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Rocker Box Inspection & Checking the Valve Clearances


After that last section, it is probably going dark by now, but don't despair. This next bit is fun. You need to remove the air filter assembly before getting started on the Rocker Box cover. Unscrew the two long cross-head bolts on the top of the air filter box, and the support brace at the side, and lift the entire assembly out of the car. At this point you should be able to see inside the top of the carburettor. On the two litre engine, it is a twin choke carburettor and you will see the pair of choke flaps which, if the engine is still warm, will be in a vertical position. You can gently move the flaps to test for operation. As the engine cools over the day, you should see the flaps close until they are almost shut. This is the automatic choke that is controlled by the temperature of the water in the cooling system. If the choke flaps are not vertical when your engine is hot, then you have a faulty choke which needs attention.

Back to the job in question. The rocker box is held in place by a set of bolts that should all be removed. Some are easier to get to than others. Make sure you keep them in the right order. With a bit of gentle persuasion, the rocker box cover will lift away and the camshaft will be visible (I loosen the hose clamp on the choke and twist it upwards to give myself a bit more room). There are 8 lobes on the cam: 4 for the inlet valves and 4 for the exhaust valves. Look at the exhaust manifold and the inlet manifold to work out which is which. Also note the spray bar on the carburettor side of the cam shaft.

The height of each valve when open is adjustable and needs to be checked. When I first bought my car, they were out by quite a bit, but have since needed adjusting only occasionally.

As before, rotate the engine clockwise using a spanner (this is much easier if the spark-plugs are removed so there is no compression to overcome) until one of the lobes is pointing up vertical. Check to see what type it is (inlet or exhaust) and slide a feeler gauge between the cam and the heel. Exhaust valve clearance is 0.25mm, Inlet valve is 0.20mm. The exhaust valve should allow a 0.25mm feeler to slide under, but not a 0.30mm. The inlet valve should allow a 0.20mm feeler to pass under but not a 0.25mm. Check each cam in turn before adjusting any. This will give you an overall feel for what you are doing. If you do need to adjust, you will need a 19mm and 15mm open ended spanner. Slacken off the 19mm locking nut on the top of the valve, and turn the 15mm adjuster until the correct gap is obtained. A bit of trial and error is needed and some of these nuts are very difficult to get a spanner on. I once had to undo and partially lift the carburettor to get to one

Some people use an old spanner which has been bent to make access easier. These adjustments are to be made on a cool engine (which of course yours is by now !).

When finished, try turning the engine on the starter while watching the top of the engine. Apart from being fascinating, after about 10 seconds you should get oil coming out of the spray bar and onto the cam lobes. Make sure that all holes are operational. If not, remove the spray bar (it is easy) and soak in petrol to clean it out.

Once you're happy that all is well, replace the rocker box cover making sure that the cork gasket does not get pinched (buy a replacement gasket every other service). Refit all the bolts and tighten hand tight. Replace the air cleaner after lightly greasing all the linkages on the carburettor that you can see. If you find that the engine is making a clattering noise from inside the rocker box, then something has gone wrong; perhaps you didn't re-tighten the locking nuts properly when you made the adjustments. It is worth re-checking and re-adjusting if you are not 100% happy.




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