Adjusting the valve clearances or 'tappets' should be done at the same regular interval as changing the oil, every 3000 miles or sooner. Doing them yourself, regularly, is advisable as you will often notice the same valves need adjusting each time, and others will often check out OK. This will often be because of valve seat wear, usually on exhaust valves, particularly on number 1 and 3 cylinders as they run hottest due to the layout of the engine. Adjusting them yourself allows you to keep a close eye on the running condition of the engine and will also save you a big mechanics bill every 3000 miles! Too many people ignore this important part of the servicing of an aircooled motor. Neglect can lead to flatspots, poor fuel consumption and hard starting. This may sound like an involved job when read out, and to be truthful it can be a bit confusing the first time you try it. With a little patience and practice, however, it should only take around 20 minutes start to finish when you've done it a few times already!

This job should be tackled with the engine cold, so it's often best to do it ahead of an oil change, I leave my engines standing overnight in readiness to do the job in the morning.

You will need: a 0.15mm [8thou] feeler gauge , a 13mm ring spanner, a long flat headed screwdriver and a pair of new rocker cover gaskets[about 50p each]

Find the distributor cap inside the engine bay. Make a note of which HTlead goes to number 1 cylinder [the numbers are stamped into the tinware, but it will be the furthest away from you on the right hand side]. Then pop the distributor cap off, and take a look at the rotor arm. You want it to be pointing at number 1. If it's not, turn the crankshaft [bottom] pulley until it does. To make sure your engine is at TDC [top dead centre] for number one, you will need to look for a dimple in the outer edge of the pulley. Once you've found it, make sure it lines up with the join in the two crankcase halves. Now you're all set to check the tappets on number one.

Get under the right hand rear wheel arch, and look for the rocker cover [rounded rectangular box on the side of the engine]. Use your screwdriver to prise down the sprung clip that holds it in place. The cover should then pull off with a bit of persuasion. Clean up the cover, and throw away the old gasket. *note*, don't re-use these gaskets, as they are a crush-fit and will leak badly if re-used.

Now you are looking at the valvetrain at the top of the cylinder head. There are 4 "rockers" which push the valves in and out in time with the engine's running. At the top of each rocker is a nut and adjusting screw. At the bottom is a pushrod that goes down into the sump. Push with one finger onto the bottom of the two right hand rockers; this is to take out any slack that might be there. Now, with your 0.15 feeler, put it round the back of the adjuster and between the valve tip and adjusting screw.
Ideally the feeler should pass cleanly between the two with only a slight dragging. However, if it is too tight, or even too big a gap, you will need to make an adjustment.

Adjustment. First loosen the locknut with your 13mm ring spanner. Be careful of your knuckles, these are tight!! Now, with the ring spanner still hanging on the nut, and the feeler held in the gap with one hand, put your screwdriver onto the screw and turn with the other hand until you have the desired gap. I often screw the adjuster in, until it binds against the feeler so that I can keep pushing the bottom of the rocker, so that there is no play at the pushrod. Once you have your gap correct, you can hold the screwdiver in the screw to stop it turning, and do the locknut back up. TIGHT!
Push the bottom of the rocker again, and check the gap. Once again, you want the feeler to pass through with only a little drag; if its out still, start again. It's trial and error and patience!!

Now you've got the gaps on number one set up, you need to do number 2. These are the ones to the left of number 1; to check these you will need to rotate the crankshaft pulley by exactly 180 degrees, so that the dimple on the pulley lines up with the case join, but at the bottom. The rotor arm should have moved 90 degrees anticlockwise and now be pointing somewhere in the direction of the front left part of the car. The gaps on number 2 will now be open and ready to check. Remember, feeler should pass through, with a tiny bit of drag; adjust if necessary.

Turn the crankshaft pulley another 180 degrees. The dimple on it should be back up the top and the rotor should point backwards and left. This will have opened up the gaps on number 3 cylinder, which is front left of the engine. So you'll now need to get under the left wheel arch and prise down the clip holding the rocker cover on that side of the engine. As with the last two, check the gaps and adjust if necessary.

One last 180 degree turn of the pulley will line things up ready to check and adjust number 4's gaps - the two rear left ones. Once all your gaps are done, put the new rocker cover gaskets inside the lip of the covers, and put them in place on the heads. Then, lift the sprung clip up as far as it will go. Using the screwdriver again, lever the clip into its groove; it should snap into place nice and snug. Now replace the distributor cap and that's it! You should now have a smooth valvetrain that's less rattley than before!