MGB Tappets

In this article I will deal with the problem of fixing rattly tappets (cam followers) in the MGB motor.

When adjusting the clearances the books suggest that they are done cold at .015" This is a good starting point. The LED models in later years had a sticker on the bonnet shut panel which said to set them at .013" HOT. So when the motor is hot remove the rocker cover and check them with the motor running. This damages your feeler gauge a bit and can splash a bit of oil around but if the motor is stopped and the clearance checked, the valves sitting on the seats rapidly cool and give an incorrect reading. When the motor is running there is usually .002" difference in clearance with the inlets being looser and the exhaust tighter. It is important to adjust the clearance when the valve is fully closed, i.e. when adjusting No 1 have No 8 fully open (it always adds up to 9 with a 4 cylinder motor and 13 with a 6 cylinder.)

DO NOT tighten the clearance until the rattle stops or you will cause a valve to burn out - inlet or exhaust.

If you still have rattles when you have finished your adjusting it could be because either the cam or the cam followers are worn. Experience has shown me that the 'original' early long lifters lasted longer than the later bucket type but I haven't had enough feedback from replacements. The later bucket type are usually showing signs of pitting before the motor has done 50,000 miles and sometimes as little as 20,000 miles. If you want to keep your expensive cam in top order I recommend that the cam followers are checked and replaced if necessary at the first sign of a rattly tappet after you have adjusted them. You could be fooled as I have as a lot of reground cams do not have the correct quietening ramps on them, and even some suspect new cams. Some cam grinders use a COOPER profile that has the same profile as a 'B' but no ramps - they always rattle. Some competition cams do not have ramps either.

Changing the tappets is relatively easy for the home mechanic with a good selection of tools. Remove the carburettors and manifolds, turn the motor to get to the opposite valve you are working on closed as you would when adjusting them, undo the tappet adjusting screw as far as it will go and using a fairly large screw driver, lever the rocker at the valve to clear the push-rod, remove the end rockers and slide the other rockers sideways, whilst at the same time removing the push-rods.

Now remove the engine side covers and extract the cam followers. If they have been there a long time the ends may have a coating of varnish on them, or even worse, be mushroomed and therefore cannot be easily removed. This then presents a problem if you don't have a tool to lift them out. You could get a piece of dowel and grind a taper on the end, cut it about 50mm long and then tap it into the follower. This gives you something to grab with the pliers. I have made up an expanding tool to fit the follower and this is attached to a threaded rod which expands it. When fitting the new followers make sure you put some oil on them first.

When replacing the side covers check that the gaskets supplied are correct for your model engine. The side cover gaskets supplied in most gasket sets are too small for the front cover which has the front lower corner cut off. The thick rubber or cork gasket is for both covers up to the 18GB engine, and the rear cover on all others, but later 18V engines use a larger thinner gasket 12A1 139 on the front cover, not the 12A1 175. Don't be tempted to reuse gaskets, you'll only end up with oil leaks.

If the manifold studs come out of the cylinder head when you undo them, take off the nut and screw them back in fairly tight. If the nut has seized on, hammer it on the flats which may loosen it, or replace the stud and nut. If they are not screwed into the cylinder head oil will leak out of the thread on the cylinder head - not much but enough to be annoying. Do NOT use bolts into the head.

The gauze in the front side cover also gets sludged up on old motors and therefore restricts the breathing of the engine consequently pressurising the engine and blowing oil out through the seals. These covers are no longer available so a good soak in a strong detergent is needed. I had one that took three days soaking to clean out. You should be able to blow through it easily.

Garth Bagnall

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