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Factory-fitted protection leaves underside vulnerable : credit: © Tom Critchell
Upgrading your L663’s underbody protection is easy, as Martin explains

Need to know

Time: 2 hours
Difficulty: 1 out of 5
Models: 2020-on Defender L663 90, 110 and 130.
Tools needed: Socket and spanner sets, Allen keys, Torx bits, jack and wooden blocks.
Parts and costs: Terrafirma engine and gearbox guards, TF8025, £TBA; Terrafirma front steering guard, TF0436/B, £335,
Work safely:
• Raise and support the vehicle safely on rated equipment.
• Wear eye protection when working underneath a dirty vehicle.

With more and more new-shape Defenders being used off-road and for overlanding and expeditions, the importance of proper underbody protection is stronger now than ever. The L663 has proven itself as a strong off-roader and a durable vehicle in harsh conditions, but as with almost every other modern 4x4, the engine and driveline are left vulnerable to big hits as the standard underbody guards are only made of thin metal.

Being left stranded if the engine or gearbox’s oil sump were to be cracked or powertrain mounts damaged is one thing, but the cost of repairing or replacing any smashed parts can be potentially eye-watering. Most components are still genuine Land Rover only and the hours of labour needed to make substantial repairs can make a real dent in the wallet – so making sure the underside of your L663 is well-protected is vital if you’re venturing onto tougher terrain.

This new kit from Terrafirma has been carefully designed to be easy to fit, and uses all the built-in mounting points that the standard thin, pressed underbody plates used. This means there’s no extra drilling or cutting needed; the 6mm thick Terrafirma armour spans the Defender’s underside more widely than the OE plates as well, which allows it to seal against the waterproof sound-deadening, further helping keep dirt, mud and water out.

Undo the screws: If your Defender has the Land Rover optional aluminium bash plate beneath the front bumper, this is the first part to be removed. It will be refitted over the top of the new Terrafirma engine guard; start by undoing the two rearmost screws.

Remove front plate: Loosen and remove the further two fixings at the front of the alloy bash plate, then unhook it and lift it off. If you don’t have a front plate but want to add one as part of your upgrades, Terrafirma sells its own version in silver or black.

Unbolt OE trays: The standard engine and gearbox undertrays use a mixture of different fixings (10mm and Torx) to hold them in place. Undo the rearmost undertray bolts first, noting where they fit. Lift the gearbox tray off, then unbolt and remove the engine undertray.

Bigger and better: Here are the new Terrafirma engine and gearbox protection plates. Instead of the thin pressed sheet metal of the originals, these are made from 6mm-thick aluminium, and they span out further towards the sills of the Defender, giving extra protection.

Transmission guard first: The new guards are held in place with a mixture of standard bolts and longer fixings that come in the kit, so have them ready and on-hand. Ask an assistant or use a jack with a block of wood to help lift the transmission guard up into place. Wind the 10mm bolts in to hold it up.

Just finger-tight: You’ll want to get both the guards in place before fully tightening the bolts, so fit the rest of the fixings but snug them just enough so that the transmission guard is held against the mounting points. The guard overlaps the OE sound-deadening; you don’t need to cut it.

Engine guard next: With the transmission guard hung in place, offer up the engine guard – with an assistant or jack – and line up the holes with the threaded bosses in the underside of the Defender. You’ll notice that the engine guard overlaps along the front edge of the transmission guard.

A fixing mixture: The large front guard that protects the engine uses mainly standard fixings, but the ones that bolt the engine and gearbox guards together are included in the kit. As per the rearmost plate, start all the bolts in the correct holes and snug them up by hand.

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Align and tighten: Visually inspect the two trays to make sure they are central and are fitted correctly over the sound-deadening material. Starting at the front of the engine guard, at the bolts that angle diagonally upwards, tighten all the fixings, working towards the back of the Defender.

Refit bash plate: With both new Terrafirma undertrays fitted, the front-most steering guard can go back on. Offer the two hooks up and into their sockets, then let the plate slot downwards so that the four holes line up with the threaded bosses in the front of the vehicle.

The final bolts: Start all four bolts by hand, and then tighten. As previously mentioned, if you don’t already have the optional metal bash plate in place, Terrafirma sells its own version in either silver (TF0436) or black (TF0436B). The black one we’re fitting has already been tested…

Better protection: Here’s a closer look at how the Terrafirma underbody plates cover the underneath of the Defender better than the standard items, and the thickness of the guards compared with the thin, pressed steel originals. They extend outwards further to give more protection.

A handy feature: There’s no need to struggle when it comes to service time either, as this convenient removable plate gives access to the sump plug. Simply undo the two 13mm bolts and lift the plate off, drain the oil, then refit the bung and bolt the plate back on when you’re finished.

Ready for action: From the front edge of the bumper to past the end of the gearbox and transfer ’box, the underside of the Defender is now well-protected against off-road knocks, keeping all the vulnerable and expensive components beneath safe. As the Terrafirma guards are designed to use the built-in undertray mounting points and nothing has been drilled or cut to fit, the Defender can be reverted to standard quickly and easily if needed.


What else needs protecting?

Enhanced underbody armour like this does a great job of taking the impact from obstacles and distributing the load through the vehicle’s structure, rather than bending and allowing the rock, stump or other inanimate object to come up and cause damage to the expensive parts behind. But what other elements of the vehicle might benefit from some extra beef?

Rock or tree sliders are a popular upgrade, and give protection to the
vehicle’s sills and doors. They brace to the structure, just like these guards, and are often strong enough to take the weight of the Land Rover.

Front and rear bumpers are also susceptible to damage, and standard items are often removed and replaced with heavier-duty steel items on older models. It’s not quite as simple on the latest generation, but a variety of finishers and protective trims can be attached to protect the surface beneath. Vinyl wrapping surfaces with either a coloured or clear material won’t help with dents, but stops the paint from picking up off-road scratches.


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