Valve clearance are Important for the correct running of your engine. If the valve clearances are too big they will be noisy (clicky or tapping) and will not open the valves fully. This will restrict the flow of air in, and the flow of exhaust gases out. If they are too small, the valves could be held open slightly when they are supposed to be closed which will lead to loss of compression and possibly burnt valve seats. A rough running smoky engine could be a number of things but checking the valve clearances are correct should be one of the things to do first.
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To start, remove the rocker cover, you may need to remove or undo other components to do this such as the breather pipe but ensure you have good access to the valve gear assembly.
The valve clearances need to be checked in a specific sequence so that your measuring the gap between the top of the valve stem and the end of the rocker. To do this you need to rotate the engine clockwise (as looking at it from the front with the exhaust on the right) so that the valve being adjusted is in its fully closed (or up) position. Rather than doing it by trial and error there is method you can use to minimise engine rotation and to help keep a note on which valves you have adjusted.
The valve is open when it is fully down such as the one arrowed in the photo above. In this particular case this is valve number 5, so going by the guide you need to adjust the clearance on valve number 4 which is circled. Valves run from number one at the front of the engine through to eight at the very back.
The gap specified by Land Rover is 0.010 in or 0.25 mm when the engine is either hot or cold. Take your feeler gauge and pull out the blades required for the specified clearance. If your feeler gauge is quite new then chances are it is in metric (0.25 mm required). Make sure you have the correct blades and rotate the engine clockwise by either turning the fan or using a suitable socket and ratchet on the crankshaft pulley. If you have a starting handle and a hole in your front bumper you can use that as well. If you find that the engine is very difficult to turn…check that the vehicle isn’t in gear
Continue to rotate the engine until number 8 valve (the one furthest away from the front of the engine) is in the fully open position (down) It will stop moving momentarily as the engine is slowly rotated. Stop rotating and check the clearance on number one tappet. Do this by inserting the feeler gauge blades between the valve stem and rocker and gently slide it continually back and forward. You are looking for a slight dragging on the feeler gauge blade but not so much it grips the blade. If you can’t fit the gauge in the clearance or the gap is too big then adjustment is necessary. Loosen the locknut a touch and turn the adjuster anticlockwise to widen the gap and clockwise to close it. Continue to slide the gauge back and forth while turning the adjuster until the correct gap is achieved. Hold the adjuster steady with a screwdriver and tighten the locknut. Check the gap again and re adjust if necessary. You may find you need to do this a couple of times until your satisfied with the clearance. Once done continue with the rest of the valves following the adjustment sequence above.
A top tip for you if you find you haven’t got much head room under the bonnet of your Land Rover. Remove the spare wheel (if mounted on your bonnet) and release the bonnet stay from the inner wing. Next lift up the bonnet so it sits against the windscreen. Leave it there or lift it up and off for unhindered
access to the engine bay. I personally have fitted a quick release clip to the bonnet stay so I can do this quickly and easily when required.