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  • Writer's pictureKingsley James

Another MGB

This MGB came to the workshop with a variety of issues. Poor running, excessively loud as well as areas of bodywork. So wear to begin, well a good place to start is making the car run properly.

In order to make it run properly I first need to no why it's not running properly. It sounded like a cylinder was misfiring and after checking the ignition system for a good spark and a few other basic checks it started to look like the head was the fault. A chemical co2 detector test confirmed the head gasket was leaking. The fluid starts off blue and if it detects co2 from fumes in the radiator it turned green or yellow in extreme cases. This one turned somewhere between green and yellow so the results are pretty conclusive.

After removing the plugs I also found that the number 3 plug ( 2nd from the left) needed to be re- gapped.

Once the head is removed the problem becomes obvious. Carbon between 3rd and 4th cylinder can only mean that gasses have been passing between those two cylinders.

The cylinder head can easily be skimmed flat to repair the problem but the same isn't quite as easy if the fault lies in the engine block. To test the engine block is flat a machined flat edge is placed on the block and a feeler guage is used to test for gaps. In this case the feeler guage would not pass under the flat edge at any point in the block. Good news for the owner as it means I didn't need to remove the engine.

Head skimmed, valves and seats re-ground.

The MGB wasn't originally designed with valves stem oil seals however without seals there is a clear pathway for oil to drain into the combustion chamber. Since there are now plenty of after market seals I opted to install a set.

Once the head rebuilt and refitted the valve clearance much be set. This refers to the small gap between the valve stem and the rocker arm.

Something that often gets overlooked with twin carbs is the balancing. Ideally they should be sucking the same amount of air. This is achieved by adjusting the balance screw while observing the kg/h (air flow). The figure shown in the picture above are a bit high for a finished set up and but were brought down along with the idle speed.

Engine finished and running nicely.

On to the excessive noise. The car was fitted with a single box sports exhaust that the owner was not keen on.

A universal in-line silencer is fitted and did a good job of bringing the noise down.

Now for the cosmetics. The MG was 95% as far as the bodywork goes. The only real let down was a very wobbly boot lid which was highlighted by scuffing it up with some 180 sand paper on a long sanding block.

After pulling as many of the dents as I can the remainding dings we're filled and then the boot was given several coats of filler primer. A red guide coat is sprayed over the primer and then sanded back to reveal and high spots.

Finally the boot is repainted to match the rest of the car. It came out pretty nice.

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