhand one which may itself have a degree of warp. Some suppliers offer refurbished manifolds on an exchange basis. Here’s what the machine shop can do with your existing manifold.

Td5 exhaust manifolds have been known to warp by as much as 5 mm. It’s not practical to machine this back – it would leave the flanges too thin.

A warped Td5 exhaust manifold is restored using a milling machine. The manifold is secured in its jaws, ready for the rotating cutter.

The cutter head rotates at high speed, moving along the manifold as it removes a thin layer of material, exposing the extent of warp.

The first cut has only touched the middle three ports, showing (pic right) that the manifold has warped away from the cylinder head at each end.

After more passes by the cutting head, each removing a little more metal, the process is completed when each flange shows a fully machined face.

With the stud threads cleaned and a new gasket in place, the replacement exhaust manifold is fitted into position onto the exhaust studs.

 

Replacing the manifold and reassembling

The turbocharger can now be positioned onto the replacement exhaust manifold, but do not tighten it into position just yet.

After fitting all ten nuts and washers on their studs, securing the manifold, gradually and evenly tighten, finally torquing to 25 Nm.

Now that the manifold is fully tightened to the head, the three nuts securing the turbocharger to the manifold can be torque tightened to 25 Nm.

Check the oil feed pipe, banjo bolt and turbo hole are clean, then connect the pipe to the turbo using the banjo bolt and new sealing washers.

With a new gasket in place, and the pipe flange cleaned and smooth, refit the EGR pipe onto the end of the exhaust manifold.

The remaining parts can now be refitted to complete the job. Given normal use, another 160,000 miles can be expected from the replacement manifold.

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