28 November 2023
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Removing the bolts can be tricky
: credit: © Alisdair Cusick
Changing exhaust manifold gaskets should be straightforward, but there are issues to look out for, as Alisdair Cusick explains
Need to know
Time: 3-4 hours
Difficulty: 1 out of 5
Models: All Rover V8-engined Land Rovers; Range Rover Classic, P38A and Discovery and Discovery II.
Tools needed: 1/2in and 9/16in six-sided socket, extensions, ratchet, flat screwdriver/punches, steel rule, wire brush, torque wrench, hammer.
Parts used: ERR6733 x 2, £1.37; bolts x 6, SH506095L, 61p each;
locktabs x 2, ERC7321, 66p each.
Work safely:
• Ensure the engine and manifolds have fully cooled before starting work.
• Wear eye protection when wire brushing and clearing dust.
• Use the right tool, for the right job.
• If in doubt, get an expert to do the job.
• Never take risks with heat or pressure.
Thanks to: Martin Domoney for his help with this feature.
We all dread noises from an engine and, when we hear a rhythmic tick, it can be easy to think the worst. Regularly repeating ticking noises from a Rover V8 can be anything from engine knock, lifter issues, or even slipped liners. None of those issues are simple to correct. But there is one cause that is: a blowing exhaust manifold gasket.
Failed exhaust manifold gaskets present as a regular ticking or blowing sound that may increase under acceleration, or go away when the engine fully warms up – a gap can close up again due to the metal expanding as it heats. If particularly bad, we may spot black marks around a manifold to cylinder head joint, where the exhaust gases are blowing by. But even when a leak starts, we should be able to smell exhaust gas under that side of the engine. Any ticking noises that behaves in this fashion can be confidently diagnosed as an exhaust manifold to head gasket having failed, rather than more serious issues.
Why exhaust gasket condition is important
Exhaust manifold gaskets do a vital job in one of the hottest parts of the engine: right in the line of the hot gas from the cylinders. They ensure toxic exhaust gas is directed away from the cabin, and prevent air being sucked into the exhaust. Note that EFI engines using the Lucas 14CUX onwards feature lambda sensors in the exhaust. These sensors sample the exhaust gas for oxygen, and then adjust the air-fuel ratio based on that reading. A fully sealed exhaust manifold joint is vital on such vehicles, as fresh air sucked into the exhaust could upset the lambda reading, potentially making the engine run rich.
Renewing the gaskets
The Rover V8 exhaust manifold is made of cast iron, but the engine is of aluminium alloy. To gain increased purchase in that softer material, the manifold bolts have a ⅜in UNC thread with 9/16in heads. From Discovery II and P38, those fixings are still ⅜in UNC, but with a 12mm bi-hex head.
The job is relatively straightforward, with eight fixings per side, but there are issues to be aware of, for the consequences can make the job a hard one. If you snap a bolt head off, or strip a thread, you’ll be having to deal with removing that remaining bolt (without causing further damage). Rounding the heads on bolts is more common, especially with the bi-hex bolts.
Editor Martin shows us how to do the job on my 1995 Range Rover Classic, which recently started showing the first signs of a failed exhaust manifold gasket on the left bank. “The key thing is to do all the best practices, to get the best purchase on each bolt head,” says Martin. “Use a well-fitting, six-sided socket; clean as much corrosion from the bolt head as you can so you get the maximum purchase.”
Aside from that, the task is straightforward. Be methodical, use hand tools so you can feel the threads working, rather than tear them with a power tool. There are two exhaust manifolds on a V8, but we’d suggest only changing the gaskets on a failed bank – leave the side that isn’t leaking. Use new fixings, and use the metal gaskets in pairs, for ease of fitment, rather than the asbestos-type single gaskets. Although this job is being done on my 1995 Range Rover Classic V8, the process is broadly the same for all Rover V8-equipped Land Rovers.
Problem area: The left bank (viewed from the front) of the V8. There’s no black blow-by evident, but there’s a ticking sound, and a smell of exhaust gas around here.
First step: Push back the locktab on each fixing. There are two on each head, but only one will be pushed down. They’re corroded, so may just break off.
Loosen each fixing: Using a six-sided 9/16in socket, first ensure it is fully seated on each bolt head, then crack them each loose in turn using a ratchet.
Top trick: If bolt heads stick in the socket, wind them fully out rather than risk damaging the thread in the head by trying to pull the socket off.
Heatshield fixing: The starter motor heat shield is held by shorter bolts with ½in heads. They screw into the heads of the rearmost lower two manifold bolts (bottom in pic).
A vital part: The heat shield comes out, ready for a quick clean-up. The surface rust will just scrub off. If the bracket is deeply corroded and weak, replace it.
Mixed fixings: After loosening them, remove all the bolts. Note the short heat shield fixings which thread into the heads of the two, longer-headed 9/16in manifold bolts (see Heatshield fixings, above).
Out with the old: The old manifold gaskets are now removed. Ideally, they should come out in larger pieces. If they fall apart, aim to account for every piece, from every port.
Investigate the cause: Looks for evidence of blow-by. Sure enough, here the first port shows clear evidence of a gap, black staining and the gasket material failing. This is the issue.
Preparation: We use new fixings, but reuse the two starter heat shield bolts and washers. These are cleaned up. Threads full of aluminium would suggest a stripped thread.
The parts, ready: New metal gaskets, new lock tabs, new fixings. The parts are cheap, so take the opportunity to refresh the fixings. No need for stainless, regular steel is fine.
All clear? To ensure any gasket remnants are fully removed, a small flat edge, such as this steel rule, is worked over the manifold face, feeling for a clean surface.
In with the new: Slide in new gaskets. Note bolt hole orientation to avoid gasket sitting offset, half covering the exhaust port rather than sitting correctly around circumference.
Right parts, right order: Arrange the lock tab and washer over the fixing. The correct order is washer (reused original) lock tab, bolt. No anti-seize paste nor thread lock.
Start the bolts: Start each bolt by hand. This importantly allows you to feel that the threads work easily, not cross-thread, nor forcing anything, which a ratchet may do.
Keep it straight: Each fixing is tightened, working from centre out, tightening down in a few stages. This encourages the manifold, which may be slightly warped, to seat correctly.
Torque: If the fixings threaded in easily, indicating they’re not cross-threaded, torque the bolts accurately to 16lb-ft (21.7Nm). We’re now ready to test the fix.
Start, listen: Start the car and listen. At idle there should no longer be a ticking sound. Blip the throttle because the extra pressure will find any leaks. All should be well.
We haven’t folded the lock tabs. Why? Although we’re confident there are no leaks, we still don’t fold over the lock tabs. This is because the gaskets and fixings need a few heat cycles to settle. Occasionally, the bolts can loosen, and need re-tightening, which we couldn’t do if the tabs had been folded over the bolt heads. After a week’s use and heat cycles, if there are still no leaks and no fixings need to be re-torqued, the lock tabs can then be folded over.
Martin's top tips
• Note how the bolts should feel going in and out.
• Have the engine cold, making it easier to work on.
• Ensure your tools fit the head of the bolts properly.
• If a bolt feels stubborn to undo, try using freeze spray to shock the bolt threads.
• Because of fuel lines nearby, I’d avoid using any source of heat to loosen the bolts.
• If a bolt is reluctant, try loosening it a touch, then tightening it, repeating the process. This old trick is useful on stubborn, corroded fixings.
• Penetrating spray may help on the threads, but can work against you in making the bolt head slippery in the socket, which this job is looking to avoid.
• When fitting the bolts, start each bolt by hand so there is less chance of cross-threading.
• If one manifold bolt is tight to start, try loosening the other bolts on that gasket, to help the gasket and manifold line up.
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