15 June 2022
Correct valve clearances are essential for a sweet running engine. Alisdair Cusick explains how to go about setting them, and why it matters
Time: 1 hour
Difficulty: 1 out of 5 stars
Models: Series I, II and III, Ninety and One Ten, and 200Tdi, 300Tdi engined vehicles.
Tools needed: Ring spanners, spark plug socket, extension and ratchet, feeler gauges, screwdriver.
Parts used: DA4033GREEN, £253.
• Wear eye protection when working under a vehicle.
• Always support a vehicle on stands, never rely on a jack.
• When a wheel is raised, chock the wheels that are in contact with
• Use the right tool for the right job.
Maintaining the correct valve or tappet clearance helps to keep the engine running efficiently, with less clatter, and increases the longevity of critical components. Valves are operated by lobes on the camshaft, which action the valve rocker arms, usually via push rods. As the camshaft raises one side of the rocker arm, the opposing side lowers, opening the valve by pushing down on the valve stem. Within that mechanism is a set amount of free play (or lash) – usually measured with the engine cold – between the rocker arm and the top of the valve stem. It’s designed to provide a working clearance while also accommodating the expansion caused when the engine reaches operating temperature.
For the engine to run well, the correct clearance gap is vital. Too narrow, and the valves may not close fully. Too large a gap, and the components will be hammering each other violently, causing accelerated wear.
Valve clearances are checked and adjusted as part of the scheduled service work because, as wear occurs in the rocker arms, cams, valves and valve seats, the clearances change, and must be reset.
Series Is have valve adjustment specified in the manual as ‘when needed’, but later cars can have an annual or mileage service interval – 12,000 miles for a 200Tdi, for example. How would you tell if your valves need adjusting? If your engine idles roughly, and feels down on power, it may be that your gaps are too tight. Equally, if the engine ticks loudly, suspect a valve clearance running wider than it should be. The tricky part is that both those conditions can develop slowly, meaning symptoms don’t present suddenly. The only way to be certain you have the correct valve clearance, is to physically measure them.
This gap is set using feeler gauges which are simply fingers of metal of accurately machined thickness that you slide into the gap between the rocker and valve stem. The gap is then altered by an adjuster screw on the rocker arm, which is secured by a locknut.
It is a simple, straightforward process that relies on knowing your vehicle’s service interval, the correct setting for your engine and, crucially, learning the correct feel of the gauge as you slide it between the rocker and valve stem. As ever, practice makes perfect, and then the process should take you half an hour or so, and help ensure your Land Rover is running at its peak.
How to set the valve clearances
I’m demonstrating this on my Series I for simplicity, but this is unusual in that, while its inlet valves are in the cylinder head in the conventional manner (overhead valves, OHV), the exhaust valves are in the side of the cylinder block (side valves) – as with the Series II 6.0-litre six-cylinder engine. On most Land Rover engines we would be setting exhaust and inlet valves together, above the cylinder head.
What and where?: Series I overhead inlet valves are under the top rocker cover, but the exhaust valves are on the engine’s left side. Most Land Rovers have overhead valves.
Uncover the job: Unbolt the rocker cover(s) and remove. Access may be restricted by pipes and cables, so be careful. Assess gasket condition, and note position of 200Tdi’s half-moon seals.
The business bit: This is what we’re adjusting. The rocker arm is pushed up by the push rod (pencil at right of pic), which pivots to push the valve down (left).
Make it easy: We’ll need to rotate the engine, which won’t be easy against engine compression. Removing the spark or glow plugs, or loosening them helps.
Clockwise from front: Rotate the engine clockwise using the crank pulley until the first valve opens. Alternatively, engage gear and jack up one wheel and turn it to set the position.
What to look for: This is what you want to see. The cam has maximum action (lift) against the first pushrod, which has opened valve number one in the cylinder head.
Plus one turn: Rotate the crank a further 360 degrees. The pushrod is now on the heel of the cam and the valve is fully closed, ready to set the valve clearance.
What gap? Check the setting for your engine in the manual. It is usually set cold. Series models have the information displayed on a plate on the rocker cover: 0.010” here.
Simple tool: Feeler gauges will measure the clearance. The fingers are precisely machined and marked with the thicknesses. Fold out the one you need, and fold the others back.
Adjuster: Undo the lock nut with a ring spanner, and back off the adjuster screw with a screwdriver. Well fitting tools are important here, to minimise free play.
Can you feel it: Slide the correct feeler between the rocker and valve stem. You want to keep it flat in the gap, and be able to move it back and forth.
Wrong way: How not to do it: forcing the gauge in at an angle and twisting under pressure hampers your ability to judge the right feel and damages the gauge.
All about feel: Sliding the feeler back and forth, tighten down the adjuster. You want to get the feel where you can slide the gauge, but it isn’t catching, nor loose.
Fix the setting: Without altering the adjuster, nor clamping down on the feeler, tighten down the locknut. I hang the spanner this way, so it sits off the screwdriver, ready.
Check it: Offer the feeler back into the gap. The correct feel should have some slip but against minimal resistance. Firm tugging means the gap is too tight; try again.
Next, please: Repeat the procedure for the other valves. Here, the second intake valve is open. I need to rotate the crank another turn to be in the setting position.
Top tip: To check the gap is set correctly, try this: the correct feeler should go in, but the next size up shouldn’t. Some prefer this two-gauge confirmation method.
Exhaust next: Repeat for the other valves, refit the plugs and rocker cover. Try the car, which may be quieter, or idle better. You now know the gaps are correct.
Rule of nine
For most four-cylinder in-line engines which have overhead inlet and exhaust valves in the cylinder head, the valve clearances can be set using the ‘Rule of Nine’. With any given valve open, count what number valve that is from the front. Subtract that number from nine. Whatever number you’re left with is the valve you’re in position to set. So, with number 1 rocker opening its valve, you’ll be setting clearance on (9 minus 1), number 8 valve. With number 5 valve from the front open, you’ll be setting number 4 valve, and so on.
Valve layouts and gaskets
Side exhaust valves: Series I side exhaust valves are accessed with the cover removed from the engine’s left side. Clearances are set in the same way as the overhead inlets.
Overhead inlet and exhaust valves: On most engines (this is a Series III petrol) the inlet and exhaust valves and rockers are all on the top of the cylinder head, beneath the rocker cover.
Gaskets check: Check the gasket in the rocker cover, and renew it if in any doubt. Half-moon seals, such as these in the 200Tdi head, should also be checked.
See more expert instruction, advice and tips in our how-to section here.